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Accueil du site > Français > Annuaire > JOLIVET Marc > Mesozoic Tian Shan project

Mesozoic Tian Shan project

Understanding the Late Palaeozoic - Mesozoic tectonic and topographic evolution of Tian Shan

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Team members and partners

This large project federates a large number of partners, both in France and in China : Géosciences Rennes, IPG Paris, Institute of Geology and Geophysics of the Chinese Academy of Sciences, Pekin University and the DARIUS Program.

It is funded by the DARIUS Program, the CNRS-INSU (Syster project) and Pekin University.

Team members :

Barrier L. (IPG Paris), Bourquin S. (CNRS - Géosciences Rennes), Dupont-Nivet G. (CRNS – Géosciences Rennes), Fu B. (IGGCAS Beijing), Guo Zh. (Pekin University), Heilbronn. G. (Univ. Rennes 1 – Géosciences Rennes), Jolivet M. (CNRS – Géosciences Rennes), Robin C. (Univ. Rennes 1 – Géosciences Rennes), Yang W. (Peking University – Univ. Rennes 1 – Géosciences Rennes), Zhang Zh. (Pekin University)

Project description and first results

The Tian Shan is a 2500 km long, up to 7400 m high, range extending through western China, Kazakhstan and Kyrgyzstan. This range belongs to the larger Central Asian Orogenic Belt (CAOB) extending from the Urals to the Pacific across the East European, Siberian North China and Tarim cratons (e.g. Sengör et al., 1993 ; Windley, 2007). Several models have been proposed for the evolution of the CAOB, which have been nicely summarized by Windley et al. (2007).

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General tectonic and topographic map of Tian Shan (from Jolivet et al., 2010)

On a general point of view, the geochemical and tectonic data from the Tian Shan suggest multiple accretions of island arcs and Precambrian blocks rifted from Gondwana and/or Siberia (e.g. Filipova et al., 2001 ; Khain et al., 2003 ; Buslov et al., 2004a). According to that model the Tian Shan range has resulted from the amalgamation of a number of terranes during the Paleozoic (e.g. Allen et al., 1993a ; Gao et al., 1998 ; Laurent-Charvet, 2001 ; Zhou et al., 2001 ; Glorie et al., 2010). The Late Devonian to Early Carboniferous collision between the Tarim and Central Tian Shan blocks was followed by a Late Carboniferous – Early Permian collision between the Tarim – Central Tian Shan block and a series of island arcs currently exposed in the Northern Tian Shan (e.g. Coleman, 1989 ; Wang et al., 1990 ; Windley et al., 1990 ; Allen et al., 1993a ; Carroll et al., 1995, 2001 ; Charvet et al., 2009 ; Biske and Seltmann, 2010). Compressive structures generated during these collision phases were then reworked by Late Paleozoic strike-slip shear zones such as the Main Tian Shan Shear Zone (MTSZ) in central Tian Shan (e.g. Allen et al., 1991 ; Che, 1994 ; Laurent-Charvet et al., 2002, 2003). This shearing phase, induced either by northward (Chen et al., 1999 ; Alexeiev et al., 2009) or northwestward (Heubeck, 2001) motion and clockwise rotation of the Tarim block, seems to have ended in Late Permian to Early Triassic, around 245 Ma (Laurent-Charvet et al., 2003).

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Tectonic evolution and amalgamation of the Tian Shan lithosphere ( from Charvet & al., 2011)

The present-day topography of the range results from crustal shortening related to the ongoing India-Asia collision that started in Early Tertiary time (e.g. Tapponnier et al., 1986 ; Avouac et al., 1993 ; Najman and Garzanti, 2000 ; DeCelles et al., 2004 ; Yin, 2006, 2009). Several intermontane basins such as the Yili basin, the Turpan basin and the Bayanbulak basin, are preserved within the interior of the Tian Shan range. The sedimentary series within these basins are typically composed of largely undeformed Tertiary detrital sediments deposited over faulted and folded Jurassic strata which lie unconformably over strongly deformed Paleozoic rocks (Chen et al., 1995 ; Graham et al., 1994, Zhou et al., 2001). Dumitru et al. (2001) carried out a preliminary large-scale apatite fission track study of the Chinese Tian Shan along a NS transect across the entire range along the Duku road. The data have been completed recently using both AFT and (U-Th)/He analysis (Jolivet et al., 2010). The results showed highly heterogeneous cooling records across the range, with three main cooling episodes in latest Paleozoic, Late Mesozoic and Late Cenozoic. From those data and in accordance with the overall topography of the range, the Tian Shan can be divided into a series of independent, generally EW-trending subranges and intervening basins. Those individual units show quite variable differential exhumation (Dumitru et al., 2001 ; Jolivet et al., 2010). Paleozoic and Mesozoic apatite fission track ages indicate that little exhumation has occurred since Early Mesozoic times over large areas within the Tian Shan range.

