西藏班-怒成矿带多龙矿集区早白垩世岩浆作用及动力学背景

发布时间：2018-03-07 09:48

本文选题：班公湖-怒江成矿带　切入点：多龙矿集区　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】：西藏多龙矿集区位于班-怒成矿带西段北侧,发育西藏首个世界级的斑岩-高硫化型浅成低温热液型铜(金)矿床。为查明多龙矿集区成矿动力学背景,本文在前人工作的基础上,以多龙矿集区色那矿区、外围东窝东矿区含矿斑岩以及美日切错组中酸性火山岩为研究重点,通过扎实的野外勘查工作,运用大量新的高精度测试分析与成矿理论,取得了以下的初步认识和成果:(1)提出东窝东矿区为多龙矿集区东延部分的新认识,获得东窝东矿区含斑岩年龄为121.0~121.5Ma,色那矿区含矿斑岩年龄为118.1±1.4Ma,与多龙矿集区超大型-大型斑岩-浅成低温热液型-隐爆角砾岩型铜(金)矿床成岩成矿年龄115~125Ma相近,即早白垩世晚期的成岩成矿。(2)多龙矿集区东窝东、色那含矿斑岩属钙碱性-高钾钙碱性-钾玄岩系列准铝质花岗岩,富集轻稀土和大离子亲石元素,亏损重稀土及高场强元素;稀土元素分配曲线呈右倾平缓型,δEu呈现中等负异常到弱正异常,具备典型岛弧岩浆岩特征。含矿斑岩具高(87Sr/86Sr)i值(0.0502~0.7111)、低的负εNd(t)值到低的正εNd(t)值(-7.7~+3.3);含矿斑岩εHf(t)为+0~+15.6,TDM C为176~1252 Ma;表明含矿斑岩是班-怒洋洋壳向北俯冲消减背景下,由玄武质新生下地壳部分熔融形成的产物,源区内可能有幔源物质混入。(3)获得美日切错组流纹岩成岩年龄为109.3±2.2Ma,安山岩年龄为108.2±2.6Ma,与冈底斯地块的大量早白垩世火山岩同期,其可能是班公湖-怒江洋壳发生双向俯冲,洋壳出现了断离(break-off)的产物。(4)美日切错组火山岩属高钾钙碱性-钾玄岩系列岩石,富集轻稀土和大离子亲石元素,亏损重稀土及高场强元素,δEu为0.65~0.80,(87Sr/86Sr)i值为0.7050~0.7053,εNd(t)值为-1.51~1.29;εHf(t)为+3.4~+15.5,TDM C为180~956Ma,表现出明显的幔源特征,暗示美日切错组火山岩是处于班-怒洋洋壳向北的俯冲背景下,由俯冲板片脱水产生流体交代地幔楔发生部分熔融形成原始玄武质岩浆,并在上升滞留在壳幔边界形成新生下地壳,新生下地壳与持续底侵幔源玄武质岩浆混合而部分熔融形成。(5)提出多龙矿集区含矿斑岩及美日切错组火山岩形成于典型活动大陆边缘构造背景的新认识,暗示班-怒洋盆在早白垩世晚期尚未关闭,洋盆仍正在向北俯冲于羌塘地块之下,且108~109Ma时板片的俯冲角度变陡,拉萨地块与羌塘地块碰撞时间应晚于早白垩世晚期(108~109Ma)。
[Abstract]:The Dulong ore concentration area in Tibet is located on the northern side of the western section of the Ban-Nu metallogenic belt. The first world-class porphyry-high sulphide epithermal copper (gold) deposit was developed in Tibet. In order to find out the metallogenic dynamic background of the Dulong ore accumulation area, On the basis of previous work, this paper focuses on the ore bearing porphyry in the Xena mining area, the Dongwodong mining area in the periphery, and the intermediate and acid volcanic rocks of the United States and Japan Jieshi formation, through solid field exploration work. By using a large number of new high-precision test and metallogenic theories, the following preliminary understandings and results are obtained: (1) A new understanding that Dongwodong mining area is the east extension part of Dulong ore gathering area is put forward. The porphyry age of Dongwodong ore area is 121.0 ~ 121.5 Ma, and the porphyry age of Xena ore area is 118.1 卤1.4 Ma, which is close to the diagenetic age of 115125 Ma in the extremely large and large porphyry type, epithermal type and cryptoexplosive breccia type copper (gold) deposit in the Dulong ore concentration area. That is, late early Cretaceous diagenesis and metallogenesis.) Donwodong ore concentration area, Xena ore-bearing porphyry belongs to calc-alkaline, high-potassium calc-alkaline-potash granites, enriched in light rare earth and large ion lithophile elements, depleted of heavy rare earth elements and high field strength elements. The distribution curve of rare earth elements is of the type of right dip flat, 未 EU shows moderate negative anomaly to weakly positive anomaly, The ore-bearing porphyry is characterized by typical island arc magmatic rocks. The ore-bearing porphyry is characterized by a high value of 87s r-86Sr ~ (-1) I (0.0502n / 0. 7111g), a low value of negative 蔚 Ndtt to a low value of positive 蔚 Ndtt (-7. 7 ~ 3. 3), and a porphyry porphyry with a TDM C of 0 ~ 15. 6 ~ 15.6 TDM C of 1761252 Maa, indicating that the ore-bearing porphyry was subducted northward in the Ban-Muyang oceanic crust, indicating that the ore-bearing porphyry was subducted in the northward subduction setting of the Ban-Muyang oceanic crust. From the partial melting of Black Tortoise's new lower crust, there may be mantle source materials mixed into the source area.) the diagenetic age of rhyolite in the United States and Japan is 109.3 卤2.2 Ma. andesite age is 108.2 卤2.6 Ma, which is at the same time as a large number of early Cretaceous volcanic rocks in the Gangdis block. It may be a bidirectional subduction of the Bangonghu and Nujiang oceanic crust, and a product of break-off in the oceanic crust. (4) the volcanic rocks of the United States and Japan fault formation belong to a series of high-potassium calc-alkaline-potacite series, which are rich in light rare earth elements and large ion lithophile elements. The loss of heavy rare earth elements and high field strength elements, 未 EU = 0.65 ~ 0.80 ~ (0.80) ~ (87) Sr _ (86) Sr ~ (-1) I = 0.7050 ~ 0.7053, 蔚 Ndt _ (t) = -1.51 ~ 1.29, 蔚 Hft) = 3.4- 15.5 ~ TDM _ (C) = 180 ~ 956 Ma. it is suggested that the volcanic rocks of the United States and Japan are located in the northward subduction background of the Ban-angyang oceanic crust, indicating that the volcanic rocks of the United States and Japan are under the background of northward subduction. The fluid metasomorphic mantle wedge was partially melted by dehydration of the subduction plate to form the primitive Black Tortoise magma, and then stayed at the crust-mantle boundary to form the new lower crust. A new understanding of the formation of ore-bearing porphyry in the Dulong ore concentration area and volcanic rocks of the United States and Japan in the typical active continental margin is proposed. It is suggested that the Ban-Nuyang basin was not closed in the late early Cretaceous, the oceanic basin was still subducting north under the Qiangtang block, and the subduction angle of the plate plate became steeper at 108109Ma. The collision time between Lhasa block and Qiangtang block should be later than that of the late Cretaceous.
【学位授予单位】：中国地质大学(北京)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P612;P588.11

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