| LA-ICP-MS zircon U-Pb dating and phenocryst EPMA of dikes, Guocheng, Jiaodong Peninsula: Implications for North China Craton lithosphere evolution |
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| 摘 要： | Widespread dike swarm, including diorite-, monzonite-porphyry and lamprophyre, intruded in the al- tered breccia gold deposits along basin marginal faults, Guocheng, Jiaodong Peninsula. Petrography exhibits biotite enclaves in amphibole phenocrysts and the presence of acicular apatites in these dikes. Electron probe microanalyses (EPMA) show that the amphibole and clinopyroxene phenocryst’s mantle in diorite porphyry and lamprophyre respectively has sharply higher MgO (Mg#) and Cr2O3 contents in contrast to their cores. The plagioclase phenocryst in monzonite porphyry has reverse zoning. These results indicate that the magma mixing between mantle-derived mafic and crust-derived felsic magmas occurred in the original process of the dikes. Zircon cathodoluminescence (CL) images show well-developed magmatic oscillatory zones and the acquired LA-ICP-MS zircon U-Pb weighted mean 206Pb/238U ages are 114±2 Ma (MSDW=1.5) for monzonite porphyry (GS1) and 116±1 Ma (MSDW=0.8) for diorite porphyry (GS2), respectively. Earlier magmatic events in the northwest Jiaodong Peninsula represented by some inherited or captured zircons also occur in these dikes. Magmatic zircons from GS1 and GS2 display consistent chondrite-normalized REE patterns and Nb/Ta values, implying that they may share a similar or same source. HREE enrichment and obvious negative Eu anomalies of these zircons preclude garnet presented in their source. Our results, combined with preciously pub- lished data, indicate that dike intrusion and gold mineralization among quartz vein, altered tectonite and altered breccia gold deposits are broadly contemporaneous throughout the Jiaodong Peninsula. These also imply that the intensive crust-mantle interaction and asthenospheric underplating had oc- curred in the Early Cretaceous in the Peninsula, together with foundering of lower crust in the early Mesozoic, representing the different stages of lithosphere thinning in the North China Craton (NNC).
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LA-ICP-MS zircon U-Pb dating and phenocryst EPMA of dikes,Guocheng, Jiaodong Peninsula: Implications for North China Craton lithosphere evolution |
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| Authors: | Jun Tan JunHao Wei LingLi Guo KeQing Zhang ChunLiang Yao JianPei Lu HongMei Li |
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| Institution: | (1) Faculty of Earth Resources, China University of Geosciences, Wuhan, 430074, China |
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| Abstract: | Widespread dike swarm, including diorite-, monzonite-porphyry and lamprophyre, intruded in the altered breccia gold deposits
along basin marginal faults, Guocheng, Jiaodong Peninsula. Petrography exhibits biotite enclaves in amphibole phenocrysts
and the presence of acicular apatites in these dikes. Electron probe microanalyses (EPMA) show that the amphibole and clinopyroxene
phenocryst’s mantle in diorite porphyry and lamprophyre respectively has sharply higher MgO (Mg#) and Cr2O3 contents in contrast to their cores. The plagioclase phenocryst in monzonite porphyry has reverse zoning. These results indicate
that the magma mixing between mantle-derived mafic and crust-derived felsic magmas occurred in the original process of the
dikes. Zircon cathodoluminescence (CL) images show well-developed magmatic oscillatory zones and the acquired LA-ICP-MS zircon
U-Pb weighted mean 206Pb/238U ages are 114±2 Ma (MSDW=1.5) for monzonite porphyry (GS1) and 116±1 Ma (MSDW=0.8) for diorite porphyry (GS2), respectively.
Earlier magmatic events in the northwest Jiaodong Peninsula represented by some inherited or captured zircons also occur in
these dikes. Magmatic zircons from GS1 and GS2 display consistent chondrite-normalized REE patterns and Nb/Ta values, implying
that they may share a similar or same source. HREE enrichment and obvious negative Eu anomalies of these zircons preclude
garnet presented in their source. Our results, combined with preciously published data, indicate that dike intrusion and gold
mineralization among quartz vein, altered tectonite and altered breccia gold deposits are broadly contemporaneous throughout
the Jiaodong Peninsula. These also imply that the intensive crust-mantle interaction and asthenospheric underplating had occurred
in the Early Cretaceous in the Peninsula, together with foundering of lower crust in the early Mesozoic, representing the
different stages of lithosphere thinning in the North China Craton (NNC).
Supported by the Doctoral Education Program Fund of Ministry of Education, China (Grant No. 20040491502), Program for Changjiang
Scholars and Innovative Research Team in University, Program of Superseding Resources Prospecting in Crisis Mines in China
(Grant No. 2006020035), and the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences |
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| Keywords: | dike EPMA zircon LA-ICP-MS magma mixing crust-mantle interaction lithosphere thinning |
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