义敦岛弧晚三叠世斑岩铜矿成矿作用

发布时间：2018-02-04 12:26

  本文关键词： 义敦岛弧 晚三叠世 斑岩铜矿 成矿作用　出处：《中国地质大学(北京)》2017年博士论文　论文类型：学位论文

【摘要】：义敦岛弧形成于晚三叠世甘孜-理塘洋板块向西俯冲过程中,其南部中甸(香格里拉)弧发育大量斑岩(矽卡岩)型矿床,区内普朗斑岩型铜矿床为全球少有的具还原性特征的超大型斑岩型铜矿床,其规模远大于区内其他“氧化性”矿床,与传统斑岩成矿系统的一般认识相悖。其原因是成矿母岩浆的来源或岩浆-流体出溶作用不同,还是成矿流体演化过程与金属沉淀机制的差异?是研究区斑岩成矿作用的关键科学问题。为此,本文从中甸弧内主要斑岩(矽卡岩)型矿床的成矿斑岩体的岩石地球化学、同位素地球化学、成矿流体演化、流体包裹体均一温度以及氢氧同位素等方面开展系统研究,取得认识如下:(1)岩体锆石U-Pb年代学研究表明,东斑岩带(普朗等)石英闪长玢岩加权平均值为223±3.7 Ma,石英二长斑岩为218±4 Ma,花岗斑岩为207±3.9 Ma。而西斑岩带(雪鸡坪等)的石英闪长玢岩为234±8 Ma。石英二长斑岩为219±2.6Ma。花岗斑岩为218±1.8 Ma。即,存在西斑岩带有略早于东斑岩带的趋势。晚三叠世甘孜-理塘洋向西俯冲,西带属于俯冲前端,其板片脱水熔融,经MASH和AFC过程,形成早于东带(后端)的岩体。(2)锆石Hf-O同位素研究表明,石英闪长玢岩的Hf(t)值偏负(普朗:-13.5到-8.9,雪鸡坪:0.4-2.4),δ18O(‰)值偏高(普朗:5.74-6.9,平均6.11±0.16;雪鸡坪:5.86-6.27,平均6.02±0.11),而石英二长斑岩的Hf(t)值偏正(普朗:-3.8到2.74;雪鸡坪:0.4到2.2),δ18O(‰)值偏低(普朗:4.95-6.17,平均5.75±0.13;雪鸡坪:5.53-6.42,平均5.69±0.12),花岗斑岩和石英二长斑岩相似。表明石英闪长玢岩来源为相对较多的壳源物质,而石英二长斑岩和花岗斑岩则幔源物质增加,指示后者具有更富的成矿物质来源。(3)石英闪长玢岩岩浆氧逸度(Ce4+/Ce3+比值)相对较低(普朗:0.6-13.9,平均为4;雪鸡坪:9.7-142.8,平均74.7),石英二长斑岩岩浆氧逸度较高(普朗:5.4-99.6,平均52.1;雪鸡坪:15.5-533.1,平均163.7),花岗斑岩和石英二长斑岩相似。表现后者更具成矿潜力,这与地质事实相符。(4)普朗矿床成矿流体演化后期有大气降水的加入,引起流体不混溶。大气降水有效萃取、携带围岩地层中有机质,较好的还原条件,导致成矿物质有效地沉淀成矿。而雪鸡坪等矿床没有还原性成分的加入,从而难以形成普朗式的超大型斑岩矿床。
[Abstract]:The Yidun island arc was formed during the westward subduction of the Ganzi-Litang ocean plate in the late Triassic, and a large number of porphyry (skarn) deposits were developed in the southern Zhongdian (Shangri-La) arc. The Plang porphyry copper deposit is one of the rare super-large porphyry copper deposits with reductive characteristics in the world, and its scale is much larger than that of other "oxidizing" copper deposits in the region. It is contrary to the general understanding of the traditional porphyry ore-forming system because of the origin of the ore-forming parent magma or the dissolution of magmatic fluid or the difference between the evolution process of ore-forming fluid and the mechanism of metal precipitation. It is a key scientific problem of porphyry metallogeny in the study area. In this paper, the geochemistry, isotopic geochemistry and ore-forming fluid evolution of the ore-forming porphyry bodies of the main porphyry (skarn) deposits in Zhongdian arc are studied. A systematic study on homogenization temperature of fluid inclusions and hydrogen and oxygen isotopes has been carried out. The results are as follows: (1) zircon U-Pb geochronology of the pluton shows that, The weighted average value of quartz diorite porphyrite in the East porphyry Zone (Plang et al.) is 223 卤3.7 Ma., the quartz monzodiorite porphyry is 218 卤4 Ma., the granitic porphyry is 207 卤3.9 Ma.The quartz diorite porphyrite in the West porphyry Zone (Xuejiiping et al) is 234 卤8 Ma. the quartz diorite porphyry is 219 卤2.6 Ma.The granitic porphyry is 218 卤1.8 Ma. There is a tendency that the western porphyry is a little earlier than the eastern porphyry belt. The late Triassic Ganzi-Litang ocean subducted westward, and the western belt belongs to the front of the subduction, and its plate is dehydrated and melted through MASH and AFC process. The Hf-O isotopic study of zircon formed earlier than the back end of the east belt shows that, In quartz diorite porphyrite, the values are negative (Prang: -13.5 to -8.9, Xue Chicken Ping: 0.4-2.4, 未 18O (鈥，

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