Tesis sobre el tema "Appalachian fold and thrust belt"

Thesis advisor: Yvette D. Kuiper
The Hudson Valley fold-thrust belt (HVB) is a narrow belt of deformed Upper Ordovician to Middle Devonian clastic and carbonate strata exposed in the western Hudson Valley of New York State. Geologic mapping at a scale of 1:10,000 was carried out near the town of Catskill. The southern portion of the map area includes a large doubly-plunging structure which features a fault-dominated southern portion plunging towards 017° and a northern fold-dominated, 206° trending, southerly plunging segment. A relay structure between two major faults or fault systems is interpreted as existing between the two domains. Farther north, the HVB narrows and folds plunge shallowly towards 212°, and then widens with folds plunging shallowly towards 017°. The changes can be explained by a localized increase in slip on the Austin Glen Detachment in the center of the map area, and subsequent loss of slip towards the north
Thesis (BA) — Boston College, 2010
Submitted to: Boston College. College of Arts and Sciences
Discipline: College Honors Program
Discipline: Geology and Geophysics

Des modèles géométriques ont été proposés pour reconstruire la géométrie de plis associés aux rampes (par exemple pli sur flexure de faille), en identifiant en particulier la profondeur de niveau de décollement et le déplacement total sur la rampe. Ces méthodes de reconstruction géométrique sont appliquées pour des plis partiellement érodés. Au cours de l'érosion, le cut-off de la rampe peut être érodé et, par conséquent, le déplacement sur la rampe est difficile à quantifier. Dans cette thèse, nous développons onze modèles thermo-géométriques. Les modèles combinent les données géométriques et les données d’enfouissement pour proposer une évolution cinématique d’un pli avec cut-off érodé. Nous supposons que la mise en place d'une unité tectonique produit une anomalie thermique dans le mur de la faille, et que cette anomalie thermique pourrait indiquer une épaisseur de bloc chevauchant. Les modèles fournissent une estimation de la profondeur de décollement et le déplacement total sur une rampe érodée, qui ne dépend pas de taux d’érosion. Dans le cas de chevauchements actifs, les modèles proposent un taux de déplacement et un âge de l'initiation de la faille en fonction de taux d'érosion. Ces données sont utilisées pour proposer un développement cinématique de coupes érodées. Nous appliquons les modèles sur les plis érodés et actif à Taiwan dans les zones de Choshui et Miaoli. On propose des coupes régionales équilibrées en utilisant la technique de modélisation directe. Dans la section Choshui, nous proposons un niveau de détachement de ~5 km à ~14 km, marquée par deux sauts successifs de rampes de ~5 km and ~4 km. En supposant un taux d'érosion à 4 mm/an, l'âge de l’initiation de chevauchement active est entre 3,3 Ma dans la partie intérieure de prisme (Chevauchement de Tili) à 0,9 Ma dans la partie extérieur (Chevauchement de Chelungpu). Le raccourcissement totale sur la coupe de Choshui est ~100 km et le taux de déplacement calculé est ~1 cm/an. Pour tester nos modèles thermo-géométriques dans une chaîne plissée inactive, on applique nos modèles sur les plis érodés associés aux failles de Pine Mountain et Jones Valley dans la chaîne plissée des Appalaches. L'application des modèles thermo-géométriques nous permet d’estimer une quantité de déplacement sur les deux failles et expliquer de manière satisfaisante l'anomalie thermique dans le mur des failles de Pine Mountain et Jones Valley. Afin d'améliorer la description de l’anomalie thermique qui se développe dans le soubassement des failles, on a étudié l'évolution des minéraux magnétiques des roches argileuses le long de quatre sections dans la chaîne plissée à Taiwan. On a remarqué que la greigite (Fe3S4) domine l'assemblage magnétique dans les roches enfouies à moins à moins de de 70°C. La magnétite (Fe3O4) se développe pour des températures d’enfouissement de ~50°C et domine l’assemblage magnétique jusqu'à ~350° C. A partir ~300°C, la pyrrhotite monoclinique (Fe7S8) se développe aux dépens de la magnétite, et à ~350°C, la magnétite n'est plus détecté. Ces résultats peuvent être utilisés en complément d'autres géothermomètres pour identifier les anomalies thermiques dans une gamme de de 50-70°C et de 300-350°C où les caractéristiques des minéraux magnétiques sont identifiées
Geometric models have been proposed to account satisfactorily for ramp-related folds (e.g. fault-bend fold), identifying in particular detachment depth and total shortening. These methods of geometric reconstruction are applied on partially eroded folds. During erosion, the fault cut-off may be removed and as a result, the displacement is difficult to quantify. In this thesis, we develop 11 thermo-geometric models combining geometric description of folds and burial data to propose kinematic evolution of folds with eroded cut-offs. We assume that the emplacement of a tectonic unit will result in a thermal anomaly in the footwall, and that this thermal anomaly might indicate a thickness of the overriding unit. The models provide an estimation of the detachment depth and the total shortening on an eroded ramp, independent of the erosion rate. In the case of active thrusts, the models provide an estimation of the slip rate and the age of the initiation of the thrust as a function of the erosion rate. These data are used to unravel the kinematic development of eroded cross-sections. We apply the models on eroded folds from Taiwan underlined by active thrusts in the Choshui and Miaoli sections. We propose regional balanced cross-sections using forward modeling technique. In the Choshui section, we propose a detachment profile with a depth between ~ 5 km and ~ 14 km, marked by two steps of ~ 5 km. Assuming erosion rate at 4 mm/a, the age of initiation of the active thrusts is ranging from 3.3 Ma inward (Tili thrust) to 0.9 Ma outward (Chelungpu thrust). The total shortening from the whole section is ~100 km and the calculated slip rate is about 1 cm/a. To test our models in a non-active fold-and-thrust belt, we study eroded folds associated to the Pine Mountain thrust and Jones Valley thrust from the Appalachian belt. The application of the thermo-geometric models provides a value of the total shortening and explains satisfactorily the thermal anomaly in the footwall of the Jones Valley thrust. In order to improve the description of the thermal anomaly, we have studied the evolution of magnetic minerals of argillaceous rocks in four sections from the Taiwan thrust belt. We found that the iron sulfide greigite (Fe3S4) is dominating the magnetic assemblage in the less buried rocks (<70°C). The magnetite (Fe3O4) develops at burial temperature of ~50°C and is dominating the magnetic assemblage up to ~350°C. By ~300°C, the monoclinic pyrrhotite (Fe7S8) develops at the expense of magnetite, and at ~350°C, the magnetite is no longer detected. These results can be used complementary to other geothermometers to identify thermal anomalies in the range 50-70°C and 300-350°C where characteristic magnetic minerals are identified

In a well-defined subrecess in the Appalachian thrust belt in northwestern Georgia, two distinct regional strike directions intersect at approximately 50°. Fault intersections and interference folds enable tracing of both structural strikes. Around the subrecess, tectonically thickened weak stratigraphic layers—shales of the Cambrian Conasauga Formation—accommodated ductile deformation associated with the folding and faulting of the overlying Cambrian–Ordovician regional competent layer. The structures in the competent layer are analogous to those over ductile duplexes (mushwads) documented along strike to the southwest in Alabama. The intersection and fold interference exemplify a long-standing problem in volume balancing of palinspastic reconstructions of sinuous thrust belts. Cross sections generally are constructed perpendicular to structural strike, parallel to the assumed slip direction. An array of cross sections around a structural bend may be restored and balanced individually; however, restorations perpendicular to strike across intersecting thrust faults yield an imbalance in the along-strike lengths of frontal ramps. The restoration leads to a similar imbalance in the surface area of a stratigraphic horizon, reflecting volume imbalance in three dimensions. The tectonic thickening of the weak-layer shales is evident in palinspastically restored cross sections, which demonstrate as much as 100% increase in volume over the restored-state cross sections. The cause of the surplus shale volume is likely prethrusting deposition of thick shale in a basement graben that was later inverted. The volume balance of the ductile duplex is critical for palinspastic reconstruction of the recess, and for the kinematic history and mechanics of the ductile duplex.

In Alabama, the Paleozoic Appalachian thrust belt plunges southwest beneath the Mesozoic-Cenozoic Gulf Coastal Plain. In Arkansas, the Paleozoic Ouachita thrust belt plunges southeast beneath the Coastal Plain. The strikes of the exposed thrust belts suggest an intersection beneath the Coastal Plain. Well data and seismic reflection profiles confirm the strike and intersection of the thrust belts, and provide information to determine the structure and general stratigraphy of each thrust belt. In east-central Mississippi, the Appalachian thrust belt curves from the regional northeast trace to westward at the intersection with the southeastern terminus of the Ouachita thrust belt, to northwest where Ouachita thrust sheets are in the Appalachian footwall, and farther west, to a west-southwest orientation. At the intersection, the frontal Appalachian fault truncates the Appalachian thrust sheets. The Appalachian thrust sheets are detached in Lower Cambrian strata and contain a distinctive Cambrian-Ordovician passive-margin carbonate succession. The Ouachita thrust sheets are detached above the carbonate succession and contain a thick Carboniferous clastic succession. The Appalachian thrust sheets east of the intersection rest on an autochthonous footwall with a thin Lower Cambrian sedimentary cover above Precambrian crystalline basement. To the west, the Appalachian thrust sheets rest on an allochthonous footwall of thick Ouachita thrust sheets. The top of Precambrian crystalline basement rocks dips southwestward beneath the Ouachita thrust belt; large-magnitude down-to-southwest basement faults enhance the deepening. Appalachian thrust sheets on the northeast are detached above relatively shallow basement, but to the west, are detached above thick Ouachita thrust sheets, which overlie deeper basement. The structure of the basement reflects the Iapetan rifted margin, where the northwest-striking Alabama-Oklahoma transform bounds the southwest side of the Alabama promontory. The trends of basement structures and subsidence toward the Ouachita thrust belt parallel the Alabama-Oklahoma transform. Shallower basement and synrift basement grabens underlie the northeast-striking Appalachian thrust belt. The curves in strike and along-strike change in footwall structure of the Appalachian thrust belt reflect controls by basement structure and by the structure of the Ouachita thrust belt.

This thesis presents a detailed 40 evolutionary model of the deepwater fold-and-thrust belt of the western Niger Delta using a 3D seismic reflection dataset. The geometries and kinematics of the fault-related folds interpreted in the study area have been compared to two series of 20 sandbox analogue models of a doubly-vergent wedge to understand the evolution of these structures. The regional interpretation of the 3D seismic dataset revealed the occurrence of four thrust domains separated by dextral tear faults. Each domain is characterised by differing deformational styles. Distinct structural styles have been interpreted in e~ch thrust domain. Section restoration of regional cross sections revealed different amounts of shortening, from 0.7 km to 2.7 km, within each domain, an overall break-forward propagation sequence, and a complex thrust interaction with reactivations and synchronous activity commonly observed. The detailed 3D interpretation and structural analysis of individual fault-related folds demonstrated ~hat these structures evolved initially as detachment folds which were subsequently faulted by break thrusts in their limbs, resulting in faulted detachment folds. At the Present Day, the structures show geometric similarities to shear fault bend folds but clearly have evolved in a non self similar way. Detailed analyses have revealed that folds are partitioned vertically with brittle duplex systems at the detachment level, , overlain by a region of pure shear homogeneous strain which itself is overlain by a pre-kinematic sequence representing the flexural lid of the folds. Fold growth is recorded by growth strata and shows an initial rapid rate of crestal uplift followed by a decrease in uplift with continued shortening. This is interpreted to be a result of fold growth by limb rotation. The above-described structural aspects are included in the new evolutionary models of fault-related folds proposed in this thesis. The 20 scaled analogue modelling of doubly-vergent wedge using high- resolution digital photography and Die analyses have clearly shown that the laboratory models also evolve in a similar fashion and develop in some way similar geometries to those in the deepwater fold belts.

