Dissertations / Theses on the topic 'NW Himalaya'

The evolution of most orogens typically records cogenetic shortening and extension. Pervasive normal faulting in an orogen, however, has been related to late syn- and post-collisional stages of mountain building with shortening focused along the peripheral sectors of the orogen. While extensional processes constitute an integral part of orogenic evolution, the spatiotemporal characteristics and the kinematic linkage of structures related to shortening and extension in the core regions of the orogen are often not well known. Related to the India-Eurasia collision, the Himalaya forms the southern margin of the Tibetan Plateau and constitutes the most prominent Cenozoic type example of a collisional orogen. While thrusting is presently observed along the foothills of the orogen, several generations of extensional structures have been detected in the internal, high-elevation regions, both oriented either parallel or perpendicular to the strike of the orogen. In the NW Indian Himalaya, earthquake focal mechanisms, seismites and ubiquitous normal faulting in Quaternary deposits, and regional GPS measurements reveal ongoing E-W extension. In contrast to other extensional structures observed in the Himalaya, this extension direction is neither parallel nor perpendicular to the NE-SW regional shortening direction. In this study, I took advantage of this obliquity between the trend of the orogen and structures related to E-W oriented extension in order to address the question of the driving forces of different extension directions. Thus, extension might be triggered triggered by processes within the Tibetan Plateau or originates from the curvature of the Himalayan orogen. In order to elaborate on this topic, I present new fault-kinematic data based on systematic measurements of approximately 2000 outcrop-scale brittle fault planes with displacements of up to several centimeters that cover a large area of the NW Indian Himalaya. This new data set together with field observations relevant for relative chronology allows me to distinguish six different deformation styles. One of the main results are that the overall strain pattern derived from this data reflects the regionally important contractional deformation pattern very well, but also reveals significant extensional deformation. In total, I was able to identify six deformation styles, most of which are temporally and spatially linked and represent protracted shortening, but also significant extensional directions. For example, this is the first data set where a succession of both, arc-normal and E-W extension have been documented in the Himalaya. My observations also furnish the basis for a detailed overview of the younger extensional deformation history in the NW Indian Himalaya. Field and remote-sensing based geomorphic analyses, and geochronologic 40Ar/39Ar data on synkinematic muscovites along normal faults help elucidate widespread E-W extension in the NW Indian Himalaya which must have started at approximately 14-16 Ma, if not earlier. In addition, I documented and mapped fault scarps in Quaternary sedimentary deposits using satellite imagery and field inspection. Furthermore, I made field observations of regional normal faults, compiled structures from geological maps and put them in a regional context. Finally, I documented seismites in lake sediments close to the currently most active normal fault in the study area in order to extend the (paleo) seismic record of this particular fault. Taken together, this data sets document that E-W extension is the dominant active deformation style in the internal parts of the orogen. In addition, the combined field, geomorphic and remote-sensing data sets prove that E-W extension occurs in a much more larger region toward the south and west than the seismicity data have suggested. In conclusion, the data presented here reveal the importance of extension in a region, which is still dominated by ongoing collision and shortening. The regional fault distribution and cross-cutting relationships suggest that extension parallel and perpendicular to the strike of the orogen are an integral part of the southward propagation of the active thrust front and the associated lateral growth of the Himalayan arc. In the light of a wide range of models proposed for extension in the Himalaya and the Tibetan plateau, I propose that E-W extension in the NW Indian Himalaya is transferred from the Tibetan Plateau due the inability of the Karakorum fault (KF) to adequately accommodate ongoing E-W extension on the Tibetan Plateau. Furthermore, in line with other observations from Tibet, the onset of E-W normal faulting in the NW Himalaya may also reflect the attainment of high topography in this region, which generated crustal stresses conducive to spatially extensive extension.
Die Hauptaufgabe von MHC-kodierten Proteinen ist die Erkennung von körperfremden Molekülen sowie das Einleiten einer adäquaten Immunantwort, womit sie eine Schlüsselrolle im Immunsystem der Wirbeltiere einnehmen. Man nimmt an, dass ihre außergewöhnliche Vielfalt eine Antwort auf die sich ständig anpassenden Parasiten und Krankheitserreger ist, durch adaptive Selektion erhalten wird und dass die individuelle Allelausstattung einen Großteil der Parasitenbelastung erklärt, wofür bereits zahlreiche MHC-Studien Hinweise gefunden haben. Trotzdem ist unser Verständnis über die wirkenden Mechanismen teilweise noch lückenhaft. Ein stark vernachlässigter Aspekt hierbei sind z.B. eventuelle Unterschiede in der Genexpression der MHC-Allele und eine geringere Expression wäre gleichbedeutend mit einer geringeren Aktivierung des Immunsystems. Ich habe hierzu zwei frei lebende Kleinsäugerarten (Delomys sublineatus, Apodemus flavicollis) unter natürlichen Selektionsbedingungen untersucht. Dabei habe ich neben der genotypischen Diversität von MHC-Genen auch deren Expression, sowie die Genexpression immunregulativer Zytokine mit in Betracht gezogen und in Relation zur individuellen Belastung mit gastrointestinalen Helminthen Das gleichzeitige Auftreten von Verkürzung und Dehnung (Extension) ist ein charakteristisches Kennzeichen bei der Bildung von Kollisionsgebirgen. Eine bis heute gängige These beinhaltet ein weit verbreitetes Auftreten von bschiebungen jedoch erst in späteren Stadien der Gebirgsbildung, bzw. nach deren Abschluÿ. Verkürzung ist hingegen während der gesamten