洋中脊热液系统成矿地质条件对比

COMPARATIVE STUDY OF METALLOGENIC GEOLOGICAL CONDITIONS BETWEEN BASALT-HOSTED AND ULTRAMAFIC ROCK-HOSTED HYDROTHERMAL SYSTEMS ON THE MID-OCEAN RIDGE

现代洋底热液作用具备多种形态、结构和岩石学组合特征。全球洋中脊附近发现的热液系统中多数与海底玄武岩相关。近年来,随着超镁铁质岩热液系统被证实是一种全新的热液系统,有关超镁铁质岩与玄武岩的热液系统之间的差异研究,成为了国际上对洋底热液作用研究的一个热点。洋中脊地区出现的玄武岩和超镁铁质岩是受不同地质因素控制的,因此,探讨不同地质因素对这两种热液系统的控制和影响,对于分析洋中脊地区热液作用的成因、分布乃至成矿都具有重要意义。针对这一课题,综述了前人有关洋中脊地区发育的玄武岩和超镁铁质岩热液系统的资料,从地质背景、围岩类型、热源供给、裂隙发育等方面进行了对比研究,提出了热源和裂隙分别受到洋中脊不同阶段的火山作用和构造作用所控制的观点:在洋中脊的火山作用阶段多发育以岩浆房为热源的玄武岩热液系统;而洋中脊的构造作用阶段更有利于沿裂隙发育超镁铁质岩热液系统。

Modern seafloor hydrothermal process occurs in a variety of morphological, structural and petro- logical settings. Most of the hydrothermal systems are found along the mid-ocean ridges with basaltic rocks as their host rock. In recent years, as the ultramafic-rock hosted hydrothermal system is confirmed as a new type of hydrothermal system, comparative studies of the difference between the ultramafic rock- hosted hydrothermal system and the basalt-hosted hydrothermal system on the seafloor become an interna- tional hot spot. The formation of basaltic and ultramafic rocks is controlled by different geological factors. Therefore, to reveal the influences of these geological factors on the formation of the two kinds of hydro- thermal systems is of significance to the study of their origin, distribution and mineralization. From this point of view, this article made a review on previous studies about the geological settings, host rocks, heat source and fissure development of the basaltic and ultramafic rock-hosted hydrothermal systems along mid- ocean ridge areas. Our results indicate that the heat source and fissure development are controlled by the development stages of mid-ocean ridge volcanism and tectonism. In the stage of volcanism, it is dominated by basalt-hosted hydrothermal systems with the heat source from axial magma chamber; while in the tec- tonic stage, ultramafic rock-hosted hydrothermal systems dominates along the deep fissures.