Zircon U-Pb ages, petrogenesis of the Luchuba pluton in West Qinling, and its geological significance
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    Abstract:

    The Luchuba pluton is located in the west segment of the Qinling Orogen. It consists of tourmaline-bearing biotite monzogranites, porphyritic-bearing and fine-grained biotite monzogranites, porhyritic biotite monzogranites, coarse-grained biotite monzogranites and medium-grained biotite quartz diorites from its center to margin and contains mafic magma enclaves. LA-ICPMS zircon U-Pb dating suggest that the Luchuba pluton formed in early Mesozoic, and it can been divided into two stages, Middle Triassic (235 Ma) and Late Triassic (218~209 Ma). The early stage is medium-grained biotite quartz diorites, characterized by low in silica and high in alkali, showing metaluminous and high K cal-alkaline series with I type features. The late biotite monzogranites are rich in silica and alkali, being metaluminous to weak peraluminous and shoshonitic to high K cal-alkaline series with I type features. From early to late stage, the REE content is decrearsed, and the two-stage granitoids are characterized by enrichment in LREE, but the late biotite monzogranites depleted in HREE. The early biotite quartz diorites have slightly negative Eu abnormity, and the late biotite monzogranites show obvious negative Eu abnormity. All the rocks are enriched in large ion lithophile elements (K, Rb, Ba), and depleted in high-field strength elements (P, Nb, Ta, Ti). The εNd(t) of biotite monzogranite and biotite quartz diorites are -8.0 and -7.0, respectively, corresponding Nd model ages from 1.43 to 1.40 Ga. The εHf(t) values of the early stage biotite quartz diorites are -4.47 to 0.53, mainly between -3 and -1, and tDMC of 1.6 to 1.3 Ga; while the εHf(t) values of late stage biotite monzogranite are -11.64 to 1.16, mainly from -7 to -2, and tDMC of 1.7 to 1.4 Ga. The host granitoids and mafic magma enclaves show linear relationship in most major elements and similar trace elements. Geochemistry and Nd-Hf isotopic compositions suggest that the host granitoids are mainly derived from Mesoproterozoic continental crust, with involvement of juvenile component. This pluton is similar to the Zhongchuan pluton, adjacent to its north, in chronology, petro-geochemistry and isotopic compositions, It may imply that there are also potential for gold mineralization surround the Luchuba pluton as that of the Zhongchuan pluton from the view of magmatism.

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Yangyang, Wangxiaoxia, Kechanghui, Wangshun'an, Lijinbao, Niezhengrong, Lvxingqiu.2015. Zircon U-Pb ages, petrogenesis of the Luchuba pluton in West Qinling, and its geological significance[J]. Acta Geologica Sinica,89(10):1735-1761

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History
  • Received:July 14,2015
  • Revised:September 13,2015
  • Adopted:September 14,2015
  • Online: October 26,2015
  • Published: