Late Devonian–early Permian accretionary orogenesis along the North Tianshan in the southern Central Asian Orogenic Belt

Abstract

The Palaeozoic orogenic process in the North Tianshan of the southern Central Asian Orogenic Belt is controversial. Systematic field study indicates that the ophiolitic fragments of the North Tianshan are mainly thrust slices and blocks of a late Palaeozoic accretionary complex, which was intruded by granitoids. U-Pb zircon dating of plagiogranites from the North Tianshan ophiolite yielded a mean age of 343.1 ± 2.7 Ma. These are typical oceanic plagiogranites but with a suprasubduction zone (SSZ) signature. Ophiolitic basalts display N-MORB, E-MORB, and OIB compositions. One gabbro with an age of 301.9 ± 2.2 Ma shows E-MORB geochemistry mixed with N-MORB and OIB. Some andesites show clear island arc characters indicated by enrichment of LILEs relative to HFSEs. Mean ages of 344.9 ± 4.2 and 298.7 ± 2.4 Ma were obtained for a granite porphyry and a mylonitic granite, respectively. The two granitoids display an island arc geochemical signature evidenced by enrichment of LILEs and depletion of HFSEs. Combined with an eastward migration of Late Devonian to Carboniferous arc magmatism and related Cu-Au-Mo deposits, we propose that trench retreat and slab rollback took place during subduction of the Junggar Ocean spreading ridge beneath the North Tianshan arc, and that the accretion may have lasted into early Permian time, an important late stage of the long-lived accretionary orogenesis in the southern Central Asian Orogenic Belt.

Accreted seamounts in North Tianshan, NW China: Implications for the evolution of the Central Asian Orogenic Belt

“…The complex marks the final collision between the CTB in the south and the Junggar terrane in the north (Gao et al, 1997;Windley et al, 2007;Xiao et al, 2008;Zhu et al, 2009;An et al, 2013;Li et al, 2015). However, the timing of final subduction between CTB and Junggar terrane remains unclear.…”

“…However, Han et al (2010) proposed that the collision occurred before the Late Carboniferous according to the presence of the Sikeshu 'stitching pluton' within the North Tianshan accretionary complex. Recently, Li et al (2015) considered that the subduction of the Junggar Ocean (a branch of the paleo-Asian Ocean) probably continued into the early Permian. Therefore, the accreted igneous rocks that it contains, such as the early Carboniferous Bayingou ophiolitic rocks of this study can shed new light on the evolution history of the North Tianshan accretionary complex.…”

Cu–Mo Differential Mineralization Mechanism of the Dabate Polymetallic Deposit in Western Tianshan, NW China: Evidence from Geology, Fluid Inclusions, and Oxygen Isotope Systematics

“…). This part of the NTAC represents a late Paleozoic continental arc that is composed mainly of late Carboniferous volcanosedimentary rocks and ophiolitic slices that formed during subduction of the Paleo–Junggar oceanic crust (Li et al ., ). The Precambrian metamorphic basement rocks of the NTAC consist of Precambrian (821–798 Ma) granitic gneiss, biotite–plagioclase gneiss, monzonite granulite, fine‐grained amphibolite, migmatite, quartzite, marble, and schists of the Wenquan Formation (exposed in Wenquan, south of Sayram Lake and Nalati; Chen et al ., ).…”

Detrital zircon U–Pb–Hf isotopes study of the Lower Carboniferous Anjihai Formation from the northern margin of the Yili Block, NW China

“…The ophiolite consists of serpentinized peridotite, gabbro, diabase, basalt, plagiogranite, and siliceous‐pelagic sedimentary rocks, which are in fault contact with the surrounding turbidites (Wang et al, ). The ophiolites were formed in the Early Carboniferous, as dated by SHRIMP zircon U–Pb methods on plagiogranite and gabbro in the Bayingou ophiolite (325 and 344 Ma; Xu, Li, et al, ; Xu, Xia, et al, ) and plagiogranite from the Kuitunhe ophiolite of (SIMS zircon U–Pb age of 343 Ma; Li et al, ).…”

“…The petrology, geochemistry, and geochronology of ophiolites and related volcanic‐arc and post‐collisional rocks have been studied to reconstruct the evolutionary history of the NTO (An, Zhu, Wei, & Lai, ; Han et al, ; Li et al, ; Long et al, ; Wang, Shu, Cluzel, Faure, & Charvet, ; Wang et al, ; Xu, Li, et al, ; Xu, Xia, et al, ). Although the exact closure time is still debated, it is widely accepted that the subduction of NTO continued at least to the Late Carboniferous (Han et al, ; Li et al, ; Wang et al, ; Wang et al, ; Xiao et al, ). However, the subduction process, especially the time‐span of the NTO is still a puzzle due to limited geochronological data.…”