【摘要】：猛洞巖群出露于中越邊境滇東南老君山地區(qū),是一套前寒武系變質(zhì)沉積-巖漿雜巖,其所處大地構(gòu)造位置特殊,對(duì)滇東南地質(zhì)演化,乃至華南大陸西端以及特提斯構(gòu)造域形成與演化具有重要的科學(xué)意義。在系統(tǒng)野外調(diào)研基礎(chǔ)上,本文利用光學(xué)顯微鏡、電子顯微鏡、電子探針等微觀研究手段,對(duì)猛洞巖群變質(zhì)-變形進(jìn)行了詳細(xì)的研究。研究發(fā)現(xiàn),猛洞巖群地層宏觀構(gòu)造發(fā)育同構(gòu)造分泌結(jié)晶脈、順層褶皺、透鏡體等,微觀構(gòu)造發(fā)育云母魚(yú)構(gòu)造、膝折構(gòu)造、石英矩形條帶等現(xiàn)象。顯微組構(gòu)統(tǒng)計(jì)表明猛洞巖群經(jīng)歷過(guò)北東-南西、南東-北西向、近東西向、北東-南西(近南北向)擠壓過(guò)程,與上述宏觀、微觀現(xiàn)象基本一致。同時(shí),猛洞巖群片巖中黑云母-石榴石溫壓計(jì)分別為429℃、0.5GPa,片麻巖中電氣石-黑云母溫度計(jì)平均溫度為546℃,為綠片巖相-低角閃巖相。石英斜長(zhǎng)角閃片麻巖中榍石和金紅石TIMS U-Pb同位素年齡分別為236Ma和170Ma。以上工作表明,滇東南猛洞巖群記錄了多期變質(zhì)-變形作用,其中主期變質(zhì)-變形年齡為236Ma,控制了變質(zhì)雜巖系的宏觀構(gòu)造格架,其應(yīng)力(σ1)為南東-北西向擠壓,近南北向、近東西向擠壓可能為與上述主應(yīng)變相匹配的次級(jí)應(yīng)變方向;但北東-南西向擠壓可能為主變質(zhì)-變形之后的另一次變質(zhì)-變形產(chǎn)物,時(shí)間限定為170Ma,代表老君山穹窿燕山早期的伸展-剪切活動(dòng)。因此,本文認(rèn)為老君山-Song Chay穹窿先后經(jīng)歷了印支期南北向推覆擠壓作用,晚印支期-早燕山期伸展-剪切作用以及中晚燕山期接觸變質(zhì)作用;且老君山穹窿開(kāi)始隆升時(shí)限為236Ma左右,與周邊的特提斯閉合、碰撞時(shí)間基本一致;至170Ma穹窿發(fā)生垮塌后的伸展剪切活動(dòng)。文山-麻栗坡NE方向廣泛發(fā)育印支期飛來(lái)峰及異地巖,可能指示包括猛洞巖群在內(nèi)的前印支期地層是一套從越南北部推覆而至的外來(lái)巖體。上述認(rèn)識(shí)為華南西端的構(gòu)造演化探討提供了證據(jù)。
[Abstract]:The Mengdong rock group is a set of Precambrian metamorphic sedimentation-magmatic complex, which is exposed in Laojunshan area of southeastern Yunnan along the Sino-Vietnamese border. It is located in a special tectonic position and has a great impact on the geological evolution of southeastern Yunnan. The formation and evolution of the western end of the South China continent and the Tethys tectonic domain are of great scientific significance. On the basis of systematic field investigation, the metamorphic deformation of Mengdong rock group is studied in detail by means of optical microscope and electron probe. It is found that the macroscopic structure of Mengdong rock group develops syntectonically secretory crystal veins, bedding folds, lens bodies, etc., and microstructures develop mica fish structure, knee fold structure, quartz rectangular strip and so on. The microscopic structure statistics show that the Mengdong rock group has experienced the extrusion process of NE-NW, S-NW, NE-NW (NSE), which is consistent with the macroscopic and microscopic phenomena mentioned above. Meanwhile, the temperature and pressure of biotite and garnet in schist of Mengdong rock group are 429 鈩，

本文編號(hào)：2248035