东昆仑西段平长梁岩体和大沙沟岩体年代学、地球化学及其构造意义

发布时间：2018-02-24 11:26

  本文关键词： 东昆仑西段 构造演化 花岗质岩石 锆石U-Pb年代学 地球化学　出处：《西北大学》2017年硕士论文　论文类型：学位论文

【摘要】：东昆仑造山带位于青藏高原北部,中央造山系西段,其广泛发育的岩浆岩是东昆仑造山带长期构造演化的物质记录。本文选取东昆仑造山带西段平长梁岩体和大沙沟岩体作为研究对象,对其形成时代、岩石成因、构造环境及构造意义分析探讨,结合研究区及邻区沉积地层特征和前人研究成果,对东昆仑造山带(西段)晚古生代—早中生代构造演化历史进行探索,取得以下主要认识:1.平长梁岩体分布于东昆中断裂南侧,呈不规则岩株和岩基产出,侵入到中元古代苦海岩群中,岩性为石英闪长岩。锆石U-Pb定年表明其形成年龄为345±2.3 Ma(MSWD=0.25)。岩石地球化学研究表明其具有低Si02(51.98%～54.63%)、全碱(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,为准铝质高钾钙碱性系列岩石。此外,∑REE相对较低,LREE富集、轻重稀土分馏明显,Eu负异常不明显(δEu=0.88～0.97),LILE中相对富集Cs、U、K、Pb等,HFSE中亏损Nb、Ta、Zr、Ti等,显示出与俯冲相关的地球化学特征,其岩浆可能起源于受俯冲带流体交代地幔楔的部分熔融,岩浆侵位过程中未受到明显的地壳混染。结合区域地质资料,认为该岩体形成于活动大陆边缘火山弧环境,可能与阿尼玛卿—布青山洋向北俯冲有关。2.大沙沟岩体位于祁漫塔格山南坡大沙沟一带,呈不规则岩株和岩基产出,岩性为正长花岗岩。锆石U-Pb定年表明其形成年龄为215±1.8Ma(MSWD=0.51)。岩石地球化学研究表明其具有高Si02(75.78%～79.08%)、富碱(K2O+Na2O=8.02%～8.66%),较高的 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,为弱过铝质高钾钙碱性花岗岩类。∑REE较高,LREE富集、轻重稀土分馏明显,Eu负异常明显(δEu=0.07～0.11),明显富集Cs、K、Th、Pb等LILE及Nd,亏损Nb、Ce、P、Ti等HFSE及Ba,同时具有高的Zr、Nb含量及Ga/Al和Y/NbL比值,显示了 A2型花岗岩的特征,表明其形成于后碰撞拉伸构造背景,是由岩石圈拆沉引起地幔物质上涌提供热源导致长英质地壳部分熔融的产物。3.根据本次研究成果并结合前人研究成果的基础上,本文认为东昆仑造山带(西段)晚古生代-早中生代构造演化如下:在前泥盆纪构造演化的基础上,阿尼玛卿—布青山洋盆在石炭纪持续扩张并向北俯冲,受俯冲带流体交代地幔楔使其部分熔融,上升侵位形成平长梁岩体;二叠纪—中三叠世早期,随着洋壳继续向北俯冲,形成了规模宏大的弧岩浆岩;中三叠世晚期,东昆仑地区进入碰撞造山阶段;晚三叠世之后,东昆仑地区开始进入后碰撞阶段,地壳加厚拆沉使长英质地壳在高温低压下部分熔融形成大沙沟岩体。
[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 鍩轰骇鍑，

本文编号：1530066