内蒙古查干拜兴晚石炭世埃达克岩的成因及其洋内俯冲作用的约束  

Petrogenesis of the Late Carboniferous adakite in Chaganbaixing, Inner Mongolia and constraints of intra-oceanic subduction

作　　者：董培培 李英杰 许展[3] 鞠文信[3] 王金芳 李红阳 DONG Peipei;LI Yingjie;XU Zhan;JU Wenxin;WANG Jinfang;LI Hongyang(College of the Earth Sciences,Heibei GEO University,Shijiazhuang,Hebei 050031,China;Hebei Key Laboratory of Strategic Critical Mineral Resources,Heibei GEO University,Shijiazhuang,Hebei 050031,China;Geological Survey Institute of Inner Mongolia,Hohhot,Inner Mongolia 010020,China)

机构地区：[1]河北地质大学地球科学学院,河北石家庄050031 [2]河北地质大学河北省战略性关键矿产资源重点实验室,河北石家庄050031 [3]内蒙古自治区地质调查院,内蒙古呼和浩特010020

出　　处：《地质学报》2021年第12期3676-3690,共15页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号41972061);中国地质调查局项目(编号1212011120711和DD20190004);河北地质大学科技创新团队项目(编号KJCXTD-2021-07)联合资助的成果。

摘　　要：由于缺少可靠的埃达克岩石的发现和系统研究,内蒙古索伦地区有无洋内初始弧火成岩组合和洋内俯冲作用尚不清楚,制约了古亚洲洋东段古生代古大洋俯冲消亡过程的进一步认识。本文报道在内蒙古苏尼特右旗蛇绿混杂岩带中新发现的晚石炭世埃达克岩,岩性为英云闪长岩。锆石LA-ICP-MS U-Pb定年显示,查干拜兴埃达克岩的形成时间为322.3±5.2 Ma,时代为晚石炭世。该埃达克岩属于低钾拉斑系列-中钾钙碱性系列岩石,SiO_(2)含量为65.57%~67.89%,Al_(2)O_(3)为15.48%~16.55%,MgO为0.76%~1.63%,Na_(2)O/K_(2)O为2.39~18.09,Sr为371×10^(-6)~486×10^(-6),Yb为0.60×10^(-6)~1.76×10^(-6),Y为4.87×10^(-6)~7.82×10^(-6)。相对富集大离子亲石元素K、Rb和Sr等,亏损高场强元素Nb、Ta、Zr、Ti和P,稀土元素总量(∑REE)较低(22.83×10^(-6)~80.63×10^(-6)),贫重稀土元素,无明显的Eu异常,显示了典型埃达克岩的地球化学特征。查干拜兴埃达克岩具有岛弧型岩浆岩特征,形成于俯冲带岛弧环境,可能为俯冲洋壳部分熔融而形成的埃达克质熔体,经俯冲带上升过程中与地幔楔橄榄岩发生相互作用而形成。根据查干拜兴埃达克岩与区域石炭纪蛇绿岩的时空分布与演化特征,表明古亚洲洋东段索伦缝合带在晚石炭世存在洋内俯冲作用。Due to the lack of reliable discovery and systematic study of adakitic rocks, it is not clear whether there is an intra oceanic initial arc igneous rock association and intra oceanic subduction in Solonker area, Inner Mongolia, which restricts the further understanding of the Paleozoic subduction extinction process of the eastern part of the paleo Asian Ocean. The study reports that the late Carboniferous adakite in the Suniteyouqi ophiolite, Inner Mongolia, consists mainly of tonalite. The zircon U-Pb LA-ICP-MS dating result reveals that the Chaganbaixing adakite is dated at 322.3±5.2 Ma, suggesting that it formed during Late Carboniferous. The adakite belongs to the low-K tholeiitic and medium-K calc-alkaline series. The rocks show following geochemical characteristics, such as high SiO_(2)(65.57%~67.89%) and Al_(2)O_(3)(15.48%~16.55%) content with sodium-rich and potassium-poor(Na_(2)O=4.13%~6.33%, K_(2)O=0.35%~1.89%, Na_(2)O/K_(2)O=2.39~18.09). For trace elements, they show high content of Sr(371×10^(-6)~486×10^(-6)) and low content of Yb(0.60×10^(-6)~1.76×10^(-6)) and Y(4.87×10^(-6)~7.82×10^(-6)). In addition, they are relatively enriched in large-ion lithophile elements(such as K, Rb, and Sr) and depleted in high-field-strength elements(such as Nb, Ta, Zr, Ti and P). Furthermore, they have low total rare-earth element(REE) contents(22.83×10^(-6)~80.63×10^(-6)), with low heavy rare-earth elements(HREE) without obvious Eu anomaly. Above geochemical characteristics indicate that the Chaganbaixing tonalite belongs to adakite. The adakite was formed in the island arc environment of subduction zone, which may have originated from partial melting of the subducted oceanic crust and then interacted with mantle wedge peridotite during the rise of subduction zone. Combined with the study of spatio-temporal evolution of the Chaganbaixing adakite and regional Carboniferous ophiolites, it is assumed that the initial intraoceanic subduction occurred at the Late Carboniferous in the Palaeo-Asian Ocean.

关 键 词：埃达克岩 岛弧型岩浆岩 晚石炭世 古亚洲洋东段 内蒙古苏尼特右旗 

分 类 号：P588.122[天文地球—岩石学] P534.45[天文地球—地质学]