滇东北盐津地区中三叠统关岭组底部绿豆岩年代学及地球化学研究  

Studies on the chronology and geochemistry of the green pisolites at the bottom of the Middle Triassic Guanling Formation in Yanjin area,northeastern Yunnan Province

作　　者：刘建清[1] 何利[1] 陈风霖 冉敬[1] 何平 何佳伟 LIU JianQing;HE Li;CHEN FengLin;RAN Jing;HE Ping;HE JiaWei(Chengdu Center,China Geological Survey,Chengdu 610081,China)

机构地区：[1]中国地质调查局成都地质调查中心,成都610081

出　　处：《岩石学报》2021年第7期2245-2255,共11页Acta Petrologica Sinica

基　　金：中国地质调查局基础地质调查项目(DD20160019-19、DD20190080)资助。

摘　　要：本文首次开展了滇东北盐津地区关岭组底部绿豆岩年代学及地球化学的研究。LA-ICP-MS对其定年结果为239.60±0.43Ma,即它们可能属于中上扬子地区中-下三叠统之间多层火山岩第二次喷发的产物,而这套火山岩第一次喷发的时间应为246-248Ma。该两组年龄与新近发表的哀牢山洋缝合带两侧碎屑锆石250Ma、240Ma两组数据吻合。由于样品烧失量大、蚀变指示强烈,本文的地球化学研究以稀土、微量元素的研究为主。根据微量元素含量,其岩石定名为英安岩。绿豆岩的稀土元素与其围岩具有相似的标准化配分曲线,稀土总量(∑REE)较高。总体上,绿豆岩成分具有典型的俯冲带弧岩浆岩的地球化学特征,富集大离子亲石元素(LILE)和轻稀土元素(LREE),亏损高场强元素(HFSE)和重稀土元素(HREE)。岩石成因研究认为其兼具幔源、壳源特征,即其岩浆起源于受俯冲带交代的亏损地幔,并有强烈的地壳沉积物的交代熔融,在其形成过程中,岩浆经历了斜长石的结晶分异作用。构造环境判别图上,投影点主要落于活动大陆边缘,极少数点落在与洋内岛弧区的界线。综上,认为250Ma、240Ma是哀牢山洋壳向两侧俯冲,伴随弧火山活动,火山灰远距离搬运到中上扬子地区的两个阶段。其中,240Ma左右哀牢山洋盆向华南地块俯冲所导致的华南地块西缘强烈的火山弧活动以及与其伴随的洋岛火山喷发所产生的火山灰的远距离搬运是形成盐津地区绿豆岩的主要物质来源。The geochronology and geochemistry of the green pisolites at the bottom of Guanling Formation in Yanjin area,northeastern Yunnan Province were studied for the first time.According to LA-ICP-MS analysis,the green pisolites might be formed in 239.60±0.43Ma after the second eruption of multi-layered volcanic rocks(tuffaceous rocks)in Middle-Lower Triassic in the Middle and Upper Yangtze Region,while the first eruption of these rocks occurred in 246-248Ma.The ages of the two groups are consistent with the newly published data of 250Ma and 240Ma from detrital zircons on either side of the Ailaoshan oceanic suture zone.Due to large amount of LOI and strong indication of alteration,the geochemistry study of this paper mainly focused on rare earth and trace elements of the green pisolites.According to the study of their trace elements,these rocks belong to a type of dacite.The trace elements and rare earth elements of the green pisolite rocks have similar standardized distribution curves with those of their surrounding rocks,with high∑REE values.In general,the compositions of the green pisolites have the typical characteristics of rocks from a subduction zone magmatic arc,being rich in LILE and LREE and deplete in HFSE and HREE.It is originated from depleted mantle materials of a subduction zone metasomatic rocks,and has strong metasomatic melting of the crustal sediments.During its formation,the magma of these rocks has undergone crystallization differentiation of plagioclase.At the same time,on the map of tectonic environment determination,the projection points are mainly located at the active continental margin,and rarely at the boundary with the oceanic island arc region.Based on comprehensive research,it is considered that 250Ma and 240Ma are two stages of subduction of Ailaoshan Ocean to both sides;accompanied by volcanic arc activity,the ashes were transported to the Middle and Upper Yangtze Region from a long distance.The green pisolites in Yanjin was formed from these volcanic ashes around 240Ma with a long-d

关 键 词：滇东北 绿豆岩 年代学 地球化学 

分 类 号：P588.142[天文地球—岩石学] P597.3[天文地球—地质学]