High-alumina basalts from the Bogda Mountains suggest an arc setting for Chinese Northern Tianshan during the Late Carboniferous

• Published in: Lithos
• Main Authors: Xie, Wei, Xu, Yi-Gang, Chen, Yi-Bing, Luo, Zhen-Yu, Hong, Lu-Bing, Ma, Liang, Liu, Hai-Quan
• Format: Report
• Language: English
• Published: ELSEVIER SCIENCE BV 2016
• Subjects: Geochemistry & Geophysics; Mineralogy; High-alumina basalt; Bogda Mountains; Arc setting; Late Carboniferous; Chinese Northern Tianshan; LARGE IGNEOUS PROVINCE; MEDICINE LAKE VOLCANO; PLUME-LITHOSPHERE INTERACTION; SUBDUCTION ZONE MAGMATISM; EMEISHAN FLOOD BASALTS; ASIAN OROGENIC BELT; U-PB GEOCHRONOLOGY; A-TYPE MAGMATISM; TRACE-ELEMENT; ISLAND-ARC; Kamchatka
• Online Access: http://ir.gig.ac.cn/handle/344008/54791; https://doi.org/10.1016/j.lithos.2016.04.005

Considerable debate persists as to the tectonic setting of the Tianshan Orogen during the Late Paleozoic, with active subduction system and intraplate large igneous provinces as two dominant schools. With aims of providing constraints on this issue, geochronological and geochemical analyses have been carried out on the late Carboniferous high-Al basaltic lava (HAB) from the Bogda Mountains. These lavas, in conformable contact with the felsic rocks, belong to the Upper Carboniferous Liushugou Group. Zircon SHRIMP U-Pb dating of two felsic ignimbrites further suggest that they were mainly erupted during 315-319 Ma. The Bogda basaltic lava is classified as HAB given their high Al contents >16% and their chemical resemblance to those from modern arcs such as Aleutian and Kamchatka. They are characterized by strong enrichment in large ion lithophile elements (LILE), strong negative Nb-Ta and Ti anomalies, and distinct positive Pb anomalies. Hence, they are significantly different from the mantle plume-related basalts, as exemplified by those from Siberian, Emeishan, and Tarim large igneous provinces. Instead, their MORB-like Nd-Hf-Pb isotopes and arc-like trace elements indicate that the Bogda HABs may have been generated from a mantle wedge metasomatized by sediment-derived melts. The sector and oscillatory zoning in clinopyroxene phenocrysts in the Bogda HABs is attributable to rapid dynamic crystallization during magma ascent. High Al content is due to delayed plagioclase nucleation likely by the high crystallization pressure rather than water content. Collectively, our data lend support to an island arc environment during the Late Paleozoic, probably related to southward subduction of the Paleo-Tianshan Ocean. (C) 2016 Elsevier B.V. All rights reserved.