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Precambrian microcontinents represent key tectonic units in the accretionary collages of the western Central Asian Orogenic Belt (CAOB), and their geological history is reasonably well established since the Mesoproterozoic but remains weakly constrained for older epochs due to a scarcity of exposed Palaeoproterozoic and Archaean rocks. Early Precambrian rocks were previously reported from several metamorphic complexes in the Kyrgyz Tianshan orogenic belt, mainly based on multigrain conventional zircon dating, but the present study only confirmed such rocks at one site, namely in the Kuilyu Complex of eastern Kyrgyzstan. New single grain SHRIMP II zircon ages, geochemical data, and whole-rock Nd isotopic compositions for granitoid gneisses of the Kuilyu Complex elucidate the age, origin and tectonic settings of this oldest continental fragment in the Tianshan. The Kuilyu Complex is part of the basement in the Ishim - Middle Tianshan microcontinent. It consist of a strongly deformed and metamorphosed supracrustal assemblage of paragneisses and schists which are tectonically interlayered with amphibolites, migmatites and granitoid gneisses. Our zircon dating indicates that the Kuilyu Complex contains two suites of Palaeoproterozoic granitoid gneisses with magmatic protolith ages of ca. 2.32-2.33 Ga and 1.85 Ga. Granitoid magmatism at 1.85 Ga was almost immediately followed by amphibolite-facies metamorphism at ca 1.83 Ga, evidenced by growth of metamorphic zircon rims. The older, ca 2.3 Ga granitoid gneisses chemically correspond to calc-alkaline, metaluminous, I-type magnesian quartz diorite and granodiorite. The protolith of the younger, ca. 1.85 Ga granite-gneiss is an alkalic-calcic, metaluminous to peraluminous, ferroan medium-grained porphyric granite with chemical features resembling A-type granites. The 2.3 Ga and 1.85 Ga granitoid gneisses have slightly to distinctly negative initial epsilon(Nd) values of -1.2 and -6.6, and similar depleted mantle Nd model ages of 2.7-2.6 Ga, which imply melting of Neoarchaean continental crust. The zircon age patterns of the Kuilyu Complex resemble those of exposed rocks in the Tarim Craton, where episodes of granitoid magmatism at ca. 2.3-2.4 and 1.85 Ga, followed by amphibolite-facies metamorphism at ca 1.85 Ga, are also recorded. Similarities in the early Precambrian magmatic and metamorphic episodes as well as similar histories during the Neoproterozoic and early Palaeozoic suggest that the Ishim-Middle Tianshan microcontinent was rifted off the Tarim Craton. Similar age patterns also suggest possible tectonic links of the Kuilyu and Tarim continental blocks with the Baidrag Block of central Mongolia. In contrast, substantial differences in age and Precambrian evolution between the Anrakhai block of southern Kazakhstan and the Kuilyu Complex argue against a previous connection and suggest the former to represent an independent continental terrane. Current data show that early Precambrian rocks in the western CAOB outside Tarim only occur at two sites, namely in the Anrakhai Complex of southern Kazakhstan and in the Kuilyu Complex of eastern Kyrgyzstan. (C) 2016 Elsevier Ltd. All rights reserved.
Marked along-strike changes in stratigraphy, mountain belt morphology, basement exhumation, and deformation styles characterize the Andean retroarc; these changes have previously been related to spatiotemporal variations in the subduction angle. We modeled new apatite fission track and apatite (U-Th-Sm)/He data from nine ranges located between 26 degrees S and 28 degrees S. Using new and previously published data, we constructed a Cretaceous to Pliocene paleogeographic model that delineates a four-stage tectonic evolution: extensional tectonics during the Cretaceous (120-75 Ma), the formation of a broken foreland basin between 55 and 30 Ma, reheating due to burial beneath sedimentary rocks (18-13 Ma), and deformation, exhumation, and surface uplift during the Late Miocene and the Pliocene (13-3 Ma). Our model highlights how preexisting upper plate structures control the deformation patterns of broken foreland basins. Because retroarc deformation predates flat-slab subduction, we propose that slab anchoring may have been the precursor of Eocene-Oligocene compression in the Andean retroarc. Our model challenges models which consider broken foreland basins and retroarc deformation in the NW Argentinian Andes to be directly related to Miocene flat subduction.
