THE INFLUENCE OF MAGMATIC PROCESS AND HYDROTHERMAL ALTERATION ON THE GEOCHEMICAL CHARACTERISTICS OF ABYSSAL PERIDOTITES

Abyssal peridotites usually occur at the end of the slow-ultraslow spreading ridges and the places near transform faults. Their exposure and the alteration thereby have important consequences to the rheology of oceanic lithosphere, the geochemical budgets of the ocean and the activities of microbial communities. They have undergone geological processes such as partial melting, reactions with the porous melt and penetrative seawater during the ascent from the upper mantle via the detachment faults. The geochemical characteristics of abyssal peridotites, therefore, are of importance in discussing their petrogenesis, serpentinization, generation of the ultramafic hosted hydrothermal system and hydrothermal mineralization. Based on the previous studies, we reviewed the exposure and alteration of abyssal peridotites along mid-ocean ridges systematically. The effects of magmatic processes and hydrothermal alteration on the geochemical characteristics of abyssal peridotites, together with the element mobility during alteration, are also discussed. Finally, we proposed that the REE pattern of abyssal peridotite is controlled by both the magmatic process and alteration. However, the magmatic process should be more significant than alteration on modifying the REE patternss.