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Geodynamic Background of Intracontinental Cenozoic Alkaline Volcanic Rocks in Laojiezi, Western Yangtze Craton: Constraints from Sr-Nd-Hf-O Isotopes
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This study was funded by the Open Foundation of the Beijing SHRIMP Center (DDC15-016), the Applied Basic Research Program Youth Project of Yunnan Province (2016DF031) and the National Basic Research Program of China (2015CB452605), which are gratefully acknowledged. We thank Longyan Jiang, who is a chief engineer of the Feilong mineral company in Yao’an, for their fieldwork assistance. Xinwei Li and Hong Zhao from the National Research Center for Geoanalysis in Beijing are thanked for their assistance with the major- and trace-element, Sr-Nd isotope and zircon Hf isotope analyses. Linlin Li and Shouye Liu from the Beijing SHRIMP Center (National Science and Technology Infrastructure) are thanked for their technical assistance, such as the sample loading, additional monitoring of instrument performance, and data processing.

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    Abstract:

    The Laojiezi alkaline volcanic rocks, which are located in the intraplate region of the Yangtze craton, coincide with the formation of the Jinshajiang-Ailaoshan-Red River alkaline rock belt. Although this belt has been widely studied by geologists because of its porphyry-related Pb-Ag-Au polymetallic deposit and geotectonic location, the material sources of this belt are still debate. Whole-rock analyses show that these rocks have high total alkali contents (3.73–11.08wt%), and their aluminum saturation index (ASI) values widely vary from 0.82 to 3.07, which comprise a metaluminous-peraluminous magma series. These rocks are characterized by high K (K2O/Na2O>1) and low Ti and Mg contents; enrichment in large-ion lithophile elements, such as Rb, Ba, K and light rare earth elements; and depletion in high field strength elements, such as Ta, Nb, P, and Ti. These rocks exhibit moderate Eu (Eu/Eu*=0.86–1.04) and Ce (Ce/Ce*=0.63–0.96) anomalies. Their (87Sr/86Sr)i, εNd(t), zircon εHf(t) and δ18O values range from 0.70839 to 0.71013, from ?10.16 to ?12.45, from ?19.6 to ?5.8, and from 5.69‰ to 8.54‰, respectively, and their Nd and Hf two-stage model ages (TDM2) are 1.67–1.86 Ga and 1.27–2.02 Ga, respectively. These data reflect the primary partial melting of Paleoproterozoic to Mesoproterozoic lower crust with minor residual continental lithospheric mantle and supracrustal metasediments. The lithosphere was likely thickened along the southeastern margin of the Tibetan Plateau following the Indian-Asian continent-continent collision (65–41 Ma). During the post-collision phase (36–16 Ma), the transition from a compressional to extensional setting triggered the convective removal of the over-thickened CLM beneath the Yangtze craton, which led to the upwelling of asthenospheric materials. This process created alkali-rich and high-K magma through the partial melting of the thickened lower crust. Magma that carried Cu-Au-Pb-Ag minerals was emplaced by strike-slip motion along the E- to W- or ENE- to WSW-trending tectonically weak zone, finally forming an alkaline porphyry Cu-Au-Pb-Ag polymetallic deposit.

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YAN Qinggao, JIANG Xiaojun, LI Chao, ZHOU Limin, WANG Zhongqiang, Sultan Baig SHER, QU Wenjun, DU Andao.2018. Geodynamic Background of Intracontinental Cenozoic Alkaline Volcanic Rocks in Laojiezi, Western Yangtze Craton: Constraints from Sr-Nd-Hf-O Isotopes[J]. Acta Geologica Sinica(),92(6):2098-20119

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History
  • Received:April 04,2018
  • Revised:July 27,2018
  • Online: December 19,2018
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