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Science in China Series D: Earth Sciences

, Volume 50, Supplement 2, pp 234–245 | Cite as

Geochemistry of the E-MORB type ophiolite and related volcanic rocks from the Wushan area, West Qinling

  • Dong YunPeng Email author
  • Zhang GuoWei 
  • Yang Zhao 
  • Zhao Xia 
  • Ma HaiYong 
  • Yao AnPing 
Article

Abstract

The mafic-ultramafic assemblages, which thrustthrust into the Wushan-Tangzang boundary fault as some blocks and outcropped in the Yuanyangzhen, Lijiahe, Lubangou and Gaojiahe area, consist mainly of meta-peridotites, gabbros and basalts. The meta-peridotites are characterized by high SiO2 and MgO contents, low ΣREE, as well as their chondrite-normalized rare earth element patterns show some similarities to that of middle oceanic meta-peridotite. The basalts from the Yuanyangzhen, Lijiahe and Lubangou area are characterized by relatively high TiO2 content, low Al2O3 content and Na2O>>K2O. Above all, it is the slight enrichment or flat REE distribution patterns and the unfractionated in HFS elements in the primitive-normalized trace elements distribution patterns that indicate these basalts are similar to that of the typical E-MORB. In comparison, the basalts from the Gaojiahe section are featured by depletion in Nb and Ta contents and enrichment in Th content which show that these were derived from an island-arc setting. From studies of the regional geology, petrology, geochemistry, geo-chronology and all above evidence, it can be suggested that the mafic-ultramafic rocks from the Wushan area are mainly dismembered E-MORB type ophiolite, which represent the fragments of the lithosphere of the Early-Paleozoic Qinling ocean. It is preferred that these rocks were formed in an initial mid-ocean ridge setting during the beginning stage of the oceanic basin spreading. This ophiolite together with the Gaojiahe island-arc basalts shows that there exists an ophiolitic mélange along the Wushan-Tangzang boundary fault, and marks the suture zone after the closure of the Qinling ocean in early Paleozoic.

Keywords

E-MORB geochemistry Shangdan suture zone west Qinling tectonics 

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Copyright information

© Science in China Press 2007

Authors and Affiliations

  • Dong YunPeng 
    • 1
    Email author
  • Zhang GuoWei 
    • 1
  • Yang Zhao 
    • 1
  • Zhao Xia 
    • 1
  • Ma HaiYong 
    • 1
  • Yao AnPing 
    • 1
  1. 1.State Key Laboratory of Continental Dynamics, Department of GeologyNorthwest UniversityXi’anChina

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