This investigation focuses on the Jurassic-Eocene sedimentary record of northwestern Montana and the geometry and kinematics of the thrust belt, in order to develop a unifying geodynamic-stratigraphic model to explain the evolution of the Cordilleran retroarc of this region. Provenance and subsidence analyses suggest the onset of a foreland basin system by Middle Jurassic time. U-Pb ages of detrital zircons and detrital modes of sandstones indicate provenance from accreted terranes and deformed miogeoclinal rocks. Subsidence commenced at ∼170 Ma and followed a sigmoidal pattern characteristic of foreland basin systems. Jurassic deposits of the Ellis Group and Morrison Formation accumulated in a back-bulge depozone. A regional unconformity/paleosol zone separates the Morrison from Cretaceous deposits. This unconformity was possible result of forebulge migration, decreased dynamic subsidence, and eustatic sea level fall. The late Barremian(?)-early Albian Kootenai Formation is the first unit in the foreland that consistently thickens westward. The subsidence curve at this time begins to show a convex-upward pattern characteristic of foredeeps. The location of thrust belt structures during the Late Jurassic and Early Cretaceous is uncertain, but provenance information indicates exhumation of the Intermontane and Omineca belts, and deformation of miogeocline strata, possibly on the western part of the Purcell anticlinorium. By Albian time, the thrust belt had propagated to the east and incorporated Proterozoic rocks of the Belt Supergroup as indicated by provenance data in the Blackleaf Formation, and by cross-cutting relationships in thrust sheets involving Belt rocks. From Late Cretaceous to early Eocene time the retroarc developed a series of thrust systems including the Moyie, Snowshoe, Libby, Pinkham, Lewis-Eldorado-Steinbach-Hoadley, the Sawtooth Range and the foothills structures. The final stage in the evolution of the compressive retroarc system is recorded by the Paleocene-early Eocene Fort Union and Wasatch Formations, which are preserved in the distal foreland. A new ∼145 Km balanced cross-section indicates ∼130 km of shortening. Cross-cutting relationships, thermochronology and geochronology suggest that most shortening along the frontal part of the thrust belt occurred between the mid-Campanian to Ypresian (∼75-52 Ma), indicating a shortening rate of ∼5.6 mm/y. Extensional orogenic collapse began during the middle Eocene.

Studies of mountain belts worldwide show that along-strike changes are common in their foreland fold-and-thrust belts. These are typically caused by processes related to fault reactivation and/or fault focusing along changes in sedimentary sequences. The study of active orogens, such as Taiwan, can provide insights into how these processes influence transient features such as seismicity, contemporaneous stress and strain fields and topography. In Taiwan, the fold-and-thrust belt comprises a roughly N-S striking, west verging imbricate thrust system that has been developing since the Late Miocene. This fold-and-thrust belt is deforming the sediments from the outer shelf to the base of the slope of the Eurasian continental margin, incorporating structural (e.g., necking zone, extensional fault system, failed rift) and morphological (e.g., the shelf, shelf/slope break, the slope) features of the margin. In this thesis, we adopt a multidisciplinary approach in order to test the hypothesis of whether or not the inherited structural and morphological architecture of the Eurasian continental margin may be influencing the development of the south central Taiwan fold-and-thrust belt. We first trace regional-scale features from the outer shelf to the slope base of the Eurasian continental margin in the Taiwan Strait into the south central Taiwan fold-and-thrust belt. We then present a regional-scale new surface geological mapping that we combine with P-wave velocity maps and sections, seismicity, and topography data to test the hypothesis in a regional-scale to investigate causal links between these features of the fold-and-thrust belt and those from the margin. We further test the hypothesis in regional-scale to see whether or not structural and morphological features inherited from the margin are affecting the contemporaneous stress and strain fields in south central Taiwan. The principal stress directions (Sgyma 1, Sygma 2, and Sygma 3) are estimated from the inversion of clustered earthquake focal mechanisms and the direction of maximum compressive horizontal stress (SH) is calculated throughout the study area. From these data the most likely fault plane orientations and their kinematics are inferred. The directions of displacement, compressional strain rate, and maximum shear strain rate derived from GPS data are also calculated and plotted. These are discussed together with the stress inversion results. Finally, the structure of the area in southwest Taiwan fold-and-thrust belt corresponding to the necking zone is investigated in more detail. We define its structure, presenting new surface geological mapping from which we construct balanced and restored cross-sections and along-strike sections. From these we compile maps of the basal thrust, thrust branch lines and, where possible, stratigraphic cut-offs. These data show that the most important along-strike change takes place at the eastward prolongation of the upper part of the margin necking zone, where there is an interpreted link between fault reactivation, involvement of basement in the thrusting, concentration of seismicity, and the formation of high topography. The contemporaneous stress and strain fields also show a marked change across the upper part of the margin necking zone. The direction of SH changes from north to south across the study area (≈ 8.2 cm/yr toward 306°), with the direction of SH remaining roughly sub-parallel to the relative plate motion vector in the north, whereas in the south it rotates nearly 45° counter-clockwise. The direction of horizontal maximum compression strain rate (Sgyma H) and associated maximum shear planes, together with the displacement field display an overall similar pattern between them, although undergoing a less marked rotation. In the southwest Taiwan fold-and-thrust belt, in the area corresponding to the margin necking zone, the detailed 3D structural analysis shows a less marked but still important along-strike change in the structure than that described for the upper part of the necking zone. This change takes place across a transverse zone that is composed of a suite of structures at the surface that we call the Hsinhua transverse zone. We suggest that this transverse zone coincides with variations in the geometry of the basal thrust which, in turn, has a causal relationship to (possibly fault bounded) basement highs and lows that are inherited from the continental margin. We interpret all these along-strike changes in the fold-and-thrust belt to be related to the reactivation of east-northeast striking faults inherited from the rifted Eurasian margin. In the upper part of the margin necking zone, the strike-slip reactivation of east-northeast striking extensional faults is causing sigmoidal offset of structures and topographic ridges, and the rotation of the SH and SgymaH directions, together with that of the horizontal displacement field. In the necking zone, the reactivation of east-northeast striking faults is also influencing the development of the fold-and-thrust belt, although with a less marked effect.

The Zagros-fold-and thrust belt has been selected to explore landscape responses to tectonic and climatic drivers using river profile steepness (ksn), relief from topography, and basin scale Hypsometric Index (HI) extracted from Shuttle Radar Topography Mission (SRTM) 30 m dataset. There are differences in the ksn and the HI value from one area to another across the Zagros range. The northeastward presence of high HI values with respect to the seismicity cut-off in the combined Dezful/Bakhtyari region is attributed to wetter conditions, in turn driven by high strain and high topographic gradients in the Bakhtyari region. Drier climate and low power rivers in the Fars region promote plateau growth, and high HI values occur south of the thrust seismicity cut-off. In spite of the regional differences in ksn and HI, there is a similarity in the integrated relief along swath profiles, consistent with the similar rate of strain and total strain across different parts of the Zagros. Digital Elevation Model (DEM)-based geomorphic indices; Hypsometric Index (HI), Surface Roughness (SR) and their combination Surface Index (SI) have been applied to quantify landscape maturity in the Kirkuk Embayment of the Zagros. Landscape maturity suggests out of sequence deformation towards the hinterland in opposite sense to classical ‘piggyback’ thrusting model. The SI shows new previously undiscovered anticlines of hydrocarbon potential. New balanced cross-section indicates shortening in the order of ~5% in the Zagros foreland. Basin-scale values of HI exhibit sharp boundary of the low/high HI transition in the south of the Himalaya consistent with the zone of the Main Himalayan Thrust (MHT), and indicate the controls of the MHT on Himalayan topography. Smaller magnitude increases in HI value across the physiographic transition (PT2) do not support the out-of-sequence model of active deformation of Himalayan tectonics. Point-counting technique was conducted for modern river sand from the Zagros suture and the Neogene sandstones of the Zagros foreland. Results show recycled orogen provenance and litharenite composition and spatial increase in quartz content towards the northwest, which might refer to provenance change and/or drainage reorganization. The more lithic composition of river sand and the Neogene sandstone refers to an uplift of the Zagros suture area, which is partly caused by the out-of sequence deformation of the Mountain Front Fault.

Understanding fluid flow in fold and thrust belts has the potential to offer enormous insight into hydrocarbon accumulations in regions dominated by such structurally complex settings. Thrusting episodes can be key in creating a complete petroleum system, aiding maturation through burial, developing trapping scenarios, creating pathways for flow though juxtaposition and acting as conduits for flow connecting source to reservoir. The ability to model thrust and fold belts is limited due to the complex nature of threedimensional modelling of thrusts. However recent advancements is structural modelling software have allowed the representation of a stratigraphical surface in two depth locations at a single surface location enabling better realisations of overlain strata in thrust zones. This work simulates the migration of hydrocarbons through fold and thrust zones using new Earth Models of the southern Sub Andean in Bolivia, created from seismic interpretation and well data analysis, and develops a new modelling workflow using multiple geological modelling applications. The migration pathways have been simulated in three dimensions using invasion percolation hydrocarbon migration modelling techniques developed by the Basin Dynamics Research Group at Keele University. These techniques allow the investigation of the relationship of stratal flow properties across thrust blocks. The methodology employed allowed the geological uncertainty of the prospect to be evaluated for hydrocarbon trapping potential, through repeatable simulations where the location point of hydrocarbon source could be controlled. The results of the modelling work provides an insight into the evolution, maturation and potential accumulation of fluids in the Bolivian case study, and has produced a predictive approach to analysing fluid flow and accumulation applicable to other hydrocarbon systems as well as application in other fields considering fluid migration pathways and accumulation.

This research project used 3D seismic data located in deep water fold and thrust belt in the Levant Basin eastern Mediterranean, to investigate the nature and kinematics of compartmentalized thrust related folds. The principal aim is to better understand thrust related fold development and interactions in compressional settings. The fold and thrust belt in the Levant Bain is mainly comprised of overlapping thrust faults of similar and opposing dips segmented or bounded by conjugate sets of strike slip faults. Detailed interpretation and analysis of the 3D geometry of the structures revealed that thrust faulting is an early process in the development of the thrust and fold pair, thrust interact with each other, and strike slip faults along strike. A preliminary end member interaction of thrust faults and strike slip faults is proposed based on observation of their bounding or segmenting pattern. The concept of fault interaction was mainly developed from the investigation of the propagation of thrust fault compartmentalised by strike slip faults. This involves a combination of kinematic analysis which includes fault displacement and shortening profiles, and the patterns of syn kinematic sediments above fold limb. Kinematic data suggests that strike slip faults are acting as barriers to thrust fault propagation. Similar barrier to fault propagation are observed between overlapping thrust faults within a single fold formed by the linkage of smaller thrust folds. The results showed that the faults are restricted as they link and transfer displacement. In addition to the propagation of thrust faults, vertical distribution of fault displacement suggests that they ramp up from detachment, this agrees with the classical models of thrust propagation folds.

