【摘要】 义敦岩浆弧位于青藏高原东南缘,由甘孜—理塘古特提斯洋在晚三叠世向西俯冲形成。由于缺乏对区内前寒武系变质岩石的研究,制约了对该岩浆弧构造演化过程和大地构造属性的深入认识。义敦岩浆弧前寒武系变质岩中发育大量的绿泥石,通过详细的镜下鉴定工作,并利用电子探针对该套变质岩中的绿泥石进行矿物化学成分分析。结果表明:该套变质岩中的绿泥石均为富铁种属的蠕绿泥石,其化学成分主要受泥质岩类控制,暗示其形成于相对还原的环境;绿泥石四面体位置置换类型为Al IV对Si的替换,八面体位置置换类型以Fe对Mg的置换为主,以Al VI对Mg的置换为辅,反映其形成于相对酸性的环境;绿泥石具有较低的Si含量,较高的Fe、Mg和Al IV含量,且成分中Al IV与Al VI含量相近,说明该绿泥石为变质成因,主要由黑云母发生水解作用形成;绿泥石温度计估算其形成的温度范围为352℃~443℃,平均值为404℃,与其共生的多硅白云母指示其形成压力为0.57~0.90GPa,平均值为0.73GPa,说明义敦岩浆弧变质基底经历了中压型变质作用。综合前人研究成果,义敦岩浆弧具有扬子地块的亲缘性。更多还原

【Abstract】 Yidun magmatic arc,which is located in the southeastern margin of Qinghai-TibetPlateau,is formed in Late Triassic by the westward subduction of Ganzi-Litang Paleo-Tethyan ocean.The study on Precambrian metamorphic rocks is lacking, which restricts better understanding of tectonic evolution progress and tectonic affinity in Yidun magmatic arc.Chlorites from Precambrian metamorphic rocks in Yidun magmatic arc are widespread developed.The detailed microscope observations and the analysis of mineral chemical compositions of the chlorites using electron microprobe were studied.The results show that all the chlorites belong to prochlorite,and their chemical compositions are controlled by pelites,suggesting they are formed in a relative reduced environment;the replacement of Si by Al IVis the main substitution in the tetrahedral site,while in the octahedral site,Mg is predominately replaced by Fe,followed by Al VI,indicating the chlorites are formed in the relative acid environment;the chlorites have lower Si contents,higher Fe,Mg and Al IVcontents,meanwhile Al IVcontent is approximately equal to Al VI content,implying the chlorites are metamorphic origin and the result of the hydrolysis of biotites;the forming temperature estimated by the chlorites thermometer ranges from 352℃to 443℃(average at 404℃),and the pressure ranges from 0.57 to 0.90 GPa(average at 0.73 GPa)inferred from the phengites intergrowth with the chlorites,suggesting the metamorphic basement of Yidun magmatic arc undergoes medium-pressure type metamorphisms.Together with previous studies,Yidun magmatic arc has an affinity of Yangtze Block.更多还原