Gebirgsbildung zu beobachten. Auch wenn Extensionsprozesse einen wesentlichen Bestandteil der Gebirgsbildung darstellen, ist deren räumlichen und zeitlichen Abfolge sowie ihre kinematische Kopplung zu Verkürzungstrukturen nur wenig gesichert. Der Himalaja, durch die Kollision von Indien und Eurasien entstanden, bildet den südlichen Rand des tibetischen Hochplateaus und stellt ein typisches aktives Kollisionsgebilde dar. Während heutzutage an der Gebirgsfront Überschiebungen beobachtet werden, können mehrere Generationen an Extensionsstrukturen in den hochgelegenen Regionen des Himalajas dokumentiert werden, die sowohl parallel als auch senkrecht zur Gebirgsfront verlaufen. Im NW Indiens zeugen Erdbebendaten sowie regionale GPS-Daten von andauernder E-W-Extension. Im Gegensatz zu anderen im Himalaja beschriebenen Extensionsstrukturen ist diese Extensionsrichtung jedoch weder parallel noch senkrecht zur NE-SW orientierten regionalen Verkürzungsrichtung. In der vorliegenden Arbeit nutze ich diesen schiefen Winkel zwischen der Ausrichtung des Gebirges einerseits und den mit E-W-Extension assoziierten Strukturen andererseits, um mögliche Ursachen für verschiedene Extensionsarten differenzieren zu können. So könnte Extension entweder durch Prozesse innerhalb des tibetischen Hochplateaus gesteuert werden, oder durch die Krümmung des Himalajas, der bogenförmig verläuft. Um dies zu untersuchen, verwende ich einen neuen störungskinematischen Datensatz aus systematischen Messungen von ca. 2000 spröden Störungsflächen im Aufschlussmaßstab über den gesamten Bereich des Himalajas in NW Indien. Zusammen mit Geländebeobachtungen, aus denen eine relative Altersabfolge abgeleitet werden konnte, ermöglicht mir dieser Datensatz zwischen sechs einzelnen Deformationsarten zu differenzieren. Die meisten dieser Deformationsarten sind zeitlich und räumlich verbunden und zeigen fortschreitende Verkürzung an, gleichzeitig werden auch signifikante Extensionsrichtungen dokumentiert. Unter anderem kann ich hier zum ersten Mal eine separierte Abfolge von Extension parallel zum Himalaja-Bogen bzw. E-W-Extension dokumentieren. Ein weiteres Ziel dieser Studie ist es, einen detaillierten Überblick über die E-W-Extension im NW indischen Himalaja zu erhalten. Basierend auf Kartierung von jungen Bruchstufen sowie geomorphologische Auswertungen, 40Ar/39Ar-daten von synkinematisch gewachsenen Muskoviten auf Abschiebungen, sowie einer Kompilierung von eigene Geländebeobachtungen gröÿerer Abschiebungen mit schon publizierten Strukturen, konnte ich die räumliche Ausdehnung der E-W-Extension sowie deren zeitliche Einordnung als jüngstes Deformationsereignis belegen. Schlussendlich konnte ich anhand von Deformation in Seeablagerungen in der Nähe der momentan aktivsten Abschiebung im Untersuchungsgebiet den Nachweis an paläoseismologischen Ereignissen entlang dieser Störung ausweiten. Mit diesem Datensatz kann ich nachweisen, dass E-W-Extension in einem wesentlich ausgedehnteren Gebiet nach Süden und Westen hin auftritt, als bisher vorhandene Daten dies vermuten lassen, und dass E-W-Extension vor 14-16 Ma begann, wenn nicht sogar noch früher. Zusammenfassend bezeugen die hier präsentierten Daten die Relevanz von Extension in einer von Verkürzung geprägten Region. Die räumliche Verteilung von Störungen sowie Überschneidungskriterien lassen vermuten, dass Extension sowohl parallel wie auch senkrecht zum Himalaja-Bogen ein essentieller Teil des südwärts gerichteten Wanderns der aktiven Überschiebungsfront und des damit assoziierten lateralen Wachstums des Gebirges ist. Nach Abwägung der groÿen Bandbreite an Modellen für Extension im Himalaja und im tibetischen Hochplateau, bin ich der Meinung, dass E-W-Extension im NW indischen Himalaja ihren Ursprung im tibetischen Hochplateau hat. Grund dafür ist, dass die Bewegung entlang der Karakorum-Störung nicht ausreichend ist, um die fortdauernde E-W-Extension im tibetischen Hochplateau zu kompensieren. In Übereinstimmung mit anderen Beobachtungen in Tibet ist es auÿerdem möglich, dass das Einsetzen von E-W-Extension im NW Himalaja ebenfalls Erreichen der hohen Topographie in dieser Gegend widerspiegelt, durch die krustale Prozesse in Gang gesetzt werden, die wiederum zu räumlich ausgedehnten Extensionsprozessen führen können.. Anhand von Leber und Milzproben beider Arten habe ich die Methode der ‚real-time PCR‘ zur relativen Quantifizierung von mRNA im Labor etabliert. Bereits für die Labormaus etablierte PCR-Primersysteme wurden an beiden Arten getestet und so konnten stabile Referenzgene gefunden werden, die Grundvoraussetzung für zuverlässige Genexpressionsmessungen. Für D. sublineatus konnte gezeigt werden, dass Helminthenbefall eine typische Th2 Immunantwort induziert, und dass der Zytokin Il4 Gehalt mit Befallsintensität strongyler Nematoden zunimmt. Es wurde für D. sublineatus kein signifikanter Zusammenhang zwischen MHC Expression oder anderen Zytokinen mit Helminthenbefall gefunden. In A. flavicollis wurde ein negativer Zusammenhang zwischen haptischer MHC-Expression und dem parasitären Nematoden Heligmosomoides polygyrus festgestellt, was auf eine Immunvermeidungsstrategie des Nematoden hindeutet. Ich fand typische positive und negative Assoziationen zwischen MHC-Allelen und anderen Helminthenarten, sowie Zeichen eines positiven Selektionsdruckes auf den MHC-Sequenzen, was sich durch eine erhöhte Rate aminosäureverändernder Mutationen zeigte. Diese nicht-synonymen Veränderungen waren auf Positionen innerhalb des zweiten Exons des DRB-Genes beschränkt, wohingegen die untersuchten Bereiche des ersten und dritten Exons stark konserviert vorlagen. Diese variablen Positionen kodieren Schlüsselstellen im Bereich der Antigenbindungsstelle im MHC Molekül. Zusammenfassend zeigt diese Arbeit, dass Genexpressionsstudien auch an Wildtieren durchgeführt und verlässliche Daten erzeugt werden können. Zusätzlich zur strukturellen Vielfalt sollten zukünftig auch mögliche Genexpressionsunterschiede bei MHC-Studien berücksichtigt werden, um ein kompletteres Bild der koevolutiven Wirt-Parasiten-Beziehungen zeichnen zu können. Dies ist vor allem dann von evolutiver Bedeutung, wenn die Parasiten in der Lage sind die MHC Expression aktiv zu beeinflussen. Die Studien konnten nicht die exakte Bedeutung von MHC-Genexpression in der antagonistischen Koevolution definieren, aber sie konnten zeigen dass diese Bedeutung stark von den jeweils beteiligten Partnern abzuhängen vermag.