Fracture distribution in a fold and thrust belt is commonly thought to vary depending on structural position, strain, lithology and mechanical stratigraphy. The distribution, geometry, orientation, intensity, connectivity and fill of fractures in a reservoir are all important influences on fractured reservoir quality. The presence of fractures is particularly beneficial in reservoirs that contain little matrix porosity or permeability, for example tight sandstones. In these examples fractures provide essential secondary porosity and permeability that enhance reservoir production. To predict how reservoir quality may fluctuate spatially, it is important to understand how fracture attributes may vary, and what controls them. This research aims to investigate the influence of structural position on fracture attribute variations. Detailed fracture data collection is undertaken on folded sandstone outcrops. 2D forward modelling and 3D model restorations are used to predict strain distribution in the fold-and-thrust belt. Relationships between fracture attributes and predicted strain are determined. Discrete Fracture Network (DFN) modelling is then undertaken to predict fracture attribute variations. DFN modelling results are compared with field fracture data to determine how well fractured reservoir quality can be predicted. Field data suggests strain is a major controlling factor on fracture formation. Fractures become more organised and predictable as strain increases. For example in high strain forelimb regions, fracture intensity and connectivity are high, and fracture orientations are consistent. In lower strain regions, fracture attributes are much more variable and unpredictable. Fracture variations often do not correspond to strain fluctuations, and correlations can be seen between fracture intensity and lithology. Reservoir quality is likely to be much more variable in low strain regions than high strain regions. DFN modelling is also challenging because fracture attribute variations in low strain regions do not correspond to strain, and therefore cannot be predicted.

Thesis (M.A.)--Florida State University, 2009.
Advisor: James F. Tull, Florida State University, College of Arts and Sciences, Dept. of Geological Sciences. Title and description from dissertation home page (viewed on Apr. 8, 2009). Document formatted into pages; contains xv, 209 pages. Includes bibliographical references.

The N-S trending Kazerun Fault zone obliquely crosses the NW-SE trending Zagros fold thrust belt in southwest of Iran. This still active fault zone is an ancient structural lineament, which has controlled the structure, sedimentation and subsidence of part of the Zagros mountain belt since the Cambrian. This study presents a new interpretation of the Kazerun Fault zone, and recognises it to be made up of four north-south trending segments, termed from north to south the Sisakht, Yasuj, Kamarij and Burazjan segments respectively. The Kazerun Fault limited the distribution of the Cambrian Hormuz salt with considerable thickness forming to the east of the fault (i.e. in the Fars region) and little or none to the west (i.e. in the Dezful Embayment). This thick salt layer decouples the cover rocks from the basement structures. The salt significantly reduces the cohesion and frictional resistance at the base of the sedimentary cover and enables deformation to the east of the fault to propagate 100km further to the southwest than in the Dezful Embayment to the west. This basal decollement and the rheological differences in the cover rocks each side of the Kazerun Fault is the reason for the arcuate plan view of the fold-thrust belt in the Fars region. There is a remarkable difference in the distribution of deformation in the cover rocks in the two regions which are separated from each other by the Kazerun Fault zone. The Sisakht, Kamarij and Burazjan segments of the Kazerun Fault acted as lateral ramps linking the three major Zagros deformation fronts, the High Zagros, the Mountain Front and the Zagros Frontal Faults respectively. These segments are characterised by huge vertical displacements with downthrow to the west. However, it is argued that the Yasuj segment only became active relatively lately, during the folding and unlike the other segments did not control the post collision sedimentation of the Zagros. A study of the digital elevation model of the Sarbalesh anticline (formed by combination of aerial photographs, the TM satellite image and topographic maps) and field data were used to analyse this anticline and its associated structures. It is suggested that synchronous folding and faulting (both thrusting and normal faulting) occurred during the formation of this boomerang shaped anticline which is situated in the junction between the Kamarij segment of the Kazerun Fault and a segment of the Mountain Front Fault. A detailed review of the sedimentation of the Iranian sector of the Zagros fold-thrust belt reveals the structural evolution of the Kazerun Fault and other major structural elements of the Zagros and shows the intimate interplay between sedimentation and tectonics. The Zagros basin experienced rifting during the Permo-Trias and the resulting horsts and grabens had a NW-SE trend i.e. parallel to the present mountain belt. These structures controlled the subsidence of the basin during this period. During the Jurassic-Early Cretaceous the area corresponding to the present day Kazerun and Izeh Fault zones was the site of transition between the two entirely different basins which occupied the Fars and Lurestan regions. Important movements along the Kazerun-Izeh Fault zone in the Mid-Cretaceous produced a series of N-S trending horst and graben structures which are marked by significant sedimentary change across them. During the Tertiary the NW-SE trending Mountain Front Fault (i.e. introduced in this study) was the major deformation front, controlling the deposition and geometry of the Zagros foreland and piggyback basins to the southwest and northeast of the fault respectively. The different deformational styles of the cover rocks in the Zagros (e.g. on either side of the Kazerun Fault zone), relates to inherited basement structures, the different rheological profiles and particularly, the presence and position of the detachment horizons within the cover rocks. In fact, these differences are mainly the result of activity along the Kazerun Fault in the Cambrian, the Kazerun-Izeh Fault in the Jurassic- Cretaceous and the Mountain Front Fault in the Tertiary. It is also argued that Zagros anticlines (the major hydrocarbon traps in the Zagros) are the result of different mechanisms. These include classical buckle folds, en echelon folds along strike-slip faults and fault related folds above thrusts and reactivated normal faults. These differences related directly to the rheological profile of the cover rocks which was controlled by activity along the Kazerun, Jzeh, Bala Rud and Mountain Front Faults. Based on this study a clearer picture of the interplay between structures, sedimentation and deformation of the Zagros fold-thrust belt has emerged. This makes it appropriate to revise the entire Zagros belt from the point of view of new hydrocarbon targets, which include folds, faults and sedimentary traps.

Tectonic shortening within the Himalayan fold-thrust belt in Nepal has been accommodated by southward displacement of large thrust sheets. Most workers focus on the impact that the Main Central, Main Boundary, and Main Frontal thrusts have had on the orogen's structural, thermal, and geomorphic evolution. However, mapping across Nepal, has revealed the presence of the Ramgarh thrust, which is another orogen-scale thrust. The Ramgarh thrust, which had previously been recognized in India and far-western Nepal, occurs within Lesser Himalayan zone rocks, and accommodates a magnitude of shortening similar to that of the Main Central thrust. This dissertation focuses on the structural and tectonic significance of the Ramgarh thrust. Minor details notwithstanding, the structural characteristics of the Ramgarh thrust remain consistent along the ∼800 km width of the fold-thrust belt in Nepal. At current levels of erosion, the Ramgarh thrust is always exposed in a hanging-wall flat on footwall flat thrust relationship with other Lesser Himalayan zone rocks, and also with overlying rocks carried by the Main Central thrust. Mapping along a north-south transect in central Nepal has permitted the construction of a balanced cross-section, which shows that the fold-thrust belt has accommodated a minimum of 489 km of tectonic shortening. A large proportion of which was accommodated by slip on the Ramgarh thrust. Integrating structural constraints provided by mapping and the cross-section with existing thermochronologic, thermobarometric, and foreland basin provenance datasets yields a kinematic model for the structural evolution of the fold-thrust belt. Recognition of the structural relationship between the Ramgarh and Main Central thrusts also permits new insight into the nature of the Main Central thrust. Structural mapping combined with Nd isotope studies from the vicinity of the Ramgarh and Main Central thrusts in Langtang National Park suggest that the Main Central thrust can be defined as a relatively narrow tectonostratigraphic contact, and not as a broad, poorly defined, shear zone. Additionally, much of the volume of highly strained rocks in the footwall of the Main Central thrust may be genetically related to deformation on faults (including the Ramgarh thrust) that lie structurally below the Main Central thrust.

The South Portuguese Zone (SPZ), which host world-class massive sulphide deposits, forms the southern fold-and-thrust belt of the Iberian Variscan orogeny. This thesis focuses on seismic-reflection and seismic-refraction processing efforts on a subset of the IBERSEIS deep seismic-reflection data set aiming at resolving the SPZ upper crust in high resolution. A comparison of different crooked-line seismic-reflection imaging schemes showed that a processing sequence involving dip-moveout corrections, a common-midpoint projection, and poststack time migration of common-offset gathers provided the most coherent images considering the crooked acquisition geometry. Correlation with surface-geological data allows four units of different reflection character to be identified: the ~0–2 km deep Upper Carboniferous Flysch group, the highly reflective ~2–4 km thick and up to ~5 km deep Volcano-Sedimentary Complex (VSC) group, and two deep Paleozoic metasedimentary units, with the shallower Phyllite-Quartzite group exposed in an antiform. Prominent diffracted energy was enhanced using a modified Kirchhoff imaging routine. High reflectivity and distinct diffractions mark extensive dike bands at 6–12 km depth, possibly related to the intense hydrothermal activity that led to the formation of the ore-bearing VSC group. Source-generated noise obscures potential signals from depths shallower than ~500m depth on the seismic-reflection sections. P- and SV-wave first-arrival traveltimes were inverted for velocity models imaging the shallowest crust. Overall, the velocity models correlate well with surface-geological data marking high (>5.25 km/s) and uniform P-velocities for the Flysch unit in the southern SPZ. A prominent P-wave low-velocity body (~4.5 km/s) is resolved where the Phyllite-Quartzite unit forms the core of an antiform. P-velocities fluctuate the most in the northern SPZ with Flysch group units exhibiting high velocities (>5.25 km/s) and VSC group bodies showing intermediate velocities (~5 km/s). Low VP/VS-ratios (~1.8) computed for the southern profile part are interpreted as less deformed Flysch-group units, whereas high VP/VS-ratios (~1.9) indicate fractured units.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1989.
Lindgren second copy is bound in one vol.
Chapter 3 co-authored by Matthew T. Heizler; chapter 4 co-authored by J. Douglas Walker. 4 folded leaves inserted in pocket of v. 1.
Includes bibliographical references.
by James Howard Knapp.
Ph.D.

