Characteristics Of Mid-ocean Ridge Rocks Alteration And Mineralization

Alteration is a common geological phenomenon in the seabed.During the alteration process,a large number of metals in rocks enter the sea water and participate in seabed,leaving "imprints" related to polymetallic mineralization in rocks.Rock alteration in the mid-ocean ridge is not only an important subject of marine geoscience research,but also of practical significance for guiding the exploration of polymetallic resources.In this paper,rock samples from the Mid-Ridge of the South Atlantic and the Mid-Ridge of the Northwest Indian Ocean are selected as research objects,and secondary mineral assemblages,metamorphic facies,alteration types and alteration degree are studied.It is found that basalts are generally fresh,and the secondary alteration minerals are mainly saponite,chlorite and other clay minerals,as well as a small amount of orange basalt glass,which belong to the typical brown facies.The contact metamorphic gabbro alteration minerals are mainly saponite and a small amount of pyrite,and the alteration fluid is low-temperature reducing fluid after mixing seawater and high-temperature fluid.In dynamically metamorphic gabbro,clinopyroxene altered into tremolite + actinolite,belonging to amphibolite facies.Serpentinization is common in peridotite samples,in which pure peridotite alteration minerals are mainly serpentine and magnetite;peridotite in gabbro alteration into serpentine + magnetite,pyroxene alteration into sericite,talc,and tremolite + actinolite.Five alteration stages can be identified in some gabbro,the highest being amphibolite facies.Secondary sulfides dominated by pyrite have been found in gabbro samples from the mid-ridge of the Northwest Indian Ocean,providing direct evidence for the influence of hydrothermal activity.Based on previous studies,the grape stone in mylonite in the Tianxiu hydrothermal area of the Northwest Indian Ocean may be an indicator of hydrothermal activity.