Petrogenesis of Early Cretaceous intermediate-feslic Volcanic Rocks in the Juxian area from the Tan-Lu Fault Zone and Their Tectonic Impilcations
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    Abstract:

    Early Cretaceous volcanic rocks in the Juxian area from the Tan-Lu fault zone are consist of trachyandensite, trachydacite and rhyolite, belong to high-K calc-alkaline to shoshonite series. These rocks are characterized by enriched LREE and LILE with Rb, K and Ba, depleted HREE and HFSE with Nb, Ta and Ti. Their Sr, Nd isotope compositions (87Sr/86Sr(t)=0.7082~0.7095, εNd(t)=-16.4~-19.8) are similar to nearby mafic rock. However, Pb isotope compositions exhibit EM1-like features (06Pb/204Pb(t)=16.523~17.038, 207Pb/204Pb(t)=15.414~15.468, 208Pb/204Pb(t)=37.058~37.427). There are no obvious correlation between 87Sr/86Sr(t), εNd(t) and SiO2, which imply no significantly crustal contamination during magmas ascent combined with high Th/U, Ce/Pb ratios, low Nb/La, Nb/U ratios. Trachyandensites show high MgO, Cr, Ni contents, and Mg# value, as well as ancient Nd isotopic model ages, suggest magmas could originated from enriched lithospheric mantle. The correlation between major oxides, trace elements and SiO2 in trachydacites and trachyandesites reflected that they were formed by fractional crystallization of comagmatic region. Studies further indicate that these volcanic rocks in Juxian area were derived from the partial melting of the NCC lithospheric mantle which had previously experienced a reconstruction of subducted Yangtze crustal melts under the lithospheric extension setting. Therefore, the Tan Lu fault zone controlled the distribution of volcanic rocks, provided an advantage site for the generation and migration of magmas, and played an important role during the NCC destruction.

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Wu Qi, Niu Manlan, Zhu Guang, Xiang Biwei, Fu Pengyuan, Xia Wenjing.2013. Petrogenesis of Early Cretaceous intermediate-feslic Volcanic Rocks in the Juxian area from the Tan-Lu Fault Zone and Their Tectonic Impilcations[J]. Acta Geologica Sinica,87(7):979-993

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History
  • Received:May 08,2012
  • Revised:September 21,2012
  • Adopted:September 25,2012
  • Online: July 19,2013
  • Published: