南盘江盆地西南缘麻栗坡八布地区碎屑岩时代的厘定及其构造意义  

Determination of forming age of clastic rocks in the Malipo Babu area of southwestern Nanpanjiang basin and its tectonic significance

作　　者：张斌辉[1] 牛浩斌[1] 卓皆文[1] 李卿 张彬[1] 陆生林[1] ZHANG Binhui;NIU Haobin;ZHUO Jiewen;LI Qing;ZHANG Bin;LU Shenglin(China Geological Survey Chengdu Center,Chengdu,610081;Team 306 of Yunnan Non- ferrous Metals Geological Bureau,Kunming,650217)

机构地区：[1]中国地质调查局成都地质调查中心,成都610081 [2]云南省有色地质局三O六队,昆明650217

出　　处：《地质学报》2019年第9期2187-2196,共10页Acta Geologica Sinica

基　　金：中国地质调查局项目（编号DD20160020-07）资助的成果

摘　　要：南盘江盆地处于特提斯构造域和滨太平洋构造域的交汇部位。盆地西南缘的麻栗坡八布地区发育一套巨厚碎屑岩,因与八布蛇绿岩直接接触而意义重大,但目前还没有准确的同位素年代学依据,属性还存在争议。本文首次报道了碎屑岩上段中沉凝灰岩夹层的锆石LA-ICP-MS U-Pb年龄,结果为226±1Ma (n=17,MSWD=1.1)。结合古生物和接触关系,证实这套碎屑岩是中-上三叠统安尼阶到卡尼阶的板纳组-兰木组-平寨组。首次从上部层位厘定出一套滨岸-潮坪相石英质细砾岩、石英砂岩、细砂岩沉积,发育平行层理、浪成交错层理、透镜状层理、干涉波痕等。从中三叠世的巨厚海相陆源碎屑浊流沉积到晚三叠世卡尼末期滨岸-潮坪相沉积的演化,代表了南盘江前陆盆地中-晚三叠世的充填序列,卡尼阶平寨组与拉丁阶个旧组的平行不整合代表了印支运动第Ⅱ幕。Nanpanjiang Basin is located in the junction area of the Tethys and Pacific Domains. Thick clastic sediments are developed in the Malipo Babu area, and therefore they are of important significance because of direct contact relationship with Babu ophiolite. Due to lacking of precise isotopic dating evidence, these sediments are still in great controversy. This study first reported the LA-ICP-MS dating age of 226±1 Ma(n=17, MSWD=1.1) for zircons from the tuff above these sediments. Combined with paleontological evidence and contact relationship, it can be confirmed that these clastic sediments are Middle-Upper Triassic Banna-Lanmu-Pinzhai Formations. Onshore-tidal-flat facies sedimentary rocks were firstly discovered, which contains quartzose fine-grained conglomerate, quartzose sandstone, fine sandstone. Sedimentary structures such as parallel bedding, wave-ripple cross beddings, lenticular beddings and interfered ripples are well developed. The evolution from huge succession of deep-water siliciclastic rocks of the Middle Triassic(Bannan-Lanmu Formation) to shallow water sediments of late Triassic(Pingzhai Formation) represents the tectonic evolution of Nanpanjiang forland basin in the Middle-Late Triassic. The unconformity between Ladinian(Gejiu Formation) and Carnian(Pingzhai Formation) represents the Indosinian orogeny Ⅱ.

关 键 词：南盘江盆地 三叠系 沉凝灰岩 印支运动 

分 类 号：P588.21[天文地球—岩石学] P597.3[天文地球—地质学] P542