南秦岭懒板凳岩体(西部)的年代学、地球化学及其地质意义

Geochronology and Geochemical Characteristics of the Western Lanbandeng Intrusion in the South Qinling Orogenic Belt and Their Geological Significance

为查明南秦岭懒板凳岩体的成因类型和形成构造环境,探讨其地质意义,本文在岩石学研究的基础上对懒板凳岩体(西部)进行了年代学及地球化学研究。结果表明,该花岗岩形成于晚三叠世(205.6±2.4 Ma),属弱过铝质高钾钙碱性岩石;具右倾型稀土配分曲线样式,δEu=0.37~0.50;微量元素表现为Rb、Th、K等的富集和Sr、P、Ti等元素的亏损。Sr初始值较低((^(87)Sr/^(86)Sr)i=0.70608~0.70665),εNd(t)为-5.80~-4.65,二阶段模式年龄介于1365~1458 Ma之间。综合研究表明,懒板凳岩体(西部)为I型花岗岩,形成于秦岭造山带印支晚期的后碰撞环境,岩浆源区为中元古代的古老地壳物质,岩浆活动与岩体附近矽卡岩型钼矿化关系较密切。

In order to reveal the petrogenesis,tectonic environment and geological significance of the Lanbandeng intrusion in South Qinling,this work conducted geochronology and geochemistry studies on the basis of detailed petrological research for the western Lanbandeng intrusion.The results show that the granite was formed in the Late Triassic(205.6±2.4 Ma),characterized by weakly peraluminous,high-K and calc-alkaline features.The granite displays distinctly LREE-enriched patterns and negative Eu anomalies(δEu=0.37~0.50)in a chondrite-normalized diagram.On primitive mantle-normalized trace element diagram,it exhibits distinct negative anomalies for Sr,P,and Ti and positive anomalies for Rb,Th and K.Sr-Nd isotopic data indicates that the initial Sr isotopic ratios are low with the values between 0.70608 and 0.70665,theεNd(t)values are from-5.80 to-4.65 and the second-stage model ages vary from 1365 Ma to 1458 Ma.Furthermore,the study shows that the granite belongs to I-type granite.The granite,derived from the reworking of Mesoproterozoic crust,was formed in a post-collisional tectonic setting during the late Indosinian.The magmatism was closely related to skarn Mo mineralization near the Lanbandeng intrusion.