大别山北部桃花岭岩体年代学、地球化学特征及构造意义

Zircon Geochronology and Geochemistry of the Taohualing Pluton in Northern Dabieshan and Their Tectonic Implications

由于缺少可靠的年代学资料和系统研究,大别山北部桃花岭岩体的时代和成因背景尚不清楚。MC-ICP-MS锆石U-Pb分析结果显示,桃花岭正长花岗斑岩侵位于154±1 Ma,花岗闪长岩侵位于142±1 Ma,表明桃花岭岩体是形成于侏罗纪末-早白垩世的复式岩体。地球化学分析表明,桃花岭花岗岩为高钾钙碱性、准铝质-弱过铝质的I型花岗岩。这些花岗岩都相对富集轻稀土,亏损重稀土,同时具有高Sr低Y和弱的Eu负异常(0.7~0.8),类似低镁埃达克质岩石,代表了加厚下地壳熔融的产物。

Due to the lack of detailed field geological and high-precision geochronological studies,the age and tectonic setting of the Taohualing pluton have been poorly understood so far.Zircon U-Pb of MC-ICP-MS dating yields the mean age of 154±1 Ma and 142±1 Ma for the syenogranite-porphyry and granodiorites,respectively,which indicates that the Taohualing pluton is a composite granite formed in the late Jurassic-early Cretaceous.The Taohualing granites are metaluminous to slightly peraluminous and high-K calc-alkaline,belonging to the I-type granites.Besides high Sr and low Y contents,the REE patterns of all the rocks show enrichment in LREEs relative to HREEs and weakly negative Eu abnormal.These geochemical characteristics are similar to the low-Mg adakitic rocks,and can be best explained by deep melting of a thickened lower continental crust.