The Late Jurassic To Early Cretaceous Tectonic Evolution Of West Zhejiang Province, SE China, And Its Implication To Regional Magmatic Activity And Metallogeny

The LA-ICP-MS zircon U-Pb dating carried out on several granitic plutons inWest Zhejiang, SE China, yields two age summits at165Ma and135Ma, indicatingtwo intensive magmatic activities in Zhejiang province during the Yanshanian. Themagmatic rocks formed before150Ma are characterized by right-trend REE patternsand Nb, Ta, Ti anomalies, whereas those formed after140Ma are featured by “V”type REE patterns and relatively weak Nb, Ta anomalies, suggesting the source regionof magma changed from a high pressure eclogite facies to a median pressure granulitefacies. The chemical compositions of plutons with ages older than150Ma showsignature of volcanic and sys-collision granites, whereas those of plutons with agesyounger than140Ma indicate a with-in-plate origin. The tectonic transformationoccurred during150to140Ma led three effects:(1) the oxygen fugacities of theJurassic magmatic rocks range from MH to FMQ, whereas, those of the Cretaceousmagmatic rocks are bellow FMQ buffer;(2) the Jurassic magmatic intrusion occurredat the intersections of the NE-and NW oriented faults, whereas the Cretaceousmagmatic intrusion mainly occurred along NE-trending faults;(3) the NE-trendingfaults was firstly compressional during the Jurassic, while, became extensional duringthe Cretaceous. During the Jurassic, the magmas with high oxygen fugacity arebenefit to the formation of porphyry Cu-Mo-Au deposit, and the intersections ofdifferent oriented faults contribute to locate deposits. During the Cretaceous, theextensional faults are benefit to the formation of hydrothermal Pb-Zn deposit.Therefore, two tectonic environments and metallogenic environments can be detectedin West Zhejiang during the Yanshanian.