METALLOGENESIS IN BACK-ARC ENVIRONMENTS - THE LAU BASIN EXAMPLE
METALLOGENESIS IN BACK-ARC ENVIRONMENTS - THE LAU BASIN EXAMPLE
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DOI：
10.2113/gsecongeo.88.8.2154
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发表时间：
1993-12-01
期刊：
影响因子：
--
通讯作者：
WIEDICKE, M
中科院分区：
文献类型：
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作者：
FOUQUET, Y;VONSTACKELBERG, U;WIEDICKE, M
在Lau盆地使用潜水Nautile进行的地质调查是对现代弧后火山脊Valu Fa脊的热液活动进行的首批详细研究之一。在火山岩差异最大的地区发现了Hine Hina、Vai Lili和白色Church三大热液田，热液存款类型受火山作用类型和由南向北递增的构造活动控制。提出了硫化物形成的三个阶段。在第一阶段（Hina Hina油田），通过火山岩物质的扩散排放产生了广泛的铁锰氧化物结壳，覆盖在火山岩物质内的硫化物矿床上。在第二阶段（Vai Lili油田），构造活动增加，断层控制的排放在海底形成烟囱。仍有弥漫性放电。在第三阶段（白色Church油田），热液活动完全受主要断裂控制，并导致硫化物丘的发育。Cl富集最好解释为与深层卤水混合，而不是亚临界相分离，没有证据表明岩浆流体的贡献。流体的一些特征，如低pH值（2）和低浓度的H2S，可以解释为海底硫化物的形成。水-岩反应带估计在海底以下约1公里，岩浆房以上约2公里。丘体内的矿物垂直分带不同于迈阿密海脊矿床，但类似于黑矿存款。在存款的表面，黄铁矿的几乎没有和大量的闪锌矿，重晶石，砷铜矿，方铅矿，和局部，自然金是显着的。每个火山岩段中矿床独特的化学特征可以通过与不同数量的分异岩石的相互作用来解释。与米西安海脊相比，Lau盆地矿床富集Ba、Zn、As、Pb、Ag、Au和Hg，贫Mo、Se和Co。冲绳海槽），成矿作用为贫Pb、As。它们的矿物学、化学成分和地质背景表明，南部Lau盆地的矿床介于大洋和大陆后弧矿床之间。
Geologic investigations with the submersible Nautile in the Lau basin represent one of the first detailed studies of hydrothermal activity on a modern back-arc volcanic ridge, the Valu Fa Ridge. Three major hydrothermal fields (Hine Hina, Vai Lili, and White Church) were discovered in the areas of the greatest differention of volcanic rocks.The type of hydrothermal deposit is controlled by the type of volcanism and by tectonic activity which increases from south to north. Three stages of sulfide formation are proposed. During the first stage (Hina Hina field), diffuse discharge through volcaniclastic material produces extensive Fe-Mn oxide crusts covering sulfide deposits within the volcanic material. During the second stage (Vai Lili field), tectonic activity increases and fault-controlled discharge forms chimneys on the sea floor. Diffuse discharge is still present. During the third stage (White Church field), hydrothermal activity is completely controlled by major faults and results in the development of sulfide mounds.Vent fluids at Valu Fa have much higher metal contents than those at midocean ridges. Cl enrichment is best explained by mixing with deep brine rather than by subcritical phase separation and there is no evidence for a magmatic fluid contribution. Some characteristics of the fluids, such as low pH (2) and low concentration of H2S, can be explained by subsea-floor sulfide formation. The water-rock reaction zone is estimated to be about 1 km below the sea floor and 2 km above the magma chamber.Vertical mineralogical zonation within the mound differs from midocean ridge deposits but is similar to that of a kuroko deposit. At the surface of the deposit, the virtual absence of pyrite and the high amount of sphalerite, barite, tennantite, galena, and locally, native gold are remarkable. The distinctive chemical characteristics of deposits in each volcanic segment are explained by interaction with variable amounts of differentiated rocks.Compared to midocean ridges, Lau basin deposits are enriched in Ba, Zn, As, Pb, Ag, Au, and Hg and depleted in Mo, Se, and Co. Relative to young intracontinental back-are basins (e.g., Okinawa trough), the mineralizations are Pb and As poor. Their mineralogy, chemical composition, and geologic setting show that the southern Lau basin deposits are intermediate between oceanic and continental back-are deposits.