Submarine volcanics-hosted iron deposits refer to those that are hosted in submarine volcanic-sedimentary succession. They are one of the most important types of iron deposits in China. Almost all of these deposits are distributed in western China, and have received much attention in recent years. Most researchers consider them to be formed in an active continental margin. However, it is still poorly understood why these iron deposits were formed in minor active continental margins. This key issue is crucial to the prospecting for this type of iron deposits in future. The previous isotopic dating shows that iron mineralization is coeval with the ore-bearing volcanic rocks, which suggests that the iron deposits are genetically related to submarine volcanism. Studies of the ore-bearing volcanic rocks show that they are a succession of tholeiitic to calc-alkaline basalt-basaltic andesiteandesite-dacite-rhyolite association with arc-like geochemical signature of negative Nb, Ta and Ti anomalies coupled with positive εNd values, which implies that the primary magmas were derived from asthenospheric mantle, and experienced extensive crystal fractionation within the crust-level magma chamber. The above geochemical characteristics reflect partial melting of the mantle with no involvement of oceanic crust, which suggests a thermal structure of warm mantle-cool crust in the subduction zone. Considering the scenario that the iron deposits occur in submarine volcanic rocks in active continental margin, the authors hold that they resulted from high-angle subduction of oceanic lithosphere. The general characteristics and genesis of the submarine volcanics-hosted iron deposits can be plausibly interpreted by this thermal structure model. The formation of the early stage of high-salinity magmatic fluids was correlated to crystal fractionation in the magma chamber in a compressional setting, whereas the magmatic fluids mixed with sea water can be attributed to the releasing of magmatic fluids in an extensional setting. Furthermore, this model can also explain why submarine volcanics-hosted iron deposits are not associated with porphyry Cu deposits in one continental arc, and even if they occur in one continental arc in some special backgrounds, the submarine volcanics-hosted iron deposits are always located on the margin of the arc, whereas the porphyry Cu deposits are developed in the main arc.
张招崇,柴凤梅,谢秋红. 热幔-冷壳背景下的高角度俯冲:海相火山岩型铁矿的形成[J]. 中国地质, 2016, 43(2): 367-379.
ZHANG Zhao-chong, CHAI Feng-mei, XIE Qiu-hong. High-angle subduction in a thermal structure with warm mantle-cool crust: Formation of submarine volcanics-hosted iron deposits[J]. Geology in China, 2016, 43(2): 367-379(in Chinese with English abstract).