Marked along-strike changes in stratigraphy, mountain belt morphology, basement exhumation, and deformation styles characterize the Andean retroarc; these changes have previously been related to spatiotemporal variations in the subduction angle. We modeled new apatite fission track and apatite (U-Th-Sm)/He data from nine ranges located between 26 degrees S and 28 degrees S. Using new and previously published data, we constructed a Cretaceous to Pliocene paleogeographic model that delineates a four-stage tectonic evolution: extensional tectonics during the Cretaceous (120-75 Ma), the formation of a broken foreland basin between 55 and 30 Ma, reheating due to burial beneath sedimentary rocks (18-13 Ma), and deformation, exhumation, and surface uplift during the Late Miocene and the Pliocene (13-3 Ma). Our model highlights how preexisting upper plate structures control the deformation patterns of broken foreland basins. Because retroarc deformation predates flat-slab subduction, we propose that slab anchoring may have been the precursor of Eocene-Oligocene compression in the Andean retroarc. Our model challenges models which consider broken foreland basins and retroarc deformation in the NW Argentinian Andes to be directly related to Miocene flat subduction.
The Indus Molasse records orogenic sedimentation associated with uplift and erosion of the southern margin of Asia in the course of ongoing India-Eurasia collision. Detailed field investigation clarifies the nature and extent of the depositional contact between this molasse and the underlying basement units. We report the first dataset on detrital zircon U-Pb ages, Hf isotopes and apatite U-Pb ages for the autochthonous molasse in the Indus Suture Zone. A latest Oligocene depositional age is proposed on the basis of the youngest detrital zircon U-Pb age peak and is consistent with published biostratigraphic data. Multiple provenance indicators suggest exclusively northerly derivation with no input from India in the lowermost parts of the section. The results provide constraints on the uplift and erosion history of the Ladakh Range following the initial India-Asia collision.
Understanding the geologic evolution of Northern Tibetan Plateau with multiple thermochronometers
(2018)
The early onset of deformation following the India-Asia collision, Neogene expanse of uplift, and complex systems that comprise strike-slip faults, thrust faults, and intermontane basins characterize the Cenozoic tectonism of Northern Tibetan Plateau and raise two prominent questions in orogenic geodynamics: 1) What mechanism(s) control(s) the transfer of stress related to the India-Asia collision across the distance of >2000 km; and 2) Why the development of high topography was delayed in the Northern Tibetan Plateau and what does it reveal about how the internal forces and external boundary conditions evolved. To address these two questions, we reconstruct a holistic spatial-temporal deformation history of the Northern Tibetan Plateau by using a range of thermochronometers, with closure temperature spanning from 350 degrees C to-60-70 degrees C. This multi-thermochronometer study reveals three stages of faulting related cooling, in the early Cretaceous, in Paleocene-Eocene and in middle-late Miocene. We observe that Paleocene-Eocene deformation was spatially restricted and mostly occurred on reactivated Cretaceous structures, indicating a control of pre-existing weakness on early Cenozoic deformation. Extensive Neogene deformation contrasts with restricted Paleocene-Eocene deformation and relatively quiescent shortening during the Oligocene-early Miocene, which implies a change in the regional tectonics regime. Global plate reconstructions show that this tectonic reorganization is coeval with an increase in Pacific-Asia plate convergence rates. We argue that this change in regional tectonics is a result of increasing constrictive environment of the eastern plate boundary, which changed the behavior of the Altyn Tagh fault the boundary fault of Northern Tibetan Plateau, causing it to change from feeding slip into structures out of the plateau to feeding slip into structures at plateau margins.
A geological transect across the suture separating northwestern South America from the Panama Arc helps document the provenance and thermal history of both crustal domains and the suture zone. During middle Miocene, strata were being accumulated over the suture zone between the Panama Arc and the continental margin. Integrated provenance analyses of those middle Miocene strata show the presence of mixed sources that includes material derived from the two major crustal domains: the old northwestern South American orogens and the younger Panama Arc. Coeval moderately rapid exhumation of Upper Cretaceous to Paleogene sediments forming the reference continental margin is suggested from our inverse thermal modeling. Strata within the suture zone are intruded by similar to 12 Ma magmatic arc-related plutons, marking the transition from a collisional orogen to a subduction-related one. Renewed late Miocene to Pliocene acceleration of the exhumation rates is the consequence of a second tectonic pulse, which is likely to be triggered by the onset of a flat-slab subduction of the Nazca plate underneath the northernmost Andes of Colombia, suggesting that late Miocene to Pliocene orogeny in the Northern Andes is controlled by at least two different tectonic mechanisms.
