發(fā)布時間：2018-02-24 11:26

  本文關鍵詞： 東昆侖西段 構造演化 花崗質巖石 鋯石U-Pb年代學 地球化學　出處：《西北大學》2017年碩士論文　論文類型：學位論文

【摘要】：東昆侖造山帶位于青藏高原北部,中央造山系西段,其廣泛發(fā)育的巖漿巖是東昆侖造山帶長期構造演化的物質記錄。本文選取東昆侖造山帶西段平長梁巖體和大沙溝巖體作為研究對象,對其形成時代、巖石成因、構造環(huán)境及構造意義分析探討,結合研究區(qū)及鄰區(qū)沉積地層特征和前人研究成果,對東昆侖造山帶(西段)晚古生代—早中生代構造演化歷史進行探索,取得以下主要認識:1.平長梁巖體分布于東昆中斷裂南側,呈不規(guī)則巖株和巖基產出,侵入到中元古代苦海巖群中,巖性為石英閃長巖。鋯石U-Pb定年表明其形成年齡為345±2.3 Ma(MSWD=0.25)。巖石地球化學研究表明其具有低Si02(51.98%～54.63%)、全堿(K20+Na20=4.16%～6.29%)、Ti02(0.77%～0.99%)和 P2O5(0.10%～0.25%),高 A1203(16.62～18.01%)、MgO(3.86%～5.47%)和 CaO(6.80%～8.29%)的特征,為準鋁質高鉀鈣堿性系列巖石。此外,∑REE相對較低,LREE富集、輕重稀土分餾明顯,Eu負異常不明顯(δEu=0.88～0.97),LILE中相對富集Cs、U、K、Pb等,HFSE中虧損Nb、Ta、Zr、Ti等,顯示出與俯沖相關的地球化學特征,其巖漿可能起源于受俯沖帶流體交代地幔楔的部分熔融,巖漿侵位過程中未受到明顯的地殼混染。結合區(qū)域地質資料,認為該巖體形成于活動大陸邊緣火山弧環(huán)境,可能與阿尼瑪卿—布青山洋向北俯沖有關。2.大沙溝巖體位于祁漫塔格山南坡大沙溝一帶,呈不規(guī)則巖株和巖基產出,巖性為正長花崗巖。鋯石U-Pb定年表明其形成年齡為215±1.8Ma(MSWD=0.51)。巖石地球化學研究表明其具有高Si02(75.78%～79.08%)、富堿(K2O+Na2O=8.02%～8.66%),較高的 A1203(11.04%～12.68%)、低 Ti02(0.04%～0.06%)、CaO(0.34%～0.64%)、MgO(0.04%～0.08%)和Fe2O3t(0.95%～1.37%)的特征,為弱過鋁質高鉀鈣堿性花崗巖類�！芌EE較高,LREE富集、輕重稀土分餾明顯,Eu負異常明顯(δEu=0.07～0.11),明顯富集Cs、K、Th、Pb等LILE及Nd,虧損Nb、Ce、P、Ti等HFSE及Ba,同時具有高的Zr、Nb含量及Ga/Al和Y/NbL比值,顯示了 A2型花崗巖的特征,表明其形成于后碰撞拉伸構造背景,是由巖石圈拆沉引起地幔物質上涌提供熱源導致長英質地殼部分熔融的產物。3.根據本次研究成果并結合前人研究成果的基礎上,本文認為東昆侖造山帶(西段)晚古生代-早中生代構造演化如下:在前泥盆紀構造演化的基礎上,阿尼瑪卿—布青山洋盆在石炭紀持續(xù)擴張并向北俯沖,受俯沖帶流體交代地幔楔使其部分熔融,上升侵位形成平長梁巖體;二疊紀—中三疊世早期,隨著洋殼繼續(xù)向北俯沖,形成了規(guī)模宏大的弧巖漿巖;中三疊世晚期,東昆侖地區(qū)進入碰撞造山階段;晚三疊世之后,東昆侖地區(qū)開始進入后碰撞階段,地殼加厚拆沉使長英質地殼在高溫低壓下部分熔融形成大沙溝巖體。
[Abstract]:The East Kunlun orogenic belt in the northern Tibetan Plateau, the western part of the Central Orogenic System, the extensive development of magmatite is long-term tectonic evolution in the East Kunlun orogenic belt. This paper selects material records of East Kunlun orogenic belt of flat long Liang Yanti and Dashagou rock as the research object, the formation of the age, petrogenesis, tectonic environment and tectonic analysis meaning, combined with the study area and its adjacent area, characteristics of sedimentary strata and previous research results, on the East Kunlun orogenic belt (West) the late Paleozoic early Mesozoic tectonic evolution of the history, main results are as follows: 1. flat long Liang Yanti distributed in Dongkun in the south side of the fault, irregular rock strain and batholith, intruded into the Middle Proterozoic Oliver rock group, the lithology is quartz diorite. Zircon U-Pb dating shows that the forming age of 345 + 2.3 Ma (MSWD=0.25). Geochemical study shows that it has a low Si02 (from 51.98% to 54. 63%), total alkali (K20+Na20=4.16% ~ 6.29%), Ti02 (0.77% ~ 0.99%) and P2O5 (0.10% ~ 0.25%), high A1203 (16.62 ~ 18.01%), MgO (3.86% ~ 5.47%) and CaO (6.80% ~ 8.29%) of metaluminous high-k calc alkaline rock series. In addition, the relative concentrations of REE low LREE enrichment of REE fractionation is obvious, no negative Eu anomaly (Eu=0.88 ~ 0.97), the LILE is relatively enriched in Cs, Pb, U, K, Ta, HFSE in the loss of Nb, Zr, Ti etc., show the geochemical characteristics associated with subduction, the magma may have originated in the subduction zone fluid metasomatism of the mantle wedge partial melting, magma emplacement process was not significantly affected by crustal contamination. Combined with regional geological data, the rock formed in active continental margin arc volcano, and A'nyemaqen - buqingshan ocean related to the northward subduction of.2. Dashagou pluton is located in the Qimantag mountains on the southern slope of Dashagou area irregular rock, rock and strain 鍩轟駭鍑，

本文編號：1530066