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Geological map of the study area (modified after the 1:200,000 geological maps [XBGMR, 1969, 1971, 1973] using satellite images and field observations) showing the main tectonic structures. For clarity, active faults are represented in detail on Figure 5. Samples from this study and from Dumitru et al. [2001] are indicated with the corresponding apatite fission track and zircon and apatite (Uâ £Th)/He ages.
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alaeogeographic evolution of the Bayanbulak - Yili area through time as seen by low temperature thermochronology (from Jolivet et al., 2010)

The vertical resolution of AFT and apatite (U-Th)/He does not allow imaging exhumation events of less than 2 km in amplitude. Consequently small tectonic movements can create several hundreds of meters of relief and a rugged topography without being detected by those low temperature thermochronology methods.
In order to better constrain the topographic evolution of the Tian Shan and to detect small-scale tectonic events that could have occurred within the protracted Mesozoic “quiet period†we initiated a detailed study of the sediment record within both the piedmont and intra-mountain basins of the Chinese Tian Shan.

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View of the northern Tian Shan piedmont and the fantastic exposure of the Late Palaeozoic to Quaternary sediment series of the South Junggar basin. Photo S. Dominguez (CNRS - Géosciences Montpellier)

A first approach consisted in using U-Pb thermochronology on detrital zircons within the Late Palaeozoic to Quaternary series exposed along the southern margin of the Junggar basins. The aim was to look for changes in the sediment sources through time and to interpret those in terms of modifications of the drainage pattern in response to relief building or destruction within the range (Yang et al., in press).

The Junggar Basin, situated north of the Tian Shan ranges, holds sub-continuous record of the still controversial tectonic evolution of this part of continental Asia. While continental detrital sedimentation initiated in late Paleozoic time, the basin has been rejuvenated as a foreland basin since the late Cenozoic period due to north-south compression induced in this region by the effects of the India-Asia collision (Burchfiel & Royden, 1991 ; Avouac et al., 1993 ; Lu et al., 1994 ; Yin et al., 1998). Thick accumulations of sediments derived mostly from the Tian Shan range area form the Mesozoic to Quaternary lacustrine to fluvial depositional sequences that are well preserved and exposed in the southern margin of the Junggar Basin (Hendrix, 2000 ; Fang et al., 2005 ; Fang et al., 2006a ; Wu et al., 2006 ; Charreau et al., 2009a).

The detrital zircon geochronology and related genetic mineralogy studies, associated with palaeocurrent measurements show that the detrital zircons (and thus probably most of the sediments) were largely derived from the Tian Shan area to the south since the basin initiated in Late Carboniferous time. We also discovered the occurrence of Jurassic syn-sedimentary volcanism within the series. The occurrence of those Jurassic volcanic zircons within the Neogene sediments as well as their continuous recycling during Late Jurassic to Cretaceous highlights the importance of sediment recycling within the evolving piedmont.

The provenance and basin-range pattern evolution of the southern margin of the Junggar Basin can be generally divided into four stages as follows (Yang et al., in press). (1) During the Late Carboniferous to Early Triassic, the provenance is relatively unimodal. The detrital material was almost exclusively derived from the late Paleozoic magmatic belt of the North Tian Shan and the northern margin of the Yili terrane. Only a small amount of sediment was derived from the Central Tian Shan. This is interpreted in terms of near-source sedimentation in basin developing in a post orogenic extensional setting or as a half-graben. Strong topography in the range is suspected. (2) A major change in the history of the Junggar Basin occurred during the Middle-Late Triassic. Until the Upper Jurassic, the southern Junggar Basin progressively extended towards the south reaching beyond the Houxia area and evolved as a passively subsiding basin. The topography resulting from the late Paleozoic – early Mesozoic tectonic movements was progressively eroded and the drainage system reached the CTS block. (3) The following noticeable event corresponds to the Lower Cretaceous - Paleogene inversion of the southern Junggar Basin illustrated by the onset of erosion of the Jurassic sedimentary series and the progressive northward migration of the edge of the basin. However, it seems that while effective, this event remained of limited magnitude and that no major topography developed in the range. (4) Finally, major Neogene reactivation of the Tian Shan range led to the development of a piedmont along the northern edge of the NTS block and the Junggar Basin became a true foreland basin. The increasing amount and diversity of early Paleozoic and Precambrian zircons recalls the strong recycling of sediments from the entire Mesozoic and Tertiary sedimentary sequences of the North Tian Shan piedmont.

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Palaeogeographic evolution of Northern and Central Tian Shan imaged by U-Pb detrital zircon geochronology (from Yang et al., 2013).