Microgeodynamics relates grain-scale deformation microstructures to macroscopic tectonic processes. Here the microgeodynamic approach combines optical and electron microscopy, including electron backscattered diffraction (EBSD), with field geology, geothermobarometry and microphysical modelling to study fault rocks deformed within a major continental strike-slip fault to quantify changes in fault zone structure and rheology with crustal depth. The overall thesis rational therefore is to test existing fault models against an exhumed example of a continental strike-slip fault zone, namely the central Karakoram Fault Zone (KFZ), NW India. This approach establishes changes in deformation processes with depth in the upper- to mid-crust and suggests that a range of fault weakening mechanisms have reduced fault rock shear strengths, typified by friction coefficients of 0.3-0.4. Metamorphic petrology and geothermobarometry are used to place the KFZ in the context of regional tectono-metamorphic evolution. It is shown using diagnostic microstructures and pressure-temperature-time paths that the fault initiated after peak metamorphism (677-736°C, 875-1059 MPa) and subsequent migmatisation (688±44°C, 522±91 MPa) and leucogranite emplacement (448±100 MPa). Retrograde phyllonites formed during later strike-slip deformation are investigated in detail using EBSD, geothermometry and microphysical modelling. The phyllonites formed at 351±34°C and had low shear strength (<30 MPa) during frictional-viscous flow. EBSD is also used to derive a novel strain proxy based on quartz crystal preferred orientation intensity. Application of this method distinguishes deformation distributions in transects across the KFZ. Deformation intensity varies from <0.2 in essentially undeformed domains to 1.6 within shear zone strands formed at 500-550°C and c. 15 km depth. Evaluation of the history of the KFZ suggests that whilst it plays a relatively minor role in accommodating India-Asia collision, it can nevertheless be used as an analogue for major continental strike-slip fault zone structure.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2005.
Includes bibliographical references (p. 35-38).
The Tso Morari culmination in the Ladakh region of northwest India is a large (>3,000 km²) structural dome cored by coesite-bearing rocks of Indian continental crustal affinity. As one of only two localities in the Himalaya where ultrahigh-pressure rocks have been found, the culmination offers important insights into the orogenic processes responsible for exhumation of subducted continental crust. New, 1:50,000 scale geologic mapping and structural analysis in the Tso Morari area reveals evidence for five distinct deformational events. Rather than simple, one step processes envisioned by investigators in many ultrahigh-pressure terrains, exhumation of the Tso Morari culmination was a polyphase process. From >90 km to mid-crustal depths, exhumation was accommodated by a diachronous set of rooted, ductile, extensional detachments that were active [approx.] 53-40 Ma. Beginning in the Late Oligocene, continued exhumation occurred by progressive unroofing along a younger, brittle-ductile detachment. Through a rolling-hinge mechanism similar to that proposed for many metamorphic core complexes of the North American Cordillera, this unroofing led to the development of the culmination into a NW trending structural dome.
(cont.) More recently, N-S-striking normal faults accommodated continued upper crustal extension throughout much of the remainder of Cenozoic time, despite the culmination's setting in the Himalayan collisional orogen.
by Ryan J. Clark.
S.M.

