四川龙门山北段马角坝中三叠统雷口坡组“绿豆岩”特征及其意义  

CHARACTERISTICS AND SIGNIFICANCE OF THE"MUNG BEAN ROCK"OF THE MIDDLE TRIASSIC LEIKOUPO FORMATION AT MAJIAOBA,NORTHERN SECTION OF LONGMEN MOUNTAINS,SICHUAN

作　　者：杨梦瑶 孙玮[1] 龚婷婷[1] 赵涵[1] 卢念喆 赵德军[1] 李泽奇 李洪奎[1] YANG Mengyao;SUN Wei;GONG Tingting;ZHAO Han;LU Nianzhe;ZHAO Dejun;LI Zeqi;LI Hongkui(Chengdu University of Technology,Chengdu,Sichuan 610059,China;Zhejiang University,Hangzhou,Zhejiang 310058,China)

机构地区：[1]成都理工大学,四川成都610059 [2]浙江大学,浙江杭州310058

出　　处：《矿物岩石》2023年第2期121-131,共11页Mineralogy and Petrology

基　　金：国家自然科学基金企业创新发展联合基金项目(批准号:U19B6003)。

摘　　要：位于扬子地台的西北缘、龙门山北段的四川江油马角坝地区娃娃岩发育一套露头清晰的“绿豆岩”剖面,由于目前关于川北地区“绿豆岩”的岩石学、岩相学以及全岩地球化学数据分析的研究较少,因此本次研究针对四川龙门山北段马角坝中三叠统雷口坡组“绿豆岩”2件样品进行岩石学、岩相学观察、6件全岩地球化学样品的分析测试,结果表明研究区内“绿豆岩”主要发育有四层,厚度为5.5 m,岩性为白云质含火山灰黏土岩,岩样手标本呈灰绿色,质地松软,主要由不规则棱角状、片状水云母和不规则粒状微小石英等中酸性火山碎屑物质及火山灰组成。根据全岩地球化学数据表明,研究区内“绿豆岩”的稀土元素分配模式图整体呈右倾分布,负Eu异常,δEu=0.654~0.700,Ce负异常,δCe=0.94~0.96。微量元素特征表明研究区内“绿豆岩”形成环境为干燥炎热的微咸水-咸水、亚氧化-还原环境。通过区域对比,认为研究区“绿豆岩”为中三叠世初期形成,而“绿豆岩”中的火山物质来源与与古特提斯洋俯冲消减作用有关,是由俯冲带控制多期构造弧火山喷发造成,初步推测“绿豆岩”火山灰主体来自西部岛弧火山活动的多期次火山活动,与特提斯洋向东俯冲至扬子板块下部有重要相关性。In the northern part of Longmen Mountains,“mung bean rock”(hydromica claystone)is developed in the Middle Triassic Leikoupo Formation in Majaoba area,Jiangyou,Sichuan Province.There are few studies on the petrological,petrographicaland geochemical data of the“mung bean rock”.In this study,the Middle Triassic Lekoupo Formation section is measured at Wawayan in Majiaoba area.Two samples are collected from four layers of“mung bean rock”(5.5 m thickness)for petrographic and petrographical study,and six samples are collected for whole-rock geochemical test and analysis.The results show that the hand specimens are gray-green in color and soft in texture.They are mainly composed of irregularly angular,flaccid hydromica,irregularly granular quartz and other intermediate acid pyroclastic materials and volcanic ash.The lithology of this rock is identified as dolomitic hydromica claystone.Geochemical analysis of the whole rock shows that the"mung bean rock"in the study area presents a right-leaning distribution pattern of rare earth elements,with negative Eu anomaly(δEu=0.654—0.700)and negative Ce anomaly(δCe=0.94-0.96).The characteristics of trace element data indicate that"mung bean rock"is formed in dry and hot brackish water-saline water,with hypoxide-reduction environment.Through regional comparison,it is concluded that the volcanic ash in“mung bean rock”formed in the early Middle Triassic is mainly from volcanic eruption activities,and the volcanic materials in“mung bean rock”is related to the multi-stage arc volcanic eruption induced by subduction of the Paleo-Tethys Ocean in the west of the study area.

关 键 词：绿豆岩 早—中三叠世 扬子地台 古特提斯洋 马角坝 

分 类 号：P588[天文地球—岩石学] P586[天文地球—地质学]