大兴安岭中段内蒙古扎赉特旗地区石炭纪高镁闪长岩、埃达克岩的发现及其对嫩江洋俯冲作用的指示  

The discovery of Carboniferous high-Mg diorites and adakites in the JalaidBanner area,the central Great Xing'an Range and their implications for the subduction of the Nenjiang ocean

作　　者：庞雪娇[1,2] 付俊彧 钱程[1,2] 杨晓平 汪岩[1,2] PANG Xuejiao;FU Junyu;QIAN Cheng;YANG Xiaoping;WANG Yan(Shenyang Center,China Geological Survey,Shenyang 110034,Liaoning,China;Northeast Geological S&T Innovation Center,China Geological Survey,Shenyang 110034,Liaoning,China)

机构地区：[1]中国地质调查局沈阳地质调查中心,辽宁沈阳110034 [2]东北地质科技创新中心,辽宁沈阳110034

出　　处：《地质通报》2024年第8期1430-1445,共16页Geological Bulletin of China

基　　金：中国地质调查局项目《东北地区数据更新及地质编图》(编号:DD20230224);《东北地区基础地质图件更新》(编号:DD20221632-05)。

摘　　要：扎赉特旗地区的晚古生代岩浆作用,对于揭示嫩江洋的俯冲过程与机制具有重要的约束意义。通过野外地质调查、岩石学、岩石地球化学和锆石U−Pb定年研究,在扎赉特旗元宝山和贾家屯地区新发现了晚石炭世早期的高镁闪长岩(年龄加权平均值为320.5±1.2 Ma)和O型埃达克岩(年龄加权平均值为317.9±3.3 Ma)。元宝山高镁闪长岩具有低SiO_(2)、高MgO、高Mg^(#)和富Na_(2)O的特点,且Ni、Cr含量高,富集轻稀土元素和大离子亲石元素,亏损高场强元素,认为其形成于消减带之上的地幔楔环境,是由消减板片部分熔融衍生的富Si质流体交代地幔岩部分熔融形成的。贾家屯石英闪长岩具有高SiO2、富Na2O、高Sr和低Yb、Y的特点,K2O/Na2O值低,稀土元素强烈分异,富集轻稀土元素和大离子亲石元素,亏损高场强元素,无负Eu异常,且贫Mg、Cr、Ni,为消减板片部分熔融后经结晶分异形成的O型埃达克岩。新发现的晚石炭世早期的埃达克岩−赞岐岩组合,与研究区石炭纪花岗岩的形成时间(333~304 Ma)同步,且高镁闪长岩与辉长岩(325.2~317.3 Ma)伴生,反映扎赉特旗地区处于松嫩地块西缘的活动大陆边缘弧环境,推测嫩江洋至少从晚石炭世早期开始就存在向东南侧松嫩地块之下的俯冲作用。The Late Paleozoic magmatism in the Jalaid Banner area is of great constraint significance in revealing the subductionprocess and closure mechanism of the Nenjiang ocean.Through field geological survey,petrology,rock geochemistry and zircon U−Pbdating,early Late Carboniferous high−Mg diorites(weighted average age 320.5±1.2 Ma)and O−type adakites(weighted average age317.9±3.3 Ma)have been discovered in Yuanbaoshan and Jiajiatun,Jalaid Banner.The Yuanbaoshan high−Mg diorite is characterizedby low SiO2,high MgO,high Mg#,rich Na2O,and high Ni and Cr contents.It is rich in light rare earth elements(LREE)and large ionlithophilic elements(LILE),loss of high field strength elements(HFSE).It is considered that the partial melting of subduction platesresults in the formation of Si−rich fluids,which displace mantle rocks and cause them to form after partial melting.The Jiajiatun quartzdiorite is characterized by high SiO_(2),Na_(2)O,Sr and low Yb,Y,K_(2)O/Na_(2)O,strong REE differentiation,enrichment of LREE and LILE,loss of HFSE,no negative Eu anomaly,poor Mg,Cr,Ni.It is an O−type adakite which formed by partial melting of subtractive platesand crystallization differentiation.The newly discovered adakite−Sanukite rock assemblage in the early Late Carboniferous is consistent with the formation time of the Carboniferous granite in the study area(333~304 Ma),and the high−Mg diorite is associatedwith gabbro(325.2~317.3 Ma).It is considered that the Jalaid Banner area was located in the active continental margin arc at thewestern edge of the Songnen massif during this period.At least since the early Late Carboniferous,the Nenjing ocean has beensubducted to the southeast beneath the Songnen massif.

关 键 词：扎赉特旗 石炭纪 高镁闪长岩 埃达克岩 俯冲作用 地质调查工程 

分 类 号：P534.45[天文地球—古生物学与地层学] P588.122[天文地球—地质学]