Kelemen, P.B., Matter, J.M., Teagle, D.A.H., Coggon, J.A., et al., 2020 Proceedings of the Drilling Project

Introduction to Science Theme 1A: gabbro traverse1 Kelemen, P.B., Matter, J.M., Teagle, D.A.H., Coggon, J.A., and the Oman Drilling Project Science Team2

Keywords: Oman Drilling Project, OmanDP, ophiolite, Zihlmann-Muller Fault Zone, Wadi Gideah, Gabbro Traverse, Site GT1, Site GT2, Site GT3

Chapter contents Gabbro Traverse

Gabbro Traverse ...... 1 Wadi Gideah, in the Wadi Tayin Massif, is the best site for study of an intact crustal section in the Samail ophiolite (Fig. F1). The sec- References...... 1 tion is well mapped by the US Geological Survey, the Oman Geo- Figures...... 2 logical Survey, the Nicolas group at the Université de Montpellier II, and Professor Tjerk Peters of the University of Bern, Switzerland (Fig. F2). Recently it has been the focus of renewed research activ- ity including an extensive sampling program by Oman Drilling Project (Oman DP) investigators Koepke, Garbe-Schonberg, and Müller and hydrothermal research by Teagle, Kelemen, and Zihl- mann, as well as other teams. Wadi Gideah drains southward from the Jabal Dimh drainage divide north of the crust–mantle transi- tion. Around the wadi, the crustal section dips gently to the south, exposing deeper levels upstream to the north and shallower levels to the south, culminating with submarine lava flows in the “Ibra syncline.” Two sites of the Gabbro Traverse were drilled within Wadi Gideah during Phase 1 of the OmanDP, Sites GT1 (layered gabbros) and GT2 (foliated gabbros). It was initially proposed to drill the dike–gabbro transition at the southern end of the Wadi Gideah where it opens out on to the Ibra Plain, but a suitable loca- tion could not be identified. Consequently, Site GT3 was relocated to Wadi Abda (23°06.845’N, 58°12.703’E) about 40 km northwest (see the Site GT3 chapter). 1 Kelemen, P.B., Matter, J.M. Teagle, D.A.H., Coggon, J.A., and the Oman Drilling Project Science Team, 2020. Introduction to Science Theme 1A: gabbro traverse. In Kelemen, P.B., References Matter, J.M., Teagle, D.A.H., Coggon, J.A., et al., Hopson, C.A. et al., 1981. Geologic section through the Samail ophiolite Proceedings of the Oman Drilling Project: College and associated rocks along a -Ibra transect, southeastern Oman Station, TX (International Ocean Discovery Mountains. Journal of Geophysical Research, 86(B4):2527–2544. Program. doi:10.1029/JB086iB04p02527 https://doi.org/10.14379/OmanDP.proc.2020 2OmanDP Science Team affiliations. Nicolas, A, Boudier, F., Ildefonse, B., Ball, E., 2000. Accretion of Oman and ophiolite—Discussion of a new structural map. MS OmanDP-105 Marine Geophysical Researches, 21:147–180. Published 24 April 2020

P.B. Kelemen et al. Introduction to Science Theme 1A

Figure F1. Geological map (after Nicolas et al., 2000) and ophiolite stratigraphic column showing the locations of all Oman Drilling Project boreholes.

Sediments 0 0 20 40 km 24°00' Lavas 24°00' 58°00' City/Town Gabbros & extrusives Sheeted Dykes OmanDP drill site 1 Depth (km) Site not permitted Peridotites Vari-textured Gabbros GT3 Plagiogranite Al Suwayq Site rejected by Metamorphic sole 2 scientists Hawasina formation Foliated Gabbros Barka 3 Crust GT2 Muscat 4

Rustaq BT1 Layered Gabbros BT1 Al Hajar 5 GT1 Samail 6 MD1 Crust-Mantle GT3 Transition CM1&2 23°00' 7 23°00' Tectonised Nizwa BA2 Mantle Peridotites CM1 & 2 GT1 BA1 8 GT2 BA1 Dunites BA3 GT3 BA4 BA1-4 ~10 Ibra Mantle ~15

~20 57°00' 58°00' BT1

Figure F2. Geological cross-section from north (Muscat) to south (Ibra and the Wahiba Sands), showing the Ibra dome and Tayin Massif (marked on the section as Jabal Dimh) of the ophiolite (after Hopson et al., 1981).

IBRA DOME JABAL DIMH JABAL ABYAD SAIHHATAT MUSCAT S N Sea level

Salt? 5 km Rock types Hawasina Formation Samail Ophiolite crustal rocks Samail Ophiolite peridotite Samail Ophiolite dunite Para-autocthonous platform carbonates Early Paleozoic and Saih Hatat metamorphic rocks

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