本文選題：西秦嶺　切入點：商丹帶　出處：《西北大學》2017年碩士論文　論文類型：學位論文

【摘要】：西秦嶺武山-唐藏縫合帶是秦嶺造山帶商丹縫合帶的西延部分,也是西秦嶺地區(qū)古生代商丹洋閉合后的遺跡。深入研究商丹帶的西延部分對于整體理解商丹縫合帶和秦嶺造山帶乃至中國中央造山系都有著重要的科學意義。在武山-關(guān)子鎮(zhèn)地區(qū),武山-關(guān)子鎮(zhèn)蛇綠巖單元和李子園群變火山巖是構(gòu)成縫合帶的主要巖石地層單元,其構(gòu)造變形、變質(zhì)記錄了洋盆關(guān)閉、碰撞造山的地質(zhì)過程,是研究秦嶺造山帶古生代大地構(gòu)造演化的理想場所。本次研究通過分析西秦嶺商丹帶的野外構(gòu)造要素和變形特征,將與板塊碰撞相關(guān)的構(gòu)造變形劃分為三期。其中以右行走滑韌性變形最為顯著,表現(xiàn)為在縫合帶內(nèi)部發(fā)育的一條韌性剪切帶。通過對該剪切帶中糜棱巖類的幾何學、運動學、顯微構(gòu)造變形、同位素年代學等研究得到了以下主要認識:1.武山韌性剪切帶是一條右行走滑剪切帶,運動學渦度在0.79-0.99之間,以簡單剪切變形為主。2.電子背散射衍射分析結(jié)果顯示剪切帶的微觀變形導致石英的多個滑移系活動,包括基面a軸滑移、菱面a軸滑移、棱面a軸滑移和棱面c軸滑移。3.礦物動態(tài)重結(jié)晶以石英亞晶粒旋轉(zhuǎn)重結(jié)晶和顆粒邊界遷移重結(jié)晶為主,重結(jié)晶類型和石英組構(gòu)反映出變形溫度在500℃到650℃之間。4.選取花崗質(zhì)糜棱巖和侵入剪切帶的花崗質(zhì)巖株進行LA-ICP-MS鋯石U-Pb年代學研究,其年齡分別為910 ±4.8 Ma和403 ±3.5 Ma,分別代表了花崗質(zhì)糜棱巖的原巖和侵入巖的結(jié)晶年齡,并且初步限定了剪切帶的活動時代。結(jié)合區(qū)域地質(zhì)和東秦嶺地區(qū)(超)高壓變質(zhì)巖石的年代學證據(jù),推斷武山韌性剪切帶的活動年代應(yīng)在403-420 Ma之間。5.將東、西秦嶺商丹縫合帶的構(gòu)造屬性和年代學證據(jù)相對比,本研究認為秦嶺造山帶在加里東期向印支期演化的過程中可能發(fā)生了構(gòu)造體制和動力學背景的轉(zhuǎn)換,商丹縫合帶的構(gòu)造變形性質(zhì)由古生代的右行走滑剪切變形轉(zhuǎn)變?yōu)橹猩淖笮袛D壓變形。
[Abstract]:The Wushan-Tang-Tibet suture zone in the West Qinling Mountains is the westward extension of the Shangdan suture belt of the Qinling orogenic belt. It is also a relic of the closure of the Paleozoic Shangdan Ocean in the West Qinling area. Further study of the west extension of the Shangdan Belt is of great scientific significance for the overall understanding of the Shangdan suture belt, the Qinling orogenic belt and even the central orogenic system in China. Wushan-Guanzi Town area, The Wushan-Guanzizhen ophiolite unit and the Liziyuan Group metamorphic rocks are the main lithostratigraphic units forming the suture zone. Their tectonic deformation and metamorphism record the geological process of oceanic basin closure and collision orogeny. It is an ideal place to study the tectonic evolution of the Paleozoic era in the Qinling orogenic belt. In this study, the field tectonic elements and deformation characteristics of the Shangdan belt in the western Qinling Mountains are analyzed. The tectonic deformation associated with plate collision is divided into three stages, of which the right strike-slip ductile deformation is the most significant, as a ductile shear zone developed within the suture zone. Microstructural deformation and isotopic chronology have been studied as follows: 1. The Wushan ductile shear zone is a right strike-slip shear zone with kinematic vorticity ranging from 0.79-0.99. The results of electron backscattering diffraction analysis show that the microcosmic deformation of shear band leads to the movement of many slip systems of quartz, including basic plane a axis slip, rhombohedral a axis slip, rhombohedral plane a axis slip, etc. The dynamic recrystallization of minerals is mainly composed of quartz subgrain rotational recrystallization and grain boundary migration recrystallization. The recrystallization type and quartz fabric reflect the deformation temperature between 500 鈩，

本文編號：1596909