Paleozoic tectonic and geodynamic evolution of Chinese Tianshan and east Junggar (NW China): Accretion of the southern central Asian orogenic belt
|Category||Tectonic & Seismotectonic|
|Location||International Geological Congress,oslo 2008|
|Author||Charvet, Jacques۱; Wang, Bo۲; Faure, Michel۱; Shu, Liangshu۲; Cluzel, Dominique۱; Chen, Yan۱; Laurent-Charvet, Sébastien۳|
|Holding Date||27 September 2008|
Chinese Tianshan and East Junggar are key areas for understanding the Paleozoic accretion of the southern Central Asian Orogenic Belt and, subsequently, how and when took place the Central Asian Ocean closure in this region.
A first accretion-collision stage built the Eo-Tianshan range, before the Early Carboniferous (Visean), in which all tectonic structures verge northwards.
Geodynamic evolution records Ordovician-Early Devonian southward subduction of a Central Tianshan (CTS) ocean beneath the Tarim active margin, from which a CTS island arc was detached during the Silurian-Devonian by opening of the South Tianshan (STS) back-arc basin. The closure of the CTS ocean and of the STS back-arc basin led to the Central Tianshan Suture Zone (CTSZ) and South Tianshan Suture Zone (STSZ) respectively, both underlined by ophiolitic mélanges and HP metamorphic rocks. The CTSZ is obliquely cut by the dextral strike-slip Main Tianshan Shear Zone or Nalati Fault, forming the faulted CTS northern boundary. However, in Western Tianshan, some sections exhibit the original geometry of the suture, where ocean-derived HP metamorphic units overthrust northward the basement of Yili. After the collision, subsequent uplift was significant, inducing Carboniferous unconformity upon eroded plutonic arc-rocks.
A second accretion-collision stage involved southward Late Devonian-Carboniferous subduction of the North Tianshan (NTS) ocean beneath the Eo-Tianshan active margin, creating the Yili-NTS magmatic arc. Late Carboniferous-Early Permian oceanic closure and collision with the Junggar block built the North Tianshan Suture Zone (NTSZ), outlined by the Bayingou ophiolitic mélange. This second collision developed north-directed structures in Yili-NTS, and some south-directed ones in CTS and STS.
The southernmost units of Mongolian Fold Belt (Kelameili suture, Harlike arc) were accreted southward to the north-eastern margin of Junggar block around Mid-Carboniferous, after a northward subduction. Late Carboniferous and Permian unconformable strata post-date the closure of oceanic domains.
The Late Carboniferous-Early Permian NTSZ, now partly hidden due to Cenozoic thrusting, is likely the trace of the last oceanic remnant of the Central Asian Ocean, e.g. the youngest suture of the CAOB separating Gondwana-derived from peri-Siberian units.
During the Permian, all these units, already welded, experienced a major wrenching, dextral in Tianshan, sinistral in Mongolian Fold Belt, due to an eastward motion of the Yili block with respect to Tarim and Siberia indicated by paleomagnetic data. That was accompanied by pull-apart basin opening and post-tectonic magmatism (volcanics and plutons). The coeval emplacement of calc-alkaline and alkaline suites is noteworthy in Tianshan as well as around Junggar. Compressional deformations resumed in the Mesozoic, advocated by Triassic and Jurassic unconformities; but they were intracontinental, as the Cenozoic one due to India-Asia collision.