This thesis attempts to unravel the complex thermal and structural history of part of the High Himalayan Slab in NW India and combines reconnaissance-style field structural mapping of an area covering ~10,000 km² with petrography, microstructural analysis, thermobarometry and geochronology techniques. The results of this work show that the oldest protoliths of the High Himalayan Slab are at least Cambrian in age and that they may have experienced a major pre-Himalayan metamorphism at c.500 Ma. The youngest protoliths are Mesozoic in age (the Tandi Group) and demonstrate that the High Himalayan Slab represents the metamorphosed equivalents of the Tibetan Sedimentary Series. Metamorphism was achieved via substantial crustal shortening and thickening following the India-Asia collision at 50-54 Ma ago. Phase relationships demonstrate that metamorphism was a regional Barrovian-type event associated with the growth of biotite-, garnet-, staurolite-, kyanite- and sillimanite-bearing assemblages in metapelites. Quantitative thermobarometry demonstrates that near-peak conditions of c.6-8 kbar and 550-650°C were attained in the deepest exposed levels. Growth of metamorphic assemblages was underway by at least 30 Ma, as indicated by U-Pb ages of metamorphic monazites. Exhumation of the High Himalayan Slab was achieved through a combination of extensional unroofing along major detachments (namely the Zanskar Shear Zone), thermal doming, thrusting along the Main Central Thrust and surface erosion. Exhumation is closely associated with the growth of sillimanite- and cordierite-bearing assemblages in pelites and the generation and emplacement of crustal melt leucogranites in the upper parts of the slab. U-Pb dating of accessory phases from one of the crustal melt leucogranites (the Gumburanjon leucogranite) constrains its crystallisation and emplacement age at c.21-22 Ma. This is only slightly older than its ⁴⁰Ar/³⁹Ar muscovite and biotite cooling ages of c.20-21 Ma, which is attributed to the emplacement of the Gumburanjon leucogranite into the immediate footwall of the ZSZ. Field and geochronological data therefore support a strong temporal and spatial relationship between upper crustal melting and extension in a convergent orogen.

