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1
Lonergan, Lidia, John Paul Platt, and Liam Gallagher. "The internal-external zone boundary in the eastern Betic Cordillera, SE Spain." Journal of Structural Geology 16, no. 2 (1994): 175–88. http://dx.doi.org/10.1016/0191-8141(94)90103-1.
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Lonergan, Lidia, John Platt, and Liam Gallagher. "The Internal-External zone boundary in the eastern Betic Cordillera, SE Spain: Reply." Journal of Structural Geology 18, no. 4 (1996): 525–27. http://dx.doi.org/10.1016/0191-8141(95)00114-s.
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Lonergan, L. "The Internal-External Zone Boundary in the eastern Betic Cordillera, SE Spain: Reply." Journal of Structural Geology 18, no. 4 (1996): 493–504. http://dx.doi.org/10.1016/0191-8141(95)00114-x.
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MartÃn-MartÃn, M. "The Internal-External Zone Boundary in the eastern Betic Cordillera, SE Spain: Discussion." Journal of Structural Geology 18, no. 4 (1996): 483–92. http://dx.doi.org/10.1016/0191-8141(95)00121-2.
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Martín-Martín, M., B. El Mamoune, A. Martín-Algarra, and J. A. Martín-Pérez. "The Internal-External Zone Boundary in the eastern Betic Cordillera, SE Spain: Discussion." Journal of Structural Geology 18, no. 4 (1996): 523–24. http://dx.doi.org/10.1016/0191-8141(95)00121-s.
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Tent-Manclu, Jose Enrique, Manuel Martin-Martin, Jose Antonio Martin-Perez, and Francisco Serrano. "Structural evolution of the early Miocene in the eastern Betic internal-external zone boundary (SE Spain)." Bulletin de la Société Géologique de France 172, no. 1 (2001): 41–47. http://dx.doi.org/10.2113/172.1.41.
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Abstract The Internal-External Zone boundary (IEZB) in the eastern Betic Cordillera partially coincides with the Cadiz-Alicante Accident, mainly a major transcurrent fault of N060E direction. The study of an area located along the IEZB at a point where it separates from the Cadiz-Alicante accident has provided details concerning the geodynamic evolution of the cordillera at the moment of its structuration. Here the Internal Zone, consists of rocks assigned to the Malaguide Complex, dating its last sedimentation to the Aquitanian, and deposits assigned to the Vinuela Group (early-middle Burdigalian). The nappes of the Internal Zone were emplaced during the latest Aquitanian and the Vinuela Group (here the El Nino Formation) sealed it but was afterwards affected by the collision with the External Zone. On the other side of the boundary, the External Zone comprises two tectonic units: the Penarrubia Unit (late Cretaceous-middle Burdigalian), which is made up mainly of limestones and marls, and the El Frances Chaotic Complex composed by a set of different lithologies, all from the External Zone in a marly matrix that could be interpreted as a collisional melange formed in the early-middle Burdigalian. The contact between the two domains corresponds to a backthrust of the External Zone over the Internal Zone which occurred in the middle Burdigalian. The deposits sealing the IEZB are dated by calcareous nannofossils and planktonic foraminifera as late Burdigalian, and comprise clasts from both domains.
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Driessche, Jean Van Den, and Henri Maluski. "Mise en évidence d'un cisaillement ductile dextre d'âge crétacé moyen dans la région de Tête Jaune Cache (nord-est du complexe métamorphique Shuswap, Colombie-Britannique)." Canadian Journal of Earth Sciences 23, no. 9 (1986): 1331–42. http://dx.doi.org/10.1139/e86-128.
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The boundary between the external zones (Rocky Mountains) and the internal zones of the eastern Canadian Cordillera is marked by a Tertiary half graben, the Rocky Mountains Trench (RMT). In the south Cordillera, east of the Shuswap metamorphic complex, the fault limiting the trench is superimposed on an early major thrust, the Late Jurassic Purceli thrust. On approaching this discontinuity, the ductile deformation of the Miette Group, a detrital Precambrian suite, is characterized by a subvertical foliation and a subhorizontal stretching lineation parallel to the fold axes. The deformation intensity, its noncoaxial characters, and its geographic extension are interpreted as resulting from a dextral crustal shear, parallel to the mapped trace of the Purcell thrust and RMT. The dextral slip is deduced from a microtectonic analysis of the observed rotational criteria and is consistent with the small angle occurring between the directions of the linear structure (stretching lineations and fold axes) and those of adjacent discontinuities. The Middle Cretaceous age (100–78 Ma) attributed to this deformation is based on the age of syn- to late-tectonic metamorphic minerals as dated by the 39Ar–40Ar method. A kinematic model involving vectorial decomposition of an oblique convergence is proposed, suggesting the simultaneous occurrence, in the Middle Cretaceous, of two suborthogonal conjugated movement directions, respectively parallel and normal to the general Cordilleran trend. [Journal Translation]
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Cook, Frederick A. "The reflection Moho beneath the southern Canadian Cordillera." Canadian Journal of Earth Sciences 32, no. 10 (1995): 1520–30. http://dx.doi.org/10.1139/e95-124.
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The transition from the crust to the mantle beneath the Canadian portion of the North American Cordillera varies in depth, geometry, and tectonic age across the orogen. These variations are rarely spatially related to the positions of morphologic or tectonic belts based on surface geology, nor to nearly 25 km of structural relief identified in outcrop and on seismic reflection data. The Moho in this region is thus interpreted to be a long-lived feature, perhaps as old as Proterozoic in the eastern part of the Cordillera, that probably has been active as a structural boundary during periods of crustal contraction and subsequent crustal stretching. Recognition of the Moho and lower crust as a zone of localized tectonic activity provides a partial explanation for the problem of where regional detachments that underlie the foreland thrust and fold belt go as they project westward to deep structural levels beneath the interior of the orogen: they likely project to the base of the crust, where they flatten and cause imbrication of crustal rocks.
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Jung, Gerlinde, and Matthias Prange. "The effect of mountain uplift on eastern boundary currents and upwelling systems." Climate of the Past 16, no. 1 (2020): 161–81. http://dx.doi.org/10.5194/cp-16-161-2020.
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Abstract. All major mountain ranges are assumed to have been subject to increased uplifting processes during the late Miocene and Pliocene. Previous work has demonstrated that African uplift is an important element to explain Benguela upper-ocean cooling in the late Miocene–Pliocene. According to proxy records, a surface ocean cooling also occurred in other eastern boundary upwelling regions during the late Neogene. Here we investigate a set of sensitivity experiments altering topography in major mountain regions (Andes, North American Cordillera, and southern and East African mountains) separately with regard to the potential impact on the intensity of near-coastal low-level winds, Ekman transport and Ekman pumping, and upper-ocean cooling. The simulations show that mountain uplift is important for upper-ocean temperature evolution in the area of eastern boundary currents. The impact is primarily on the atmospheric circulation which is then acting on upper-ocean temperatures through changes in strengths of upwelling, horizontal heat advection and surface heat fluxes. Different atmosphere–ocean feedbacks additionally alter the sea surface temperature response to uplift. The relative importance of the different feedback mechanisms depends on the region, but it is most likely also influenced by model and model resolution.
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Zelt, B. C., R. M. Ellis, and R. M. Clowes. "Crustal velocity structure in the eastern Insular and southernmost Coast belts, Canadian Cordillera." Canadian Journal of Earth Sciences 30, no. 5 (1993): 1014–27. http://dx.doi.org/10.1139/e93-085.
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Seismic refraction data recorded along a 330 km cross-strike profile through the eastern Insular and southernmost Coast belts of the Canadian Cordillera are interpreted using an iterative combination of traveltime inversion and amplitude forward modelling. The resultant model is characterized by large lateral variations in velocity. The most significant of these variations is a decrease in upper and middle crustal velocities to the east of the surface trace of the Harrison fault, which likely represents the transition from crust of the Insular superterrane to that of the Intermontane superterrane. This interpretation is consistent with some present geological models that place the possible (probable) location of the suture between the two superterranes less than 20 km east of the Harrison fault. Velocities at the base of the upper crust average 6.4 and 6.2 km/s west and east of the fault, respectively. Mid-crustal velocities average 6.6–6.9 km/s to the west and 6.35–6.45 km/s to the east of the fault. Lower crustal velocities also decrease slightly to the east. Other features of the velocity model include (i) a thin near-surface layer with velocities between 2.5 and 6.1 km/s; (ii) upper crustal thickness of 12.5 km, thinning to 8 km at the eastern boundary of the Western Coast Belt (WCB); (iii) high velocity (6.6–6.9 km/s) mid-crustal layer west of the Harrison fault extending to 21 km depth; (iv) high-velocity (6.75–7.1 km/s) lower crustal layer; (v) low-velocity gradient upper mantle with depth to Moho at 34–37 km beneath most of the Coast Belt, decreasing to 30 km beneath the eastern Insular Belt, a depth much less than previous estimates. The inferred crustal velocity structure beneath the WCB is consistent with the three-layer electrical conductivity structure for this area derived from magnetotelluric surveys. The association of high resistivities with the upper crust suggests that the upper 8–12 km represents the massive cover of plutonic rocks which characterizes the WCB. Middle and lower crustal velocities beneath the WCB are consistent with Wrangellian velocities found beneath Vancouver Island, suggesting Wrangellia may extend at depth eastward as far as the Harrison fault.
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Spence, George D., and Nancy A. McLean. "Crustal seismic velocity and density structure of the Intermontane and Coast belts, southwestern Cordillera." Canadian Journal of Earth Sciences 35, no. 12 (1998): 1362–79. http://dx.doi.org/10.1139/e98-070.
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Seismic refraction - wide-angle reflection data were recorded along a 450 km profile across the Intermontane, Coast, and Insular belts of the Canadian Cordillera. Crust and upper mantle structure was interpreted from traveltime inversion and forward-amplitude modelling, and the resultant seismic velocities were used to constrain modelling of the Bouguer gravity data along the profile. A high-velocity, high-density block in the upper 8 km of crust was interpreted as the subsurface extension of Harrison terrane; the Harrison fault at its eastern boundary may extend to at least 8 km depth and perhaps 20 km. Throughout the crust, both seismic velocities and densities are in general high beneath the Insular belt, low beneath the Coast and western Intermontane belts, and intermediate beneath the eastern Intermontane belt. However, densities are unusually low in the lower crust beneath the Coast belt (2800 kg/m3), relative to velocities (6.6-6.8 km/s). This indicates that Coast belt plutonic material is present throughout the crust; strong upper mantle reflectivity, previously interpreted on a Lithoprobe reflection line beneath the western Coast belt, may be high-density residue associated with the unusually low density plutonic material. Based on gravity data, Wrangellia must terminate sharply against the western edge of the Coast belt. In the lower crust, the lowest seismic velocities are found vertically beneath the surface trace of the Fraser fault, where velocities just above the Moho only reach 6.5 km/s, in contrast with 6.8 km/s beneath the western Coast belt and eastern Intermontane belt. This provides support for a subvertical geometry for the Fraser fault, perhaps with a broad zone of diffuse shearing in the lower crust. At this location, the Fraser fault does not appear to vertically offset the Moho, which is well-constrained at a uniform depth of km east of the Harrison fault.
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Monger, Jim W. H. "Logan Medallist 1. Seeking the Suture: The Coast-Cascade Conundrum." Geoscience Canada 41, no. 4 (2014): 379. http://dx.doi.org/10.12789/geocanj.2014.41.058.
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The boundary between rocks assigned to the Intermontane superterrane in the interior of the Canadian Cordillera and those of the Insular superterrane in the westernmost Cordillera of British Columbia and southeastern Alaska lies within/along the Coast Mountains, in which is exposed the core of an orogen that emerged as a discrete tectonic entity between 105 and 45 million years ago. Evidence from the Coast Mountains and flanking areas indicates that parts of the Intermontane superterrane (in Stikinia and Yukon-Tanana terranes) were near those of the Insular superterrane (Wrangellia and Alexander terranes) by the Early Jurassic (~180 Ma). This timing, as well as paleobiogeographic and paleomagnetic considerations, appears to discount a recent hypothesis that proposes westward-dipping subduction beneath an intra-oceanic arc on Insular superterrane resulted in arc-continent collision and inaugurated Cordilleran orogenesis in the Late Jurassic (~146 Ma). The hypothesis also relates the subducted ocean that had separated the superterranes to a massive, faster-than-average-velocity seismic anomaly in the lower mantle below the eastern seaboard of North America. To create such an anomaly, subduction of the floor of a large ocean was needed. The only surface record of such an ocean in the interior of the Canadian Cordillera is the Cache Creek terrane, which lies within the Intermontane superterrane but is no younger than Middle Jurassic (~174 Ma). This terrane, together with the probably related Bridge River terrane in the southeastern Coast Mountains, which is as young as latest Middle Jurassic (164 Ma) and possibly as young as earliest Cretaceous (≥ 130 Ma), appear to be the only candidates in Canada for the possible surface record of the seismic anomaly. SOMMAIRELa limite entre les roches assignées au Superterrane d’intermont de l’intérieur des Cordillères canadiennes et celles du Superterrane insulaire dans la portion la plus à l’ouest de la Cordillère de Colombie-Britannique et du sud-est de l’Alaska se trouvent dans et au long de la Chaîne côtière, au sein de laquelle affleure le noyau d’un orogène qui est apparu comme entité tectonique distincte entre 105 et 45 millions d’années. Des indices de la Chaîne côtière et des régions environnantes montrent que des portions du Superterrane d’intermont (dans les terranes de Stikinia et de Yukon-Tanana) se trouvaient alors près de celles du Superterrane insulaire (terranes de Wrangellia et d’Alexander) au début du Jurassique (~180 Ma). Cette chronologie, ajoutée à certains facteurs paléobiogéographiques et paléomagnétiques semblent discréditer une hypothèse récente voulant qu’une subduction à pendage ouest sous un arc intra-océanique sur le Superterrane insulaire résultait d’une collision entre un arc et le continent, initiant ainsi l’orogénèse de la Cordillère à la fin du Jurassique (~146 Ma). Cette hypothèse relie aussi l’océan subduit qui séparait les superterranes à une anomalie de vitesse sismique plus rapide que la normale dans le manteau inférieur sous le littoral maritime oriental de l’Amérique du Nord. Pour créer une telle anomalie, la subduction du plancher d’un grand océan était nécessaire. La seule indication de surface de l’existence d’un tel océan à l’intérieur de la Cordillère canadienne est le terrane de Cache Creek qui, bien qu’il se trouve dans le Superterrane d’intermont, est plus ancien que le Jurassique moyen (~174 Ma). Ce terrane, avec son équivalent probable de Bridge River dans le sud-est de la Chaîne côtière, qui est aussi jeune que la fin du Jurassique (164 Ma) et peut-être aussi jeune que le début du Crétacé (≥ 130 Ma), semblent être les seuls candidats au Canada offrant des vestiges en surface de cette anomalie sismique.
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Lonergan, Lidia, and John P. Platt. "The Malaguide-Alpujarride boundary: a major extensional contact in the Internal Zone of the eastern Betic Cordillera, SE Spain." Journal of Structural Geology 17, no. 12 (1995): 1655–71. http://dx.doi.org/10.1016/0191-8141(95)00070-t.
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Leslie-Panek, Jennifer, and Margot McMechan. "A seismic structural overview of Liard Basin, Northeast British Columbia, Canada." Interpretation 9, no. 2 (2021): T523—T532. http://dx.doi.org/10.1190/int-2020-0078.1.
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The Liard Basin is an important subbasin of the Western Canada Sedimentary Basin located in Northeast British Columbia along the eastern margin of the Canadian Cordillera. It contains significant potential unconventional gas resources but is largely underrepresented in public literature. Using available-for-purchase 2D seismic data, a regional structural interpretation of the basin was completed providing the first seismically controlled, high-level overview of the structural features of the basin and its surrounding area. The shape of the Liard Basin largely reflects the orientation of older Paleozoic and Proterozoic extensional structures that localized structures formed during Cretaceous-Tertiary compressive deformation. The eastern boundary of the basin is marked by the well-documented Bovie Structure. The Liard Anticline and the Liard River Anticline found near 60°N latitude are the only large structures located within the Liard Basin proper. Inversion of the herein named Liard Basin Boundary Structure, a west-side-down fault zone of Early Paleozoic age, localized the northwest boundary of the basin with the Liard Fold and Thrust Belt. A triangle zone bounds the Rocky Mountain Foothills and the Liard Basin to the southwest. Reflectors in the Proterozoic strata below the Liard Basin were deformed by compressive and then extensional structures prior to the deposition of Paleozoic strata. Proterozoic strata are involved in all of the major structures of the adjacent Liard Fold and Thrust Belt, the Rocky Mountain Foothills, and the Bovie Structure. These structures controlled the location of the Liard Basin.
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Ghosh, Dipak K. "Nd–Sr isotopic constraints on the interactions of the Intermontane Superterrane with the western edge of North America in the southern Canadian Cordillera." Canadian Journal of Earth Sciences 32, no. 10 (1995): 1740–58. http://dx.doi.org/10.1139/e95-136.
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Sr and Nd isotopic compositions of the late Paleozoic metavolcanics and Late Triassic to early Tertiary granitoids from four magmatic episodes in the southern Canadian Cordillera from the Kootenay Arc to the Fraser Fault have been used to (i) identify the sources of these rocks, (ii) constrain the compressive tectonic history from Middle Jurassic to Paleocene, and (iii) constrain the western boundary of the basement in this region. The 215–190 Ma old primitive granitoids (εNd = +3.1 to 8.7; 87Sr/86Sr = 0.7028 − 0.7043) of the Late Triassic and Early Jurassic magmatic episode were emplaced in the Paleozoic oceanic crust of Quesnellia (εNd = +2.9 to +9.3) prior to its obduction over the basement. In contrast, during the younger magmatic episodes (Middle–Late Jurassic, Cretaceous, and early Tertiary), the granitoids from western Quesnellia show primitive isotopic compositions, and those from eastern Quesnellia show eastward-increasing crust-contaminated compositions. The contaminated characters of the Middle–Late Jurassic (180–150 Ma) granitoids from eastern Quesnellia (εNd = +2.8 to −9.1; 87Sr/86Sr = 0.7041 − 0.7083) suggest that by 180 Ma, the eastern part of Quesnellia obducted over the North American cratonic basement by an amount of about 100 km (Eocene extension corrected) measured from westward shifts of the Nd and Sr isopleths. The eastward-increasing crustal-contamination patterns in the Cretaceous (120–80 Ma) and the Paleocene igneous rocks also show westward shifts of these isopleths by 20 and 70 km, respectively. Thus, we observe that a total 190 km of obduction took place, this amount is similar to the amount of shortening measured in the Rocky Mountains Fold and Thrust Belt, and the western boundary of the North American basement presently lies at least 25–75 km east of the Fraser Fault.
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Jakobs, Giselle K., Paul L. Smith, and Howard W. Tipper. "An ammonite zonation for the Toarcian (Lower Jurassic) of the North American Cordillera." Canadian Journal of Earth Sciences 31, no. 6 (1994): 919–42. http://dx.doi.org/10.1139/e94-083.
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This is the second in a series of papers intended to establish a Lower Jurassic ammonite zonation that takes into account the biostratigraphic and biogeographic peculiarities of the North American succession. In North America the lower boundary of the Toarcian is drawn at the first appearance of Dactylioceras above the last occurrence of Amaltheus and Fanninoceras. The lower Toarcian is represented by the Kanense Zone; the middle Toarcian by the Planulata and Crassicosta zones; and the upper Toarcian by the Hillebrandti and Yakounensis zones. Section 5 on the Yakoun River in the Queen Charlotte Islands is designated the stratotype for the Planulata, Crassicosta, and Hillebrandti zones; section 3 on the Yakoun River is designated the stratotype for the Yakounensis Zone; an ideal stratotype for the Kanense Zone is not presently known. Reference sections further illustrating the faunal associations that characterize the zones are designated in eastern Oregon (Snowshoe Formation) and northern British Columbia (Spatsizi Group). The Dactylioceratidae, Harpoceratinae, and Hildoceratinae provide the most important zonal indicators for the lower Toarcian; Dactylioceratidae, Phymatoceratinae, and Bouleiceratinae for the middle Toarcian; and Phymatoceratinae, Grammoceratinae, and Hammatoceratinae for the upper Toarcian. Phymatoceras hillebrandti is described as a new species.
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Sánchez, Javier, Brian K. Horton, Eliseo Tesón, Andrés Mora, Richard A. Ketcham, and Daniel F. Stockli. "Kinematic evolution of Andean fold-thrust structures along the boundary between the Eastern Cordillera and Middle Magdalena Valley basin, Colombia." Tectonics 31, no. 3 (2012): n/a. http://dx.doi.org/10.1029/2011tc003089.
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Tamay, José, Jesús Galindo-Zaldivar, John Soto, and Antonio J. Gil. "GNSS Constraints to Active Tectonic Deformations of the South American Continental Margin in Ecuador." Sensors 21, no. 12 (2021): 4003. http://dx.doi.org/10.3390/s21124003.
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GNSS observations constitute the main tool to reveal Earth’s crustal deformations in order to improve the identification of geological hazards. The Ecuadorian Andes were formed by Nazca Plate subduction below the Pacific margin of the South American Plate. Active tectonic-related deformation continues to present, and it is constrained by 135 GPS stations of the RENAGE and REGME deployed by the IGM in Ecuador (1995.4–2011.0). They show a regional ENE displacement, increasing towards the N, of the deformed North Andean Sliver in respect to the South American Plate and Inca Sliver relatively stable areas. The heterogeneous displacements towards the NNE of the North Andean Sliver are interpreted as consequences of the coupling of the Carnegie Ridge in the subduction zone. The Dolores–Guayaquil megashear constitutes its southeastern boundary and includes the dextral to normal transfer Pallatanga fault, that develops the Guayaquil Gulf. This fault extends northeastward along the central part of the Cordillera Real, in relay with the reverse dextral Cosanga–Chingual fault and finally followed by the reverse dextral Sub-Andean fault zone. While the Ecuadorian margin and Andes is affected by ENE–WSW shortening, the easternmost Manabí Basin located in between the Cordillera Costanera and the Cordillera Occidental of the Andes, underwent moderate ENE–WSW extension and constitutes an active fore-arc basin of the Nazca plate subduction. The integration of the GPS and seismic data evidences that highest rates of deformation and the highest tectonic hazards in Ecuador are linked: to the subduction zone located in the coastal area; to the Pallatanga transfer fault; and to the Eastern Andes Sub-Andean faults.
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ALFARO, P., J. M. ANDREU, J. M. ANDREU, A. ESTÉVEZ, J. M. SORIA, and T. TEIXIDÓ. "Quaternary deformation of the Bajo Segura blind fault (eastern Betic Cordillera, Spain) revealed by high-resolution reflection profiling." Geological Magazine 139, no. 3 (2002): 331–41. http://dx.doi.org/10.1017/s0016756802006568.
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The blind reverse Bajo Segura Fault is located at the eastern extreme of the Trans-Alboran shear zone (Betic Cordillera, southeast Iberian Peninsula). The surface expression of recent activity of this blind ENE–WSW fault is represented by coseismic surface anticlines and growth synclines on both sides of the anticlines. In the synclines, the deformation of the most recent Quaternary materials is obscured by a sedimentary unit more than 30 m thick which was deposited during the later part of the Late Pleistocene and the Holocene. The present study reports three high-resolution seismic profiles made in the northern growth syncline, which was the one developed most by the Bajo Segura Fault. In these seismic profiles we recognize the boundary between pre-growth strata and growth strata. This marker, Early Pliocene in age, dates the start of the activity of this blind reverse fault. The geometry observed in the seismic profiles of the syntectonic strata, dating from the Late Pliocene and Quaternary, indicates a limb rotation folding mechanism. On seismic profile 2, the complex geometry of the Benejúzar anticline forelimb can be attributed to several splay faults close to the surface of Bajo Segura Fault.
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Welford, J. Kim, Ron M. Clowes, Robert M. Ellis, George D. Spence, Isa Asudeh, and Zoltan Hajnal. "Lithospheric structure across the craton-Cordilleran transition of northeastern British Columbia." Canadian Journal of Earth Sciences 38, no. 8 (2001): 1169–89. http://dx.doi.org/10.1139/e01-020.
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The lithospheric structure of the transition from the craton to the Cordillera in northeastern British Columbia is interpreted from inversion of seismic refraction wide-angle reflection data along a 460-km profile, and from 3-d (3-dimensional) inversion and 2.5-d forward modelling of Bouguer gravity data. The seismic profile extends westward from the sediment-covered edge of cratonic North America across the Foreland and Omineca morphogeological belts to the eastern boundary of accreted terranes, beyond the Tintina Fault. Across the ancient cratonic margin, the resultant models reveal a westward-thickening package of low upper crustal velocities (6.2 km/s and less) and low densities to almost 20 km depth below the Western Canada Sedimentary Basin, overlying a west-facing ramp of higher velocities and densities in the middle and lower crust. These features are inferred to represent passive-margin sediments deposited on the ancient rifted margin during the mid-to-late Proterozoic and early Paleozoic. A wedge-shaped high-velocity (7.3 km/s) crustal layer at the base of the crust beneath the edge of cratonic North America is interpreted to be the result of magmatic underplating during rifting. In the Cordilleran Foreland Belt, high velocities (6.4 km/s) in the upper 5 km of the crust indicate rocks upthrust from the middle crust. A narrow trench of low velocities in the near-surface, which is imaged ~20 km to the west of the inferred location of the Tintina Fault, is interpreted to represent the actual location of the fault or a major splay. From east to west, the Moho decreases in depth from ~40 km to ~34 km below the rifted margin of ancestral North America, then defines a small root at ~38 km depth below the high topography and upper crustal velocities of the eastern Foreland Belt, and gradually shallows to ~34 km beneath the Omineca belt. An enigmatic laterally heterogeneous upper mantle has anomalously high velocities (up to 8.3 km/s) beneath the Foreland Belt, flanked by regions of low velocities (7.77.8 km/s). Results indicate that the location of the Cordilleran deformation front west of the ramped cratonic margin directly affected the tectonic evolution of the region.
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Hasegawa, H. S. "Seismogenesis in Eastern Canada." Seismological Research Letters 59, no. 4 (1988): 219–25. http://dx.doi.org/10.1785/gssrl.59.4.219.
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Abstract The pattern of seismicity in eastern Canada depends on the presence of weak zones from previous major tectonic orogenies and how these weak zones are reactivated by local and regional stress fields and geophysical processes. Within the Canadian Shield, away from seismotectonic trends, there is a low level of seismicity and earthquakes tend to be small, less than M5. However, along seismically active trends, earthquakes as large as M7 have occurred. The seismotectonic features fall into four main categories: positive (uplift) continental basement linears; grabens formed by old plate separation; passive rifted margins offshore; and extinct spreading ridges. Two of the positive seismotectonic trends are the Boothia Uplift-Bell Arch that transects the northeastern part of the craton and northeastern Baffin Island, where the effects of postglacial rebound on the upper crustal stress field are the most pronounced. The St. Lawrence Valley (and interconnecting grabens) is a seismically active graben system that contains the most seismically active region (the Charlevoix zone) in eastern Canada. The extinct spreading ridge along the Labrador Sea and the Mesozoic rifted margin along Baffin Bay and Labrador Sea contain clusters of moderate seismicity. There are diffuse zones of moderate seismicity over some geological provinces (e.g. Central Metasedimentary Belt in western Quebec) apart from major tectonic features, a confined seismic zone (within an intrusion) in the Miramichi region and seismicity at the intersection of faults in northern Ontario. In the Nahanni region, which is situated near the boundary between the northeast Cordillera and the Interior Platform, the commencement of a noteworthy earthquake sequence with magnitude up to Ms 6.9 indicates considerable stress-strain build-up over a large area. There is an anticline in the epicentral area that is bounded by thrust faults and mountain ranges. In order to enhance our understanding of causative factors of current seismicity, it is necessary to determine in greater detail the tectonic forces and geophysical processes that are reactivating pre-weakened faults along the seismotectonic trends and over broad, diffuse seismogenic regions. Some of these factors are the rate of stress build-up, stress concentration at the intersection of faults and between mountain ranges, residual stress, the role of pore fluids, individual block movement, whether this movement is due to postglacial rebound or to other underlying viscoelastic phenomena and the rate of sediment deposition along the continental slope. Paleoseismicity is useful not only for the reconstruction of old large earthquakes but also for providing insight as to why surface fault offsets have not been observed in regions where large earthquakes (and associated high rate of microseisrnicity) have occurred within the past several hundred years.
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Gray, Keith D., V. Isakson, D. Schwartz, and Jeffrey D. Vervoort. "Orogenic link ∼41°N–46°N: Collisional mountain building and basin closure in the Cordillera of western North America." Geosphere 16, no. 1 (2019): 136–81. http://dx.doi.org/10.1130/ges02074.1.
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Abstract Polyphase structural mapping and mineral age dating across the Salmon River suture zone in west-central Idaho (Riggins region; ∼45°30′N, ∼117°W–116°W) support a late Mesozoic history of penetrative deformation, dynamothermal metamorphism, and intermittent magmatism in response to right-oblique oceanic-continental plate convergence (Farallon–North America). High-strain linear-planar tectonite fabrics are recorded along an unbroken ∼48 km west-to-east transect extending from the Snake River (Wallowa intra-oceanic arc terrane; eastern Blue Mountains Province) over the northern Seven Devils Mountains into the lower Salmon River Canyon (ancestral North America; western Laurentia). Given the temporally overlapping nature (ca. 145–90 Ma) of east-west contraction in the Sevier fold-and-thrust belt (northern Utah–southeast Idaho–southwest Montana segment), we propose that long-term terrane accretion and margin-parallel northward translation in the Cordilleran hinterland (∼41°N–46°N latitude; modern coordinates) drove mid- to upper-crustal shortening >250 km eastward into the foreland region (∼115°W–113°W). During accretion and translation, the progressive transfer of arc assemblages from subducting (Farallon) to structurally overriding (North American) plates was accommodated by displacement along a shallow westward-dipping basal décollement system underlying the Cordilleran orogen. In this context, large-magnitude horizontal shortening of passive continental margin strata was balanced by the addition of buoyant oceanic crust—late Paleozoic to Mesozoic Blue Mountains Province—to the leading edge of western Laurentia. Consistent with orogenic float modeling (mass conservation, balance, and displacement compatibility), diffuse dextral-transpressional deformation across the accretionary boundary (Salmon River suture: Cordilleran hinterland) was kinematically linked to eastward-propagating structures on the continental interior (Sevier thrust belt; Cordilleran foreland). As an alternative to noncollisional convergent margin orogenesis, we propose a collision-related tectonic origin and contractional evolution for central portions of the Sevier belt. Our timing of terrane accretion supports correlation of the Wallowa terrane with Wrangellia (composite arc/plateau assemblage) and implies diachronous south-to-north suturing and basin closure between Idaho and Alaska.
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Dahlquist, Juan A., Sebastián O. Verdecchia, Edgardo G. Baldo, et al. "Early Cambrian U-Pb zircon age and Hf-isotope data from the Guasayán pluton, Sierras Pampeanas, Argentina: implications for the northwestern boundary of the Pampean arc." Andean Geology 43, no. 1 (2016): 137. http://dx.doi.org/10.5027/andgeov43n1-a08.
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An Early Cambrian pluton, known as the Guasayán pluton, has been identified in the central area of Sierra de Guasayán, northwestern Argentina. A U-Pb zircon Concordia age of 533±4 Ma was obtained by LA-MC-ICP-MS and represents the first report of robustly dated Early Cambrian magmatism for the northwestern Sierras Pampeanas. The pluton was emplaced in low-grade metasedimentary rocks and its magmatic assemblage consists of K-feldspar (phenocrysts)+plagioclase+quartz+biotite, with zircon, apatite, ilmenite, magnetite and monazite as accessory minerals. Geochemically, the granitic rock is a metaluminous subalkaline felsic granodiorite with SiO2=69.24%, Na2O+K2O=7.08%, CaO=2.45%, Na2O/ K2O=0.71 and FeO/MgO=3.58%. Rare earth element patterns show moderate slope (LaN/YbN=8.05) with a slightly negative Eu anomalies (Eu/Eu*=0.76). We report the first in situ Hf isotopes data (εHft=-0.12 to -4.76) from crystallized zircons in the Early Cambrian granites of the Sierras Pampeanas, helping to constrain the magma source and enabling comparison with other Pampean granites. The Guasayán pluton might provide a link between Early Cambrian magmatism of the central Sierras Pampeanas and that of the Eastern Cordillera, contributing to define the western boundary of the Pampean paleo-arc.
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Symons, David TA, Philippe Erdmer, and Phil JA McCausland. "New 42 Ma cratonic North American paleomagnetic pole from the Yukon underscores another Cordilleran paleomagnetism-geology conundrum." Canadian Journal of Earth Sciences 40, no. 10 (2003): 1321–34. http://dx.doi.org/10.1139/e03-047.
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Eocene posttectonic plutons of the Beaver River alkalic complex in southeastern Yukon intruded DevonianMississippian and Triassic sandstones in the Foothills of the Canadian Cordillera. A paleomagnetic collection of 27 sites from three separate plutons produced 326 specimens that were analyzed using alternating field and thermal step demagnetization methods. The A component characteristic remanent magnetization (ChRM) resides in magnetite with normal polarity in the 42.6 ± 0.8 Ma Beaver River pluton, reversed polarity in the 42.1 ± 0.7 Ma Larson Creek East pluton, and both polarities in the 41.3 ± 0.4 Ma Larson Creek West pluton, corresponding with magnetic polarity chrons 20n, 19r, and the boundary between chron 19r and 18n, respectively. The ChRMs of the plutons are indistinguishable (2σ) with a mean for the 42.0 ± 0.5 Ma complex of D = 158.8°, I = 73.1° (N = 21 sites, α95 = 3.0°, k = 116.8). A positive paleomagnetic contact test shows the A component to be primary, and the poorly isolated B component suggests the host rocks for Larson Creek West are Early to Middle Devonian. The paleopole for the Beaver River complex at 79.2°N, 145.8°E (N = 21, dp = 4.8°, dm = 5.4°; Q = 7) is concordant with interpolated 42 Ma reference poles for the North American craton. In contrast, paleopoles from the accreted Intermontane and eastern Coast Belt terranes record clockwise rotations of 24° ± 10° (Eocene) and 13° ± 5° (OligocenePliocene), indicating that the allochthonous Intermontane terranes have been progressively driven ~240 ± 120 km eastwards up and over pericratonic and cratonic North American lower crust by Pacific plate subduction since the mid-Eocene.
