南秦岭封子山岩体的年代学、地球化学、Hf同位素特征及其地质意义

对南秦岭封子山岩体进行了锆石U-Pb年代学、岩石地球化学以及Hf同位素的研究，以确定其形成时代、岩体成因及形成时的构造环境.LA-ICP-MS锆石U-Pb定年测试结果表明，该岩体形成于新元古代晚期（716~710 Ma）.锆石Hf同位素分析显示ε_Hf（t）为-3.16~1.17，二阶段模式年龄（T_DM2）为1.84~1.52 Ga.地球化学特征显示封子山岩体具高硅（62.92%~73.57%）、高钠（3.33%~4.22%），富集轻稀土元素，富集K、Rb、Ba、Th、U等大离子亲石元素，亏损Nb、Ta、Ti、P等高场强元素的特征，Eu显示弱负异常（δEu=0.79~0.95），为准铝质-弱过铝质中钾钙碱性Ⅰ型花岗岩.结果表明，封子山岩体主要来源于陡岭群片麻岩的部分熔融.封子山岩体形成于裂谷扩张与小洋盆间杂并存的构造环境，是洋壳向陆壳俯冲作用的产物，可能是Rodinia超大陆聚合与裂解事件在该地区作用的响应. 

Geochronology,Geochemistry and Hf Isotopes of Fengzishan Pluton in South Qinling and Its Geological Significance

This study presents zircon U-Pb dating, geochemistry and zircon Lu-Hf isotopic data for the Fengzishan granitic intrusion located in South Qinling to constrain its formation age, petrogenesis and tectonic setting. LA-ICP-MS zircon U-Pb dating results suggest that the Fengzishan granitic intrusion was formed in Late Neoproterozoic (716-710 Ma). Zircon Hf isotopic data show the ε_Hf(t) values of -3.16-1.17 and T_DM2 values of 1.84-1.52 Ga. Geochemical characteristics show that they are high in silica (62.92%-73.57%) and Na (3.33%-4.22%) contents and relatively enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE) (e.g. K, Rb, Ba, Th, U), poor in high field strength elements (HFSE) (Nb, Ta, Ti, P) and slightly negative Eu anomalies (δEu =0.79-0.95), displaying metaluminous to weak peraluminous and medium potassium calc-alkaline Ⅰ-type granites. These characteristics suggest that the magma was primarily derived from partial melting of gneiss of the Douling Group. The Fengzishan granitic intrusion was produced by subduction of oceanic crust into continental crust and was formed in the tectonic setting of rift expansion coexisting with small ocean basin.The formation of the Fengzishan granitoid was probably the response to the amalgamation and separation of the global Rodinia supercontinent.