[S-CG54] Hard-Rock Drilling: Oman to Oceanic Lithosphere to Island Arc Formation and Beyond

[SCG54-13] Drilling the leading edge of the mantle wedge and the underlying metamorphic sole of the Samail Ophiolite: Hole BT1B, Oman Drilling Project

*Tomoaki Morishita¹, Peter B Kelemen², Judith Coggon³, Juerg Matter³, Michelle Harris⁶, Katsuyoshi Michibayashi⁴, Eiichi TAKAZAWA⁵, Damon A H Teagle³, Marguerti Godard⁷, Science Party Oman Drilling Project Phase I⁸ (1.School of Natural System, Colleage of Science and Technology, Kanazawa University, 2.Lamont-Doherty Earth Observatory, Columbia University, USA, 3.Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, 4.Shizuoka University, 5.Niigata University, 6.School of Geography, Earth and Environmental Sciences, Plymouth University, 7.Geosciences Montpellier, CNRS University of Montpellier, 8.Oman Drilling Project Phase 1 Science Party)

Keywords:Oman Drilling Project, Carbonatized Peridotite

Hole BT1B (23°21.861’ N, 58°10.957’ E) was drilled by the Oman Drilling Project (OmDP) on the north side of Wadi Mansah in the Samail ophiolite, Oman. OmDP is an international collaboration supported by the International Continental Scientific Drilling Program, Deep Carbon Observatory, NSF, IODP, JAMSTEC, and the European, Japanese, German and Swiss Science Foundations, with in-kind support in Oman from the Ministry of Regional Municipalities and Water Resources, Public Authority of Mining, Sultan Qaboos University, and the German University of Technology. Hole BT1B was cored from 6 to 23 March 2017, to a depth of 300.05 m. The outer surfaces of the cores were imaged and described onsite before being curated, boxed and shipped to the IODP drill ship Chikyu.

Hole BT1B sampled 3 bands of carbonated peridotite (listvenite) consisting of carbonates + quartz + Fe-oxyhydroxides, plus minor relict spinel ± chromian mica (fuchsite), 2 carbonate-veined serpentinite bands at 80-100 and 180-185 m depth, and then a few cm of ultracataclasite and 70 cm of fault gouge at 197 m depth, followed by 103 m of the metamorphic sole. Onboard Chikyu, core underwent X-ray computed tomography (CT) and multi-sensor logging, imaging and spectroscopy, macroscopic and thin section observations, physical properties measurements, and XRF, XRD and ICP-MS analyses. Listvenites formed and deformed viscously at < 150°C. Brittle deformation is recorded by older veins and generally younger breccias and faults. Listvenites are as dense as gabbros, with generally higher P-wave speeds. The metamorphic sole is composed of fine-grained to microcrystalline metasediments and metabasalts. Metasediments have qtz + plag and mica + amphibole layers, with minor epidote, and become less abundant and poorer in K downhole. Metabasalts are massive, with more epidote and less qtz & mica. Pleochroic blue-green actinolite and possible needles of pumpellyite in quartz suggest low T/P. Sediment and basalt compositions are similar, resembling alkali basalt.