地质学报2017，Vol.91Issue(8)：1776-1795,20.
内蒙古梅劳特乌拉蛇绿岩中埃达克岩的发现及其演化模式
Discovery of Early Permian Intra-oceanic Arc Adakite in the Meilaotewula Ophiolite, Inner Mongolia and its Evolution Model
摘要
Abstract
The study reports the discovery that the Early Permian intra-oceanic arc Huhede adakite was found to occur in the Meilaotewula SSZ ophiolite in Xiwuqi,Inner Mongolia.The Huhede adakite occuring along the Hegenshan suture zone emplaced within the Late Carboniferous Meilaotewula SSZ-type ophiolite mélange consisting mainly of fine-grained and medium-grained granodiorites.The zircon U-Pb LA-ICP-MS dating yielded an emplacement age of 294.7 ± 1.7Ma for the adakite,suggesting that it formed during Early Permian.The adakite belongs to low-K tholeiitic and middle-K calk-alkaline series.The rock is characterized by high SiO2 (64.93％ ～69.50％),Al2O3 (15.72％ ～ 19.11％),Sr(368 × 10-6 ～700.40 × 10-6),and low MgO(0.80％～1.48％),Yb(O.95× 10-6 ～1.76 × 10-6),Y(5.26 × 10-6 ～9.27× 10-6) contents,with Na2O/K2O ratio varying from 3.01 to 8.60;relatively enriched in large ion lithophile elements(LILE),such as K,Rb and Sr,and depleted in high field strength elements(HFSE),such as Nb,Ta,Zr,Ti and P.Low total REE (32.68 × 10-6 ～66.69 × 10-6),with distinct REE fractionation (Lay/YbN =3.31～5.10),no obvious negative Eu anomaly.All of the geochemical characteristics indicate that the Huhede pluton belongs to adakite.The Huhede adakite and the Meilaote SSZ ophiolite mélange constitute the more complete,continuous rock assemblage series consisting of serpentined augite peridotite,beded-massive gabbro,pillow basalt,boninite,Nb-enriched basalt,and high-Mg andesite formed by the Meilaotewula intraoceanic arc initial subduction.The petrological and geochemical characteristics suggest that the Huhede adakite should be plutonic rocks produced by the intra-oceanic arc subduction initiation intra-oceanic arc environment during early stage,demonstrating that the initial subduction of the Hegenshan suture of the Paleo-Asian Ocean started in the Early Permian.Based on the main characteristics and recognition of the Late Carboniferous-Early Permian Meilaotewula intra-oceanic arc,the formation and evolution model of the initial intra-oceanic arc subduction has been preliminarily established.关键词
埃达克岩/洋内弧岩浆岩/锆石U-Pb定年/早二叠世/梅劳特乌拉SSZ型蛇绿岩Key words
Adakite/intra-oceanic arc magmatic rock/zircon U-Pb dating/Early Permian/Meilaotewula SSZ ophiolite引用本文复制引用
王金芳,李英杰,李红阳,董培培..内蒙古梅劳特乌拉蛇绿岩中埃达克岩的发现及其演化模式[J].地质学报,2017,91(8):1776-1795,20.基金项目
本文为国家自然科学基金(批准号: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)和河北省教育厅科技项目(编号:ZC20165013)资助的成果. （批准号:41502211）
