Zircon U-Pb age and geochemistry of Mesozoic intermediate and acidic volcanic rocks from the Shandong segment (Jiaodong area)of the Tan-Lu fault
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    Abstract:

    In this paper,LA-ICP-MS zircon U-Pb dating was carried out for four samples of volcanic rocks from Qingshan Group in Jiaodong area and, as a result, their concordant ages were obtained, which are 119.4±0.9 Ma, 118.2±1.0 Ma,120.2±0.9 Ma and 120.0±0.8 Ma, respectively. The results show that all the volcanic rocks in Jiaodong area were formed from about 120 Ma to 118 Ma in the Early Cretaceous period. The ages of Qingshan Group volcanic rocks from Shandong Province controlled by Tan-Lu fault are similar to those from the Su-Wan segment of the Tan-Lu fault zone,but younger than those around the Tan-Lu fault zone,which indicates that the duration of volcanic eruption along Tan-Lu fault is probably longer than the duration in other areas under the background of lithospheric thinning in eastern China. Geochemically, all the intermediate and acidic volcanic rocks have high K2O, ALK, LREE values and low MgO, TiO2, Ni, Cr, HREE values. According to the geochemical features, the volcanic rocks can be subdivided into trachyte-trachydacite and rhyolite. The trachyte-trachydacite is characterized by LILE enrichment(Rb,Ba,K)and HFSE depletion(Nb,Ta,Ti,P), but the rhyolite exhibits stronger depletion of Ba,Sr and HFSE (Ti,P). Compared with the rhyolite,the trachyte-trachydacite possesses higher Sr and Ba values as well as La/Nb and Ba/Nb ratios,but lower Rb/Ba ratios and δEu values. All these data indicate that they might have been derived from different magma sources. It is inferred that the trachyte-trachydacite rocks were derived from the mixture of the partial melting of the lower crust(Yangtze Craton or North China Craton)and enriched lithospheric mantle. In addition, the rhyolites were related to the partial melting of the lower crust in the regional extension environment and high geothermal anomaly background with crystallization differentiation during the magma evolution.

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曹光跃,薛怀民,王金光,2014,郯庐断裂山东段(胶东)中生代中酸性火山岩的锆石U-Pb年代学及地球化学特征[J].岩石矿物学杂志,33(6):1019~1038. CAO Guang-yue, XUE Huai-min, WANG Jin-guang,2014,Zircon U-Pb age and geochemistry of Mesozoic intermediate and acidic volcanic rocks from the Shandong segment (Jiaodong area)of the Tan-Lu fault[J]. Acta Petrologica et Mineralogica,33(6):1019~1038.

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History
  • Received:February 27,2014
  • Revised:October 11,2014
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  • Online: December 02,2014
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