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Osorio Afanador, Diego, and Francisco Velandia. "Late Jurassic syn-extensional sedimentary deposition and Cenozoic basin inversion as recorded in The Girón Formation, northern Andes of Colombia." Andean Geology 48, no. 2 (2021): 237. http://dx.doi.org/10.5027/andgeov48n2-3264.
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The Yariguíes Anticlinorium, a regional structure located at the western flank of the Eastern Cordillera of Colombia, includes the thickest record of continental sedimentary rocks accumulated near to the Jurassic-Cretaceous boundary. The sedimentary rocks are lithoarenites and feldspathic arenites, grouped in the Girón Formation, and deposited in a Late Jurassic extensional basin interpreted in this work as a rift basin. We analysed the sedimentologic and compositional characteristics of two sections that accumulated in a complex rift system. We identified important thickness variations, from 3,350 m in the type section to at least 525 m in a reference section in the Zapatoca area, as well as petrographic and lithofacies changes. This led us to confirm that the Girón Formation encompasses all the continental facies, whose source rock correspond mainly to the exhumed blocks of the Santander Massif during the Late Jurassic. The synrift successions were segmented by transverse structures and regional longitudinal faults of the rift-shoulder, as the Suárez Fault. The tectonic frame of the study area shows the relevance of the W-E compressional regimes, explaining the local kinematics as a heritage of the former configuration and tectonic inversion of the basins. However, clockwise rotation of the stress field was detected from the stress tensor analysis. The latest orientation of the stress tensors and shear joints are related to the effect of the transpressional Bucaramanga and Lebrija faults along the study area.
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de Keijzer, Martin, Paul F. Williams, and Richard L. Brown. "Kilometre-scale folding in the Teslin zone, northern Canadian Cordillera, and its tectonic implications for the accretion of the Yukon-Tanana terrane to North America." Canadian Journal of Earth Sciences 36, no. 3 (1999): 479–94. http://dx.doi.org/10.1139/e98-096.
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The Teslin zone in south-central Yukon has previously been described as a discrete zone with a steep foliation unique to the zone. It includes the Anvil assemblage and the narrowest portion of the Yukon-Tanana terrane (the Nisutlin assemblage), and is defined by post-accretionary faults: the Big Salmon fault to the west and the d'Abbadie fault system to the east. The zone was interpreted as a lithospheric suture or a crustal-scale transpression zone, and as the root zone of klippen lying on the North American craton to the east. We demonstrate that deformation and metamorphism are the same inside and outside the zone. The steep transposition foliation in the zone, in contrast to adjacent rocks to the east, coincides with the steep limb of a regional F3 structure. This fold has a shallow limb in the easternmost part of the zone and immediately east of the zone. Thus we reject earlier interpretations. If a suture exists between the obducted Anvil and Yukon-Tanana Nisutlin assemblages and North America, it is a shear zone that occurs at the base of the obducted rocks, which has been folded by the F3 fold. However, evidence that this thrust boundary is a lithospheric suture is lacking. A consequence of our interpretation is that North American rocks pass under the eastern Teslin zone and outcrop to the west of the Nisutlin and Anvil assemblages. This geometry precludes the possibility of the Teslin zone being the root zone of the klippen.
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MOLYNEUX, S. G., E. RAEVSKAYA, and T. SERVAIS. "The messaoudensis–trifidum acritarch assemblage and correlation of the base of Ordovician Stage 2 (Floian)." Geological Magazine 144, no. 1 (2006): 143–56. http://dx.doi.org/10.1017/s0016756806002676.
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The Global Stratotype Section and Point (GSSP) for Stage 2 of the Ordovician System, now the Floian Stage and approximately equivalent to the lower and middle Arenig of England and Wales, is defined by the first appearance datum (FAD) of the graptolite Tetragraptus approximatus in the Diabasbrottet Quarry section at Mount Hunneberg, Sweden. One of the issues this raises is how to correlate the base of Stage 2 at the GSSP with areas and successions that do not contain a correlative graptolite fauna. The distinctive Cymatiogalea messaoudensis–Stelliferidium trifidum acritarch assemblage is present in the upper Tremadocian Araneograptus murrayi Graptolite Biozone of NW England and ranges across the Tremadocian–Stage 2 boundary there (the Tremadoc–Arenig boundary of Anglo-Welsh nomenclature). It also occurs widely at other high southern Ordovician palaeolatitudes around the margin of Gondwana, being reported from Ireland, Wales, the Isle of Man, Belgium, Germany, Spain and Turkey, and may also be present in Bohemia and Argentina (Eastern Cordillera). It therefore has the potential to contribute towards the recognition and correlation of the base of Stage 2 in those areas. Of particular interest are the First Appearance Datums of various taxa within the stratigraphical range of the messaoudensis–trifidum assemblage, notably that of Aureotesta clathrata simplex, which is considered to be close to the base of Stage 2 in NW England.Elements of the messaoudensis–trifidum assemblage also occur in Baltica, the palaeoplate on which the GSSP for the base of Stage 2 is located. However, many of the taxa used to subdivide the messaoudensis–trifidum assemblage around Gondwana have not been recorded from Baltica and may be restricted palaeobiogeographically to the Gondwanan margin. Furthermore, acritarch microfloras have not been reported from the Diabasbrottet Quarry section itself, and there are hiatuses across the base of Stage 2 in the two sections from Baltica considered in this paper. Hence, direct correlation of the base of Stage 2 between the GSSP and other sections using acritarchs is not yet possible. Nevertheless, some taxa, for example the genera Peteinosphaeridium and Rhopaliophora, are shown to have FADs at similar stratigraphical levels in the late Tremadocian Stage of both Baltica and Gondwana, and therefore have the potential to correlate time slices in the late Tremadocian Stage between palaeoplates.
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Singleton, John S., Nikki M. Seymour, Stephen J. Reynolds, Terence Vomocil, and Martin S. Wong. "Distributed Neogene faulting across the western to central Arizona metamorphic core complex belt: Synextensional constriction and superposition of the Pacific–North America plate boundary on the southern Basin and Range." Geosphere 15, no. 4 (2019): 1409–35. http://dx.doi.org/10.1130/ges02036.1.
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Abstract We present fault data from a belt of Miocene metamorphic core complexes in western and central Arizona (USA) to determine patterns of brittle strain during and after large-magnitude extension, and to evaluate the magnitude of postextensional dextral shear across the region. In the White Tank Mountains, coeval WNW- to NW-striking dextral, normal, and oblique dextral-normal faults accommodated constrictional strain with extension subparallel to the direction of ductile stretching during core complex development. Northwest-striking oblique dextral-normal faults locally accommodated similar strain in the Harquahala Mountains, whereas in the South Mountains, constriction was primarily partitioned on NE-dipping normal faults and conjugate NW- and north-striking strike-slip faults. We interpret brittle constrictional strain to have developed during the late stages of large-magnitude extension associated with core complex development and folding of detachment fault corrugations. The oblique orientation of the Arizona core complex belt with respect to the extension direction likely resulted in a minor component of dextral transtension, accounting for much of the constrictional strain. In addition, far-field stresses associated with the transtensional Pacific–North America plate boundary may have contributed to constriction, which characterizes most Neogene detachment fault systems in the southwest Cordillera. Following cessation of detachment fault slip across the Arizona core complex belt (ca. 14–12 Ma), distributed NW-striking dextral and oblique dextral–NE-side-up (reverse) faults modified the topographic envelope of corrugations to an orientation clockwise of the core complex extension direction. Based on our analysis of this misalignment, we interpret the postdetachment fault dextral shear strain to increase northwestward from 0.03 across the South Mountains (0.5–0.6 km total slip across 18 km) to >0.03–0.07 across the Harquahala and Harcuvar Mountains (1.2–2.5 km of total slip across ∼35 km) and ∼0.2 across the Buckskin-Rawhide Mountains (7–8 km across 36 km). This along-strike variation in dextral shear is consistent with the regional pattern of distributed strain associated with the Pacific–North America plate boundary, as cumulative dextral offset in the lower Colorado River region increases toward the eastern Mojave Desert region to the northwest.
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Díaz, D., A. Maksymowicz, G. Vargas, E. Vera, E. Contreras-Reyes, and S. Rebolledo. "Exploring the shallow structure of the San Ramón thrust fault in Santiago, Chile (∼33.5° S), using active seismic and electric methods." Solid Earth Discussions 6, no. 1 (2014): 339–75. http://dx.doi.org/10.5194/sed-6-339-2014.
