摘要
南秦岭地区印支期花岗质岩浆侵入活动频繁,出现了不同类型的花岗岩,高锶低钇花岗岩就是其中的一种,前人对其进行了广泛的研究,但仍有不同的认识。枣木栏岩体位于南秦岭光头山岩体群北部,为典型的印支期高锶低钇花岗岩,前人对其缺乏研究。本文在对其详细野外地质调查的基础上,进行了较系统的岩石学、岩石地球化学、LA-ICP-MS锆石U-Pb年代学研究,认为其主体为石英闪长岩,岩石中发育大量的暗色包体,低SiO_2(53.72%~62.21%),高镁(MgO:3.84%~7.19%),高Mg~#(65~70),属于准铝质高钾钙碱性岩石。岩石具有高Sr(402×10^(-6)~811×10^(-6))、低Y(5.91×10^(-6)~12.7×10^(-6),<18×10^(-6))和重稀土,Yb含量为0.58×10^(-6)~1.22×10^(-6),<1.8×10^(-6)),高Sr/Y比值(35~94)的高锶低钇中酸性岩(Adakite)的典型地球化学特征。LA-ICP-MS锆石U-Pb年龄为199±3Ma(MSWD=4.3),限定枣木栏岩体的形成时代为晚三叠世晚期—早侏罗世早期。结合区域地质资料,认为其应该是主碰撞造山后期,地壳加厚背景下形成的具有高锶低钇属性的壳幔混合花岗岩。同时表明南秦岭地区在200Ma左右,仍为后碰撞构造环境,为区域构造演化提供了信息。
Objectives： In Southern Qinling Mountains, a large number of post collisional granite emplacements, most of the granites belongs to high K calc alkali series, its geochemical characteristics shows high Sr and lower Y, just like adakite. Extensive research has been carried out by predecessors,but there are still different opinions. Zaomulan granitic pluton is one of them, but lack of systematic research. We study LA ICP MS zircon U Pb dating, geochemistry and its geological implications. In order to provide information for regional tectonic evolution. Methods： Base on detailed field geological survey, we choose 7 samples of Zaomulan granitic pluton. A systematic study is carried out on LA ICP MS zircon U Pb dating and geochemistry. According to the analysis result, combining with regional geologic data, we discussed the regional tectonic evolution. Results： Resarch shows the main body is quartz diorite, Lower SiO2（53.72%～62.21%）,Higher MgO（3.84%～7.19%）,High Mg#（65～70）,there are large numbers of durk enclaves in the granitic pluton , belong to metaluminous high K calcalkaline granties. High Sr（402×10-6～811×10-6） and extremely loss Y （5.91×10-6～12.7×10-6, 〈18×10-6）and HREE, the content of Yb is 0.58×10-6～1.22×10-6,less than 1.8×10-6, with high Sr/Y（35～94）,which shows the typical geochemical characteristics of high Sr and low Y granite （Adakite） . LA ICP MS zircon U Pb age is 199±3Ma （MSWD=4.3）,Lately in the lately Triassic to early in the Early Jurassic. Conclusions： Zaomulan granitic pluton is consists of quartz diorite, the geochemical characteristics of the pluton belong to metaluminous high K calcalkaline granties. Best explained by deep melting of a thickened lower continental crust,and belong to crust—mantle mixing genesis types. The age of 199±3Ma for Zircons represents the crystalline age of the intrusion. indicate that southern Qinling orogenic belt was still in post collisional period in 200Ma,and provides the material for the regional tectonic evolution.
出处
《地质论评》
CAS
CSCD
北大核心
2017年第6期1497-1511,共15页
Geological Review
基金
陕西省公益性地质调查项目(项目编号:20150101)的成果~~