The south eastern Pyrenees allowed us to study the relationships between fluid flow and deformation in a complete section of a well-preserved fold and thrust belt. Furthermore, this study enables us to decipher the main controls on fluid flow and to perform a conceptual model of fluid migration in fold and thrust belts by comparing the southern Pyrenees with other orogens worldwide. A combination of field-based and petrographic observations together with geochemical analyses was used to determine the origin of fluids from which these cements precipitated, the conditions of fluid migration and the fluid-rock relationships. These methods were applied to carbonate host rocks and calcite and dolomite cements precipitated in fractures and in intergranular and vug porosities. The integration of the methodology allowed us to define up to 20 fluid flow events for the Upper Pedraforca thrust sheet, Eight for the Lower Pedraforca thrust sheet, seven for the Vallfogona thrust, which is the southern margin of the Cadí thrust sheet, and two for both the Abocador thrust and the Puig-reig anticline, which are located in the foreland Ebro basin. During the late foreland stage of the south Pyrenean fold and thrust belt, the Puig-reig anticline formed. Structural and microstructural analysis developed in this fold demonstrate that at outcrop scale fracturing was controlled by rigidity contrasts between layers, diagenesis and structural position within the anticline, whereas grain size, cementation and porosity controlled deformation at the microscopic scale. Petrographic and geochemical studies of calcite precipitated in host rock porosity and fault planes reveal the presence of two migrating fluids, which represents two different stages of evolution of the Puig-reig anticline. During the layer- parallel shortening, hydrothermal fluids with temperatures between 92 and 130 ºC circulated through the main thrusts to the permeable host rocks, reverse and most of strike-slip faults precipitating as cement Cc1. During the fold growth, meteoric waters circulated downwards through normal and some strike-slip faults and mixed at depth with the previous hydrothermal fluid, precipitating as cement Cc2 at temperatures between 77 and 93 ºC. Integration of the results from the Puig-reig anticline in this work and the El Guix anticline indicates that hydrothermal fluids did not reach the El Guix anticline, in which only meteoric and evolved meteoric waters circulated along the fold. In the south Pyrenean foreland basin, Hydrothermal fluids at temperatures up to 154 °C, migrated from the Axial zone to the foreland basin and mixed with connate fluids in equilibrium with Eocene sea-water during lower and middle Eocene (underfilled foreland basin). As the thrust front progressively emerged, low-temperature meteoric waters migrated downwards the foreland basin and mixed at depth with the hydrothermal fluids from middle Eocene to lower Oligocene (overfilled non-marine foreland basin). The comparison of the fluid flow models from the Southern Pyrenees with other orogens worldwide, seems to indicate that the presence or absence of thick evaporitic units highly control fluid composition during the development of fold and thrust belts. Whereas in thrusts not detached along thick evaporite units, mixed fluids are progressively more depleted in δ18O and have a lower temperature and lower Fe and Sr contents as the thrust front emerges, in thrust detachments through thick evaporite units, the mixed fluids are enriched in δ18O. From U-Pb geochronology applied to calcite cements, 47 ages for the South Pyrenean fold and thrust belt are obtained. Results indicate that fluid migration took place during the Pyrenean compression and that deformation migrated from the upper thrust sheets to the lower thrust units and to the foreland from 70.5 ± 1.1 Ma to 25 ± 17 Ma. These U-Pb ages also indicate that each of the thrust sheets registers its own deformational history as well as the history of the underlying thrust units emplaced during tectonic stacking. For instance, the Upper Pedraforca thrust sheet records the entire compressional history of the SE Pyrenees. Likewise, the wide distribution of U- Pb ages within each tectonic unit indicates that deformation was continuous rather than episodic. Calcite veins with Neogene ages ranging from 18.9 ± 0.8 Ma to 2.6 ± 1.3 Ma are interpreted as having been formed during the Neogene rift and post-rift Western Mediterranean events stretching across NE Iberia. These ages are the first evidence demonstrating deformation within the SE Pyrenees during these post-compressional events. In the Lower Pedraforca thrust sheet, during syn-sedimentary hydroplastic normal faulting affecting poorly-consolidated Upper Cretaceous sediments and Eocene syn-orogenic sediments, calcite cements did not precipitate. During the burial and the layer-parallel shortening, however, calcite cements Cc1 to Cc4 precipitated from fluids in a relatively paleohydrological system. Cc3 precipitated from high-salinity fluids (~+5.4 ‰ VSMOW) with 87Sr/86Sr ratios of 0.707922 and at temperatures around 70 ºC. Contrarily, during folding and thrusting, calcite cements Cc5 to Cc8 precipitated in a more open paleohydrological system. Cc6 precipitated from high-salinity fluids (~+5 ‰ VSMOW) with 87Sr/86Sr ratios 0.707817 and at temperatures around 75 ºC. The controls of deformation on the paleohydrological system observed in the Lower Pedraforca thrust sheet have strong similarities with that observed other areas worldwide under both compressional and extensional regimes. In the Upper Pedraforca thrust sheet, brines at 125 and 145 ºC migrated through fractures during the Early Cretaceous extension. During the Late Cretaceous-Paleocene compression, formation waters at temperatures around 80 ºC and in equilibrium with Late Cretaceous seawater migrated through main thrust fault zones. As the Upper Pedraforca thrust sheet emplaced, the influence of meteoric waters increased, resulting in the slightly decrease of the salinity of migrating fluids. During the Eocene-Oligocene reactivation of this thrust unit, also formation waters at temperatures between 90 and 100 ºC migrated through main thrust fault zones. However, the influence of meteoric waters increased with respect to the Late Cretaceous-Paleocene compression, indicating exhumation of the Upper Pedraforca thrust sheet. Stable, clumped and strontium isotopes together with elemental composition and rare earths and yttrium analysis indicate that during the emplacement of the Upper and Lower Pedraforca thrust sheets, from Late Cretaceous to middle Eocene, the fluid system was dominated by high- salinity formation fluids and meteoric waters at temperatures ranging between 70 and 90 ºC. In these thrust sheets, fluids migrated above evaporite detachments that acted as barriers for the input of deep sourced fluids. Contrarily, during the emplacement of the Cadí thrust sheet and during the deformation affecting the northern side of the Ebro foreland basin from middle Eocene to Oligocene, high-salinity hydrothermal fluids derived from the deeper parts of the Axial zone and at temperatures between 100 and 177 ºC, migrated through fractures to the thrust front. Hydrothermal fluid flow induced the development of thermal anomalies in the Vallfogonala and Abocador thrusts and in the Puig-reig anticline, which are structures rooted at depth with the basement. These fluid flow patterns observed during the growth of the south eastern Pyrenean fold and thrust belt are similar to that observed in the western side of this orogen. The evolution of the fluid regime during the growth of the southern Pyrenees has strong similarities to that observed in other orogens worldwide such as the Sevier thrust belt, the western Alps, the Ionian zone in Albania, the Nuncios fold Complex in Mexico as some examples. From these similarities a conceptual model of fluid flow in fold and thrust belts in which the style of deformation is one of the main controlling parameters is performed. In this model, whereas in thin-skinned fold and thrust belts the fluid system is controlled by formation, marine and meteoric waters, in thick-skinned fold and thrust belts the system is controlled by the input of deep-sourced hydrothermal fluids, which induce the formation of thermal anomalies. In both situations, during the layer-parallel shortening stretching thrust sheets, the paleohydrological system was closed and the fluid-rock interaction was low. In contrast, during later folding and thrusting the system opened to the input external fluids and the interaction between fluids and their adjacent host rocks decreased progressively.
En aquesta tesi s’ha realitzat un estudi de la relació entre la migració de fluids i la deformació en una secció completa del cinturó de plecs i encavalcaments Sudpirinenc. A més a més, en aquest estudi s’han desxifrat els principals paràmetres que controlen la migració de fluids per tal de presentar un model conceptual de circulació de fluids en cinturons de plecs i encavalcaments comparant el sud dels Pirineus amb altres orògens d’arreu del món. Per determinar l’origen dels fluids, les condicions sota les quals van migrar i les relacions fluid-roca, s’han integrat observacions de camp i petrogràfiques amb anàlisis geoquímics. Aquests mètodes s’han aplicat en roques carbonatades i ciments de calcita i dolomita precipitats en fractures i en la porositat intergranular i vacuolar present en les roques encaixants. La integració de la metodologia abans esmentada ha permès la identificació de 20 episodis de migració de fluids en el mantell superior del Pedraforca, vuit en el mantell inferior del Pedraforca, set en l’encavalcament de Vallfogona, que és el marge sud del mantell del Cadí, i dos per l’encavalcament de l’Abocador i l’anticlinal de Puig-reig, els quals estan situats en la conca d’avantpaís de l’Ebre. Durant el darrer estadi d’avantpaís endorreic del cinturó de plecs i encavalcaments Sudpirinenc, es va formar l’anticlinal de Puig-reig. Els anàlisis estructurals i microestructurals desenvolupats en aquest plec demostren que a escala d’aflorament la fracturació és controlada pel contrast de rigidesa entre estrats, la diagènesi de les roques encaixants i la posició estructural de l’anticlinal. Per altra banda, a escala microscòpica, la fracturació és controlada per la mida de gra, la cimentació i la porositat. L’estudi petrogràfic i geoquímic de ciments de calcita precipitats en la porositat de la roca encaixant i entre plans de fractura revela la presència de dos tipus de fluids, els quals representen dos estadis diferents de l’evolució de l’anticlinal de Puig-reig. Durant els estadis inicials de compressió, fluids hidrotermals a una temperatura que varia entre 92 i 130 ºC van migrar des dels encavalcaments principals fins a les roques encaixants més permeables, falles inverses i la majoria de les falles direccionals, i van precipitar com a ciment Cc1. Durant el creixement de l’anticlinal, fluids meteòrics van percolar a través de falles normals i algunes falles direccionals i es van barrejar amb els fluids hidrotermals abans esmentats. El fluid resultant d’aquesta barreja va precipitar com a ciment Cc2 a una temperatura que varia entre 77 i 93 ºC. La integració dels resultats obtinguts a l’Anticlinal de Puig-reig amb els ja obtinguts per altres autors a l’anticlinal del Guix indica que els fluids hidrotermals no van arribar a l’anticlinal del Guix, en el qual només aigües meteòriques i de formació van migrar a través d’aquest plec. En la conca d’avantpaís Sudpirinenca, durant l’Eocè inferior i mig, fluids hidrotermals a una temperatura de fins a 154 ºC van migrar des de la Zona Axial fins a la conca d’avantpaís i es van barrejar amb aigües connates en equilibri amb aigua marina Eocena. A mesura que el front d’encavalcament emergia a partir de l’Eocè superior fins a l’Oligocè, aigües meteòriques de baixa temperatura van percolar fins a les zones més profundes de la conca d’avantpaís i es van barrejar amb els fluids hidrotermals. La comparació dels models de circulació de fluids del sud dels Pirineus amb altres orògens d’arreu del món, semblen indicar que la presència o absència de potents unitats evaporítiques controlen la composició dels fluids durant el desenvolupament de cinturons de plecs i encavalcaments. En mantells d’encavalcaments no desenganxats sobre unitats potents d’evaporites, els fluids són progressivament més empobrits en δ18O, Fe i Sr i es troben a una menor temperatura a mesura que el front d’encavalcament emergeix. En canvi, en mantells d’encavalcament desenganxats sobre unitats potents d’evaporites els fluids són progressivament més enriquits en δ18O. A partir de geocronologia d’U-Pb aplicada en ciments de calcita, 47 edats s’han obtingut al sud-est dels Pirineus. Els resultats indiquen que la migració de fluids va tenir lloc durant la compressió Pirinenca i que la deformació va migrar des dels mantells superiors cap als inferiors i cap a l’avantpaís des dels 70.5 ± 1.1 Ma als 25 ± 17 Ma. Aquestes edats també indiquen que cadascun dels mantells d’encavalcament Sudpirinencs registra la seva pròpia història de deformació i la dels mantells que té immediatament per sota durant l’apilament tectònic. Per exemple, el mantell superior del Pedraforca enregistra la història compressiva complerta del sud- est dels Pirineus. La distribució de les edats obtingudes per geocronologia d’U-Pb indiquen que la deformació va ser continua en comptes d’episòdica. Les venes de calcita amb edats d’entre 18.9 ± 0.8 Ma i 2.6 ± 1.3 Ma indiquen que es van formar durant els episodis de rift i post rift que van afectar el nord-est de la península ibèrica durant el Neògen, i indiquen per primera vegada deformació en els mantells Sudpirinencs durant aquests episodis post-compressius. En el mantell inferior del Pedraforca, durant l’extensió sinsedimentària afectant sediments poc consolidats del Cretaci superior i de l’Eocè, no hi va haver precipitació de ciments de calcita entre els plans de fractura. Durant l’enterrament d’aquests sediments i la deformació inicial paral·lela als estrats en canvi, els ciments de calcita Cc1 a Cc4 van precipitar a partir de fluids en un sistema paleohidrològic relativament tancat. El ciment Cc3 va precipitar a partir de fluids amb una alta salinitat (~+5.4 ‰ VSMOW), amb relacions 87Sr/86Sr de 0.707922 i a una temperatura d’uns 70 ºC. Contràriament, durant el plegament, els ciments Cc5 a Cc8 van precipitar en un sistema paleohidrològic més obert. El ciment Cc6 també va precipitar a partir de fluids d’alta salinitat (~+5 ‰ VSMOW), amb relacions 87Sr/86Sr de 0.707817 i temperatures al voltant de 75 ºC. Els controls de la deformació sobre el sistema pelohidrològic observats en el mantell inferior del Pedraforca són molt similars als observats en altres àrees d’arreu del món sota deformació compressiva i extensiva. En el mantell superior del Pedraforca, salmorres a temperatures entre 125 i 145 ºC van migrar a través de fractures durant l’extensió del Cretaci inferior. Durant la compressió del Cretaci superior-Paleocè, aigües de formació a una temperatura al voltant de 80 ºC i en equilibri amb aigües marines del Cretaci superior van migrar a través de les principals zones d’encavalcament. A mesura que el mantell superior del Pedraforca s’emplaçava, la influència d’aigües meteòriques augmentava induint la dilució dels fluids que migraven a través de les fractures. Durant la reactivació d’aquest mantell durant l’Eocè i l’Oligocè, aigües de formació a temperatures d’entre 90 i 100 ºC van migrar a través de les principals zones d’encavalcament. Tot i així, la creixent influència de fluids meteòrics al llarg del temps va augmentar respecte a la compressió de Cretaci superior indicant l’exhumació del mantell superior del Pedraforca. La integració de dades d’isòtops estables i d’estronci, clumped isotopes, així com el contingut elemental i de terres rares indica que durant l’emplaçament del mantell superior i inferior del Pedraforca, des del Cretaci superior fins a l’Eocè mig, el sistema de fluids estava dominat per iagües de formació i fluids meteòrics a una temperatura d’entre 70 i 90 ºC. En aquests mantells d’encavalcament els fluids migraven per sobre de nivells de desenganxament formats per evaporites que van actuar com a barreres per a l’entrada de fluids profunds. Contràriament, des de l’Eocè mig fins a l’Oligocè, durant l’emplaçament del mantell del Cadí i durant la deformació que va afectar el marge nord de la conca d’avantpaís de l’Ebre, fluids hidrotermals d’alta salinitat i una temperatura d’entre 100 i 177 ºC van migrar a través de fractures des de zones profundes de la Zona Axial fins al front d’encavalcament Sudpirinenc. La migració de fluids hidrotermals va afavorir el desenvolupament d’anomalies tèrmiques a l’encavalcament de Vallfogona i de l’Abocador i a l’anticlinal de Puig-reig, estructures que estan arrelades amb el basament. Els patrons de migració de fluids observats el sud-est dels Pirineus són molt similars als que s’observen al sud-oest d’aquest orogen. L’evolució del règim de fluids durant el creixement del cinturó de plecs i encavalcaments Sudpirinenc té moltes similituds amb els patrons de migració de fluids en altres orògens d’arreu del món, tals com el cinturó d’encavalcaments de Sevier, el sud-oest dels Pirineus, la zona Iònica d’Albània i el complex de plecs de Nuncios de Mèxic, com a alguns exemples. A partir d’aquestes similituds es presenta un model conceptual de migració de fluids en cinturons de plecs i encavalcaments en el qual l’estil de deformació és un dels principals paràmetres de control. En aquest model, mentre que en zones de tectònica epitelial el sistema de fluids està controlat per aigües de formació, marines i meteòriques, en zones afectades per deformació de pell gruixuda el sistema està controlat per fluids profunds que afavoreixen la el desenvolupament d’anomalies tèrmiques. En les dues situacions durant l’inici de la deformació el sistema paleohidrològic està relativament tancat i la interacció fluid-roca és baixa. En canvi, durant els últims estadis de deformació aquest sistema s’obre a l’entrada de fluids externs, induint la disminució de la interacció entre fluids i el seu encaixant.