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Abstract. The crustal-scale west-vergent San Ramón thrust fault system at the foot of the main Andean Cordillera in central Chile is a geologically active structure with Quaternary manifestations of complex surface rupture along fault segments in the eastern border of Santiago city. From the comparison of geophysical and geological observations, we assessed the subsurface structure pattern affecting sedimentary cover and rock-substratum topography across fault scarps, which is critic for evaluating structural modeling and associated seismic hazard along this kind of faults. We performed seismic profiles with an average length of 250 m, using an array of twenty-four geophones (GEODE), and 25 shots per profile, supporting high-resolution seismic tomography for interpreting impedance changes associated to deformed sedimentary cover. The recorded traveltime refractions and reflections were jointly inverted by using a 2-D tomographic approach, which resulted in variations across the scarp axis in both velocities and reflections interpreted as the sedimentary cover-rock substratum topography. Seismic anisotropy observed from tomographic profiles is consistent with sediment deformation triggered by west-vergent thrust tectonics along the fault. Electrical soundings crossing two fault scarps supported subsurface resistivity tomographic profiles, which revealed systematic differences between lower resistivity values in the hanging wall with respect to the footwall of the geological structure, clearly limited by well-defined east-dipping resistivity boundaries. The latter can be interpreted in terms of structurally driven fluid content-change between the hanging wall and the footwall of a permeability boundary associated with the San Ramón fault. The overall results are consistent with a west-vergent thrust structure dipping ∼55° E at subsurface levels in piedmont sediments, with local complexities being probably associated to fault surface rupture propagation, fault-splay and fault segment transfer zones.
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Rojas, Maisa. "Multiply Nested Regional Climate Simulation for Southern South America: Sensitivity to Model Resolution." Monthly Weather Review 134, no. 8 (2006): 2208–23. http://dx.doi.org/10.1175/mwr3167.1.
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Abstract Results are reported from two 5-month-long simulations for southern South America using the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5). The periods of simulation correspond to May–September 1997 and 1998, which were anomalously wet and dry winters for central Chile, respectively. The model setup includes triply nested, two-way-interacting domains centered over the eastern South Pacific and the western coast of southern South America, with horizontal grid intervals of 135, 45, and 15 km. Boundary conditions are provided from NCEP–NCAR reanalyzed fields. The analysis focuses on two subregions of central Chile (30°–41°S). Region 1 (32°–35°S), which is where the observed interannual precipitation differences are largest, is topographically very complex, with a mean height of the Andes Cordillera around 4500 m. Region 2 (35°–39°S) has relatively smooth terrain, as the mean height of the Andes drops to 3000 m. Station precipitation and temperature data are used for model validation. The model exhibits a negative temperature bias (from 2° to 5°C), as well as a positive precipitation bias (40%–80%). This precipitation bias can be partially explained by a positive moisture bias over the ocean in the model. In addition, these biases are highly correlated to the representation of terrain and station elevation in the model. The highest-resolution domain has the smallest precipitation bias for low-elevation stations, but a large positive bias at high altitudes (up to 300%). It also has a better representation of the spatial distribution of the precipitation, especially in region 1, where topography has a larger impact on the precipitation. Overall, the model domain with highest resolution best reproduces the observed precipitation and temperature, as well as the interannual differences. However, this study also shows that large improvements in the simulations of the surface variables are obtained when downscaling from 135 to 45 km, but much smaller improvements are found when downscaling from 45 to 15 km. These simulations represent the first effort in simulating seasonal precipitation in this topographically complex region of the Southern Hemisphere.
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Moynihan, D. P., and D. R. M. Pattison. "Barrovian metamorphism in the central Kootenay Arc, British Columbia: petrology and isograd geometry." Canadian Journal of Earth Sciences 50, no. 7 (2013): 769–94. http://dx.doi.org/10.1139/cjes-2012-0083.
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A narrow, partly fault-bounded belt of Barrovian amphibolite facies rocks transects the central Kootenay Arc in the internal zone of the southeastern Canadian Cordillera. The following zones of increasing metamorphic grade are recognised in metapelites: chlorite/biotite, garnet, staurolite, kyanite, sillimanite, and sillimanite + K-feldspar. The garnet and higher-grade zones outline two joined domains: a N- to NNE-trending curved belt, >100 km long and 5–20 km wide, that is approximately parallel to the strike of stratigraphic units; and a SSE-trending belt, >70 km long and 10–15 km wide, that transects strike. Isograds in the N–NNE-trending belt outline an elongate bull’s-eye pattern with highest-grade rocks in the centre, coincident with the position of a structural culmination. Isogradic surfaces have an elongate domal form centred around this culmination. Rocks in the kyanite and sillimanite zones were metamorphosed at ~25 km (∼7 kbar (1 kbar = 100 MPa)) and >650 °C during Early Cretaceous crustal thickening; rocks in the garnet zone experienced peak temperature conditions (∼500 °C) at lower pressure, suggesting the piezothermic array for the belt has a positive slope. The western flank of the N- to NNE-trending belt is cut by the west-dipping Gallagher fault zone (GFZ), whereas the eastern boundary of the SSE-trending fork is marked by the Purcell Trench fault (PTF). These Palaeocene–Eocene normal faults truncate Early Cretaceous isogradic surfaces and juxtapose regions with contrasting structural and metamorphic histories. Low-grade rocks in the hanging wall of the GFZ underwent peak regional metamorphism during the Early–Middle Jurassic, prior to intrusion of the 159–173 Ma Nelson batholith at a depth of ∼12–14 km. With the exception of a zone along the southern “tail” of the Nelson batholith, rocks in the hanging wall of the GFZ were not affected by Cretaceous metamorphism or penetrative deformation. Rocks in the amphibolite-facies belt yield Palaeocene–Eocene K–Ar and 40Ar/39Ar mica cooling ages, whereas K–Ar biotite ages in the hanging wall of the GFZ record Jurassic – Early Cretaceous cooling, and those in the hanging wall of the PTF are mid-Cretaceous. Although the GFZ and PTF accommodated differential exhumation during the Palaeogene, significant relief on isogradic surfaces was established prior to normal faulting, during Early Cretaceous metamorphism and deformation.
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REY, J. "Extensional Jurassic tectonism of an eastern Subbetic section (southern Spain)." Geological Magazine 135, no. 5 (1998): 685–97. http://dx.doi.org/10.1017/s0016756898001277.
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The subsidence and stratigraphic evolution in an eastern section of the Subbetic Zone (External Zones of the Betic Cordilleras, Spain) during Jurassic and early Cretaceous times have been examined. The sediments have been deposited on a passive margin undergoing rifting. The data indicate that the activity was complex and spasmodic, with two distinct rift and post-rift phases. The beginning of the first syn-rift and post-rift phases are recorded by two regional sedimentary breaks, in the Late Carixian and in the Bathonian, respectively. The second rift and post-rift phases began, with less clearly defined limits, during the Oxfordian and at the Jurassic–Cretaceous boundary, respectively.
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Hildebrand, Robert S., and Joseph B. Whalen. "Arc and Slab-Failure Magmatism in Cordilleran Batholiths I – The Cretaceous Coastal Batholith of Peru and its Role in South American Orogenesis and Hemispheric Subduction Flip." Geoscience Canada 41, no. 3 (2014): 255. http://dx.doi.org/10.12789/geocanj.2014.41.047.