The Karakoram Axial Batholith in N. Pakistan records the magmatic development of the Eurasian continental margin since the late Jurassic. Magmatism prior to the collision of India with Eurasia at c.45Ma is represented by subduction-related, calc-alkaline granodiorite plutonism. The chemical variation within these plutons is caused by high-level fractionation processes. However, heterogeneous isotope data suggests that the source of these magmas was the mantle wedge, enriched by87 a subducted slab component, with the melts being contaminated by a Sr-rich crustal component. There are two types of post-collisional leucogranite. The Sumayar pluton is related to restricted partial melting of sillimanite-grade metapelites triggered by fluxing of fluids from the underthrust Indian crust. This water-saturated, minimum melt is considered to be an analogue of the High Himalayan leucogranites. The other Karakoram leucogranites are related by fractionation to a more basic monzogranitic parent, whose geochemistry indicates a lower crustal source. However, melting of typical crust cannot explain the anomalously high large ion lithophile element (LILE) content of the monzogranites. Associated with the granites are ultra- potassic, LILE-enriched lamprophyres. This LILE-enrichment is attributed to alteration of the mantle wedge by fluids and/or siliceous melts from the slab. Amphibole in the resulting metasomatic assemblage acts as a sink for the otherwise incompatible LILE. As a result of heating and thermal relaxation beneath the thickened continental crust, enriched amphibole, stable in the pre-collisional mantle wedge beneath the Karakoram, dehydrated or melted some 20Ma after collision to give the lamprophyres. Fluid precursors to this melting contaminated the source region of the granites selectively enriching it in LILE and triggering/promoting melting. The identification of the above magma-types, which have different generative processes and magmatic triggers, in other collisional environments will lead to information about the evolution of similar orogenic belts.

Thesis (M.S.)--University of Cincinnati, 2008.
Advisor: Craig Dietsch. Title from electronic thesis title page (viewed Sep. 4, 2008). Includes abstract. Keywords: High-Pressure; blueschist; Tso Morari; Himalaya. Includes bibliographical references.

This thesis attempts to construct an integrated model for the tectonothermal evolution of the Suru valley region of the High Himalayan Crystalline unit of north-west India, and combines detailed field mapping, petrographic and microstructural analysis, thermobarometric techniques and metamorphic modelling. This work confirms that the metasedimentary lithologies of the Suru valley correspond to the Palaeozoic-Mesozoic Tethyan shelf sediments found in Kashmir and Zanskar and that the meta-igneous bodies correlate with Permian rift-related igneous units. This demonstrates that all the metamorphism in the Suru valley is Himalayan in age. Subsequent to India-Asia collision at ~54 Ma the units of the Suru valley underwent a polyphase deformational and metamorphic history. The large scale structure of the area is that of kilometre-scale, SWvergent recumbent folds that are domed by a later structure, the Suru Dome. Barrovian metamorphism resulting from collision and burial reached a maximum of kyanite grade, and is believed to be syn- to post-kinematic with respect to the formation of the large folds. Thermobarometric analysis indicates that peak conditions relating to this Barrovian event were of the order of 9.5-10.5 kbar and 620-650 ⁰C. A later metamorphic event associated with doming throughout the Zanskar Himalaya and crustal anatexis in the core of the High Himalaya caused re-equilibration of deeper Suru Dome rocks to conditions of 8.7-9.7 kbar and 630-640 ⁰C. Metamorphic modelling, involving phase diagram construction and P-T path determination using Gibbs method calculations, suggests that metamorphic garnets grew under conditions of burial and heating. Rapid exhumation of the High Himalayan Crystallines on the Main Central Thrust and the Zanskar Shear Zone occurred shortly after peak metamorphism. The results suggest that phase diagram construction and P-T path calculation should be used in conjunction in order to confidently model metamorphic rocks.

