[S-CG41] Hard-Rock Drilling Science: From Continental to Deep Sea Drilling, and Oman Project

[SCG41-P07] Serpentinization in the Salahi mantle section, the Oman Ophiolite

*Yohki YOSHIBA¹, Eiichi TAKAZAWA^1,2 (1.Faculty of Science Niigata University, 2.Japan Agency for Marine-Earth Science and Technology)

Keywords:Oman ophiolite, serpentinization, mantle section, hydrous alteration, antigorite

The Oman ophiolite is presumed to be an oceanic lithosphere formed in Neo-Tethys Sea during the late Cretaceous and settled at the eastern end of the Arabian Peninsula through an uplift process associated with subduction. The peridotites of the Oman ophiolite are subject to serpentinization with various degree, and the Salahi mantle section is no exception. In this study, we observed the process of serpentinization recorded in the peridotites from the central part of the Salahi mantle section to the Moho transition zone. The samples used in this study have a relatively low degree of serpentinization, which is suitable for studying the process of hydrothermal alteration of marine lithosphere at an earlier stage.

The results of microscopic observation of altered minerals and identification of mineral species by laser Raman spectroscopy indicated that all samples underwent low temperature type serpentinization. In addition, antigorite, a high-temperature serpentine and talc were widely distributed, and tremolite and chlorite were observed in some samples. These results suggest that there was hydrothermal alteration at 400-900 °C. Moreover, the preservation of the mesh structure and bastite, and the cutting of minerals stable at high temperatures by minerals stable at lower temperatures, suggest that these rocks underwent hydrothermal alteration with a gradual decrease in temperature and serpentinization beneath the ocean floor. The source of the water seems to be hydrous fluid infiltrated from the basal thrust, or seawater supplied along faults in the crustal section.