Rock magnetism and magnetic minerals as evidence for low-temperature fluid-rock interaction within serpentinized peridotites of Semail Ophiolite

Abstract:

Semail Ophiolite is one of the largest ophiolite complex that preserves past oceanic lithosphere and extensive obduction structures and imposes immense scientific potential. Thus, intensive drilling and core description was held along unexplored parts of the ophiolite under the name of Oman Drilling Project. As a part of the project, serpentinized peridotite cores were obtained from 3 boreholes located at Wadi Lawayni, Oman and intensive analysis was performed upon 50 samples per each core. Initial physical property measurements were done during core logging onboard D/V Chikyu in 2018. Further magnetic experiments such as AF and thermal demagnetization were conducted at University of Iceland. Mineralogical and chemical observations including analysis on atomic weight percentage and grain size were done using JEOL JSM-7100F scanning electron microscope at Seoul National University.

Here we present some of the notable results that reveal meaningful correlations between magnetic properties and mineral structure. For example, while magnetic susceptibility generally remains low throughout the measured samples, unusually high values (>0.02 SI) were observed in certain depth intervals. Microscopic images indicate that the magnetic minerals incorporated in such intervals share common characteristics in grain density, structure and composition. Magnetic measurements also reveal positive correlations with permeability and porosity. These observations are apparent evidences for low-temperature hydrothermal alterations and implies that Fe(III) was transported intensively via fluid intrusions during the serpentinization process.