青海拉脊山中酸性侵入岩的地球化学特征、成岩时代及构造意义

发布时间：2018-05-09 10:14

本文选题：拉脊山 + 中酸性侵入岩　；参考：《中国地质大学(北京)》2015年硕士论文

【摘要】：祁连微大陆是祁连造山带内的古隆起区之一,其南以宗务隆山-青海南山造山带与欧龙布鲁克微大陆相邻,北以北祁连造山带与阿拉善微大陆相隔,基底岩系由早元古代高级变质岩系和具有盖层属性的中新元古代陆棚沉积岩系构成,为具有典型二元结构特征的新元古代古陆块,其上覆盖古生代沉积地层。受后期构造肢解,现今呈北西至近东西走向的疏勒南山-拉脊山缝合带将祁连微大陆分割为中祁连和南祁连微陆块。拉脊山缝合带南、北两侧分别与前寒武纪结晶基底呈断层接触,是一条具有多期活动属性的缝合带,古生代-中新生代经历了多期强烈的构造变动。其内部主体为早古生代(主要为寒武纪)的火山岩,并存在一条包含纯橄岩、辉橄岩、辉石岩、辉长辉绿岩、硅质岩的拉脊山蛇绿混杂岩带,也见有大量斜长花岗岩、石英闪长岩、花岗闪长岩、闪长岩等中酸性侵入体。本文着重讨论出露于拉脊山蛇绿混杂岩带南侧的三个小型中酸性侵入岩体的岩石学、地球化学特征和成岩时代,及其构造意义。三个中酸性小岩体分别位于拉脊山西北峰、山隘和主峰东侧,呈带状分布,整体走向为北西-南东,与拉脊山蛇绿岩带走向相近。三个小岩体均以闪长岩为主要岩石类型,其次为花岗闪长岩、石英闪长岩,岩石中常见有辉石闪长岩、角闪辉长岩等暗色岩包体,岩体内部还常见有二长花岗岩等酸性岩透镜体或岩脉。三个闪长岩岩体中岩石的主量元素成分表明其属准铝质钙碱性岩系列;微量元素蛛网图显示其多具有Nb、Ta、Ti明显亏损,Zr、Hf相对亏损的岛弧玄武岩浆结晶岩石的成分特征;Sr、Nd同位素组成揭示它们的成岩母岩浆具有源于壳幔过渡带,显示以岩石圈地幔部分熔融为主,伴有地壳物质叠加的特征。综合研究认为,拉脊山蛇绿混杂岩带南侧三个闪长岩体的成因类型属于I型花岗岩类,为钙碱性岩系列,结合稀土和微量元素含量特征认为它们可能是岛弧玄武质熔浆上侵,形成岛弧辉长岩堆晶后,残余熔浆(伴有岩浆房周边地壳物质的加入)结晶产物。LA-ICP-MS锆石U-Pb年龄测定结果揭示岩体的成岩年龄约为460-465Ma,即形成于中奥陶世。拉脊山蛇绿岩混杂岩带南侧三个中酸性侵入体成因和成岩年龄的最新研究认识揭示拉脊山缝合带中奥陶世存在岛弧俯冲、洋壳消减、岛弧岩浆上侵的构造体制。
[Abstract]:The Qilian microcontinent is one of the paleouplift areas in the Qilian orogenic belt. The southern Qilian orogenic belt is adjacent to the Euronbrook microcontinent, and the northern Qilian orogenic belt is separated from the Alashan microcontinent to the south. The basement rock series is composed of the early Proterozoic high grade metamorphic rock series and the MesoNeoproterozoic shelf sedimentary series with the property of caprock. It is a Neoproterozoic paleo-block with typical dualistic structure and covers the Paleozoic sedimentary strata. By later structural dismemberment, the Suture Zone of Sunan Mountain and Lachin Mountains, which is from north to west to near east to west, divides the Qilian microcontinent into middle Qilian and South Qilian microcontinental blocks. The southern and northern sides of the Lachinshan suture zone are in contact with the Precambrian crystalline basement respectively. It is a multi-stage active suture zone, and the Paleozoic to Mesozoic Cenozoic has undergone many strong tectonic changes. The main body is the volcanic rocks of early Paleozoic (mainly Cambrian), and there is a Lajieshan ophiolite melange belt containing pure olivine, pyroxenite, pyroxenite and siliceous rocks. Quartz diorite, granodiorite, diorite and other intermediate-acid intrusions. In this paper, the petrology, geochemistry, diagenetic age and tectonic significance of three small intermediate-acid intrusive rocks exposed to the southern side of the Lachinshan ophiolite melange belt are discussed. The three small intermediate-acid rock bodies are located in the northwest peak of Laki Mountain, the east side of the pass and the main peak, with a zonal distribution, and the whole strike is north-west to the south east, which is close to the strike of the Lachinshan ophiolite belt. The main rock types are diorite, followed by granodiorite and quartz diorite. There are usually gabbro diorite, hornblende gabbro, etc. There are also two-feldspar granite and other acid rock lenses or veins in the rock mass. The principal element compositions of the three diorite rocks indicate that they belong to the quasi-aluminous calc-alkaline rock series. The trace element cobwebs show that most of them are characterized by the composition characteristics of island arc Black Tortoise magmatic crystallization rocks, which are obviously depleted in NbTa-Ta-Ti and their igneous parent magma originates from the crust-mantle transition zone, and their isotopic compositions reveal that the diagenetic parent magma originates from the crust-mantle transition zone. It is shown that the lithospheric mantle is mainly partially melted with the characteristics of crustal material superposition. It is considered that the three diorite bodies on the southern side of the Lachinshan ophiolite melange belt belong to type I granites and belong to the calc-alkaline rock series. Combining with the characteristics of rare earth elements and trace elements, it is considered that they may be the island arc Black Tortoise magma uplift. After the island arc gabbro is formed, the residual magma (with the addition of crustal material around the magma chamber) crystallizes. LA-ICP-MS zircon U-Pb dating results show that the diagenetic age of the rock mass is about 460-465Ma. that is, it was formed in the Middle Ordovician. The recent study on the genesis and diagenetic age of three intermediate-acid intrusions in the southern side of the Lachinshan ophiolite melange reveals the tectonic system of island arc subduction, oceanic crust subduction and island arc magma intrusion in the middle Ordovician in the Laji Mountain suture zone.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588.12

【参考文献】