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Macaulay E.A.,University of Potsdam | Sobel E.R.,University of Potsdam | Mikolaichuk A.,Central Asian Geological Geophysical Association | Mikolaichuk A.,National Academy of science | And 2 more authors.

New low-temperature thermochronological data from 80 samples in eastern Kyrgyzstan are combined with previously published data from 61 samples to constrain exhumation in a number of mountain ranges in the Central Kyrgyz Tien Shan. All sampled ranges are found to have a broadly consistent Cenozoic exhumation history, characterized by initially low cooling rates ( Source

Kroner A.,Chinese Academy of Geological Sciences | Kroner A.,University Mainz | Alexeiev D.V.,Russian Academy of Sciences | Rojas-Agramonte Y.,Chinese Academy of Geological Sciences | And 9 more authors.
Gondwana Research

The North Tianshan orogenic belt in Kyrgyzstan consists predominantly of Neoproterozoic to early Paleozoic assemblages and tectonically interlayered older Precambrian crystalline complexes and formed during early Paleozoic accretionary and collisional events. One of the oldest continental fragments of late Mesoproterozoic (Grenvillian) age occurs within the southern part of the Kyrgyz North Tianshan. Using SHRIMP zircon ages, we document two magmatic events at ~ 1.1 and ~ 1.3 Ga. The younger event is characterized by voluminous granitoid magmatism between 1150 and 1050 Ma and is associated with deformation and metamorphism. The older event is documented by ~ 1.3 Ga felsic volcanism of uncertain tectonic significance and may reflect a rifting episode. Geochemical signatures as well as Nd and Hf isotopes of the Mesoproterozoic granitoids indicate melting of still older continental crust with model ages of ca 1.2 to 2.4 Ga.The Mesoproterozoic assemblages are intruded by Paleozoic diorites and granitoids, and Nd and Hf isotopic systematics suggest that the diorites are derived from melts that are mixtures of the above Mesoproterozoic basement and mantle-derived material; their source is thus distinct from that of the Mesoproterozoic rocks. Emplacement of these plutons into the Precambrian rocks occurred between 461 and 441 Ma. This is much younger than previously assumed and indicates that small plutons and large batholiths in North Tianshan were emplaced virtually synchronously in the late Ordovician to early Silurian.The Mesoproterozoic rocks in the North Tianshan may be remnants of a once larger continental domain, whose fragments are preserved in adjacent blocks of the Central Asian Orogenic Belt. Comparison with broadly coeval terranes in the Kokchetav area of northern Kazakhstan, the Chinese Central Tianshan and the Tarim craton point to some similarities and suggests that these may represent fragments of a single Mesoproterozoic continent characterized by a major orogenic event at ~ 1.1. Ga, known as the Tarimian orogeny. © 2012 International Association for Gondwana Research. Source

Wack M.R.,Ludwig Maximilians University of Munich | Gilder S.A.,Ludwig Maximilians University of Munich | Macaulay E.A.,University of Potsdam | Sobel E.R.,University of Potsdam | Mikolaichuk A.,Central Asian Geological Geophysical Association

We present paleomagnetic data from the northern flank of the Tianshan range, southeast of Lake Issyk-Kul (Kyrgyzstan). 613 cores were collected in two parallel sections with a total thickness of 960. m (Chon Kyzylsuu, CK) and 990. m (Jeti Oguz, JO), as well as 48 cores at six sites in a nearby anticline. Rock magnetic analyses identify both magnetite and hematite in the fluvial-lacustrine sediments. The concentration of both minerals, the magnetite:hematite ratio, and the average magnetite grain size increase upward in both sections. Anisotropy of anhysteretic remanent magnetization defines a tectonic fabric with sub-horizontal maximum axes that parallel the strike direction together with intermediate and minimum axes that streak out about a great circle orthogonal to the maximum axes suggestive of a tectonic fabric emplaced during folding. Stepwise thermal demagnetization isolates interpretable magnetization components in 284 samples that define 26 polarity chrons in CK and 19 in JO. A positive fold test, dual polarities and systematic changes in rock-magnetic parameters with depth suggest that the high temperature magnetization component was acquired coevally with deposition. An age model based on a visual magnetostratigraphic correlation of both sections with the geomagnetic polarity time scale defines absolute ages from 26.0 to 13.3. Ma, with a fairly constant sedimentation rate of 9-10. cm/ka. A correlation based on a numerical algorithm arrives at a slightly different conclusion, with deposition ages from 25.2 to 11.0. Ma and sedimentation rates from 5 to 8. cm/ka. In comparison with sedimentation rates found at other magnetostratigraphic sections in the Tianshan realm, we infer that the sedimentary record in this part of the Issyk-Kul Basin precedes the more rapid phase of uplift of the Kyrgyz Tianshan. The onset of deposition and concomitant erosion of the adjacent Terskey Range is in good agreement with independent assessments of the exhumation history of this mountain range, with erosion increasing at 25-20. Ma and accelerating after 11-13. Ma. © 2014 Elsevier B.V. Source

Rojas-Agramonte Y.,Chinese Academy of Geological Sciences | Rojas-Agramonte Y.,University Mainz | Kroner A.,Chinese Academy of Geological Sciences | Kroner A.,University Mainz | And 11 more authors.
Gondwana Research

We report detrital zircon ages for Precambrian and early Palaeozoic metasediments from the Tianshan orogen in Kyrgyzstan, an important component of the Central Asian Orogenic Belt and compare these with published ages from the Chinese Tianshan and the Tarim craton. These data provide information on possible source terrains and suggest that Precambrian basement is widespread in the Tianshan and may, at least in part, represent continental fragments rifted off the Tarim craton during the early history of the Central Asian Orogenic Belt. Distinct differences in the Precambrian zircon age distribution between the North and Middle Tianshan of Kyrgyzstan support earlier ideas that these two terranes had different crustal histories prior to their amalgamation in the early Palaeozoic. We envisage an archipelago-type scenario for the Palaeo-Asian Ocean south of the Siberian craton in the late Neoproterozoic to early Palaeozoic in which numerous island arcs and Precambrian crustal fragments derived from Tarim drifted northwards (in present coordinates) and were amalgamated and tectonically stacked together during several ocean closure and accretion-collision events. This is surprisingly similar to what has been envisaged for the evolution of Indonesia where Mesozoic rifting of fragments from the Australian margin was followed by Cretaceous collisions and Cenozoic collision of Australia with the SE Asian margin. In both Central Asia and Indonesia continental crust has arrived in the region in multiple episodes and has been fragmented and juxtaposed by subduction-related processes. Continental growth during this process was minimal. © 2013 International Association for Gondwana Research. Source

Macaulay E.A.,University of Potsdam | Sobel E.R.,University of Potsdam | Mikolaichuk A.,Central Asian Geological Geophysical Association | Landgraf A.,University of Potsdam | And 2 more authors.

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 ∼26-20 Ma, and (3) significant increase in exhumation starting at ∼10 Ma. © 2013. American Geophysical Union. All Rights Reserved. Source

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