摘要
莫尔道嘎地处额尔古纳地块北段,该地区大量侵入岩和侵入-变质杂岩以往被认为属新元古代,类型有风水山片麻杂岩、中基性杂岩、巨斑状钾长花岗岩、二长花岗岩岩。对该地区新元古代侵入岩和侵入-变质杂岩进行系统采样,采用LA-ICP-MS锆石U-Pb测年方法进行了测年研究。结果显示:研究区除个别岩体(混合岩化钾长花岗岩)为新元古代形成外,绝大部分以往认为的新元古代侵入岩或变质侵入杂岩为早中生代形成,揭示了研究区有强烈的早中生代构造岩浆作用。结合区域上同时代早中生代岩石的分布和年代学资料,额尔古纳和大兴安岭北段的早中生代侵入岩和变质杂岩可以分为243～246、210～229、200～205Ma 3个时期,其中200～205Ma一组最为发育。243～246Ma一组主要为莫尔道嘎地区中基性杂岩,形成背景与二叠纪末期兴蒙造山之后伸展作用有关。而210～229Ma的花岗岩和变质杂岩组合具有非常典型的大陆碰撞岩石组合特征:钙碱性系列过铝质、S型花岗岩,岩石副矿物以黑云母+角闪石+白云母为主,混合岩和淡色花岗岩(白云母花岗岩),深熔岩(莫尔道嘎巨斑状钾长花岗岩),缺乏同时期火山岩等;其形成与早中生代时期蒙古—鄂霍茨克洋封闭引起的陆陆碰撞有关。研究区早中生代花岗质侵入岩、变质杂岩特征及其同位素测年结果显示:蒙古—鄂霍茨克洋中段可能在中三叠世末期—晚三叠世早期封闭,这时已经开始发生陆陆碰撞,碰撞高峰时期可能在晚三叠世末期,早于以往认为的早侏罗世。
Moerdaoga district is situated in the northern Eerguna block.There occur a lot of Precambrian intrusive and metamorphic rocks,including Fengshuishan complex,intermediate and mafic complex,macrophenocryst syenogranite,adamelite,etc.The authors collected a series of intrusive rock thought to form in Neoprotozoic period,and separated the zircons from the rocs for U-Pb dating by LA-ICP-MS method.The obtained ages suggested that the majority of rocks,which were thought to form in Neoprotozoic period,emplaced in Early Mesozoic period,except the migmatic syenogranite formed in Neoprozoic.It can be conclude that there took place intensive tectonic and magmatic activities in Moerdaoga and adjacent areas during the Early Mesozoic period.According their ages,the Early Mesozoic intrusive and metamorphic complexes in Eerguna and northern Daxinganling Mountain could be divided into such three groups as 243-246 Ma,210-229 Ma,200-205 Ma,and the 200-205 Ma group is the most extensive.The 243-246 Ma group is dominated by the intermediate and mafic intrusive complex,maybe related to the extension occurred in after the Late Permian orogensis of Xing＇an-Mongol collision.The rocks formed from 200 Ma to 229 Ma are dominated by granite and metamorphic complexes which have such characteristics formed in continental collision setting as calc-alkaline,per aluminous,S-type granite,migmatites,biotite,muscovite and horbenlende as well as lacking associated volcanic rocks.The geology and geochemistry of the Early Mesozoic granites and metamorphic complex indicate that the middle part of Mongol-Okhotsk Ocean（Transbaikal） might be closed at the end of Middle Triassic to the beginning of Late Triassic period when the collisional orogeny might start.The peak collision might took place at the end of Triassic period（200 Ma±）.The confirmation of the Early Mesozoic granite and its geodynamic setting in Eerguna and northern Daxing＇anling is also important to reconsider the geological evolution of the area.
出处
《吉林大学学报（地球科学版）》
EI
CAS
CSCD
北大核心
2011年第6期1831-1864,共34页
Journal of Jilin University：Earth Science Edition
基金
'十一.五'国家科技支撑计划项目(2006BAB01A10)
国家重点自然科学基金项目(41030421)
中国地质调查局地质调查项目(1212011120992)