This thesis uses industry 3D seismic to investigate the nature and distribution of strain in a deep water fold and thrust belt and describes the complex fault plane and stratal geometries that result from fold and thrust linkage. The principal aim is to gain a better understanding of the structural architecture and evolution of toe-of-slope compressional settings. To this end, the project represents a logical series of arguments involving the study of individual structures and fold and fault pairs, to considering a fold belt as a whole. The outer thrust belt of the Niger Delta is observed to comprise of synthetic and antithetic faults that interact and link along strike. A preliminary geometric classification is proposed for antithetic thrust fault linkage zones based on observations of fault surface and stratal geometries. The relationship between fault interaction and fold characteristics is also investigated. The connectivity of stratigraphic horizons across fault surfaces and through transfer zones is shown to vary with the type of linkage and with depth. Conclusions drawn on the along strike variability of fault network density, orientation and vertical extent are shown to have significant application to modelling of fluid flow. The concept of numerous and geometrically distinct thrust fault linkages forming through-going folds is developed through the investigation of a single isolated fold that comprises a number of linking forethrusts and backthrusts. This case study, involving the quantification of the development of this relatively simple structure, allows conclusions to be drawn on fold growth that are later applied to a more complex and closely spaced fold belt. The internal structural geometry of faults and stratigraphic horizons within the single fold are described though detailed three-dimensional mapping. The analysis of the distribution of fault and fold strain, both on individual thrusts within the fold and for the structure as a whole, suggest efficient displacement transfer between numerous linking faults that accommodated shortening as a coherent unit. In addition to this, variations in the magnitude of fault heave are compensated by complementary trends in fold strain. A study of syn-kinematic units demonstrates that the single structural culmination present today was initially made up of a number of folds with local structural highs. Major thrust surfaces within the fold are also interpreted to be the product of the along strike linkage and amalgamation of initially distinct faults. These observations made on the isolated fold are applied to a complex, closely spaced fold belt. The relative timing of individual faults and folds agree with established models of a progressive foreland propagating sequence of thrust faults but also display out-of-sequence events. Findings demonstrate a significant period of synchronous development between all structures in the fold belt. Aggregation of fault and fold shortening profiles indicate that displacement transfer occurs along strike and also in a dip-parallel direction between within the fold belt. Bulk shortening is thus conserved along strike within the syn-kinematic units and low lateral heave gradients suggest efficient displacement transfer between all constituent structures. The evidence presented here shows that all elements of a fold belt can be kinematically linked during growth. Irregularities in the distribution of deformation in pre-kinematic units corroborate findings that the folds are the product of along strike linkage of discrete segments, in a similar manner to that documented in extensional systems.

The key driving mechanisms for establishing deep-water fold-thrust belt are either lithospheric stress or gravity-driven associated with margin instability or a combination of both. Despite long academic interest, we still lack of detailed understanding of the interaction between the deformation mechanisms (gravity- and tectonic-driven). The results of an evaluation of the interaction between the deformation mechanisms, with focused attention upon the NW Borneo deep-water fold-thrust belt, are reported. A methodology integrating a detailed structural analysis of the deep-water fold-thrust belt from the available subsurface data and equivalent onshore outcrop is utilized in this study. Detailed structural analysis of 2D seismic profiles is used to present a basin-scale seismic-stratigraphic framework and detailed description of the general appearance of the deformational style along the deltaic system. Sub-seismic scale investigation of well-exposed outcrops onshore NW Sabah is used to extract information on onshore tectonic deformation, making it possible to evaluate the differences of structural architecture related to different deformation mechanisms. The result has led to an improved understanding of the regional-scale structural geometry along the NW Borneo margin. Regional scale cross-sections are used to demonstrate a regional-scale analysis of the NW Borneo margin that includes structural restoration. The results allow an assessment of the relative timing of deformation, the domain interaction and the possible processes and parameters that control deformation. This has led to an improved insight relating to the kinematic nature of the allochthon and the interaction between the deformation mechanisms. Structural restorations are also used to evaluate of areas of compressionally and extensionally dominated systems, in order to verify the main proses responsible for the margin evolution. This study illustrates outcrop-scale to seismic-scale analysis and quantitative measurements combined with seismic interpretations, with the aim to identify the interaction between gravity-and tectonic-driven deformation, and their controls on the geometry and evolution of deep-water fold-thrust systems. Additionally, the margin evolution and the implications on NW Borneo are evaluated.

The thesis presented here spins off from the 2-year oil-industry project entitled “Salt Tectonics Modelling at Kuqa Foreland Fold and Thrust Belt, Tarim Oilfield” that was a collaboration between the American-based company China Petroleum Corporation (CNPC USA) and GEOMODELS Research Institute (via Fundació Bosch i Gimpera). This research project stems from the need to understand the structural character and evolution of the Kuqa fold- and-thrust belt (NW Xina) in order to identify exploration targets at the Mesozoic subsalt level. Specifically, the aim of the study was to identify exploration targets at the Paleogene subsalt structural level of the Kuqa foreland basin and adjoining fold and thrust belt, in particular beneath the Qiulitage fold-and-thrust system. In this scenario, the project research was focused on the definition and understanding of the different salt structures, their relationship with the geodynamic context and the different types of related hydrocarbon traps. To achieve these objectives, it was agreed to carry out six regional cross-sections, three of them balanced and restored as well as eleven balanced cross-sections of the Qiulitage fold-and-thrust system, three of them restored. In addition, regional structural maps were produced showing the salt and subsalt structures as well as their relationships with salt distribution and thickness. This line of research has been complemented with the realization of eight numerical discrete-element models and eight scaled sandbox analogue models of tectonic wedges incorporating variations in the rheology of a weak layer and in the syn- kinematic sedimentary rate. In order to accomplish these tasks, the company provided around 1500 km of 2D seismic lines and geophysical logs from numerous wells drilled in the area. In addition, two field campaigns were organized between June (15 days) and September 2015 (21 days) where structural data were collected to recognize the surface structure of the Kuqa fold-and-thrust belt. Moreover, several transects were realized during these field campaigns to recognize the surface expression of interpreted structures in the seismic lines. In this context, this thesis deals only with the results obtained from the structural analysis based on surface and subsurface data and analogue modelling. These results are presented in this manuscript which includes the following chapters. CHAPTER 1 that provides a summary of the thesis. CHAPTER 2 which provides a general introduction to the geology and the kinematic evolution of the Tian Shan intraplate range. Then, the chapter focuses in the southern frontal structure of the central Tian Shan Range, the Kuqa fold-and-thrust belt, describing both the stratigraphy and the main features of its structure. Finally, the main objectives of this thesis are presented. CHAPTER 3 that deals with the structural analysis carried out in the Kuqa fold-and- thrust belt with the field and subsurface data. The chapter shows the input data and the interpretation of both surface and subsurface data. The chapter describes the obtained results of three regional cross-sections as well as the regional structural maps of salt distribution and thickness. In addition, the chapter provides a kinematic evolution of the Kuqa fold-and-thrust belt and discusses the main parameters controlling it. CHAPTER 4 that describes the data, methodology, procedure and results obtained in the analogue modelling experiments. These experiments where designed to analyze the influence of the rheological properties of two superimposed décollement layers but mainly the one of the syn-tectonic sedimentation. So, after a brief introduction to the purpose of the experimental program and the methodology used, this chapter describes the experimental results separating them according to the applied syn-kinematic sedimentary rate. Then, the obtained results are compared and discussed mainly focusing on: the influence of the mechanical properties of a weak layer; the syn-kinematic sedimentary rate in the geometry and kinematics of brittle-viscous tectonic wedges; as well as the interaction between sub-salt and salt-detached structures. CHAPTER 5 which compares the experimental results with the structure and kinematic of the Kuqa fold-and-thrust belt defined from our structural field and subsurface analyses that is described in the Chapter 3. CHAPTER 6 which depicts the main conclusions of this thesis. CHAPTER 7 formed by the references mentioned throughout the text.
El cinturó de plecs i encavalcaments de Kuqa, situat a l’avantpaís meridional de la serralada del Tian Shan occidental, va ser deformat contractivament durant el Mesozoic superior i el Cenozoic tal com queda registrat a les seqüències sin-tectòniques continentals. A més a més, la seva evolució estructural va ser fortament controlada per la presència de sal sin- orogència (d’edat Eocè-Oligocè) i dels décollements pre-sal. En aquest context, presentem un conjunt de sis talls geològics, tres d’ells restituïts, a través del cinturó de plecs i encavalcaments de Kuqa que proporcionen una nova interpretació de la estructura per sota de les evaporites, en la qual els materials paleozoics i mesozoics estan deformats per un apilament d’encavalcaments involucrant (i) un sistema d’encavalcaments de pell fina desenganxats en nivells de carbó triàsics-juràssics, i (ii) un conjunt d’encavalcaments de basament de vergència nord. Les restitucions regionals mostren tres estadis evolutius pel cinturó de plecs i encavalcaments de Kuqa: i) una extensió mesozoica menor; ii) una compressió primerenca (Cretaci superior fins Miocè inferior) amb taxes d’escurçament i sedimentació baixes; i iii) un estadi de compressió tardana (Pliocè superior-Pleistocè) caracteritzat per un creixement major i progressiu de les taxes d’escurçament i sedimentació. Per tal d’esclarir la influència de la taxa de sedimentació, els canvis laterals en la reologia dels décollements, i la interacció entre décollements en l’estil de deformació de l’avantpaís de cinturons de plecs i encavalcaments presentem un estudi experimental que inclou quatre models analògics 3D inspirats en el cinturó de plecs i encavalcaments de Kuqa. Els resultats experimentals mostren que augmentant la taxa de sedimentació es retarda el desenvolupament d’estructures contractives frontals desenganxades a la sal, afavorint la formació i reactivació d’encavalcaments i retro-encavalcaments a les zones internes. El nostre estudi revela que a mesura que la viscositat del décollement pre-cinemàtic augmenta la deformació es propaga lentament cap a l’avantpaís. Per altre banda, les estructures sub-sal poden: (i) determinar la extensió areal de la sal i per tant l’extensió del cinturó de plecs i encavalcaments desenganxats en ell i, (ii) retardar o inclús prevenir la propagació de la deformació sobre el nivell salí cap a l’avantpaís.

