陕西南秦岭四海坪岩体锆石UPb年龄及地质意义

通过对四海坪岩体地质学、岩石学以及主量、微量、稀土元素地球化学研究，表明四海坪岩体主要岩石类型有灰白色中细粒黑云母二长花岗岩和灰白色似斑状黑云母二长花岗岩，属于高钾钙碱性系列，具有准铝质-过铝质的特点，富集Rb、Th、K、Nd等，贫Ba、Nb、Ta、La、P、Eu等，明显亏损Nb、Ta、P。稀土含量中等偏低，轻重稀土分异程度高，稀土元素对球粒陨石标准化分配曲线呈明显的右倾分配模式，反映四海坪花岗岩形成于板内环境，岩浆主要来源于地壳熔融。通过LA-ICP-MS锆石U-Pb年代学研究，显示四海坪花岗岩形成于中侏罗世（168.2±1.1Ma），偏晚于前人获得的胭脂坝岩体锆石U-Pb年龄，反应四海坪-胭脂坝岩体群多期次侵入，从晚三叠世到中侏罗世存在多期次岩浆活动。

Zircon U-Pb Dating and Geochemical Characteristics of Sihaiping Pluton from Southern Qinling Orogenic Belt in Shaanxi

Based on the geology, petrology and geochemistry studies, off whitemedium-granule-biotite-adamellite and porphyritic biotite-adamellite from the Sihaiping intrusion were identified. The Sihaipinggranitoid belongs to high-K calc-alkaline serieswith aluminous-peraluminous characteristics, which was enriched in Rb, Th, K and Nd,depleted in Ba, Nb, Ta, La, P and Eu, with significant loss of Nb, Ta and P. In addition, this intrusion has moderate-low REE concentration and right deviated distribution curve. It suggests that Sihaiping granite mass might be formed in aintra-plate setting.The magma came from the partial melting of earth crust. LA-ICP-MS zircon U-Pb analysis suggested that Sihaiping intrusion was formed at 168.2±1.1Ma, which is later than U-Pb age of Yanzhiba intrusion. Combining with previous researches, Sihaiping-Yanzhiba intrusions had experienced several magmation from late Triassic to middle Jurassic.