贺根山缝合带晚石炭世TTG岩浆事件:奥长花岗岩锆石U-Pb年龄和地球化学制约  

Late Carboniferous TTG magmatic event in the Hegenshan suture zone:zircon U-Pb geochronology and geochemical constraints from the Huduge trondhjemite

作　　者：王金芳 李英杰 李红阳 董培培 WANG Jinfang;LI Yingjie;LI Hongyang;DONG Peipei(College of the Earth Sciences,Heibei GEO University,Shijiazhuang,Hebei,050031)

机构地区：[1]河北地质大学地球科学学院,石家庄050031

出　　处：《地质学报》2021年第2期396-412,共17页Acta Geologica Sinica

基　　金：国家自然科学基金(编号41972061、41502211);中国地质调查局“内蒙古1∶5万高力罕牧场三连等四幅区调”(编号1212011120711)项目资助的成果。

摘　　要：本文以贺根山缝合带呼都格奥长花岗岩体为研究对象,通过野外地质调查和岩石学、地球化学、锆石U-Pb年代学研究,讨论岩石成因、构造环境、TTG岩浆事件及古亚洲洋俯冲消亡过程。岩石地球化学研究表明,呼都格岩体富硅(SiO_(2)=66.27%~71.59%)、高铝(Al_(2)O_(3)=15.23%~15.94%)、富钠(Na_(2)O=4.13%~6.59%)、低钾(K_(2)O=1.72%~2.53%),相对高锶(Sr=196.60×10^(-6)~465.40×10^(-6))、低钇(Y=5.70×10^(-6)~12.63×10^(-6)),富集Ba、Sr等大离子亲石元素和LREE,亏损Nb、Ta、Ti、P等高场强元素和HREE,无明显Eu异常。岩石学和岩石地球化学特征表明,呼都格岩体属于以奥长花岗岩为主的英云闪长岩-奥长花岗岩-花岗闪长岩TTG岩石组合。这套TTG组合除Sr、Mg、Ni和Cr含量相对较低之外,与高Si埃达克岩的地球化学特征相类似,形成于大洋俯冲带岛弧环境,可能为俯冲洋壳脱水熔融成因。锆石LA-ICP-MS U-Pb测年获得两组年龄为306.3±1.9Ma和315.5±1.9Ma,表明该岩体侵位于晚石炭世,反映了贺根山缝合带晚石炭世大洋俯冲带TTG岩浆事件。结合其与梅劳特乌拉-高力罕蛇绿岩-TTG岩带前弧玄武岩、高镁安山岩/高镁闪长岩、埃达克岩、TTG、富铌弧玄武岩/辉长岩的岩石构造组合,认为古亚洲洋二连-贺根山洋盆在晚石炭世可能处于洋壳俯冲消减、TTG岩浆活动和新生陆壳生长洋陆转换过程中。The TTG magmatic event was an important geological process for the juvenile crustal growth.The Huduge trondhjemite is located in the Meilaotewula SSZ type ophiolite of the Hegenshan suture zone in the Xi Ujimqin Banner of Inner Mongolia.We present results of field geological survey,petrology,geochemistry and zircon U Pb geochronology to discuss the petrogenesis,tectonic setting,the TTG magmatic event and the final closure time subduction process of the Erenhot Hegenshan ocean basin(EHOB)of the Paleo Asian Ocean(PAO).Petrogeochemical studies show that the Huduge pluton has high SiO_(2)(66.27%~71.59%),Al_(2)O_(3)(15.23%~15.94%),Na_(2)O(4.13%~6.59%),Sr(196.60×10^(-6)~465.40×10^(-6))and low K_(2)O(1.72%~2.53%),Y(5.70×10^(-6)~12.63×10^(-6))contents,is enriched in Ba,Sr large ion lithophile elements and LREE,and depleted in Nb,Ta,Ti,P high field strength elements and HREE.There is no pronounced Eu anomaly.The lithological and geochemical characteristics show that the Huduge pluton belongs to tonalite trondhjemite granodiorite(TTG)assemblages dominated by trondhjemite.The geochemical characteristics of the TTG assemblages are similar to those of high SiO2 adakites except for the relatively low Sr,Mg,Ni,Cr content.The TTGwas probably formed in island arc setting of oceanic subduction zone and comprises of island arcmagmatic rocks.It is inferred that the TTG might have been derived from the dehydration melting of the subducted oceanic crust.The zircon U Pb LA ICP MS dating provides two formation ages:306.3±1.9 Ma and 315.5±1.9 Ma,indicating that the pluton was emplaced in the Late Carboniferous,reflecting the TTG magmatism and juvenile crustal growth events of oceanic subduction zone in the Hegenshan suture zone during the Late Carboniferous.Based on the petrotectonic assemblage of the fore arc basalts,high Mg andesite/high Mg diorite,high SiO_(2) adakites,TTG and Nb enriched basalt/gabbro in the Meilaotewula Gaolihan ophiolite TTG belt,itis suggested that while the EHOB of the PAO may have been in the ocean contine

关 键 词：奥长花岗岩 TTG 晚石炭世 洋陆转换 贺根山缝合带 

分 类 号：P534.45[天文地球—古生物学与地层学]