【摘要】：西南印度洋中脊(SWIR)作為超慢速擴張洋中脊,是全球洋中脊系統(tǒng)的重要組成部分。其熱液活動自從上世紀90年代開始日益受到關(guān)注。本文對在超慢速擴張西南印度洋中脊斷橋熱液區(qū)所采集到的巖石及熱液硫化物進行了詳細的礦物學、地球化學分析,結(jié)合海底攝像拖體等資料,系統(tǒng)研究了斷橋熱液區(qū)的成礦地質(zhì)背景、成礦特征、成礦物質(zhì)來源、成礦時代、成礦模式及控礦因素。1、西南印度洋中脊斷橋熱液區(qū)玄武巖屬于低鉀拉斑玄武巖系列,斑晶主要以斜長石和橄欖石為主。元素組合特征和Sr、Nd、Pb同位素特征表明其主要來自于虧損地幔,陸殼和遠洋沉積物可能對其有一定的混染作用。2、斷橋熱液區(qū)殘留煙囪體硫化物及塊狀硫化物礦物組合主要為黃鐵礦-黃銅礦-閃鋅礦-白鐵礦。斷橋熱液區(qū)的成礦序列可初步劃分5個礦物學組合,分別是粒狀黃鐵礦(Py1)+黃銅礦+粒狀閃鋅礦(Sp1)+中間固溶體(Iss);樹枝狀黃鐵礦(Py2)+閃鋅礦(粒狀,Sp1)+等軸古巴礦(Iso);膠狀黃鐵礦(Py3)+白鐵礦(Mar)+膠狀閃鋅礦(Sp2);黃鐵礦+膠狀閃鋅礦(Sp2);以及成礦晚期的無定型硅+銅鹽的沉淀。研究區(qū)硫化物的Cu、Fe和Zn的平均含量分別為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)含量高于大部分熱液區(qū)�，F(xiàn)代海底熱液系統(tǒng)中不尋常的高Pb、Cd、As、Sb和Ag被解釋為熱液流體最初富集這些元素;另外一個可能原因是元素的再活化作用及隨后的礦床區(qū)域提純過程造成的。3、SWIR斷橋熱液區(qū)硫化物樣品206Pb/204Pb、207Pb/204Pb和208Pb/204Pb變化范圍分別為:18.237-18.396、15.512-15.721 和 38.101-38.792。SWIR 斷橋熱液區(qū)硫化物的Pb主要來自玄武巖,海水的貢獻非常低。殘留煙囪體22件硫化物子樣品δ34S分布范圍較窄,為+4.426-+4.7159‰;而塊狀硫化物樣品的δ34S值明顯高于煙囪體硫化物,分布范圍為+4.945-+5.621‰。研究區(qū)δ34S值的組成被解釋為玄武巖和海水還原S的混合模式。根據(jù)二端元的混合模式,估算出斷橋熱液區(qū)海水硫酸鹽的貢獻S約為20-27%。Sr同位素數(shù)據(jù)顯示,熱液流體為演化的海水。4、230Th/238U年代學結(jié)果表明,斷橋熱液區(qū)最老的硫化物年齡為84.338(±0.534)kyrs,來自于該熱液區(qū)的北部。而最年輕的硫化物則來自于該熱液區(qū)的中部,為0.737(±0.023)kyrs。斷橋熱液區(qū)存在四次主要熱液事件: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、斷橋熱液區(qū)主要熱源為其下軸部巖漿房(AMC)提供的巖漿熱源及輝長質(zhì)巖漿侵入;高角度正斷層是斷橋熱液區(qū)主要控礦構(gòu)造,它在垂向上可能與淺部的構(gòu)造斷裂及熱收縮斷裂組合成流體疏導網(wǎng)絡(luò)。與此同時,巖漿作用過程以及構(gòu)造作用過程帶來的熱量使得下滲的海水被加熱并驅(qū)動了熱液循環(huán)。
[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，

本文編號：2345521