Early Permian subduction-related transtension in the Turpan Basin, East Tianshan (NW China): implications for accretionary tectonics of the southern Altaids

Abstract

The interaction of the Palaeo-Pacific and Palaeo-Asian Oceans is an enigmatic issue as their temporal and spatial features are controversial. To address this issue, we present a systematic study of large volumes of early Permian volcanic rocks and intrusions developed in the East Tianshan. The represented samples of basaltic andesites and rhyolites yield zircon crystallization ages of 285.1 ± 5.9 Ma and 275.3 ± 1.8 Ma, respectively. The basalts have normal mid-ocean ridge basalt (N-MORB) and arc-related geochemical signatures with high TiO2 contents, negative Rb, Th, U, Nb and Ta anomalies and positive Eu anomalies. Basaltic andesites and andesites have arc-related geochemical characteristics with moderate TiO2 contents and relatively negative Nb, Ta and Ti anomalies, together with slightly negative to positive Eu anomalies. The rhyolites show an affinity with A2-type granite with high SiO2, K2O + Na2O, Fe/Mg, Ga, Zr, Nb, Y, HFSE, REE and Y/Nb levels (>1.2). These geochemical data suggest that the rocks formed in a supra-subduction zone. The presence of high ϵNd(t) values of +4.6 to +8.2 and low (87Sr/86Sr) i (0.70342–0.70591) values indicates that the volcanic rocks originated from a depleted mantle. We propose that oblique subduction with slabs breaking off gave rise to transtension and to the emplacement of large volumes of mantle-derived melts in the early Permian in the East Tianshan, serving as an important record of the subduction zone of the Palaeo-Pacific Ocean.

Mineralization of the Tuwu Porphyry Cu Deposit in Eastern Tianshan, NW China: Insights From In Situ Trace Elements of Chlorite and Pyrite

“…The Devonian to Carboniferous rocks mainly consists of tholeiite to calc-alkaline basalts, andesite, dacite rhyolite, volcaniclastic rocks, and sedimentary (Ma et al, 1997;Li et al, 2004;Xiao et al, 2004;Hou et al, 2005;Tang et al, 2006;Mao et al, 2014b). The arc-related granitic intrusions are formed from Ordovician to Permian (Song et al, 2002;Li et al, 2004;Chen et al, 2005;Hou et al, 2005;Sun et al, 2005;Wu et al, 2006;Chao et al, 2006;Guo et al, 2006;Mao et al, 2010Mao et al, , 2019Long et al, 2016;Zhang et al, 2017).…”

“…The Permian granitoids are extensive, and a zone of earlier Permian mafic-ultramafic complexes is located along the Kangguer forearc terrane and stretches several hundred kilometers (Ma et al, 1997;Mao et al, 2002;Han C. M. et al, 2004;Xiao et al, 2004;Zhou et al, 2004;Qin et al, 2011). Multiple types of mineral deposits developed in the Dananhu-Haerlik arc, including porphyry Cu (Au/Mo) deposits (Rui et al, 2002;Chen et al, 2005;Wu et al, 2006;Zhang et al, 2006;Shen et al, 2014a;Wang et al, 2015;Mao et al, 2018), hydrothermal vein Cu (Au) deposits (Fang et al, 2002;Mao et al, 2014a;Yu et al, 2019), Cu-Ni sulfide deposits (Mao et al, 2002;Han B. F. et al, 2004;Xiao et al, 2004;Zhou et al, 2004;Mao et al, 2006;Han et al, 2010;Qin et al, 2011), VMS Cu-Zn-(Au/Ag) polymetallic deposits (Mao et al, 2010(Mao et al, , 2019Deng et al, 2016;Li et al, 2002), and Au deposits (Wang et al, 2006).…”

“…Along with the multiple processes of continental accretion, crust-mantle interactions, and transformation in the eastern Tianshan orogen, numerous polygenetic mineral deposits have been formed, and most have been superimposed by late complex ore-forming processes. These deposits include the Honghai (Huangtupo) Cu-Zn deposit (Deng et al, 2016;Mao et al, 2019), Xiaorequanzi Cu-Zn deposit (Long et al, 2019;Mao et al, 2020), Yamaisu Cu-Fe deposit, Hongyuntan Cu-Fe deposit (Sun et al, 2017;Han et al, 2018;Zhang et al, 2018), and Tuwu-Yandong Cu deposit (Wang Y. F. et al, 2016;Xiao et al, 2017). Research on superimposed metallogenic systems is very important for recognizing the regional metallogenic history and guiding mineral exploration activities in the eastern Tianshan.…”

Subduction zone processes and crustal growth mechanisms at Pacific Rim convergent margins: modern and ancient analogues

“…Such magmatic products may still show strong subduction influence in their geochemical character, although they may look different from magmatic arc sequences in terms of their lithostratigraphy and isotopic compositions. Mao et al (2019) propose that Early Permian (285-275 Ma) extrusive and intrusive rocks in the Turpan Basin in the East Tianshan Mountains of NW China (see brown box with number 11 in Fig. 1) formed as a result of transtensional deformation and attendant magmatism in a fore-arc sliver setting during the closure of the Palaeo-Asian Ocean.…”

“…Mao et al (2019) propose that Early Permian (285–275 Ma) extrusive and intrusive rocks in the Turpan Basin in the East Tianshan Mountains of NW China (see brown box with number 11 in Fig. 1) formed as a result of transtensional deformation and attendant magmatism in a fore-arc sliver setting during the closure of the Palaeo-Asian Ocean.…”