引用本文：朱赖民,张国伟,郭波,李犇.2008.东秦岭金堆城大型斑岩钼矿床LA ICP MS锆石U Pb定年及成矿动力学背景[J].地质学报,82(2):204-220. ZHU Laimin,ZHANG Guowei,GUO Bo,LI Ben.2008.U-Pb (LA-ICP-MS) Zircon Dating for the Large Jinduicheng Porphyry Mo Deposit in the East Qinling, China, and Its Metallogenetic Geodynamical Setting[J].Acta Geologica Sinica,82(2):204-220.
U-Pb (LA-ICP-MS) Zircon Dating for the Large Jinduicheng Porphyry Mo Deposit in the East Qinling, China, and Its Metallogenetic Geodynamical Setting
State key Laboratory of Continental Dynamics, Department of Geology，Northwest University，Xi’an, 710069
Abstract:A precise U-Pb dating based on single particle zircon laser probe dating technology (LA-ICPMS), and comparative study of petrological and geochemical characteristics have been applied to the Jinduicheng ore-bearing porphyry and Laoniushan biotite-monzonitic granite north of the large Jinduicheng porphyritic molybdenum deposit in the Eastern Qinling. The weighted average ages by LA-ICPMS zircon U-Pb dating of the Laoniushan biotite-monzogranite and the Jinduicheng ore-bearing porphyry are 146.35±0.55 Ma and 140.95±0.45 Ma respectively, which are consistent with the lower limit of molybdenite Re-Os model ages by previous researchers. This indicates that the mineralization took place almost at the same with or slightly later than that of the diagenesis, with metallogenesis and diagenesis occurring in the same system in Jurassic-Cretaceous, which was coupled with the extensional geodynamical event during the later stage of tectonic system transformation occurring in East China at about 140 Ma. The formation of massif and mineralization of molybdenum occurred at the transitional period of compression-extension between the Jurassic and the Cretaceous, which corresponded to geodynamical setting of intracontinental orogeny and extension after the collision of the North China Block and the Yangtze Block. The two plutons have the similar variation on major elements and geochemical parameters, both of them belong to cal-alkaline series rock with silica super-saturation. Geochemically, the two plutons are enriched relatively in LILE, depleted in high field strength element (HFSE), with LREE especially enriched, obvious differentiation between LREE and HREE, and or no distinct negative Eu anomaly. The distribution of trace elements and rare elements are similar to that of intraplate granite and post-collision granite. Geochemical data indicate that the metallogenetic substance was deep earth in origin, and was mixing of the lower crust and upper mantle. Thus, the metallogenesis of the Jinduicheng ore deposit betided at the transformation period from continental convergency to extension as a result of thinning of lithosphere and uprising of ore-forming substance from asthenosphere, which jointly caused interaction between the crust and the mantle, sped melting of the thickened lower crustal material, and then resulted in Mo-rich grantitic magma. When the magma moved along structures developed within the upper crust, ore-bearing fluid derived from condensation fraction of the magma filled the structures and replaced country rock, thus forming the deposits