Seismic Tomography of the Oman Ophiolite

• Applicant: Dr. Christian Weidle
• Subject Area: Geophysics
• Term: from 2016 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 314082754

Along the eastern passive continental margin of the Arabian plate, the world's largest and best preserved ophiolite is exposed atop the Oman Mountains. Its emplacement is related to obduction, a plate tectonic phenomenon whose dynamics are still poorly understood.In spite of being the best-studied ophiolite of the world - the area has been a field laboratory for geologists since the 1960s - rather little is still known about the internal structure of the Oman mountains and the 3-D geometry of the ophiolite. Geodynamic reconstructions of obduction and ophiolite emplacement are hitherto schematic and it is thus of utmost importance to constrain the geometry of a real ophiolite in order to improve these models. Few localized geophysical studies imaged the base of the ophiolite in Oman to 5 km depths but since the entire ~12 km thick sequence of oceanic rocks is exposed in the area, there must be significant lateral variations in their geometry. It is also entirely unknown in how far internal variations of both the oceanic as well as the undelying continental lithosphere have supported ophiolite emplacement.In order to investigate this we use data from a temporary seismic network in the Oman Mountains consisting of 50 broadband seismometers and with a network aperture of ca. 500 x 200km with an average station spacing between 20 and 60km. This data yield unprecedented options for seismic tomography of the world's reference ophiolite.The best methodical option to image the ophiolite - basically a high-velocity layer over slower continental crust - in 3-D on a regional scale is surface wave tomography based on observation of ambient noise and teleseismic earthquakes. Our network provides the required lateral density of observations to measure surface wave dispersion down to 3s period and to develop a 3-D anisotropic model of the lithosphere below northern Oman. The model is expected to give high lateral and vertical resolution of structural variations within the ophiolite and the underlying continental crust and mantle lithosphere. To constrain the latter, additional S-wave Receiver Function imaging will give detailed information on discontinuities within the formerly subducted continental mantle lithosphere.The new model will further our understanding in emplacement dynamics of ophiolite atop a continental margin, in reconstructing continental subduction prior to ophiolite emplacement and give insights in the present-day geodynamic setting of the Oman Mountains. Our endeavor is in various aspects complimentary to the pending ICDP Oman Drilling Project which will provide localized information of geological parameters which can serve as anchor points for our 3-D model. Vice versa, our model will allow to extrapolate localized observations into their regional framework and at the same time serve as a benchmark experiment between drill-core observation and seismic images of oceanic lithosphere in general.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Thomas Meier
• Cooperation Partner: Professor Dr. Frank Krüger