1. Petrogenesis of Late Carboniferous-Early Permian mafic-ultramafic-felsic complexes in the eastern Central Tianshan, NW China: The result of subduction-related transtension?
- Author
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Mao, Qigui, Ao, Songjian, Windley, Brian F., Zhang, Zhiyong, Song, Dongfang, Zhang, Ji'en, Wan, Bo, Tan, Wei, Han, Chunming, and Xiao, Wenjiao
- Abstract
[Display omitted] • The mafic-ultramafic-acidic complexes formed in Late Carboniferous (300 Ma). • Fractionation of the mantle-derived tholeiitic magma formed the A 2 -type granite. • The slab break-off formed the complexes in oceanic slab subduction setting. Knowledge of the Late Paleozoic accretionary processes responsible for the Altaids (or southern Central Asian Orogenic Belt) is critical for a better understanding of continental growth in Central Asia. Here, we systematic study the Late Carboniferous mafic-ultramafic-felsic complexes in eastern Central Tianshan to understand the tectonic evolution of the southern Altaids. Two gabbros yield zircon crystallization ages of 301.5 ± 2.3 Ma and 300.7 ± 2.6 Ma and one granite is dated as 301.6 ± 1.5 Ma. The gabbros are tholeiitic and characterized by typical subduction-related geochemical signatures with low TiO 2 contents, enrichments in Rb, Ba, U, K, Pb and Sr, negative Nb and Ta anomalies, and negative to positive Eu and Ti anomalies. The granites are the A 2 -type granites with high contents of SiO 2 , K 2 O + Na 2 O, Ga, Zr, Nb, Y, HFSE, REE, and high ratios of Fe/Mg and Y/Nb (>1.2). The gabbros and granites have high ε Nd (t) values of +1.64 to +5.03, zircon ε Hf (t) values of −2.8 to +9.1, and low (
87 Sr/86 Sr) i (0.704007–0.705437) values. These geochemical characters demonstrate that the rocks in the complexes are fractionation genesis and that the A-type granitic rocks are the highest fractionation facies of tholeiitic mafic rocks. These results suggest that they were originated from the asthenospheric garnet-free mantle in a supra-subduction zone. Combined with regional data, we suggest that the oblique subduction with slab break-off of the Southern Tianshan oceanic plate plausibly induced asthenospheric upwelling to form the tholeiitic magma, and which intrude along the strike-faults the Central Tianshan-Yamansu arc. Accordingly, these results reveal the Paleo-Asian Ocean continued to subduct at the southern Altaids in the Late Carboniferous. [ABSTRACT FROM AUTHOR]- Published
- 2021
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