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The LA-ICP-MS zircons U-Pb ages and geochemistry of the Baihua basic igneous complexes in Tianshui area of West Qinling
Authors:Pei  XianZhi  Ding  SaPing  Zhang  GuoWei  Liu  HuiBin  Li  ZuoChen  Li  GaoYang  Liu  ZhanQing  Meng  Yong
Institution:1.Key Laboratory of Western China’s Mineral Resources and Geological Engineering, Ministry of Education, Xi’an, 710054, China
;3.Faculty of Earth Science and Land Resources, Chang’an University, Xi’an, 710054, China
;2.State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi’an, 710069, China
;
Abstract:

Baihua meta-igneous complex consists mainly of pyroxenite-gabbro(diorite)-diorite-quartz diorite. They form a complete comagmatic evolutionary series. The geochemical characteristics of basic-intermediate basic igneous rocks indicate that they belong to a tholeiite suite. The REE distribution pattern is nearly flat type and LREE is slightly enriched type, and their primitive mantle-normalized and MORB-normalized trace element spider diagrams are generally similar; the LIL elements (LILE) Cs, Ba, Sr, Th and U are enriched, but Rb, K and the HFSEs Nb, P, Zr, Sm, Ti and Y are relatively depleted. All these show comagmatic evolution and origin characteristics. The tectonics environment discrimination of trace element reveals that these igneous complexes formed in an island-arc setting. The LA-ICP-MS single-zircons U-Pb age of Baihua basic igneous complex is 434.6±1.5 Ma (MSWD = 1.3), which proves that the formation time of the island-arc type magmatite in the northern zone of West Qinling is Late Ordovician or Early Silurian, also reveals that the timing of subduction of paleo-ocean basin represented by the Guanzizhen ophiolite and resulting island-arc-type magmatic activities is probably Middle-Late Ordovician to Early Silurian.

Keywords:
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