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New Rock Magnetic Analysis of Ultramafic Cores from the Oman Drilling Project and Its Implications for Alteration of Lower Crust and Upper Mantle
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  • Gilbert Hong,
  • Jessica L Till,
  • Annika Greve,
  • Sang-Mook Lee
Gilbert Hong
School of Earth and Environmental Sciences, Seoul National University

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Jessica L Till
University of Iceland
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Annika Greve
Utrecht University
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Sang-Mook Lee
School of Earth and Environmental Sciences, Seoul National University
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Detailed rock magnetic analyses of ultramafic rock samples recovered from the Wadi Tayin massif as part of the Oman Drilling Project provide a unique opportunity to understand the magnetic properties of oceanic lithosphere and its alteration since obduction. We examined 300 - 400-meter-long cores from 3 sites (BA1B, BA3A, and BA4A) that transected the crust-mantle boundary. Serpentinization which produces a small amount of magnetite from olivine alteration appears to play an important role in shaping the magnetic signature of the rocks recovered from these holes. Our investigation reveals new features which have not been reported in previous studies of ophiolite largely based on surface rock samples. It appears that when serpentinization reaches a certain point (65%) a sharp increase in magnetic susceptibility occurs. In general, the uppermost section (0 – 40 m) shows higher susceptibility than the deeper part. Also, higher susceptibility is found in dunite-dominated sections than those composed of harzburgite. Overall, our observations indicate that mantle rocks of Semail ophiolite were produced by multi-stage hydrothermal alterations.