西南印度洋中脊断桥热液区成矿作用研究
发布时间：2018-11-20 17:25
【摘要】：西南印度洋中脊(SWIR)作为超慢速扩张洋中脊,是全球洋中脊系统的重要组成部分。其热液活动自从上世纪90年代开始日益受到关注。本文对在超慢速扩张西南印度洋中脊断桥热液区所采集到的岩石及热液硫化物进行了详细的矿物学、地球化学分析,结合海底摄像拖体等资料,系统研究了断桥热液区的成矿地质背景、成矿特征、成矿物质来源、成矿时代、成矿模式及控矿因素。1、西南印度洋中脊断桥热液区玄武岩属于低钾拉斑玄武岩系列,斑晶主要以斜长石和橄榄石为主。元素组合特征和Sr、Nd、Pb同位素特征表明其主要来自于亏损地幔,陆壳和远洋沉积物可能对其有一定的混染作用。2、断桥热液区残留烟囱体硫化物及块状硫化物矿物组合主要为黄铁矿-黄铜矿-闪锌矿-白铁矿。断桥热液区的成矿序列可初步划分5个矿物学组合,分别是粒状黄铁矿(Py1)+黄铜矿+粒状闪锌矿(Sp1)+中间固溶体(Iss);树枝状黄铁矿(Py2)+闪锌矿(粒状,Sp1)+等轴古巴矿(Iso);胶状黄铁矿(Py3)+白铁矿(Mar)+胶状闪锌矿(Sp2);黄铁矿+胶状闪锌矿(Sp2);以及成矿晚期的无定型硅+铜盐的沉淀。研究区硫化物的Cu、Fe和Zn的平均含量分别为2.5 wt%、27.6 wt%和 3.1 wt%,而 Pb(≤7500 ppm,平均 1455 ppm)、As(≤830 ppm),Ag(15.6-100ppm),Sb(≤98.9ppm)和 Cd(≤920 ppm)含量高于大部分热液区。现代海底热液系统中不寻常的高Pb、Cd、As、Sb和Ag被解释为热液流体最初富集这些元素;另外一个可能原因是元素的再活化作用及随后的矿床区域提纯过程造成的。3、SWIR断桥热液区硫化物样品206Pb/204Pb、207Pb/204Pb和208Pb/204Pb变化范围分别为:18.237-18.396、15.512-15.721 和 38.101-38.792。SWIR 断桥热液区硫化物的Pb主要来自玄武岩,海水的贡献非常低。残留烟囱体22件硫化物子样品δ34S分布范围较窄,为+4.426-+4.7159‰;而块状硫化物样品的δ34S值明显高于烟囱体硫化物,分布范围为+4.945-+5.621‰。研究区δ34S值的组成被解释为玄武岩和海水还原S的混合模式。根据二端元的混合模式,估算出断桥热液区海水硫酸盐的贡献S约为20-27%。Sr同位素数据显示,热液流体为演化的海水。4、230Th/238U年代学结果表明,断桥热液区最老的硫化物年龄为84.338(±0.534)kyrs,来自于该热液区的北部。而最年轻的硫化物则来自于该热液区的中部,为0.737(±0.023)kyrs。断桥热液区存在四次主要热液事件:84.3(±0.5)-68.9(±0.7)kyrs;48.4(±0.4)-43.9(±0.9)kyrs;34.8(±0.3)-25.3(±0.1)kyrs;17.3(±0.1)kyrs-0.737(±0.023)kyrs。5、断桥热液区主要热源为其下轴部岩浆房(AMC)提供的岩浆热源及辉长质岩浆侵入;高角度正断层是断桥热液区主要控矿构造,它在垂向上可能与浅部的构造断裂及热收缩断裂组合成流体疏导网络。与此同时,岩浆作用过程以及构造作用过程带来的热量使得下渗的海水被加热并驱动了热液循环。
[Abstract]:As a super-slow spreading mid-ocean ridge, (SWIR) is an important part of the global mid-ocean ridge system. Its hydrothermal activity has been paid more and more attention since the 1990's. In this paper, detailed mineralogical and geochemical analysis of rocks and hydrothermal sulfides collected from the hydrothermal region of the middle ridge bridge in the southwestern Indian Ocean extending at a very slow speed have been carried out, and combined with the data of submarine camera towing, etc. The metallogenic geological background, metallogenic characteristics, ore-forming material source, metallogenic age, metallogenic model and ore-controlling factors in the hydrothermal zone of the faulted bridge are systematically studied. 1. The basalts in the hydrothermal zone of the middle ridge of the southwest Indian Ocean belong to the low potassium tholeiite series. The porphyry crystals are mainly plagioclase and olivine. The elemental assemblage and Sr,Nd,Pb isotopic characteristics indicate that they are mainly derived from depleted mantle and may be mixed by continental crust and oceanic sediments. The sulfides and massive sulphide mineral assemblages of the residual chimney bodies in the fault-bridge hydrothermal region are mainly pyrite chalcopyrite sphalerite and bauxite. The metallogenic sequence of the fault-bridge hydrothermal region can be divided into five mineralogical assemblages, namely, granular pyrite (Py1) chalcopyrite (Sp1) intermediate solid solution (Iss);. Dendritic pyrite (Py2) sphalerite (granular, Sp1) etc., (Iso); colloidal pyrite (Py3), albinite, (Mar) sphalerite (Sp2), pyrite colloidal sphalerite (Sp2); And the precipitate of amorphous silicon-copper salt in late metallogenic stage. The average contents of Cu,Fe and Zn of sulfides in the study area were 2.5 wt%,27.6 wt% and 3.1 wt%, respectively, and Pb (鈮，
本文编号：2345521
[Abstract]:As a super-slow spreading mid-ocean ridge, (SWIR) is an important part of the global mid-ocean ridge system. Its hydrothermal activity has been paid more and more attention since the 1990's. In this paper, detailed mineralogical and geochemical analysis of rocks and hydrothermal sulfides collected from the hydrothermal region of the middle ridge bridge in the southwestern Indian Ocean extending at a very slow speed have been carried out, and combined with the data of submarine camera towing, etc. The metallogenic geological background, metallogenic characteristics, ore-forming material source, metallogenic age, metallogenic model and ore-controlling factors in the hydrothermal zone of the faulted bridge are systematically studied. 1. The basalts in the hydrothermal zone of the middle ridge of the southwest Indian Ocean belong to the low potassium tholeiite series. The porphyry crystals are mainly plagioclase and olivine. The elemental assemblage and Sr,Nd,Pb isotopic characteristics indicate that they are mainly derived from depleted mantle and may be mixed by continental crust and oceanic sediments. The sulfides and massive sulphide mineral assemblages of the residual chimney bodies in the fault-bridge hydrothermal region are mainly pyrite chalcopyrite sphalerite and bauxite. The metallogenic sequence of the fault-bridge hydrothermal region can be divided into five mineralogical assemblages, namely, granular pyrite (Py1) chalcopyrite (Sp1) intermediate solid solution (Iss);. Dendritic pyrite (Py2) sphalerite (granular, Sp1) etc., (Iso); colloidal pyrite (Py3), albinite, (Mar) sphalerite (Sp2), pyrite colloidal sphalerite (Sp2); And the precipitate of amorphous silicon-copper salt in late metallogenic stage. The average contents of Cu,Fe and Zn of sulfides in the study area were 2.5 wt%,27.6 wt% and 3.1 wt%, respectively, and Pb (鈮，
本文编号：2345521
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