Basement-cored ranges formed by reverse faulting within intracontinental mountain belts are often composed of poly-deformed lithologies. Geological data capable of constraining the timing, magnitude, and distribution of the most recent deformational phase are usually missing in such ranges. In this paper, we present new low temperature thermochronological and geological data from a transect through the basement-cored Terskey Range, located in the Kyrgyz Tien Shan. Using these data, we are able to investigate the range's late Cenozoic deformation for the first time. Displacements on reactivated faults are constrained and deformation of thermochronologically derived structural markers is assessed. These structural markers postdate the earlier deformational phases, providing the only record of Cenozoic deformation and of the reactivation of structures within the Terskey Range. Overall, these structural markers have a southern inclination, interpreted to reflect the decreasing inclination of the reverse fault bounding the Terskey Range. Our thermochronological data are also used to investigate spatial and temporal variations in the exhumation of the Terskey Range, identifying a three-stage Cenozoic exhumation history: (1) virtually no exhumation in the Paleogene, (2) increase to slightly higher exhumation rates at similar to 26-20Ma, and (3) significant increase in exhumation starting at similar to 10Ma.
A broad array of new provenance and stable isotope data are presented from two magnetostratigraphically dated sections in the south-eastern Issyk Kul basin of the Central Kyrgyz Tien Shan. The results presented here are discussed and interpreted for two plausible magnetostratigraphic age models. A combination of zircon U-Pb provenance, paleocurrent and conglomerate clast count analyses is used to determine sediment provenance. This analysis reveals that the first coarse-grained, syntectonic sediments (Dzhety Oguz formation) were sourced from the nearby Terskey Range, supporting previous thermochronology-based estimates of a ca. 25-20 Ma onset of deformation in the range. Climate variations are inferred using carbonate stable isotope (delta O-18 and delta C-13) data from 53 samples collected in the two sections and are compared with the oxygen isotope compositions of modern water from 128 samples. Two key features are identified in the stable isotope data set derived from the sediments: (1) isotope values, in particular delta C-13, decrease between ca. 26.0 and 23.6 or 25.6 and 21.0 Ma, and (2) the scatter of delta O-18 values increased significantly after ca. 22.6 or 16.9 Ma. The first feature is interpreted to reflect progressively wetter conditions. Because this feature slightly post-dates the onset of deformation in the Terskey Range, we suggest that it has been caused by orographically enhanced precipitation, implying that surface uplift accompanied late Cenozoic deformation and rock uplift in the Terskey Range. The increased scatter could reflect variable moisture source or availability caused by global climate change following the onset of Miocene glaciations at ca. 22.6 Ma, or enhanced evaporation during the Mid-Miocene climatic optimum at ca. 17-15 Ma.
Differential exhumation in the Puna Plateau and Eastern Cordillera of NW Argentina is controlled by inherited paleostructures and resulting paleotopography related to the Cretaceous Salta Rift paleomargins. The Ceno zoic deformation front related to the development of the Andean retro-arc orogenic system is generally associated with >4 km of exhumation, which is recorded by Cenozoic apatite fi ssion-track (AFT) and (U-Th-[Sm])/He ages (He ages) in the Eastern Cordillera of NW Argentina. New AFT ages from the top of the Nevado de Cachi document Oligocene (ca. 28 Ma) cooling, which, combined with existing data, indicates exhumation of this range between ca. 28 Ma and ca. 14 Ma. However, some of the highest ranges in the Eastern Cordillera preserve Cretaceous ages indicative of limited Cenozoic exhumation. Samples collected from an similar to 3-km-elevation transect along the northern part of the Sierra de Quilmes paleorift fl ank (Laguna Brava) show AFT ages between ca. 80 and ca. 50 Ma and He ages between ca. 45 and ca. 10 Ma. Another set of samples from an similar to 1-km-elevation transect farther to the southwest (La Quebrada) shows Cretaceous AFT ages between ca. 116 Ma and ca. 76 Ma, and mainly Cretaceous He ages, in agreement with AFT data. Analysis of existing AFT and He ages from the area once occupied by the Salta Rift reveals a pattern characterized by Cretaceous ages along paleorift highs and Cenozoic ages within paleorift hanging-wall basins and later foreland basin depocenters. This pattern is interrupted by the Sierras Pampeanas at similar to 28 degrees S, which record mid-Cenozoic ages. Our data are consistent with a complex inherited pattern of pre-Andean paleostructures, likely associated with paleotopography, which was beveled by the Cenozoic regional foreland basin and reactivated during the late Neogene (ca. <10 Ma), strongly controlling the magnitude of Cenozoic uplift and exhumation and thus cooling age distribution. This, combined with variable lithologic erodibility, resulted in an irregular distribution of themochronological ages.