摘要
内蒙古兴安盟杜尔基地区花岗岩位于大兴安岭中南段,大地构造位置上处于古亚洲洋构造域、蒙古—鄂霍茨克洋构造域和滨西太平洋构造域的叠加部位。该区域集中保存了大量与造山事件有关的构造和岩浆记录,是研究大兴安岭地区造山过程、演化及后期造山作用叠加和改造的理想地区。杜尔基花岗岩主要由中细粒二长花岗岩、中粗粒二长花岗岩、正长花岗岩、二长花岗斑岩组成。从主量元素上看,杜尔基地区花岗岩属于过铝质高钾钙碱性系列,整体呈现高硅、高碱、过铝、低钙的特征。岩体中SiO_2含量大于72%,表现为高分异花岗岩的特征。黑云母是本地区花岗岩中主要的暗色矿物,P_2O_5与SiO_2呈现负相关性,这些特征指示杜尔基地区花岗岩具有Ⅰ型岩浆岩的特点。本文采用了激光剥蚀电感耦合等离子质谱(LA-ICP-MS)技术,对杜尔基地区花岗岩中的锆石进行U-Pb同位素测试。测试结果表明,位于杜尔基镇北侧中细粒二长花岗岩岩体的侵位年龄为(131.5±0.3)Ma;位于杜尔基镇中部的正长花岗岩体岩的侵位年龄为(213±1)Ma,其中并含有一定量的(238±2)Ma的年龄信息,为捕掳锆石,表明在正长花岗岩侵位之前可能还存在一期238 Ma的岩浆活动;位于杜尔基镇西侧的正长花岗岩岩体的侵位年龄为(131±1)Ma,其中含有一定量的(150±1)Ma的年龄信息,为捕掳锆石,表明在正长花岗岩侵位前存在一期较早的岩浆活动。可将杜尔基地区花岗岩岩浆活动划分为3期:中晚三叠世(213 Ma),晚侏罗世(150 Ma),早白垩世(130Ma)。杜尔基岩体所呈现的3期岩浆活动,均指示了一个拉张的构造背景,而缺少与俯冲相关的岩浆活动。从年龄上看,杜尔基岩体总体缺少早侏罗纪的岩浆活动,因而与其周边的孟恩陶勒盖锌铅银矿具有成因上的联系的可能性不大。
Located in the southern part of the Da Hinggan Mountains of Inner Mongolia, Dorolj granite lies on the superimposition position between ancient Asian tectonic domain, Mongol-Okhotsk tectonic domain and West Pacific plate tectonic domain. The rocks have preserved large amounts of tectonic and magmatic signatures of two orogenic events, and hence Dorolj granite is an ideal object for studying the orogenic process, evolution and post-orogenic superimposition and transformation. Dorolj granite is composed of four units, i.e., medium-fine grained monzonitic granite, coarse-medium grained monzonitic granite, syenogranite, and medium-fine grained biotite-bearing monzonitic granite. Major elements show that Doro]j granite belongs to peraluminous high K calc-alkaline rock series, and is characterized by high silicon, high alkali, peraluminous nature and low calcium. The biotite is the main dark mineral, and P2O5 decreases with increasing SIO2. These characteristics indicate that the Dorolj plutons belong to the I-type granite. The authors tried to probe into the petrology and chronology of the Dorolj granite using the laser ablation inductively coupled plasma mass spectrometry （LA-ICP-MS）. The results show that the medium-fine grained monzonitic granite located on the northern side has the emplacement age of （132±0.3）Ma, whereas the syenogranite granite located in the middle part has the emplacement age of （213±1）Ma with （238±2）Ma zircon xenocrysts, indicating that there existed an early magma activity. In addition, the syenogranite located on the western side has the emplacement age of （131 ± 1）Ma with （150± 1）Ma zircon xenocrysts. Dorolj magmatic ages have a large span and can be divided into three ranges： （1） the late Triassic （213 Ma）; （2） the late Jurassic （150 Ma）; （3） Early Cretaceous （130 Ma）. These three episodes of magma indicate an extensive environment without any subduction events. Based on the age data obtained by the authors, the Dorolj granites lack magmatism of Jurassic period. It is thus held that the Dorolj granites had nothing to do with the Mengentaolegai silver-polymetallic deposit.
出处
《中国地质》
CAS
CSCD
北大核心
2015年第4期891-908,共18页
Geology in China
基金
国家国际科技合作专项"中美环太平洋成矿带成矿规律对比与资源评价技术研究"(201110FA22460)资助
