Abstract:
This paper is the result of geological survey engineering.
Objective Jiaodong area is the largest gold ore concentration area in China and the most important copper−molybdenum polymetallic ore deposit area in Shandong Province. Strengthening the study of petrography, petrogeochemistry and chronology of Mesozoic granites is conducive to further promoting the prospecting of gold and polymetallic deposits in this area.
Methods Taking the medium−fine grained monzogranite and granite porphyry as the main research object, this study primarily carried onlaser ablation inductively coupled plasma mass spectrometry (LA−ICP−MS) U−Pb chronology on the zircon, whole−rock geochemistry,whole−rock Sr−Nd−Pb and zircon Hf isotopic study, aiming to confirm the timing and discuss the petrogenesis and tectonic settings of the Sanheshan pluton in Southwest Jiaodong.
Results The results of LA−ICP−MS zircon U−Pb show that the medium−fine grained monzogranite was formed in (115.42 ± 0.27) Ma and the granite porphyry was formed in (115.21±0.25) Ma, both of which are belonging to the Late Early Cretaceous of Mesozoic. Geocahemical research shows that the medium−fine grained monzogranite and granite porphyry are both belong to themetaluminous high−K calc−alkaline series I−type granites; LREE are more obvious than HREE,with weak Ce negative anomaly and obvious Eu moderate negative anomaly; trace elements enriched in Rb, K, Zr and Hf, depleted in Sr, Ba, Nb, P and Ti. The whole rock Sr−Nd−Pb and zircon Hf isotope analysis results show that the Sanheshan pluton was originated from the remelting lower crust, and was contaminated by mantle materials.
Conclusions The Sanheshanpluton was formed in the continental extension background caused by the subduction of the Pacific plate relative to the Eurasian plate in the Early Cretaceous, which was the product of crust−mantle interaction during the lithospheric thinning in eastern China.
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