The Himalayan orogen provides a natural laboratory to test models of orogenic development due to large-scale continental collision. The Greater Himalayan Series (GHS), a lithotectonic unit continuous along the entire length of the belt, comprises the metamorphic core of the Himalayan orogen and underlies the highest topography. GHS rocks are exposed as a moderately north-dipping slab bounded below by the Main Central Thrust (MCT) and above by the South Tibetan Detachment System (STDS) of normal faults. Coeval reverse- and normal-sense motion on the crustal-scale MCT and STDS ductile shear zones allows the GHS to be modeled as an extruded wedge or channel of mid-crustal material. Due to this unique tectonic setting, the deformation path of rocks within the bounding shear zones and throughout the core of the GHS profoundly influences the efficiency of extrusion and exhumation processes. Attempts to quantify GHS deformation and metamorphic evolution have provided significant insight into Himalayan orogenic development, but these structural and petrologic studies are often conducted in isolation. Penetrative deformation fabrics developed under mid-upper amphibolite facies conditions within the GHS argue that deformation and metamorphism were coupled, and this should be considered in studies aimed at quantifying GHS teconometamorphic evolution.

This work focuses on two projects related to the coupled deformation, thermal and metamorphic evolution during extrusion and exhumation of the GHS, focused on the lower and upper margins of the slab. A detailed examination of the P--T history of a schist collected from within the MCT zone of the Sutlej River, NW India, provides insight into the path experienced by these rocks as they traveled through the crust in response to the extreme shortening related to India-Asia collision. Combined forward thermodynamic and diffusion modeling indicates compositional zoning preserved in garnet has remained unmodified since growth and can be related directly to the P--T--X evolution of rocks from this zone. Classic porphyroblast--matrix relationships coupled with the above models provide a structural framework within which to interpret the microstructures and provide additional constraints on the relative timing of metamorphic and deformation events.

A combined microstructural and quartz petrofabric study of rocks from the highest structural levels of the GHS in the Zanskar region was completed. This work provides the first quantitative estimate of temperatures attending normal-sense shearing along the Zanskar Shear Zone, the westernmost strand of the STDS. Results indicate penetrative top-N (extensional) deformation occurred at elevated temperatures and resulted in the telescoping of isothermal surfaces present during shearing and extrusion of GHS rocks. Simple geometric models invoking heterogeneous simple shear parallel to the overlying detachment require dip-slip displacement magnitudes on the order of 15--40 km, identical to estimates derived from nearby barometric analyses.

Finally, focus is given to the rotational behavior of rigid inclusions suspended in a flowing viscous matrix from a theoretical perspective. Predictions of clast rotational behavior have been used to construct several kinematic vorticity estimation techniques that have become widely adopted for quantitative studies of naturally deformed rocks. Despite the popularity of the techniques, however, basic questions regarding clast-based analyses remain open. Therefore a numerical model was constructed and a systematic investigation of 2- and 3D clasts suspended in steady and non-steady plane-strain flows was undertaken to determine likely sources of error and the intrinsic strengths and limitations of the techniques.
Ph. D.

The westernmost spur of the Tibetan Plateau stretches to Eastern Ladakh in India. It is a region which remains poorly explored because of challenging conditions and long periods of political instability. At the same time, it is one of the highest places on earth supporting angiosperm life, which goes beyond 6000 m a.s.l. here. The whole region, due its remoteness, is practically unaffected by plant invasions and direct human activities. Thus, Ladakh represents a kind of "natural experiment", providing very long gradient of elevation suitable for comparative functional ecology as well as for testing various hypotheses concerning limitations of vascular plants. Arid climate and extreme elevations are the common factors. Our team pursued the goal of systematic botanical and ecological exploration of Ladakh, started by late Leoš Klimeš. This thesis provides insight into the main vegetation types, clonality in plants, plant-plant interactions and soil phototroph communities.