Thesis (B. Sc. (Hons.))--University of Adelaide: Dept. of Geology and Geophysics, 1993.
On title page: "National Grid reference: Kingscote (SI-53-16) 1:250 000 sheet Snug Cove (SI-53-6626-I) & Borda (SI-53-6626-IV) 1:50 000 sheets." Includes bibliographical references (leaves [9-14]).

Applying the anisotropy of magnetic susceptibility to analogue models provides detailed insights into the strain distribution and quantification of deformation within contractional tectonic settings like fold-and-thrust belts (FTBs). Shortening in FTBs is accommodated by layer-parallel shortening, folding, and thrusting. The models in this research reflect the different deformation processes and the resulting magnetic fabric can be attributed to thrusting, folding and layer-parallel shortening. Thrusting develops a magnetic foliation parallel to the thrust surface, whereas folding and penetrative strain develop a magnetic lineation perpendicular to the shorting direction but parallel to the bedding. These fabric types can be observed in the first model of this study, which simulated a FTB shortened above two adjacent décollements with different frictional properties. The different friction coefficients along the décollements have not only an effect on the geometric and kinematic evolution of a FTB, but also on the strain distribution and magnitude of strain within the belt.  The second series of models performed in this study show the development of a thrust imbricate and the strain distribution across a single imbricate in more detail. Three models, with similar setup but different magnitudes of bulk shortening, show strain gradients by gradual changes in principal axes orientations and decrease in degree of anisotropy with decreasing distance to thrusts and kinkzones. These models show that at the beginning of shortening, strain is accommodated mainly by penetrative strain. With further shortening, formation of thrusts and kinkzones overprint the magnetic fabric locally and the degree of anisotropy is decreasing within the deformation zones. At thrusts, an overprint of the magnetic fabric prior deformation towards a magnetic foliation parallel to the thrust surfaces can be observed. A rather complex interplay between thrusting and folding can be analysed in the kinkzones. In general, this thesis outlines the characteristics of magnetic fabric observed in FTBs, relates different types of magnetic fabric to different processes of deformation and provides insights into the strain distribution of FTBs.

Following cessation of contractional deformation, the Sevier orogenic belt collapsed and spread west during a middle Eocene to middle Miocene (∼48-20 Ma) episode of crustal extension coeval with formation of metamorphic core complexes and regional magmatism. The sedimentary and structural record of this event is a network of half-grabens that extends from southern Canada to at least central Utah. Extensional structures superposed on this fold-thrust belt are rooted in the physical stratigraphy, structural relief and sole faults of preexisting thrust-fold structures. Commonly, the same detachment surfaces were used to accommodate both contractional and extensional deformation. Foreland and hinterland extensional elements of the Cordillera that are normally widely separated are uniquely collocated in central Utah where the thrust belt straddles the Archean-Proterozoic Cheyenne belt crustal suture. Here, the Charleston-Nebo allochthon, an immense leading-edge structural element of the Sevier belt collapsed during late Eocene-middle Miocene time when the sole thrust was extensionally reactivated by faults of the Deer Creek detachment fault system and the allochthon was transported at least 5-7 km back to the west. Concurrently, the north margin of the allochthon was warped by flexural-isostatic rise of a Cheyenne belt crustal welt and its footwall was intruded by crustal melts of the Wasatch igneous belt. Collectively, these elements comprise the Cottonwood metamorphic core complex. Extensional processes were also important in the formation of the Jurassic-Cretaceous Great Valley forearc basin. Advocates of a thrust-wedge hypothesis argued that this forearc experienced prolonged Jurassic-Cretaceous contraction and proposed that northwest-southeast-striking fault systems were evidence of a west-dipping blind Great Valley-Franciscan sole thrust and related backthrusts. Based on interpretation of seismic reflection, borehole, map and stratographic data, I propose that these faults and associated bedding geometries are folded synsedimentary normal faults and half-grabens. Thus, late-stage diastrophic mechanisms are not required to interpret a forearc that owes much of its present-day bedding architecture to extensional processes coeval with deposition.

The deformation front of an orogen is defined as a zone or surface separating regions of different deformation styles or strain intensities. The large-scale development and migration of deformation front structures can be described and understood using critical wedge theory. At the foreland of a fold-thrust belt, the deformation front can be marked by a number of structures - an imbricate fan or frontal monocline, a ramp anticline or tip-line fold pair or a passive-roof duplex (triangle zone). This study considers two fold-thrust belts, the Zagros Simply Folded Belt, Iran and the Sawtooth Range, Montana. Both regions are developed in a passive margin carbonate sequence, overlain by a clastic succession. Remote sensing and field observations, combined with the interpretation of seismic data, are used to define the variation in fold structures within the belts and at the deformation fronts, and to constrain the migration of the deformation fronts. Palaeo-deformation fronts in the Zagros Simply Folded Belt are dominantly characterised by ramp anticlines, but the recent deformation front is marked in part by a reactivated fault structure above a salt diapir. The deformation front along the majority of the Sawtooth Range is a classic imbricate fan sequence, however, a triangle zone is observed in at least one segment of the belt. The development of each of these classes of structures is strongly influenced by the nature of inherited basement structures as well as by the mechanical stratigraphy of the sediment pile and the detachment type. The field and remote sensing components of the study are complemented by an analogue modelling study which is designed to investigate one of these factors, namely the effect of varying the geometry of an upper detachment horizon within the sediment pile. Results imply that the geometry of the upper detachment exerts a first order control on the development of deformation front structures. Triangle zones are found to develop where the upper detachment is narrow with respect to the width of the deformed zone. Conversely, foreland-verging structures develop where this upper detachment is wide with respect to the deformed zone.. When model results are compared to the field areas described above, this effect is shown to be a valid explanation for the structures developed. These results imply thatforeland triangle zones may be more common than currently documented, which has additional implications for hydrocarbon exploration and production. In addition, this thesis demonstrates the value of remote sensing methods for both hydrocarbon and mineral exploration.

This thesis uses geodetic satellite data to measure present-day crustal deformation in the Zagros fold-thrust belt (SW Iran). Geodetic-type measurements are also used in down-scaled models that simulate the surface deformations seen in convergent settings like the Zagros fold-thrust belt.

Global Positioning System (GPS) measurements of three surveys between 1998 and 2001 indicate 9 ± 3 mm/yr and 5 ± 3 mm/yr shortening across the SE and NW Zagros respectively. GPS results show that in addition to the different rates and directions of shortening on either side of the NS trending Kazerun fault, local along-belt extension occurs to the east.

Differential SAR interferograms of ERS1 & 2 images between 1992 and 1999 detect 8 ± 4 mm/yr uplift rate across a newly recognized fault in SW Qeshm Island. This can be attributed to a steep imbricate thrust that may still represent the local Zagros deformation front.

The salt diapirs in the Zagros rise from a source layer that acts as a low-frictional decollement that decouples the deformation of the cover sediments from their basement in the eastern Zagros whereas the cover to the west deforms above a high-friction decollement. Physical models were prepared to simulate cover deformation in the Zagros by shortening a sand pack above adjacent high- and low-frictional decollements (represented by a ductile layer). The strain distributions differed above the two types of decollements; it was more heterogeneous above the salt where local extension in the shortening direction was dominant. A separate work also investigated systematically the role of basal friction on cover deformation in convergent settings. Accurate height measurements of the model surface by laser-scanner indicated a deformation front more distal than usual, particularly in the low-basal frictional models. The volume reduction in our shortened sand models correlated directly with their basal friction.

Studies have shown that faults exhibit complex geometries that are often highly simplified and cross sections may not be sufficient to highlight the spatial variation of fault surface topography and the complex relationship with the wall rock. The main contributions of this thesis to structural geology are novel methods for investigating links between fault shape and wall rock structure. Curvature plots of sixteen faults show that thrust faults in deepwater Niger Delta exhibit corrugations on a range of wavelength and amplitude. The corrugations are characterized by large-scale anticlastic and synclastic geometries parallel to fault transport direction. The structure of the volumes in the immediate vicinity of the faults was investigated using slices of seismic attribute data sampled parallel and adjacent to thirteen faults. In half of the faults the hanging wall is more disrupted than the footwall, while in the other half the footwall is more disrupted than the hanging wall, implying that thrust zones exhibit complex geometries that existing models have yet to address. In addition, disruptions near fault surfaces may be related to discrete zones of intense fault surface maximum curvature, anomalous surface gradient and change in pattern of anticlastic and synclastic fault Gaussian surface curvature in the fault transport direction. No significant wall rock disruption was observed where fault surface curvature is planar.

Temporal-spatial evolution of the Central Andean foreland basin system relates directly to growth of the adjacent Andean orogenic belt during Late Cretaceous to Recent shortening. As the locus of shortening and crustal thickening propagated eastward, so too did the foreland basin system. Eastward growth of the orogenic wedge induced uplift and erosion of large portions of the basin, removing much of the detrital record of mountain building. Analyses of remnants of the Oligocene-Miocene foreland basin system in the Eastern Cordillera help define the kinematic evolution of the thrust belt in southern Bolivia. A series of north-trending depocenters, regarded collectively as a wedge-top depozone, evolved during growth of fold-thrust structures of the then-frontal part of the orogenic wedge. Growth strata and cross-cutting and onlapping relationships between contractional structures and synorogenic strata delineate the chronology of deformation. New 40Ar dates and published K-Ar dates define a minor Oligocene phase of west-vergent backthrusting followed by primarily east-vergent thrusting during Miocene time. These dates, combined with depositional histories, require synchronous and out-of-sequence thrust displacement during the Miocene. Depocenters are composed of alluvial-fan deposits on their flanks and lacustrine and braided-stream deposits in their axes. Most stratigraphic units are confined to individual depocenters, suggesting that streams rarely had sufficient power to cut across growing folds. An arid climate since ∼10-15 Ma may explain the preservation of large parts of the Late Cretaceous-Miocene foreland basin system in southern Bolivia. In contrast, northern Bolivia exhibited a humid climate over this time interval and most parts of any foreland basin were completely eroded. Critical taper theory suggests that rapid erosion in a humid fold-thrust belt may induce subcritical conditions in which thrust-front propagation is inhibited and internal deformation is promoted. An arid thrust belt may be expected to exhibit critical to supercritical conditions that favor thrust-front migration and in-sequence thrusting. Such phenomena are observed in Bolivia, suggesting that climate and erosion exert fundamental controls on the geometry and kinematics of the Andean orogenic belt.

