甘肃龙首山芨岭地区花岗岩特征及锆石LA-ICP-MS U-Pb定年

发布时间：2018-03-21 21:28

本文选题：花岗岩　切入点：岩相学　出处：《东华理工大学》2015年硕士论文　论文类型：学位论文

【摘要】：甘肃龙首山芨岭地区为祁连-秦岭铀成矿省之龙首山-祁连山铀成矿带的重要组成部分,也是我国碱交代热液型铀矿最为典型的地区。花岗岩是该区碱交代型铀矿化主要围岩。受当时研究手段、测试方法等局限,前人对该区花岗岩形成时代的精确厘定相对滞后。本次论文对龙首山芨岭地区花岗岩开展岩相学、地球化学及锆石LA-ICP-MS U-Pb定年等研究,探讨花岗岩成岩时代、岩石成因、岩浆来源、岩浆演化及花岗岩与构造演化之间的成因联系。取得以下主要认识:(1)通过野外观察及岩相学的研究,确定芨岭地区花岗岩的岩性主要为黑云母二长花岗岩、二长花岗斑岩、花岗质细晶岩及斑状黑云母二长花岗岩。(2)芨岭地区花岗岩的主量元素具富碱、低镁特征,属于准铝质高钾钙碱性系列岩石。Harker图解中Si O2与K2O呈正相关关系,与Na2O、Al2O3、Mg O、Ca O、Mn O、Ti O2、P2O5呈负相关关系,反映钾钠长石及镁铁矿物的结晶分异过程。(3)芨岭地区花岗岩的稀土元素具LREE富集,HREE分馏相对不明显特征,稀土元素总量较大,除LSS12-05 Eu具有强烈负异常外,其他样品均表现出Eu弱负异常,弱亏损特征,可能与斜长石在岩浆源区部分熔融过程中的残余有关。(4)芨岭地区花岗岩的微量元素具相对富集Ba、Rb、Th、U等大离子亲石元素(LILE)且相对贫Ta、Nb、Zr、Hf、Ti、P等高场强元素(HFSE)特征。不同类型花岗岩中,除花岗质细晶岩在微量元素含量上与其他岩性差别较大外,其他类型花岗岩组成及特征均较相似。(5)芨岭地区花岗岩的锆石LA-ICP-MS U-Pb定年结果显示,花岗岩的形成时代从早到晚可划分为两个年龄段:428.6±8.1Ma~412.8±9.0Ma及401.3±5.0Ma,属于志留纪-泥盆纪岩浆作用的产物,记录了芨岭地区在加里东晚期到海西早期至少经历了两期的岩浆作用。(6)芨岭地区花岗岩属于I型花岗岩,其岩浆物质主要来源于地壳,可能也有部分幔源物质混入,形成于后碰撞构造环境。(7)从早期到晚期,芨岭地区花岗岩演化的岩性由黑云母二长花岗岩→二长花岗斑岩→斑状黑云母二长花岗岩→花岗质细晶岩转变,颜色由灰白色变成肉红色。分异程度及交代结构种类逐渐增加。造岩矿物碱性长石、石英增多,副矿物种类增多。主量元素Fe、Mg、Ti减少,Na增加,稀土总量及轻稀土含量先增后降。
[Abstract]:The Jiling area of Longshoushan in Gansu Province is an important part of the uranium metallogenic belt of the Longshou-Qilian Mountains in Qilian Qinling uranium metallogenic province. Granite is the main surrounding rock of alkali metasomatism uranium mineralization in this area. In this paper, the lithofacies, geochemistry and zircon LA-ICP-MS U-Pb dating of granites in the Jiling area of Longshoushan are studied, and the diagenetic age and petrogenesis of the granites are discussed. The source of magma, the genetic relationship between magma evolution and granite and tectonic evolution. (1) through field observation and petrographic study, it is determined that the lithology of granites in Jiling area is mainly biotite monzogranite. The main elements of granites in Erchang granitic porphyry, granitic granites and porphyry biotite binomorphic granites are alkali-rich and low-magnesium. They belong to the quasi-aluminous high-potassium calc-alkaline series rocks. Harker diagrams show a positive correlation between Sio _ 2 and K _ 2O. There is a negative correlation between Na _ 2O _ 3 Al _ 2O _ 3, mg _ 2O _ 3, mg _ 2O _ 3, mn, mn, O _ 2O _ 2 and P _ 2O _ 5, which reflects the crystallization differentiation process of potassium albite and magnetite. The rare earth elements of granites in Jiling area are characterized by LREE enrichment and hree fractionation, and the total amount of rare earth elements is relatively large. Except for the strong negative anomaly of LSS12-05 EU, the other samples showed weak negative anomaly and weak depletion of EU. It may be related to the residual of plagioclase in the partial melting process of magma source region.) the trace elements of granites in the Jiling area are relatively enriched in large ion lithophile elements such as Bahl RbTU) and are relatively poor in high field strength elements such as Ta-NbSe, ZrHfTI-P, etc., and the characteristics of HFSEs are found in different types of granites. The zircon LA-ICP-MS U-Pb dating results of granites in the Jieling area show that the composition and characteristics of other types of granites are similar to those of other types of granites, except that the contents of trace elements in granitic fine-grained rocks are quite different from those of other types of rocks. The granites can be divided into two age groups: 428.6 卤8.1Ma~412.8 卤9.0Ma and 401.3 卤5.0 Ma, which belong to Silurian Devonian magmatism. It is recorded that the granites in the Jiling area experienced at least two periods of magmatism from the late Caledonian to the early Hercynian.) the granites in the Jiling area belong to I-type granites, whose magmatic material is mainly derived from the crust, and some mantle materials may also be mixed in. From the early to the late period, the lithology of granite evolution in Jiling area was changed from biotite monzogranite to biotite monzogranite. 鈫扙rchang granitic porphyry. 鈫扨orphyry biotite monzomorphic granite. 鈫扵he granitic fine-grained rocks change from grayish white to fleshy red. The degree of differentiation and metasomatism structure gradually increase. The alkaline feldspar, quartz and accessory minerals are increased. The total amount of rare earth and the content of light rare earth first increased and then decreased.
【学位授予单位】：东华理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588.121;P597.3

【参考文献】