聚敛边缘的成矿演化

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聚敛边缘岛弧的成矿型式与弧壳的厚度及其岩石演化有关,其本身受岛弧岩石平均硅氧含量和弧壳平均厚度之间的正相关关系影响。一般来说,较厚地壳区的锡、汞、锑和氟含量极高。虽然矿床的组成主要受深部地壳和地幔特征的控制,但许多矿床的实际形状和类型,却受控于上地壳特征,特别是碳酸盐和硅酸盐围岩的相对丰度。浅成热液贵金属矿床通常与陆地、硅质火山作用有关,一般形成于岛弧演化的较晚期。如果岛弧火山作用过早中止,那么这类矿床就不存在,或者如果增厚的或热的洋壳的俯冲作用造成岛弧上部剧烈隆起及随后发生侵蚀,那么这类矿床就会被剥蚀而消失。同样,交代石灰岩的筒状-层状铅-锌-银矿床往往只赋存于有大面积厚的石灰岩单元的地体中,它们通常形成于浅水陆架环境。对聚敛边缘有些重要类型的矿床仍是知之甚少。原始海洋火山弧中的酸性硫酸盐矿床伴随形成于岛弧演化早期阶段的双峰火山岩套出现。虽然碱性斑岩铜矿的形成似乎更远离海沟,形成于斜俯冲期或岛弧回返期,但是它与钙-碱性斑岩铜矿密切相关(通常在同一火山岛弧中)。块状氧化铁矿床和相关的贱、贵金属矿化与岛弧演化后期形成的硅质岩浆有很大关系。除构造和岩石特征外,成矿型式还可反映出全球挤压机理,最主要的是全球海水缺氧性和板块重组。全球海水缺氧形成了缺氧底部水补给下伏含水层的深水环境,它有利于沉积喷气矿化,并能引起地下成矿作用。板块重组在上地壳造成拉伸环境和因早期俯冲板块而变化的洋壳有利于部分熔融的条件下,可引起成矿作用。 The metallogenic pattern of the convergent marginal island arc is related to the thickness of the arc shell and its rock evolution and is itself influenced by the positive correlation between the average silicon oxygen content of the island arc rock and the average thickness of the arc shell. In general, thicker crust regions have extremely high levels of tin, mercury, antimony and fluorine. Although the composition of the deposit is dominated by deep crust and mantle features, the actual shape and type of many deposits are controlled by the characteristics of the upper crust, particularly the relative abundance of carbonate and silicate rock. The epithermal precious metal deposits are usually related to the role of terrestrial and siliceous volcanoes and generally form in the later evolution of island arcs. Such deposits do not exist if the island arc volcano ceases prematurely, or if the thickening or thermal subduction of the oceanic crust causes a sharp uplift of the upper part of the arc and subsequent erosion, then the deposits are denuded disappear. Similarly, the tubular-stratiform Pb-Zn-Ag deposits that account for limestone tend to occur only in large areas of limestone units, which are usually formed in shallow shelf environments. There is still little known of some important types of deposits that converge on the margin. Acidic sulphate deposits in the original marine volcanic arc accompanied by a bimodal volcanic suite formed in the early stages of island arc evolution. Although alkaline porphyry copper appears to form farther away from the trench than was formed during a ramp-dip or island arc return period, it is closely related to calc-alkaline porphyry copper deposits (usually within the same volcanic island arc). The massive iron oxide deposits and associated basement and precious metal mineralization have a strong relationship with the magmatic magma formed at the later stage of island arc evolution. In addition to the tectonic and lithological features, the metallogenic pattern can also reflect the global squeeze mechanism, the most important is the global sea water anoxic and plate reorganization. Global seawater anoxic forms a deep-water environment that recharges underlying aquifers with anoxic bottom waters, favoring sedimentary jet mineralization and causing underground mineralization. Plate reorganization can lead to metallogenesis under the condition that the upper crust caused the stretching environment and the oceanic crust changed due to the early subducting sections favored the partial melting.
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