2:45 PM - 3:00 PM
[MIS08-17] Drilling of crust-mantle transition zone in Wadi Tayin massif, the Oman ophiolite
Keywords:ophiolite, ICDP, Oman Drilling Project, upper mantle, lower crust, Moho discontinuity
Hole CM1A (UTM: 40Q 637000E, 2533870N) is an inclined hole, 60 degrees northward. The cores of 404.15 m in length was recovered. The top 160 m of the borehole is mainly composed of layered gabbro and is locally interlayered with melanocratic layers rich in olivine. The middle part from 160 to 310 m is mainly composed of massive dunite, accompanied by a small amount of gabbro and wehrlite. The top of the MTZ is located at 160 m where rock lithology dramatically changes. Several ten’s centimeters thick fracture zones with fault gouges often develop in the upper part of MTZ, and the peridotite is severely serpentinized. The lower part of the MTZ of 150 m in thickness seems less serpentinized because the equigranular texture of olivine is more visible and crystals are reflective. Furthermore, the first harzburgite appeared at 310 m reaching the bottom of MTZ. The deeper part corresponds to the mantle section. Even after the appearance of harzburgite, dunite dominates harzburgite from 310 m to 362 m. Hole CM1 B is a vertical rotary borehole of 237 m deep, located 3 m south of Hole CM1A. Geophysical logging has been scheduled using this borehole. The comparison with the oceanic Moho and integrated analysis of core and logging will be done.
Hole CM2A (UTM: 40 Q 637000 E, 2534270 N) is a vertical hole located 400 m north from Hole CM1A, and a core of 300 m in length was recovered. Drilling started from the upper part of the MTZ, the first harzburgite appeared at 140 m and reached the mantle section. From 140 to 300 m the cores consist mainly of harzburgite and dunite with a small amount of gabbro. It is stratigraphically comparable with Hole CM1A with a marker at the lower boundary of MTZ defined by the first appearance of harzburgite. Hole CM2B is drilled parallel to Hole CM2A and geophysical logging has been scheduled.