L'objectif de cette thèse est l'étude de la structure et la cinématique du Zagros oriental (Iran) et de la zone de transition avec le prisme du Makran appelée syntaxe de Bandar Abbas. Une étude structurale de terrain a permis de mettre en évidence le contrôle exercé par la stratigraphie mécanique - et donc les conditions paleogéographiques - sur le style structural d'un côté à l'autre de la syntaxe. La restauration de la première coupe équilibrée à travers le sud-est de la ceinture du Zagros permet de montrer que le Zagros plissé a subi deux phases téctoniques majeures, une première impliquant uniquement la couverture suivie par une deuxième impliquant le socle. Le raccourcissement accommodé dans la section depuis le Miocène moyen est d'au moins 45 km. La présence d'une puissante série évaporitique à la base de la couverture a favorisé le developpement de grands plis de décollement. L'analyse d'exemples de terrain dans la région d'étude ainsi que de profils sismiques dans le Zagros Central permet de discuter la cinématique de ces plis ainsi que les facteurs contrôlant leur style, notamment la mobilité du sel, l'existence de multiples décollements et le rôle tardif des failles de socle. Enfin, une modélisation géophysique de la structure lithosphérique du Zagros permet de discuter les facteurs fondamentaux qui ont guidé l'évolution récente de l'orogène. On met en évidence une amincissement lithosphérique qui pourrait être lié à un détachement récent du slab plongeant. Ce processus pourrait expliquer la transition récente d'une tectonique de couverture à une tectonique de socle
This thesis focuses on the structure and kinematics of the south-eastern Zagros Mountains (Iran) and the transitional structures with the adjacent Makran accretionary prism, known as the Bandar Abbas syntaxis. The structural style, as evidenced by a field-based structural study, is strongly controlled by changing mechanical stratigraphy and therefore paleogeographic conditions from one side to the other of the syntaxis. Restoration of the first complete balanced cross-section through the south-eastern Zagros fold-thrust belt shows that the external part of the orogen (a) underwent two main phases of deformation, i. E. A thin-skinned phase of deformation followed and partly overprinted by a thick-skinned phase, and (b) absorbed at least 45 km of shortening since middle Miocene times. The presence of an exceptionally thick layer of salt at the base of the cover allowed the development of huge detachment anticlines. Field examples from our study area and seismic profiles from Central Zagros allow us to discuss the still poorly understood kinematics of these folds as well as examine the various factors controlling the style of folding, essentially salt mobility, multiple decollement levels and late basement faulting. Finally, geophysical modelling of the deep lithospheric structure of Zagros brings new insight on the fundamental factors controlling the recent orogenic kinematics. In particular, a previously undocumented thinning of the lithosphere beneath Zagros could be attributed to recent slab break-off and is thought to have controlled the recent switch from thin-skinned to thick-skinned tectonics

La convergence oblique entre les plaques Caraïbes et Amérique du Sud à partir de l'Oligocène a conduit à la formation de la cordillère « Serranía del Interior » (SDI) et de son avant pays au sud (bassin de Maturín) et la ceinture plissée de Monagas. D’abord transpressif (direction NW-SE), le déplacement entre les deux plaques devient à compter de ~12 Ma principalement une translation O-E qui s’accommode principalement sur la faille d’El Pilar. Cependant, des indices de compression active ont été identifiés à la terminaison de la faille d'Urica dans la chaine plissée de Monagas. Pour discuter des mécanismes de cette déformation compressive actuelle, nous avons mis en œuvre une interprétation sismique (2D et 3D), une étude géomorphologique et une étude paléomagnétique. Depuis le front sud de la SDI dans la chaîne plissée de Monagas, l'interprétation sismique et l’analyse géomorphologique se sont concentrées sur les chevauchements de San Félix, Tarragona, Punta de Mata, Jusepín et Amarilis. Deux discordances miocènes (Mid-Miocene Unconformity (MMU) de ~10 Ma et Late Miocene Unconformity (LMU) de ~5,3 Ma) ont été cartographiées sur la sismique. En s’appuyant sur la LMU, il a été calculé à l’aplomb de ces accidents un taux de soulèvement plio-pléistocène de ~0,4 mm/a. Invisibles sur la sismique, des déformations ont aussi été observées en surface sur ces accidents (des terrasses fluviatiles basculées, plissées et faillées et des anomalies de drainage). Datées par des méthodes cosmonucléides (10Be et 26Al), l’âge des terrasses alluviales déformées sont compris entre ~90 ka sur le chevauchement de Tarragona et ~15 ka dans la zone de Punta de Mata. Un taux minimal de soulèvement pléistocène terminal à l’aplomb des chevauchements a été calculé entre 0,1 et 0,6 mm/a. Cette gamme de vitesse recouvre celle renvoyée par la LMU et montre que la déformation n'a pas varié significativement pendant les derniers 5,3 Ma. Ces observations montrent que les chevauchements de Tarragona, Pirital El Furrial et d’autres plus jeunes développés dans la formation Carapita restent actifs. Cette déformation superficielle s’estompe rapidement vers l’est près de la ville Maturín. Nous interprétons cette déformation comme liée au jeu récent de la faille d'Urica qui se termine au sud en queue de cheval. La faille d’Urica accommoderait donc une partie du déplacement entre plaques Caraïbe et Amérique du Sud. Une étude paléomagnétique a été réalisée dans les blocs de Caripe et Bergatín au sein de la SDI où 27 localités ont été échantillonnées dans les sédiments du Crétacé au Paléocène. Une observation clé de cette étude a été la mise en évidence d'une composante paléomagnétique stable déviée vers le Nord Est avec des polarités normale et inverse. Les analyses statistiques de ces composantes indiquent une acquisition postérieure au plissement de la SDI (< ~12 Ma). La déclinaison moyenne dans les blocs de Caripe et de Bergatín indique une rotation horaire de R=37º±4 º autour d’un axe vertical. Le taux de rotation post-Miocene moyen avoisine ~3.7º/Ma et reste probablement actif. Nous proposons de rattacher cette rotation horaire à un système de failles type "Riedel" (Urica et San Francisco) en relation avec la faille d’El Pilar
In Northeastern Venezuela, the tectonic provinces of the Serranía Del Interior thrust belt (high hills), the Monagas Thrust belt (foothills) and the Maturín foreland basin formed as a result of the oblique convergence between the Caribbean and South American plates since the Oligocene. GPS data show that post 12 My wrenching component between the plates is accommodated predominantly by the E-W strike-slip El Pilar Fault. However, evidence of active compression has been identified in the southern limit of the NW-SE dextral Urica Fault, specifically, in the Monagas Fold and Thrust Belt. In order to constrain the neotectonics of this area, this thesis presents a combined approach, which includes geomorphological study, seismic and paleomagnetism. In the Monagas Fold and Thrust Belt, the geomorphological study and the seismic interpretation were focused on five zones. From the foothills to the deformation front, these zones are: San Felix, Tarragona, Punta de Mata, Jusepín and Amarilis. These areas show surface deformations such as topographic uplifts, tilted terraces, folded terraces, faulted terraces, and drainage anomalies. The dating of the river terraces through 10Be and 26Al methods indicates that these terraces formed in the Late Pleistocene. The oldest terrace located in the Tarragona zone has a maximum exposure age of ~90 ky and the youngest located in the Punta de Mata zone of ~15 ky. From this dating, a minimum vertical deformation rate between ~0.6-0.1 mm/y was calculated for this area. Using the seismic interpretation of a 3D block, the surfaces of two unconformities (MMU and LMU) have been mapped. The age obtained for the LMU (~5.3 My), yield a Plio-Pleistocene uplift rate between ~0.3-0.4 mm/y, which is close to the vertical deformation rate calculated from the terraces dated. These similar rates seem to indicate that the deformation rate in the MFTB has not changed significantly for the last 5.3 My. The deformed surfaces observed in the field and in DEM images coincide vertically with the deep structures interpreted in the seismic lines. I propose that the deformation on the surface is linked to the Tarragona, Pirital, Furrial thrusts and the Amarilis Backthrust activity and to the youngest thrusts developed in the Carapita Formation. However, this surface deformation dies out near the city of Maturín, therefore, the neotectonic deformation is inferred to be caused by local tectonics. I propose that this local compressive deformation could have been generated by a horsetail termination in the southern limit of the Urica Fault which reactivated the oldest thrusts (Tarragona and Pirital thrusts) and deformed the post-Middle Miocene units until reaching the surface. In the zones where the El Pilar Fault mainly accommodates the wrenching component, block rotation is likely. For that reason, a paleomagnetic study was conducted in the Caripe and Bergatín blocks of the Serranía Del Interior where 27 sites were sampled in Cretaceous to Paleocene sediments. Statistics analyses of the components yield a negative bedding-tilt test, indicating that this component was acquired post ~12 My after the folding process in the Serranía del interior. The average declination indicates a clockwise block rotation of R = 37º ± 4º and a post-Middle Miocene rotation rate of ~3.7º/My in both the Caripe and Bergatín blocks. This rotation rate is probably still active. I propose to relate the regional clockwise rotation to the development of a synthetic Riedel shear system formed by the El Pilar Fault (master regional fault) and by the Urica and San Francisco synthetic Riedel shears

The Himalayan fold-thrust belt and Tibetan Plateau are the result of the collision between the Indian and Eurasian continents. This dissertation documents the kinematics and tectonic history of the Himalayan fold-thrust belt of western Nepal and the northern Tibetan Plateau. In the Himalayan fold-thrust belt, the Main Central thrust emplaced a hanging wall flat of Greater Himalayan rock over a footwall flat of Lesser Himalayan rock in Early Miocene time. Subsequent growth of the Lesser Himalayan duplex (LHD) uplifted and rotated the Ramgarh thrust sheet, Main Central thrust, and overlying Greater Himalayan rock to the surface. Thus, growth of the LHD is responsible for the northward dips in the Greater Himalaya. New Nd isotopic data from throughout Nepal indicate that Lesser Himalayan rocks consistently have more negative epsilonNd values than Greater and Tibetan Himalayan rocks. Growth of the LHD is documented in the syntectonic sediments of the Neogene Siwalik Group. At ∼10-11 Ma in central and western Nepal, the epsilonNd values of the Siwalik Group shift toward more negative values which indicate detrital input from rocks in the LHD. Regional mapping in western Nepal and three balanced cross sections provide a three-dimensional view of the fold-thrust belt. These cross sections suggest over 900 km of shortening in upper crustal rock from the Indus suture to the Main Frontal thrust. This suggests a corresponding ∼900 km long wedge of lower crustal rock was consumed by the Himalayan-Tibetan orogen. This wedge may have been inserted under the Tibetan Plateau, helping it obtain its anomalously thick crust. If lower crustal rocks have been inserted under the Tibetan Plateau, the Himalayan collision can account for ∼70% of the overthickened crust. This leaves ∼30% to be accounted for by other mechanisms. The Tula uplift documents shortening along the northern edge of the Tibetan Plateau. The lithic composition of its sandstone, deformation, and erosion of strata suggests that significant regional uplift and thickening occurred since Late Jurassic time and is still occurring. These relationships suggest that the northern Tibetan Plateau region was tectonically active, and undergoing shortening, long before the early Tertiary India-Eurasian collision.

