發(fā)布時間：2019-01-18 07:59

【摘要】：南非林波波帶位于卡普瓦爾克拉通與津巴布韋克拉通之間,是世界著名的太古代到早元古代的經(jīng)過多期構(gòu)造事件和高級變質(zhì)的構(gòu)造帶。林波波帶根據(jù)其構(gòu)造和巖石組合特征,可進一步劃分為北邊緣帶、中央帶和南邊緣帶。中央帶麻粒巖相尤其是高壓麻粒巖相變質(zhì)巖石的研究受到國內(nèi)外學者廣泛關注,尤其林波波帶中央帶變質(zhì)作用P-T軌跡及林波波帶構(gòu)造演化存在很多爭論。本文通過對南非林波波帶中央帶Sand River地區(qū)基性麻粒巖的研究,來探討林波波帶中央帶Sand River地區(qū)基性麻粒巖的成因及林波波帶中央帶構(gòu)造演化歷史。Sand River地區(qū)位于南非林波波帶中央帶東北部,對南非林波波帶中央帶Sand River地區(qū)麻粒巖相巖石進行了巖相學、傳統(tǒng)地質(zhì)溫壓計、變質(zhì)相平衡、地球化學及變質(zhì)作用等方面的初步研究可得,該麻粒巖原巖類型為島弧拉斑玄武巖,其變質(zhì)作用演化可劃分三個不同的變質(zhì)階段:(1)峰期高壓變質(zhì)階段;(2)早期退變質(zhì)階段;(3)晚期退變質(zhì)階段。峰期(M1)的礦物組合為Grt+Cpx+Qtz+Ilm+Mag;早期退變質(zhì)(M2)礦物組合是Opx+Pl±Grt±Cpx+Qtz,;晚期退變質(zhì)(M3)礦物組合是Amph+Pl±Opx±Grt±Cpx+Qtz,。退變質(zhì)作用PTt軌跡為順時針型近等溫降壓到降溫降壓的過程。傳統(tǒng)地質(zhì)溫壓計估算得到峰期(M1)變質(zhì)溫壓條件為T=820-900℃,P=13.5-15.4kbar;早期退變質(zhì)(M2)形成溫壓為800-890℃和8.8-11.2kbar;晚期退變質(zhì)(M3)溫壓條件為540-650℃和2.7-4.4kbar。相平衡模擬得到峰期高壓變質(zhì)區(qū)(M1區(qū))溫壓條件為T=810-890℃,P=12.5-14.5kbar;早期退變質(zhì)區(qū)(M2區(qū))變質(zhì)溫壓條件為T=830-880℃,P=6.5-7.5kbar;晚期退變質(zhì)區(qū)(M3區(qū))變質(zhì)溫壓條件為T=580-670℃,P=4.5-5.5kbar。兩種方法估算的變質(zhì)作用PT結(jié)果基本一致。本研究認為林波波帶中央帶Sand River地區(qū)麻粒巖可能形成于20億年前后,與津巴布韋克拉通與卡普瓦爾克拉通陸陸碰撞過程中的地殼加厚有關,巖體在經(jīng)歷地殼加厚及麻粒巖相變質(zhì)之后,由于構(gòu)造運動,被快速抬升到了地殼淺部,從而發(fā)育了近等溫降壓(ITD)的退變質(zhì)PTt軌跡。在地殼淺部層位,巖體又可能受到了流體的影響,從而經(jīng)歷了晚期的角閃巖相變質(zhì)作用。
[Abstract]:The South African Limbowave belt is located between the Cape Walcraton and the Zimbabwe Craton. It is a world famous Archean to early Proterozoic tectonic event and high grade metamorphic tectonic belt. According to the characteristics of structure and rock assemblage, the limbo wave zone can be further divided into three zones: the northern marginal zone, the central zone and the southern marginal zone. The study of granulite facies in central zone, especially high-pressure granulite facies metamorphic rocks, has been widely concerned by scholars at home and abroad, especially the P-T locus of the central zone metamorphism and the structural evolution of the Limbowave zone. In this paper, the basic granulites in the Sand River region of the central zone of the South African Limbo Wave Zone are studied. The origin of basic granulites in the Sand River area of the central zone of the Limbo wave belt and the history of tectonic evolution of the central zone of the zone are discussed. The. Sand River area is located in the northeast of the central zone of the Limbo wave belt in South Africa. A preliminary study of granulite facies rocks in the Sand River area of the Limbowave belt, South Africa, in terms of petrography, traditional geological thermometers, metamorphic facies balance, geochemistry and metamorphism can be obtained. The granulite is a type of island arc tholeiite and its metamorphic evolution can be divided into three different metamorphic stages: (1) peak period high-pressure metamorphic stage; (2) early retrograde metamorphic stage, (3) late retrograde metamorphic stage. The mineral assemblage of peak period (M1) is Grt Cpx Qtz Ilm Mag; early retrograde metamorphism (M2) mineral assemblage is Opx Pl 鹵Grt 鹵Cpx Qtz,; late retrograde metamorphism (M3) mineral assemblage is Amph Pl 鹵Opx 鹵Grt 鹵Cpx Qtz,. The PTt trajectory of retrograde metamorphism is the process of clockwise near isothermal depressurization to cooling and lowering blood pressure. The temperature and pressure conditions of peak period (M1) metamorphism are estimated by traditional geological thermometers as TX 820-900 鈩，

本文編號：2410484