Field mapping and, structural, microstructural, and chronological analyses confirm the existence of a segment of the Gurla-Mandhata-Humla fault, an orogen-parallel strike-slip dominated shear zone in the upper Karnali valley of northwestern Nepal. This shear zone forms the upper contact of, and cuts obliquely across the Greater Himalayan Sequence (GHS). Data from this study reveal two phases of GHS deformation. Phase 1 is characterized by U-Th-Pb monazite crystallization ages (~26–12 Ma, peak ~18–15 Ma), consistent with typical Neohimalayan metamorphic ages, and the final stages of south-directed extrusion of the GHS. Phase 2 is characterized by south-dipping high-strain foliations and intensely developed ESE-WNW trending, shallowly plunging mineral elongation lineations, indicating orogen-parallel extension. Thermochronology of muscovite defining these fabrics implies that the area was cooling and experiencing orogen-parallel extension by ~15–9 Ma. Mineral deformation mechanisms and quartz c-axis patterns of these fabrics record a rapid increase in temperature from ~350°C along the shear zone, to ~650°C at ~2.5 structural km below the shear zone. Such temperature gradients may be remnants of telescoped and/or flattened isotherms generated during south-directed extrusion of the GHS. Overprinting ESE-WNW fabrics record progressive deformation of the GHS at lower temperatures. Progressive deformation included a significant component of pure shear, as indicated by symmetric high-temperature quartz c-axis fabrics and a lower-temperature vorticity estimate (~59% pure shear). A transition in c-axis fabrics from type I to type II cross-girdles at ~ 1.2 km below the fault could indicate a transition from plane strain towards constriction. Together, these data suggest orogen-parallel extension was occurring as a result of transtension. This study reveals a transition from south-directed extrusion of the GHS to orogen-parallel extension between ~15–13 Ma. Comparing these data with tectonic events across the Himalaya reveals an orogen-wide middle Miocene transition, coeval with the uplift of eastern Tibet. This is consistent with interpretations invoking radial spreading of Tibet and east-directed lower-crustal flow to explain orogen-parallel extension. Our study leads to the suggestion that a transition affecting mid- to lower-crustal processes may be responsible for the cessation of south-directed extrusion of the GHS and onset of east-directed lower-crustal flow.
Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2012-09-23 02:16:09.326

abstract: Understanding the evolution of the Himalayan-Tibetan orogen is important because of its purported effects on global geodynamics, geochemistry and climate. It is surprising that the timing of initiation of this canonical collisional orogen is poorly constrained, with estimates ranging from Late Cretaceous to Early Oligocene. This study focuses on the Ladakh region in the northwestern Indian Himalaya, where early workers suggested that sedimentary deposits of the Indus Basin molasse sequence, located in the suture zone, preserve a record of the early evolution of orogenesis, including initial collision between India and Eurasia. Recent studies have challenged this interpretation, but resolution of the issue has been hampered by poor accessibility, paucity of robust depositional age constraints, and disputed provenance of many units in the succession. To achieve a better understanding of the stratigraphy of the Indus Basin, multispectral remote sensing image analysis resulted in a new geologic map that is consistent with field observations and previously published datasets, but suggests a substantial revision and simplification of the commonly assumed stratigraphic architecture of the basin. This stratigraphic framework guided a series of new provenance studies, wherein detrital U-Pb geochronology, 40Ar/39Ar and (U-Th)/He thermochronology, and trace-element geochemistry not only discount the hypothesis that collision began in the Early Oligocene, but also demonstrate that both Indian and Eurasian detritus arrived in the basin prior to deposition of the last marine limestone, constraining the age of collision to older than Early Eocene. Detrital (U-Th)/He thermochronology further elucidates the thermal history of the basin. Thus, we constrain backthrusting, thought to be an important mechanism by which Miocene convergence was accommodated, to between 11-7 Ma. Finally, an unprecedented conventional (U-Th)/He thermochronologic dataset was generated from a modern river sand to assess steady state assumptions of the source region. Using these data, the question of the minimum number of dates required for robust interpretation was critically evaluated. The application of a newly developed (U-Th)/He UV-laser-microprobe thermochronologic technique confirmed the results of the conventional dataset. This technique improves the practical utility of detrital mineral (U-Th)/He thermochronology, and will facilitate future studies of this type.
Dissertation/Thesis
Ph.D. Geological Sciences 2011

博士
國立臺灣大學
地質科學研究所
100
Abstract The work presented in this dissertation is the outcome of research carried out in the Himalaya and the Central Philippine. Rock samples were collected from the studied areas and a combination of radiometric dating techniques was applied in an effort to get better insight into various aspects in respective areas. New fission track data document the cooling and exhumation history of Kulu-Beas Valley in NW Himalaya, India. There is a large set of existing thermochronological data from the eastern and northern parts of NW Himalaya, while, there is very little thermochronological data from the southern part. For this study, (between lattitude 31°30’-32°20’ and longitude 76°30’-77°15’), the cooling history through 250°C-110°C has been investigated by FT chronology on zircon and apatite. The young Pliocene-Pleistocene cooling ages obtained in this study are in good harmony with the ages obtained from neighboring Sutlej Valley and these ages show very good correlation with the precipitation in this part. It is suggested, based on our data that the “zone of high erosion” that lies in the Sutlej Valley extends up to the Beas Valley. In addition, the pattern of ages suggests non-uniform exhumation for different units of NW Himalaya. Late Miocene cooling ages from the fault zone are related to the activity on the thrusts present in the area. Tectonic reconstructions of the Philippines are severely hampered by a paucity of geochronologic and exhumation age constraints. First time reported apatite and zircon fission track, 40Ar/39Ar and U/Pb data from Central Philippines place time constraints on the collision of Palawan Continental Terrane (PCT) with Philippine Mobile Belt (PMB). In Mindoro, the geochronological data from different parts of the metamorphic complex show different age patterns. From the north coast, we obtained Permian U/Pb ages while from the southern exposure of the metamorphics, the ages are very young. Moreover, old inherited zircons are reported from the west and also from the southern part but such old zircons are not observed in the samples from the north coast. U/Pb ages from the metamorphics of Palawan are distinctly different in ages. Results are compared with the age obtained from Tablas Island where Romblon Metamorphics are exposed. The results reveal diverse protolith ages for metamorphics in these islands. In addition, the data provide clues for the provenance of detrital zircons from Panay Island, Mindoro Island and Palawan. The very young cooling ages, as constrained by low-temperature fission track dating, indicate recent and non-uniform exhumation. Layout of the Thesis This dissertation is divided into eight chapters. The different chapters are designed to address problems pertaining to individual areas. Chapter 1 provides an introduction about the areas and the potential problems I have tried to deal with in this study. Here, I also discuss, in short, about the existing problems that need to be addressed. Chapter 2 deals with the methodology used in this study. I provide detailed description of each method used and their principles. Chapter 3 describes the regional geology of the areas in general. Various units of Himalaya and tectonic setting of the Philippine is discussed here. Chapter 4 gives the details of work done in NW-Himalaya and the results obtained using FT dating. The results have revealed very young exhumation in this part of the NW Himalaya. In Chapter 5, I discuss about the samples collected from Panay Island, which were analyzed to constrain various issues related to collision of Palawan Continental Terrane with Philippine Mobile Belt. These samples were dated using a combination of Fission Track Dating, 40Ar/39Ar Dating and U/Pb Dating methods. North-east of the Panay lies the island of Mindoro. NW Mindoro and later East Mindoro was targeted in an attempt to use thermochronology in revealing its affinity to PCT and the relation of detrital zircons with South China during Mesozoic (Chapter 6). The results reveal diverse protolith ages for the Mindoro Metamorphics. In Chapter 7, the results of U/Pb dating from Central Palawan are discussed. Chapter 8 summarizes the results and interpretations.

Le segment Nord-Ouest himalayen (Kohistan-Ladakh et Karakorum, NE Pakistan et NO Inde) est une zone appropriée pour étudier les étapes de la convergence de deux continents (Inde et Asie), en contexte océanique puis continental sur 110 Ma. Une approche pluridisciplinaire (géologie structurale, pétro-géochimie, thermo-barométrie, géochronologie Ar-Ar) a été utilisée. Les étapes intra-océaniques de la convergence sont étudiées via les séries d'arc du Nord-Ladakh. Cette étude permet de raccorder l'arc océanique du Kohistan à l'W, à la marge active tibétaine à l'Est. L'étude des isotopes du Sr, Nd et Pb des laves d'arc fournit des rapports isotopiques élevés rappelant l'anomalie " DUPAL ". Des laves adakitiques et riches en Nb-Ta et Ti sont également présentes. Ces données suggèrent l'interaction entre liquides issus de la fusion de la croûte subduite et le manteau, à la suite de la subduction de la ride néo-téthysienne, comme déjà proposé pour l'initiation de l'obduction de l'ophiolite d'Oman, en réponse à une inversion tectonique: la remontée de l'Inde vers le Nord. Les étapes de la convergence post-collisionnelle, après une phase de raccourcissement NE-SW entre 60 et 40 Ma, sont marquées par une partition de la déformation: Une bande E-W de dômes recoupe les structures précoces, dans un contexte de raccourcissement N-S et d'extrusion verticale, associée à un métamorphisme HT dans le faciès des granulites et à un magmatisme à affinité mantellique (25 - 5 Ma). Cette granulitisation de la croûte asiatique pourrait être liée à un apport de chaleur mantellique lié au détachement du slab indien. La faille décrochante du Karakorum sert de limite entre Karakorum et Tibet et accommode l'extrusion latérale de celui-ci. Des granulites sont exhumées dans la zone de faille probablement d'ampleur lithosphérique. Le déplacement le long de la faille semble hétérogène, avec un rejet total de 300 km basé sur la corrélation des blocs de Lhasa et du Karakorum.