The High Arctic has been a complex region of collisional and extensional tectonism through the Mesozoic and Cenozoic. Svalbard, the sub-aerial exposure of the northwestern Barents Shelf, is an excellent natural laboratory investigating for High Arctic tectonism. Using apatite and zircon (U-Th)/He low-temperature thermochronometry combined with geological constraints, we resolve Cretaceous through Paleogene time-temperature histories for four regions of the Southwestern Province. Our results indicate a temperature gradient from south to north of ~185°C to >200°C, respectively, as a consequence of sedimentary burial and elevated geothermal gradient ( 45°C/km) from High Arctic Large Igneous Province activity. Late Cretaceous cooling affected all regions during regional exhumation related to initial rifting in the Eurasian Basin. During Eurekan tectonism: 1) our models indicate a heating event (55-47 Ma) characterized by overthrusting and a lack of erosion of the West Spitsbergen Fold-and-Thrust Belt, with Central Basin sediments derived from northern Greenland, followed by 2) a subsequent cooling event (47-34 Ma) corresponding to a shift in tectonic regime from compression to dextral strike-slip kinematics; exhumation of the WSFTB coincided with strikeslip tectonics.

This dissertation investigates natural deformation processes over multiple earthquake cycles in the seismically active, southern Junggar basin, NW China and additionally explores the capabilities of 3D geomechanical restoration as an effective tool for fractured reservoir characterization. Chapter 1 presents a detailed 3D fault model of the active Southern Junggar Thrust (SJT) – constrained by seismic reflection data – in the southern Junggar basin. This work demonstrates the significance of mid-crustal detachments as a physical mechanism to accommodate destructive, multi-segment earthquakes in active thrust sheets. Moreover, it highlights the efficacy of surface folds to delineate fault geometries at depth in the absence of subsurface data constraints. Chapter 2 describes active thrust sheet deformation across the Tugulu anticline, which sits in the hanging wall of the SJT, from Late Quaternary to present. Holocene terrace deformation records of surface faulting and folding yield consistent fault slip rates. We develop a quantitative method for extracting fault slip rates from terrace fold geometries using a mechanical modeling approach, yielding a 250 kyr history of SJT slip. This study provides new insights into natural fold growth associated with fault slip. Moreover, it addresses several shortcomings of traditional seismic hazards assessment methodologies. Chapter 3 characterizes the styles, timing, and sequence of deformation across southern Junggar. Southern Junggar underwent extension followed by tectonic inversion and shortening, forming a series of imbricate structural wedges. A kinematic model for the evolution of shear fault-bend fold wedges is presented. We discuss the implications of structural style, fold growth and thrusting sequence on the ~175 Myr evolution of this fold-and-thrust belt and its petroleum system. Chapter 4 investigates the impact of natural fold strains on fractured reservoir properties in the Permian Basin, West Texas. This study details the ability of 3D geomechanical restorations to accurately model natural strain distributions associated with fold growth. Modeled strains from geomechanical restorations are integrated with proxies for natural deformation and production data to describe how tectonic strain impacted observed gas production, water cuts and reservoir temperatures. When used in conjunction with additional datasets, geomechanical restoration shows promise for predictive abilities in characterizing conventional and unconventional fractured reservoir properties.
Earth and Planetary Sciences

No presente trabalho buscou-se compor um quadro geológico-estrutural da Faixa Paraguai meridional e compreender as relações estratigráficas entre os litotipos da Formação Puga e grupos Cuiabá e Corumbá. Foram realizados trabalhos de reconhecimento geológico e perfis geológico-estruturais de detalhe, com análise estrutural e petrográfica, em conjunto com a integração de dados e mapas existentes, análise de imagens de satélite, fotos aéreas e modelos digitais de terreno. A Faixa Paraguai meridional evoluiu como um típico fold-andthrust belt. A evolução geológica do cinturão principia por processos de rifteamento, provavelmente no final do Criogeniano, evoluindo para mar restrito e margem passiva até o final do Ediacarano. A fase rifte é caracterizada pelas formações Puga e Cerradinho. A fase margem passiva está representada pelas formações Bocaina, Tamengo e Guaicurus. Propõe-se que o Grupo Cuiabá na área estudada seja constituído por depósitos marinhos profundos, turbidíticos distais depositados comitantemente aos sedimentos do Grupo Corumbá. O processo colisional responsável pela inversão da bacia com a deformação e metamorfismo associados ocorreu durante o Cambriano, com magmatismo pós-colisional no Cambriano Superior. O estilo estrutural torna-se progressivamente mais complexo de oeste para leste. São observadas até três fases de dobramento coaxiais sobrepostas com eixos subhorizontais de direção N-S. Associam-se a sistemas de falhas de empurrão com deslocamento da capa para oeste. As lineações de estiramento e indicadores cinemáticos observados sugerem que a convergência colisional em direção ao bloco Rio Apa que deu origem à faixa móvel não foi completamente frontal, existindo algum grau de obliquidade, com vetores de convergência em torno de WNWENE. Os micaxistos do Grupo Cuiabá mostram o estilo estrutural mais complexo, com três fases de dobramentos coaxiais e foliações tectônicas mais intensas. Haveria correlação temporal entre S3 gerada nos micaxistos, comumente referidos como Grupo Cuiabá, a leste com a foliação S2 gerada na porção central e a clivagem S1 gerada no limite da área cratônica a oeste, padrão que pode ser explicado pela migração do front deformacional de leste para oeste. É sugestivo que as principais falhas de empurrão coincidam com limites bacinais importantes, onde ocorrem variações de espessura e representatividades das formações basais. No processo de inversão da bacia provavelmente os empurrões reativaram as antigas falhas lístricas principais do estágio rifte.
This work aims to characterize the geological and structural context of the Southern Paraguay Folded Belt, and to understand the stratigraphic relationships between the Puga Formation, Corumbá and Cuiabá groups. Regional geological reconnaissance work and detailed geological-structural field sections were carried out, with petrographic and structural analysis, together with integration of existing data and maps and analysis of satellite images, aerial photos and digital terrain models. The southern Paraguay Belt is a typical fold-andthrust belt. Its geological evolution began with rifting (Puga and Cerradinho formations), probably at the end of Criogenian, and evolved to restricted sea and passive margin (Bocaina, Tamengo and Guaicurus formations) in the late Ediacaran. It is proposed that the Cuiabá Group in the study area consists of distal marine deposits coeval with the Corumbá Group. The collisional process responsible for basin inversion and associated deformation and metamorphism occurred in the Cambrian, with post-collisional magmatism in the Upper Cambrian. The structural style becomes increasingly complex from west to east. Up to three overprinted coaxial folding phases are observed with north / south upright axial planes dipping to east and axes plunging gently to North or South. A system of thrust faults is associated with displacement of the hangwall to the west. Down-dip to oblique and strike-slip stretching lineations are also observed, with kinematic indicators showing movement varying from inverse to sinistral. This suggests that the collisional convergence toward the Rio Apa block which generated the mobile belt was not strictly frontal, but had some degree of obliquity, with convergence vectors around SSW - ENE. The Cuiabá Group mica-schists show the most complex structural style with three superimposed coaxial fold phases and more intense tectonic foliations. It is proposed that there would be time correlation between the S3 foliation in the mica-schists in the easternmost area, with the S2 foliation in the central area and the S1 cleavage at the limit of the cratonic area to the west. This pattern can be explained by the westward migration of the deformational front. It is suggestive that the main thrusts coincide with major basin boundaries, where greater variations in thickness and expression of the basal formations occur. During the basin inversion the thrusts probably reactivated the former main listric faults of the rift stage.

Thesis (B. Sc.(Hons.))--University of Adelaide, Dept. of Geology and Geophysics, 1997.
Australian National Grid Reference Hamley Bridge 6629-iii 1:50 000 Sheet. Includes bibliographical references (leaves 29-31).

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 40-46).
The Maria Fold and Thrust Belt (MFTB) and Colorado River Extensional Corridor (CREC) were the sites of atypically extreme compression in Mesozoic time and extension in Cenozoic time, respectively. The orientations of these deformational structures are at odds with the Sevier and Laramide thrust belts and the Basin and Range Extensional Province surrounding these areas, a fact that remains largely unexplained. Data pertaining to metamorphic grade, deformational structures, and plutonism are compiled and reported in order to characterize compression and metamorphism. Field data on the 18.6 Ma Peach Spring Tuff are collected and presented and data on cooling ages are compiled in order to characterize extension. It is suggested that high metamorphic temperatures and ductile compressional structures are related to Late Cretaceous S-type plutonism; furthermore, it is suggested that later extension is related to earlier metamorphism and compression. It is demonstrated that the spread in attitudes of the Peach Spring Tuff correlates well with the degree of post- 18.6 Ma extension. Finally, a favored model is presented for the Mesozoic-Cenozoic evolution of the MFTB and CREC.
by James R. Pershken.
S.B.

The work presented in this thesis utilizes several geological methods to investigate the origin and evolution of the supracrustal rocks in the Palaeoproterozoic Hamrånge Group (HG) in the south-central Swedish Svecofennian. The first paper is based on whole-rock geochemistry to show the plate tectonic setting of volcanic rocks within the HG. This indicates that the environment was probably an oceanic volcanic arc. Geochronology, used in paper two, shows that the volcanism was active at 1888±6 Ma and that the sediments forming the stratigraphically overlying quartzite were deposited after 1855±10 Ma, with provenance ages overlapping both the volcanic rocks and the 1.86-1.84 Ga continental margin Ljusdal granitoids. In the third paper, thermobarometry was applied to samples from the HG, the migmatitic Ockelbo sub-domain to the south, and the 1.81 Ga Hagsta Gneiss Zone (HGZ) that separate these two units. The results show distinct differences in the metamorphic conditions that have affected the HG and the Ockelbo sub-domain, supporting previous interpretations that the HGZ is an important crustal structure, possibly a terrane or domain boundary. Paper four deals with the structural geology of the Hamrånge area. The study shows that the volcanic rocks and the underlying mica schist have been subjected to three deformation episodes (D1-D3), while the uppermost quartzite was most likely only affected by D2 and D3. While structures related to D1 are rarely seen, D2 resulted in a penetrative foliation, strong lineations and NW-vergent folding and thrusting. D3 is a result of a N-S compression that formed regional E-W folds and steep, ca. NW-SE shear zones, e.g. the HGZ. The results presented in this thesis, integrated with previously published data, outline a model for the geological evolution of the Hamrånge area: At 1.89 Ga a volcanic arc formed that subsequently collided with a continental margin resulting in the first deformation episode, D1, and probably a metamorphic event. This was possibly followed by an extensional period, after 1855±10 Ma, forming a basin that accumulated sediments later to form the quartzite stratigraphically on top of the volcanic rocks. The second deformation episode, D2, formed a fold-thrust belt when the supracrustal HG was thrusted to the NW, on top of the 1.86-1-84 Ga Ljusdal Domain. Flattening and a second metamorphic period followed this thickening of the crust. The last ductile deformation, D3, caused by regional tectonic forces, resulted in F3-folds that matured into ca. 1.8 Ga large-scale, steep shear zones transecting the Fennoscandian Shield.

Thesis (B. Sc.(Hons.))--University of Adelaide, Dept. of Geology and Geophysics, 1998.
Two folded, coloured maps in packet pasted onto back cover. National Grid Reference (SI 54-9) 6629-11; 12, 19, 20 (SI 54-5) 6530-06; 07, 6630-01 1:10 000 sheets. Includes bibliographical references (6 leaves ).