發(fā)布時間：2019-03-06 08:25

【摘要】：位于保山-撣泰地塊東緣的西盟群,長期以來被認(rèn)為是該地塊在我國境內(nèi)唯一出露的"前寒武紀(jì)"基底變質(zhì)巖系,但其缺乏可靠的年代學(xué)數(shù)據(jù)和化石支持。本文基于詳細(xì)地野外考察和顯微構(gòu)造分析認(rèn)為,西盟群變質(zhì)巖系可解體為花崗質(zhì)糜棱巖和淺變質(zhì)巖。前者主要出露于西盟穹形隆起的核部,遭受了強(qiáng)烈的韌性剪切變形;后者分布于隆起的邊緣及東西兩側(cè),歸屬為帕克組、王雅-允溝組。通過變形巖石的石英EBSD組構(gòu)分析,揭示出位于西盟隆起核部的巖石經(jīng)歷了中等溫度條件(550~650℃,角閃巖相)下的變形作用,并疊加了較低溫度條件(400~550℃,綠片巖相)下的變形作用;而靠近西盟隆起邊部的巖石僅經(jīng)歷了較低溫度條件(400~550℃,綠片巖相)下的變形作用。本文還對西盟群變質(zhì)巖中的3個花崗質(zhì)糜棱巖樣品進(jìn)行了LA-ICP-MS鋯石U-Pb測年,得到的鋯石U-Pb年齡分別為455±3Ma、456±3Ma和454±3Ma。結(jié)合前人獲得的年代學(xué)數(shù)據(jù)和化石資料,認(rèn)為西盟群變質(zhì)巖系的原巖主要由兩個不同時期的物質(zhì)組成,即中-晚奧陶世(~460Ma)侵入的花崗巖及寒武紀(jì)的碳酸鹽巖和碎屑巖夾少量基性火山巖等;前者遭受強(qiáng)烈變質(zhì)變形作用的改造,形成花崗質(zhì)糜棱巖;后者遭受低級變質(zhì)作用形成千枚巖、片巖、大理巖等淺變質(zhì)巖。進(jìn)而表明,前人將西盟群作為保山地塊的"前寒武系"結(jié)晶基底變質(zhì)巖系是不合理的。
[Abstract]:Ximeng Group, located in the eastern margin of Baoshan-Shantai massif, has long been regarded as the only "Precambrian" basement metamorphic series of this massif in China, but it lacks reliable chronological data and fossil support. Based on the detailed field investigation and microstructural analysis, it is considered that the metamorphic rock series of Ximeng Group can be disintegrated into granitic mylonite and shallow metamorphic rock. The former is mainly exposed to the nucleus of the Ximeng dome and suffers strong ductile shear deformation, while the latter is distributed on the margin and east-west sides of the uplift, belonging to the Parke formation and Wangya-Yungou formation. By means of quartz EBSD fabric analysis of deformed rocks, it is revealed that the rocks located in Ximeng uplift underwent deformation under medium temperature conditions (550 鈩，

本文編號：2435363