Early Indosinian Weiya Gabbro in Eastern Tianshan, China: Elemental and Sr-Nd-O Isotopic Geochemistry, and Its Tectonic Implications

• Published in: Acta geologica Sinica (Beijing) Vol. 81; no. 3; pp. 424 - 432
• Main Authors: Zunzhong, ZHANG, Lianxing, GU, Changzhi, WU, Jianping, ZHAI, Weiqiang, LI, Junhua, TANG
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01.06.2007
• Subjects: eastern Tianshan; intra-continental subduction; mantle metasomatism; Weiya gabbro; Xinjiang
• ISSN: 1000-9515; 1755-6724
• DOI: 10.1111/j.1755-6724.2007.tb00965.x

: The Weiya gabbro in eastern Tianshan was formed during the early Indosinian. This rock, with low ratios of Ce/Pb (5.74‐10.16), is notably characterized by enrichment in large ion lithophile elements (LILE), such as Rb, K, Ba and Pb, and in high field strength elements (HSFE), such as U and Th, but depletion in Nb and Ta. All samples of the Weiya gabbro display similar chondrite‐normalized patterns with moderate enrichment in LREE (72.58–135.61ppm), moderate depletion in HREE (15.26‐25.31 ppm) and mild fractionation between LREE and HREE (L/H=4.09‐5.98). The average initial Sr value of the rock is 0.7069, and δ18 O values of the rock range from 5.67%‐8.04%. In terms of Nd isotope ratios, the Weiya gabbro is characterized by positive Nd(t) values (0.52‐0.76). All these characteristics indicate that the source region of the Weiya gabbro was metasomatized by fluids released from subducted young continental crust, with limited crustal contamination during magma ascent and emplacement. Continental (A‐type) subduction was induced by northward subduction of the Paleo‐Tethyan oceanic plate during the latest Permian to Triassic. From this point of view, it is supposed that tectonic conversion from the Paleo‐Asian to the Paleo‐Tethys regime occurred during the latest Permian or earliest Triassic.