發(fā)布時(shí)間：2018-03-10 12:33

  本文選題：大別山東緣　切入點(diǎn)：糜棱巖　出處：《合肥工業(yè)大學(xué)》2017年碩士論文　論文類型：學(xué)位論文

【摘要】：大別造山帶是研究高壓-超高壓巖石折返的經(jīng)典地區(qū)。前人對(duì)其進(jìn)行了多年的研究工作,但目前對(duì)造山帶折返過程仍存在很大的爭議。由于早白堊世的穹窿活動(dòng)改造了造山帶折返的構(gòu)造信息,加大了研究的難度,而現(xiàn)有的折返模式大都沒有考慮早白堊世隆升對(duì)其構(gòu)造信息的影響。大別山東緣桐城-潛山段出露高壓變質(zhì)巖,其位于北大別單元岳西穹窿東側(cè),受穹窿抬升的影響相對(duì)比較單一,更容易恢復(fù)至其原始的構(gòu)造特征。因此在該區(qū)開展構(gòu)造和年代學(xué)研究,可以為研究大別造山帶的折返過程提供證據(jù)。詳細(xì)的野外觀察發(fā)現(xiàn),大別山東緣桐城-潛山段出露一系列近東西走向的韌性剪切帶,與出露的郯廬北東-北東東向韌性剪切帶產(chǎn)狀明顯不同,且向西進(jìn)入北大別單元后即消失不見,其形成應(yīng)當(dāng)與造山活動(dòng)有關(guān)。因此本次以該區(qū)出露的韌性剪切帶為研究對(duì)象,對(duì)該區(qū)進(jìn)行薄片分析、石英c軸組構(gòu)分析和U-Pb鋯石定年,并對(duì)其進(jìn)行構(gòu)造恢復(fù)。詳細(xì)的顯微鏡下觀察顯示,近東西向韌性剪切帶內(nèi)的糜棱巖樣品中長石主要發(fā)生脆性破裂,石英主要發(fā)生SR動(dòng)態(tài)重結(jié)晶,指示變形溫度為400℃左右;殘斑拖尾、書斜構(gòu)造、云母魚等指示為左行剪切;糜棱巖石英c軸組構(gòu)的主控滑移系同樣記錄了400℃左右的變形溫度。鋯石CL圖像顯示該區(qū)鋯石大部分具有核-邊結(jié)構(gòu),核部巖漿鋯石具明顯的震蕩環(huán)帶,Th/U比值為1左右,獲得了730-770 Ma的年齡;邊部鋯石具明顯的變質(zhì)鋯石特征,Th/U比值小于0.1,獲得220 Ma左右的年齡。通過對(duì)其構(gòu)造恢復(fù),發(fā)現(xiàn)近東西向韌性剪切帶的原始產(chǎn)狀具有一致的面理陡立,走向近東西,左行剪切,線理向西傾20°左右的特征。通過這些研究,并結(jié)合前人的研究,可以得出,本次測得的220Ma左右的鋯石變質(zhì)年齡可能代表了該區(qū)高壓巖石早期折返的時(shí)間;而近東西向韌性剪切帶的活動(dòng)發(fā)生在220Ma之后,190Ma之前,與高壓巖石的折返同時(shí)發(fā)生,發(fā)生在折返的晚期階段,近東西向韌性剪切帶可能是該區(qū)高壓巖石向東折返時(shí)南部比北部折返的速度更快而造成的“錯(cuò)位”形成的。
[Abstract]:The Dabie orogenic belt is a classic area for studying the exhumation of high-pressure and ultra-high pressure rocks. However, the exhumation process of orogenic belt is still controversial at present. Because of the early Cretaceous dome movement, the tectonic information of orogenic belt exhumation has been modified, which makes it more difficult to study. However, most of the existing exhumation models do not consider the influence of early Cretaceous uplift on the tectonic information. High pressure metamorphic rocks from Tongcheng to buried hill member in the eastern margin of Dabie Mountain are located on the east side of Yuexi fornix of the Beidabie unit. The influence of dome uplift is relatively simple, and it is easier to recover to its original structural characteristics. Therefore, the study of structure and chronology in this area can provide evidence for studying the exhumation process of Dabie orogenic belt. A series of east-west trending ductile shear zones appeared in the Tongcheng buried hill section on the eastern margin of the Dabie Mountains, which were obviously different from the Tan-Lu east-north east-north ductile shear zone, and disappeared when they entered the Beidabie unit in the west. Its formation should be related to orogenic activity. Therefore, the ductile shear zone exposed in this area is taken as the research object, and thin slice analysis, quartz c-axis fabric analysis and U-Pb zircon dating are carried out in this area. The detailed microscopic observation shows that the feldspar is mainly brittle rupture in mylonite samples in the near east-west ductile shear zone, and SR dynamic recrystallization occurs in quartz, indicating that the deformation temperature is about 400 鈩，

本文編號(hào)：1593354