【摘要】：青海省循化道帷地區(qū)物質(zhì)組成和地殼結(jié)構(gòu)十分復(fù)雜,構(gòu)造演化歷史悠久,存在多條NWW向、NW-NNW向斷裂,其中在南部發(fā)育的金庫街-多支壩斜沖斷層(區(qū)域上稱為隆務(wù)河-大夏河斷裂),構(gòu)成了北側(cè)祁連造山帶中化隆微地塊和拉脊山構(gòu)造帶與南側(cè)西秦嶺造山帶北緣構(gòu)造帶之間的分界斷裂。本文選取青海省循化地區(qū)出露的不同變質(zhì)程度的火山巖為研究對象,通過野外地質(zhì)調(diào)查和巖石學(xué)、礦物學(xué)、巖石地球化學(xué)及同位素年代學(xué)等方面的綜合研究,獲得如下成果和認(rèn)識:(1)青海省循化地區(qū)出露的化隆巖群主要由斜長角閃巖和少量變粒巖組成,其變質(zhì)程度可達(dá)中低角閃巖相,通過角閃石-斜長石變質(zhì)溫壓計(jì),獲得其變質(zhì)溫度約達(dá)691~772℃,變質(zhì)壓力約0.39~0.64GPa�；r群巖石地球化學(xué)數(shù)據(jù)反映,斜長角閃巖原巖為玄武巖,變粒巖原巖為安山巖,該套變質(zhì)火山巖形成環(huán)境為弧后盆地環(huán)境。從化隆巖群斜長角閃巖中獲得鋯石U-Pb年齡指示化隆巖群形成年齡為(1852±18)Ma,確定其原巖形成時代為古元古代。(2)在青海省循化地區(qū)北側(cè)出露的深溝組主要為變安山巖夾變玄武巖組合。該套變玄武巖主要由富集地幔分離結(jié)晶形成,變安山巖可能由地殼部分熔融形成,該套變火山巖形成于裂谷環(huán)境。獲得變玄武巖鋯石U-Pb年齡為(503.1±6.6)Ma,指示深溝組形成于中寒武世。這些特征指示了拉脊山構(gòu)造帶在中寒武世處于裂谷早期階段。(3)在青海省循化地區(qū)北東側(cè)出露的晚寒武世六道溝組主要為變玄武巖夾變安山巖組合。該套變火山巖組合具有E-MORB特征,其形成環(huán)境為裂谷環(huán)境。其變玄武巖野外產(chǎn)出具有變余枕狀構(gòu)造,且其由富集地幔分離結(jié)晶的巖石成因,暗示在拉脊山構(gòu)造帶在晚寒武世處于裂谷晚期階段。(4)拉脊山構(gòu)造帶地區(qū)自早中寒武世以來,在南祁連洋向北俯沖消減、板片回轉(zhuǎn)的地球動力學(xué)背景下,中祁連地塊可能受到軟流圈地幔上涌并引起大陸拉張裂解,形成了裂谷型中基性火山巖組合。在持續(xù)的俯沖作用下,南祁連洋部分洋殼巖塊及洋島/海山巖塊逐一向北拼貼于中祁連地塊,由于俯沖持續(xù)的應(yīng)力擠壓導(dǎo)致拉脊山大陸裂谷關(guān)閉。
[Abstract]:The material composition and crustal structure of the Xunhua Daozhang area in Qinghai Province are very complex, and the tectonic evolution has a long history. There are many NWW directions and NW-NNW trending faults. Among them, the Jinku Street-Multi-branch Dam oblique thrust fault (known in the region as the Longwu River-Daxia River fault) developed in the south, It constitutes the boundary faults between the middle Hualong microblock and the Lachinshan tectonic belt in the northern Qilian orogenic belt and the northern tectonic belt of the west Qinling orogenic belt in the south. In this paper, the volcanic rocks of different metamorphic degrees in Xunhua area of Qinghai Province are selected as the research objects, and through field geological investigation and comprehensive study of petrology, mineralogy, petrogeochemistry and isotopic chronology, etc. The main results are as follows: (1) the exposed Hualong rock group in Xunhua area of Qinghai Province is mainly composed of amphibolite and a small amount of metamorphic rocks, the metamorphism of which can reach the medium and low amphibolite facies, and the metamorphic temperature and pressure meter of amphibolite-plagioclase metamorphic, The metamorphic temperature is 691 ~ 772 鈩，

本文編號：2427852