Palaeozoic tectonic evolution of the Tianshan belt, NW China

Abstract

International audienceThe Chinese Tianshan belt is a major part of the southern Central Asian Orogenic Belt, extending westward to Kyrgyzstan and Kazakhstan. Its Paleozoic tectonic evolution, crucial for understanding the amalgamation of Central Asia, comprises two stages of subduction-collision. The first collisional stage built the Eo-Tianshan Mountains, before a Visean unconformity, in which all structures are verging north. It implied a southward subduction of the Central Tianshan Ocean beneath the Tarim active margin, that induced the Ordovician-Early Devonian Central Tianshan arc, to the south of which the South Tianshan back-arc basin opened. During the Late Devonian, the closure of this ocean led to a collision between Central Tianshan arc and the Kazakhstan-Yili-North Tianshan Block, and subsequently closure of the South Tianhan back-arc basin, producing two suture zones, namely the Central Tianshan and South Tianshan suture zones where ophiolitic mélanges and HP metamorphic rocks were emplaced northward. The second stage included the Late Devonian-Carboniferous southward subduction of North Tianshan Ocean beneath the Eo-Tianshan active margin, underlined by the Yili-North Tianshan arc, leading to the collision between the Kazakhstan-Yili-NTS plate and an inferred Junggar Block at Late Carboniferous-Early Permian time. The North Tianshan Suture Zone underlines likely the last oceanic closure of Central Asia Orogenic Belt; all the oceanic domains were consumed before the Middle Permian. The amalgamated units were affected by a Permian major wrenching, dextral in the Tianshan. The correlation with the Kazakh and Kyrgyz Tianshan is clarified. The Kyrgyz South Tianshan is equivalent to the whole part of Chinese Tianshan (CTS and STS) located to the south of Narat Fault and Main Tianshan Shear Zone; the so-called Middle Tianshan thins out toward the east. The South Tianshan Suture of Kyrgyzstan correlates with the Central Tianshan Suture of Chinese Tianshan. The evolution of this southern domain remains similar from east (Gangou area) to west until the Talas-Ferghana Fault, which reflects the convergence history between the Kazakhstan and Tarim blocks

Reconstructing the Late Palaeozoic – Mesozoic topographic evolution of the Chinese Tian Shan: available data and remaining uncertainties

“…However, the large-scale structure of the Tian Shan lithosphere was set by complex accretions of island arcs and amalgamation of continental blocks during the whole Palaeozoic (e.g. Windley et al, 1990;Charvet et al, 2011). This initial structure that was completely established by Late Permian, and especially the major tectonic boundaries separating the various terranes played a first order role in the subsequent evolution of the range.…”

“…1 and 3a) (e.g. Han et al, 2009;Wang et al, 2009;Charvet et al, 2011;Xia et al, 2012). However, the modalities of that last accretion event are still discussed.…”

“…Hence, alternative models proposed that the Carboniferous magmas would have been generated during southward subduction of the North Tian Shan Ocean (in these models a branch of the wide Paleo-Asian Ocean) underneath the Yili block (e.g. Wang et al, 2006Wang et al, , 2009Han et al, 2009;Charvet et al, 2011). The North Tian Shan ophiolite sequence would correspond to an accretionary wedge developed in front of a Carboniferous forearc.…”

“…This subduction ended with the Late Carboniferous -Early Permian closure of the North Tian Shan Ocean and the collision between the Yili block and the North Tian Shan -Junggar blocks (e.g. Gao et al, 1998Charvet et al, 2011) (Figs. 2 and 3a).…”

Geological evolution of Central Asian Basins and the western Tien Shan Range

“…Windley et al 1990;Allen et al 1992;Xiao et al 2004;Hegner et al 2010) and southerly directed (e.g. Charvet et al 2007Charvet et al , 2011Lin et al 2009;Ma et al 2014) models have been proposed. The South Tien Shan is situated along the SW margin of the Central Asian Orogenic Belt (CAOB, ¼Altaids;Şen-gör et al 1993, a key region for our understanding of both the amalgamation of Eurasia (see above) and the Phanerozoic growth of the CAOB (Windley et al 1990(Windley et al , 2007Bazhenov et al 1999;Gao et al 2009;Kröner et al 2014).…”