Nd-Sr-Pb isotopic compositions of cordierite granite on southern margin of the Qaidam block, NW China, and constraints on its petrogenesis, tectonic affinity of source region and tectonic implications

作者：Ba Jin^*; Chen Neng Song; Wang Qin Yan; Wang Xin Yu; Zhang Lu; Wang Shu Qing

来源：Earth Science - Journal of China University of Geosciences, 2012, 37(SUPPL. 1): 80-92.

DOI：10.3799/dqkx.2012.S1.008

• Genetic mechanism
• Heat sources
• High temperature
• Isotopic composition
• Isotopic geochemistry
• Magma intrusion
• Major and trace elements
• Mantle upwellings
• Melting conditions
• NW China
• Partial melting
• Pb isotopes
• Peraluminous
• Petrogenesis
• Qaidam block
• Shallow depths
• Source region
• Tectonic affinity
• Tectonic evolution
• Tectonic implications
• Tibetan Plateau
• Underplating
• Upper continental crust
• Yangtze block

The Jinshuikou cordierite granite (JCG) is the only strong peraluminous granite pluton discovered so far on northwestern margin of the Tibetan plateau. This cordierite granite contains mafic minerals of cordierite, garnet and biotite, characterizing mafic peraluminous granite. However, more comprehensive investigations of its genetic mechanism and implications for affinity and tectonic evolution of the basement of the Qaidam block is needed. This paper studies systematically on major and trace elements and Nd-Sr-Pb isotopic geochemistry of the JCG following the geology and petrographical observation. The JCG pluton shows A/CNK=1.12-2.05, K2O/Na2O=0.44-2.99, Rb/Sr=0.42-1.23, Nb/Ta=11.88-15.30, and is enriched in Rb, Th and U, but depleted in Sr and Ba, significant negative Eu anomalies (δEu=0.41-1.01, average at 0.62), ISr=0.7114-0.7503 and ΕNd(t)=-9.30 to-13.32.These data suggest that magma for the JCG was derived from partial melting of biotite-bearing metagreywacke in the upper continental crust, and that the melting conditions featuring high temperature but shallow depth level suggest existence of an extra heat source, implying that deep processes of subducted plate delamination, asthenospheric mantle upwelling, mafic magma intrusion and underplating might occurred at southern margin of the Qaidam block in the late caledonian. The JCG pluton has Nd model age (TDM2) of 1.9-2.2 Ga and initial Pb isotope ratios 206Pb/204Pb of 18.181-18.389, 207Pb/204Pb values of 15.582-15.632 and 208Pb/204Pb values of 37.914-38.243, suggesting that the basement of the Qaidam block is geochemically akin to that of the Yangtze block.

• 出版日期2012