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We examined the temporal and spatial relations of rock units within the Western Cordillera of Peru where two Cretaceous basins, the Huarmey-Cañete and the West Peruvian Trough, were considered by previous workers to represent western and eastern parts respectively of the same marginal basin. The Huarmey-Cañete Trough, which sits on Mesoproterozoic basement of the Arequipa block, was filled with up to 9 km of Tithonian to Albian tholeiitic–calc-alkaline volcanic and volcaniclastic rocks. It shoaled to subaerial eastward. At 105–101 Ma the rocks were tightly folded and intruded during and just after the deformation by a suite of 103 ± 2 Ma mafic intrusions, and later in the interval 94–82 Ma by probable subduction-related plutons of the Coastal batholith. The West Peruvian Trough, which sits on Paleozoic metamorphic basement, comprised a west-facing siliciclastic-carbonate platform and adjacent basin filled with up to 5 km of sandstone, shale, marl and thinly bedded limestone deposited continuously throughout the Cretaceous. Rocks of the West Peruvian Trough were detached from their basement, folded and thrust eastward during the Late Cretaceous–Early Tertiary. Because the facies and facing directions of the two basins are incompatible, and their development and subjacent basements also distinct, the two basins could not have developed adjacent to one another. Based on thickness, composition and magmatic style, we interpret the magmatism of the Huarmey-Cañete Trough to represent a magmatic arc that shut down at about 105 Ma when the arc collided with an unknown terrane. We relate subsequent magmatism of the early 103 ± 2 Ma syntectonic mafic intrusions and dyke swarms to slab failure. The Huarmey-Cañete-Coastal batholithic block and its Mesoproterozoic basement remained offshore until 77 ± 5 Ma when it collided with, and was emplaced upon, the partially subducted western margin of South America to form the east-vergent Marañon fold–thrust belt. A major pulse of 73–62 Ma plutonism and dyke emplacement followed terminal collision and is interpreted to have been related to slab failure of the west-dipping South American lithosphere. Magmatism, 53 Ma and younger, followed terminal collision and was generated by eastward subduction of Pacific oceanic lithosphere beneath South America. Similar spatial and temporal relations exist over the length of both Americas and represent the terminal collision of an arc-bearing ribbon continent with the Americas during the Late Cretaceous–Early Tertiary Laramide event. It thus separated long-standing westward subduction from the younger period of eastward subduction characteristic of today. We speculate that the Cordilleran Ribbon Continent formed during the Mesozoic over a major zone of downwelling between Tuzo and Jason along the boundary of Panthalassic and Pacific oceanic plates.SOMMAIRENous avons étudié les relations spatiales et temporales des unités de roches dans la portion ouest de la Cordillère du Pérou, où deux bassins crétacés, la fosse d’accumulation de Huarmey-Cañete et la fosse d’accumulation péruvienne de l’ouest, ont été perçues par des auteurs précédents comme les portions ouest et est d’un même bassin de marge. La fosse de Huarmey-Cañete, qui repose sur le socle mésoprotérozoïque du bloc d’Arequipa, a été comblée par des couches de roches volcaniques tholéitiques – calco-alcalines de l’Albien au Thithonien atteignant 9 km d’épaisseur. Vers l’est, l’ensemble a fini par former des hauts fonds. Vers 105 à 101 Ma, les roches ont été plissées fortement puis recoupées par une suite d’intrusions vers 103 ± 2 Ma, durant et juste après la déformation, et plus tard dans l’intervalle 94 – 82 Ma, probablement par des plutons de subduction du batholite côtier. Quant à la fosse d’accumulation péruvienne de l’ouest, elle repose sur un socle métamorphique paléozoïque, et elle est constituée d’une plateforme silicoclastique – carbonate à pente ouest et d’un bassin contigu comblé par des grès, des schistes, des marnes et des calcaires finement laminés atteignant 5 km d’épaisseur et qui se sont déposés en continu durant tout le Crétacé. Les roches de la fosse d’accumulation péruvienne de l’ouest ont été décollées de leur socle, plissées et charriées vers l’est durant la fin du Crétacé et le début du Tertiaire. Parce que les facies et les profondeurs de sédimentation de ces deux fosses d’accumulation dont incompatibles, et que leur développement et leur socle sont différents, ces deux fosses ne peuvent pas s’être développées côte à côte. À cause de l’épaisseur accumulée, de sa composition et du style de son magmatisme, nous pensons que la fosse d’accumulation de Huarmey-Cañete représente un arc magmatique qui s’est éteinte vers 105 Ma, lorsque l’arc est entré en collision avec un terrane inconnu. Nous pensons que le magmatisme subséquent aux premières intrusions mafiques syntectoniques et aux réseaux de dykes de 103 ± 2 Ma sont à mettre au compte d’une rupture de plaque. Le bloc Huarmey-Cañete-batholitique côtier et son socle mésoprotérozoïque sont demeurés au large jusqu’à 77 ± 5 Ma, moment où il est entré en collision et a été poussé par-dessus la marge ouest sud-américaine partiellement subduite, pour ainsi former la zone de chevauchement de vergence est de Marañon. Nous croyons que la séquence majeure de plutonisme et d’intrusion de dykes qui a succédé à la collision finale à 73–62 Ma doit être reliée à une rupture de la plaque lithosphérique sud-américaine à pendage ouest. Le magmatisme de 53 Ma et plus récent qui a succédé à la collision finale, a été généré par la subduction vers l’est de la lithosphère océanique du Pacifique sous l’Amérique du Sud. Des relations temporelles et spatiales similaires qui existent tout le long des deux Amériques représentent la collision terminale d’un ruban continental d’arcs avec les Amériques durant la phase tectonique laramienne de la fin du Crétacé–début du Tertiaire. Elle a donc séparé la subduction vers l’ouest de longue date de la période de subduction vers l’est plus jeune caractérisant la situation actuelle. Nous considérons que le ruban continental de la Cordillère s’est constitué durant le Mésozoïque au-dessus d’une zone majeure de convection descendante entre Tuzo et Jason, le long de la limite entre les plaques océaniques Panthalassique et Pacifique.
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Powerman, Vladislav, Richard Hanson, Anna Nosova, Gary H. Girty, Jeremy Hourigan, and Andrei Tretiakov. "Nature and timing of Late Devonian–early Mississippian island-arc magmatism in the Northern Sierra terrane and implications for regional Paleozoic plate tectonics." Geosphere 16, no. 1 (2019): 258–80. http://dx.doi.org/10.1130/ges02105.1.
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Abstract The Northern Sierra terrane is one of a series of Paleozoic terranes outboard of the western Laurentian margin that contain lithotectonic elements generally considered to have originated in settings far removed from their present relative locations. The Lower to Middle Paleozoic Shoo Fly Complex makes up the oldest rocks in the terrane and consists partly of thrust-imbricated deep-marine sedimentary strata having detrital zircon age signatures consistent with derivation from the northwestern Laurentian margin. The thrust package is structurally overlain by the Sierra City mélange, which formed within a mid-Paleozoic subduction zone and contains tectonic blocks of Ediacaran tonalite and sandstone with Proterozoic to early Paleozoic detrital zircon populations having age spectra pointing to a non–western Laurentian source. Island-arc volcanic rocks of the Upper Devonian Sierra Buttes Formation unconformably overlie the Shoo Fly Complex and are spatially associated with the Bowman Lake batholith, Wolf Creek granite stock, and smaller hypabyssal felsic bodies that intrude the Shoo Fly Complex. Here, we report new results from U-Pb sensitive high-resolution ion microprobe–reverse geometry (SHRIMP-RG) dating of 15 samples of the volcanic and intrusive rocks, along with geochemical studies of the dated units. In addition, we report U-Pb laser ablation–inductively coupled plasma–mass spectrometry ages for 50 detrital zircons from a feldspathic sandstone block in the Sierra City mélange, which yielded abundant Ordovician to Early Devonian (ca. 480–390 Ma) ages. Ten samples from the composite Bowman Lake batholith, which cuts some of the main thrusts in the Shoo Fly Complex, yielded an age range of 371 ± 9 Ma to 353 ± 3 Ma; felsic tuff in the Sierra Buttes Formation yielded an age of 363 ± 7 Ma; and three felsic hypabyssal bodies intruded into the Sierra City mélange yielded ages of 369 ± 4 Ma to 358 ± 3 Ma. These data provide a younger age limit for assembly of the Shoo Fly Complex and indicate that arc magmatism in the Northern Sierra terrane began with a major pulse of Late Devonian (Famennian) igneous activity. The Wolf Creek stock yielded an age of 352 ± 3 Ma, showing that the felsic magmatism extended into the early Mississippian. All of these rocks have similar geochemical features with arc-type trace-element signatures, consistent with the interpretation that they constitute a petrogenetically linked volcano-plutonic system. Field evidence shows that the felsic hypabyssal intrusions in the Sierra City mélange were intruded while parts of it were still unlithified, indicating that a relatively narrow time span separated subduction-related deformation in the Shoo Fly Complex and onset of Late Devonian arc magmatism. Following recent models for Paleozoic terrane assembly in the western Cordillera, we infer that the Shoo Fly Complex together with strata in the Roberts Mountains allochthon in Nevada migrated south along a sinistral transform boundary prior to the onset of arc magmatism in the Northern Sierra terrane. We suggest that the Shoo Fly Complex arrived close to the western Laurentian margin at the same time as the Roberts Mountains allochthon was thrust over the passive margin during the Late Devonian–early Mississippian Antler orogeny. This led to a change in plate kinematics that caused development of a west-facing Late Devonian island arc on the Shoo Fly Complex. Due to slab rollback, the arc front migrated onto parts of the Sierra City mélange that had only recently been incorporated into the accretionary complex. In the mélange, blocks of Ediacaran tonalite, as well as sandstones having detrital zircon populations with non–western Laurentian sources, may have been derived from the Yreka and Trinity terranes in the eastern Klamath Mountains, where similar rock types occur. If so, this suggests that these Klamath terranes were in close proximity to the developing accretionary complex in the Northern Sierra terrane in the Late Devonian.
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Margold, Martin, John C. Gosse, Alan J. Hidy, Robin J. Woywitka, Joseph M. Young, and Duane Froese. "Beryllium-10 dating of the Foothills Erratics Train in Alberta, Canada, indicates detachment of the Laurentide Ice Sheet from the Rocky Mountains at ~15 ka." Quaternary Research 92, no. 2 (2019): 469–82. http://dx.doi.org/10.1017/qua.2019.10.
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AbstractThe Foothills Erratics Train consists of large quartzite blocks of Rocky Mountains origin deposited on the eastern slopes of the Rocky Mountain Foothills in Alberta between ~53.5°N and 49°N. The blocks were deposited in their present locations when the western margin of the Laurentide Ice Sheet (LIS) detached from the local ice masses of the Rocky Mountains, which initiated the opening of the southern end of the ice-free corridor between the Cordilleran Ice Sheet and the LIS. We use 10Be exposure dating to constrain the beginning of this decoupling. Based on a group of 12 samples well-clustered in time, we date the detachment of the western LIS margin from the Rocky Mountain front to ~14.9 ± 0.9 ka. This is ~1000 years later than previously assumed, but a lack of a latitudinal trend in the ages over a distance of ~500 km is consistent with the rapid opening of a long wedge of unglaciated terrain portrayed in existing ice-retreat reconstructions. A later separation of the western LIS margin from the mountain front implies higher ice margin–retreat rates in order to meet the Younger Dryas ice margin position near the boundary of the Canadian Shield ~2000 years later.
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Bobrowsky, Peter, and Nathaniel W. Rutter. "The Quaternary Geologic History of the Canadian Rocky Mountains." Géographie physique et Quaternaire 46, no. 1 (2007): 5–50. http://dx.doi.org/10.7202/032887ar.
Full textAbstract:
ABSTRACT The Canadian Rocky Mountains figured prominently during the glacial history of western Canada. First as a western limit or boundary to the Laurentide Ice Sheet, second as an eastern margin of the Cordilleran Ice Sheet, and finally as a centre of local Montane ice. Throughout the Quaternary, complex interactions of glacier ice from these three ice sources markedly changed the physical form of the Rocky Mountains, Trench and Foothills areas. Investigations into the Quaternary history of this region have been ongoing since the beginning of the last century. Since about 1950, the number of studies performed in this area have increased significantly. This paper briefly reviews the historical accomplishments of Quaternary work in the region up to the period of about 1950. From this time to the present, individual study efforts are examined in detail according to the three geographic regions: 1) the northern Rocky Mountains (from the Liard Plateau south to the McGregor Plateau), 2) the central Rocky Mountains (from the McGregor Plateau south to the Porcupine Hills) and 3) the southern Rocky Mountains (from the Porcupine Hills south to the international border). In the northern region, geologic data suggest a maximum of two Rocky Mountain glaciations and only one Laurentide glaciation and no ice coalescence. In the central region, three of four Rocky Mountain events, and at least two Laurentide events are known. Only in the central region is there good evidence for ice coalescence, but the timing of this event is not clearly established. In the south, at least three Rocky Mountain episodes and a variable number of Laurentide episodes are recognized. There is no evidence for ice coalescence. A number of facts support the proposal that Cordilleran ice crossed the Continental Divide and joined with local Montane ice at several locations. However, this expansion of western ice occurred before the Late Wisconsinan in all areas but Jasper. In general, the chronological data presented suggest that the Late Wisconsinan glaciation in the Rocky Mountains was a short-lived event which started around or after 20 ka years ago and ended before 12 ka ago.
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"A geochemical approach to allochthonous terranes: a Pan-African case study." Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences 331, no. 1620 (1990): 533–48. http://dx.doi.org/10.1098/rsta.1990.0088.
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The recognition of Mesozoic and Cenozoic terranes can best be made from palaeomagnetic, structural and palaeontological studies, but older regions of continental crust require geochemical constraints to evaluate crustal growth through terrane accretion. For Precambrian shields, the pattern of Pb and Nd isotopic provinces may reveal the mechanism of crustal growth. The Afro-Arabian Shield was generated by calc-alkaline magmatism between 900 and 600 Ma ago. This example of Pan-African crustal growth underlies an area of at least 1.2 x 10 6 km 2 , which may extend to 3.5 x 10 6 km 2 beneath Phanerozoic sediments and Tertiary volcanic cover. Field evidence and trace element geochemistry suggest that Pan-African tectonics began as a series of intra-oceanic island arcs that were accreted to form continental lithosphere over a period of 300 Ma. The great majority of Nd and Pb isotope ratios obtained for igneous rocks from the shield are indicative of a mantle magma source. Although many of the dismembered ophiolites cannot be identified with inter-terrane sutures in their present location, the eastern margin of the Nabitah orogenic belt is a major tectonic break that coincides with a critical boundary between Nd and Pb isotopic provinces and is marked by a linear array of ophiolite fragments across the length of the shield. Other terrane boundaries have not been identified conclusively, both because coeval island arcs can not be distinguished readily on isotopic grounds and because many ophiolites are allochthonous. However, the calculated rates of crustal growth (measured as volume of magma, extracted from the mantle per unit time) between 900 and 600 Ma are similar to those calculated for Phanerozoic terranes from the Canadian Cordillera. Such high rates in the Afro-Arabian Shield suggest that island arc terranes have accreted along a continental margin now exposed in NE Africa, together with minor continental fragments. If crustal growth rates during this time were no greater than contemporary rates, ca . 4000 km of arc length are required, which is considerably less than that responsible for crustal growth in the SW Pacific.
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Carrillo, Emilio, Roberto Barragán, Christian Hurtado, et al. "Depositional Sequences in Northern Peru: New Insights on the Palaeogeographic and Palaeotectonic Reconstruction of Western Gondwana During Late Permian and Triassic." Journal of the Geological Society, March 25, 2021, jgs2020–186. http://dx.doi.org/10.1144/jgs2020-186.
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Late Permian to Early Jurassic strata in northern Peru allows us to carry out a seismo-stratigraphic, litho-tectonic and chemostratigraphic analysis connecting the Andean-Amazonian foreland basins of Huallaga, Ucayali, southern Marañón, and the Eastern Cordillera. This analysis and data integration from Ecuador to western Brazil and southern Peru and Bolivia, allow us to redefine the timing of the major documented tectonic phases and corresponding palaeogeographies of western Gondwana from the late Permian to Triassic. Three litho-tectonic sequences and four associated deformation stages are recognized: 1) A sequence, tectonic relaxation, during late Permian; 2) A-B intra-sequence, folding-and-thrusting attributed to a continuation in time of the Gondwanide Orogeny, during the Early to Middle Triassic; 3) B sequence, rifting, attributed to Gondwana breakup during the Middle and Late Triassic; and 4) C Sequence, thermal sag, during the Late Triassic. Evaporites and carbonates (A sequence) dominated a low subsidence basin with southern restricted marine inflow at the Permian-Triassic boundary. A novel palaeogeographic model for these evaporites suggests that this saline basin extended up to 50,000 km2 in a restricted environment area with a potential bullseye pattern. The last pulse of the Gondwanide Orogeny and associated fold and thrust belt (A-B intra-sequence) exhumed previous the sequence generating emerged areas with little to no sedimentation. Red beds (B sequence) characterize the rifting stage, representing the syn-depositional infill of continental grabens, likely extending to the Acre Basin in Brazil. Finally, during the thermal sag, a marine inflow likely from the northwestern part of Peru generated sedimentation of carbonates and evaporites (C Sequence) to the west and east of the Peruvian margin. This sediment differentiation was, in part, controlled by the existence of pre-existing grabens associated to the previous rifting stage. This interpretation, together with other evaporitic occurrences attributed here to a Late Triassic epoch in south and north Peru and west Brazil, suggest the existence of an evaporitic basin filling an undeformed area of probably ca. 170,000 km2. It is therefore suggestive of the existence of a Late Triassic (Norian to Rhaetian; 217 to 204 Ma) salt giant controlled by thermal sag in western Gondwana. Our results are of great relevance for any future interpretation related to mass extinctions, paleoclimatic analysis and ocean dynamics during the Permian and Triassic as well as natural resources distribution between Ecuador and Bolivia.
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Jochen Hürtgen, Andreas Rudersdorf, Christoph Grützner, and Klaus Reicherter. "Morphotectonics of the Padul-Nigüelas Fault Zone, southern Spain." Annals of Geophysics 56, no. 6 (2014). http://dx.doi.org/10.4401/ag-6208.
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The Padul-Nigüelas Fault Zone (PNFZ) is situated at the south-western mountain front of the Sierra Nevada (southern Spain) in the Internal Zone of the Betic Cordilleras and belongs to a NW-SE trending system of normal faults dipping SW. The PNFZ constitutes a major tectonic and lithological boundary in the Betics, and separates the metamorphic units of the Alpujárride Complex from Upper Tertiary to Quaternary deposits. Due to recent seismicity and several morphological and geological indicators, such as preserved fault scarps, triangular facets, deeply incised valleys and faults in the colluvial wedges, the PNFZ is suspected to be a tectonically active feature of the south-eastern Granada Basin. We performed morphotectonic GIS analyses based on digital elevation models (DEM, cell size: 10 m) to obtain tectonic activity classes for each outcropping segment of the PNFZ. We have determined the following geomorphic indices: mountain front sinuosity, stream-length gradient index, concavity index and valley floor width to height ratio. The results show a differentiation in the states of activity along the fault zone strike. The western and eastern segments of the PNFZ indicate a higher tectonic activity compared to the center of the fault zone. We discuss and critically examine the comparability and reproducibility of geomorphic analyses, concluding that careful interpretation is necessary, if no ground-truthing can be performed.