發(fā)布時間：2018-04-08 10:19

  本文選題：東秦嶺　切入點：商丹構(gòu)造帶　出處：《西北大學》2017年碩士論文

【摘要】：商丹構(gòu)造帶作為華北板塊和揚子板塊的分界線,是商丹洋發(fā)生俯沖、消減到閉合過程的產(chǎn)物。商丹構(gòu)造帶主體是一套綠片巖相至低角閃巖相的火山-沉積巖系,如蛇綠混雜巖、變質(zhì)火山巖、變質(zhì)碎屑巖、大理巖等。商丹構(gòu)造帶中還發(fā)育一系列酸性至超基性的侵入巖,包括輝長巖、閃長巖和花崗巖等,其中有很多呈透鏡狀線性展布的基性-超基性侵入巖體,這些侵入巖大都保存有完好的巖漿巖結(jié)構(gòu),成巖時代為早古生代。已有的研究對這些巖體的成因、演化有著不同的認識,且對丹鳳地區(qū)基性-超基性侵入巖缺乏相應的研究。這些侵入巖的成巖時代、構(gòu)造背景及巖漿成因?qū)μ接懕鼻貛X構(gòu)造演化有重要的地質(zhì)意義。本文在系統(tǒng)總結(jié)前人研究的基礎上,選取東秦嶺丹鳳地區(qū)的古城溝輝長巖體作為研究對象,開展了詳細的野外地質(zhì)學、巖石學、地球化學和地質(zhì)年代學等方面的研究,得到以下幾點認識:(1)丹鳳地區(qū)的古城溝輝長巖體規(guī)模較小,呈透鏡狀平行于商丹斷裂帶展布,與丹鳳巖群火山巖呈侵入接觸關(guān)系。巖體以輝長巖為主,也有少量輝長閃長巖和閃長巖。從巖體邊緣向中心,巖石的基性程度變高,巖石的礦物顆粒變粗。古城溝輝長巖體中心部位變形較弱,邊部變形程度較強,發(fā)育透入性構(gòu)造面理,為輝長質(zhì)初糜棱巖。(2)LA-ICP-MS鋯石U-Pb定年結(jié)果表明,古城溝輝長巖體的加權(quán)平均年齡為425.1±1.7Ma(MSWD=0.10)和424.3±1.3Ma(MSWD=0.16),表明古城溝輝長巖形成于志留紀文洛克世。(3)古城溝輝長巖體具有富Na低K的鈣堿性-亞堿性特征,稀土元素為右傾配分模式,LREE/HREE=8.03-11.95,LaN/YbN=9.82-17.64,δEu為0.93-1.31,Eu異常不明顯或弱正異常。大離子親石元素Cs、K、Sr、Ba明顯富集,高場強元素U、Th、Nb、Ta、Hf、Zr相對虧損,Th/Ta值為6.00-13.67。古城溝輝長巖不屬于商丹構(gòu)造帶內(nèi)早古生代的蛇綠混雜巖巖石單元,其地球化學特征表明古城溝輝長巖體形成于活動大陸邊緣環(huán)境。輝長巖巖漿來源于板塊俯沖消減作用引起的地幔楔形區(qū)部分熔融,除了消減組分的加入,巖漿在上升的過程中還受到了地殼混染作用的影響。(4)結(jié)合古城溝輝長巖體和其它北秦嶺基性-超基性侵入巖已有的研究成果,建立了北秦嶺從晉寧期晚期到加里東期的構(gòu)造演化過程:600Ma左右商丹洋處于成熟期;約515Ma開始,商丹洋洋殼開始向北俯沖;約440Ma前后,進入深層次俯沖階段,部分地方發(fā)生了初始板塊碰撞;約422Ma,商丹洋閉合,進入陸-陸碰撞階段。
[Abstract]:The Shangdan tectonic belt as the dividing line between North China plate and the Yangtze plate, is taking Dan Yang subduction, subduction to the product of the closing process of the Shangdan tectonic belt. The main body is a set of greenschist to low amphibolite facies volcano sedimentary rocks, such as OPHIOLITIC MELANGE, metamorphic volcano rocks, metamorphic clastic rocks marble, etc. the Shangdan tectonic belt has developed a series of acidic to ultrabasic intrusive rocks, consists of gabbro, diorite and granite, which has many basic and lenticular linear distribution of ultrabasic intrusive rocks, these intrusive rocks mostly preserved intact structure magmatite, diagenesis the early Palaeozoic era. The existing research on the causes of these rock evolution, there are different understandings, and the lack of corresponding research - based ultrabasic intrusive rocks in this area. These intrusive rock diagenetic age, tectonic background and magmatic origin of North Qinling Mountains tectonic evolution There are important geological significance. Based on the previous research summary system, taking the ancient city of East Qinling Mountains ditch gabbro Danfeng area as the research object, carried out detailed field geology, petrology, geochemistry and geochronology and so on, are the following: (1) the ancient city ditch gabbro body size small Danfeng area, lenticular parallel to the Shangdan fault zone, showing intrusive contact relationship with the Danfeng Group volcano rock. The rock with gabbro, with small gabbro diorite and diorite rock. From the edge to the center, the rock basic degree becomes higher, the mineral particles of rock thicker. Gu Cheng Gou gabbro center weak deformation, edge deformation degree is strong, the development of penetrative foliation, as gabbroic protomylonite. (2) LA-ICP-MS zircon U-Pb dating results show that the weighted average of the ancient city ditch gabbro Age is 425.1 + 424.3 + 1.7Ma (MSWD=0.10) and 1.3Ma (MSWD=0.16), show the ancient city of gabbro formed in the Silurian Gou Wen Rock (3). The City Ditch gabbro body with calc alkaline - rich Na low K sub alkaline characteristics of rare earth elements for the distribution pattern of LREE, LREE/HREE=8.03-11.95, LaN/YbN=9.82-17.64, Delta Eu is 0.93-1.31. Eu anomaly is not obvious or weak positive anomaly. Large ion lithophile elements Cs, K, Sr, Ba are obviously enriched in high field strength elements U, Th, Nb, Ta, Hf, Zr relative loss, Th/Ta value of the ancient city of 6.00-13.67. ditch gabbro does not belong to the Shangdan tectonic belt in the early Paleozoic OPHIOLITIC MELANGE rock unit, the geochemical characteristics of the ancient city ditch gabbro formed in active continental margin environment. Gabbro magma originated from plate subduction caused by partial melting in the mantle wedge, by addition of components, processes of magma on the rise in the crust has been mixed Influence of dyeing effect. (4) combined with the ancient city of Qinling Mountains north ditch gabbro body and other mafic ultramafic intrusive rocks research has been established in northern Qinling Mountains, from Jinning to the late Caledonian period tectonic evolution process: 600Ma's Dan Yang is in mature period; about 515Ma, Shangdan ocean crust the northward subduction; about 440Ma before and after entering the deep subduction stage, the initial collision parts; about 422Ma, Shang Dan ocean closed, into the continental collision stage.

【學位授予單位】：西北大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：P59;P588.124
，

本文編號：1721177