--> --> Early Tectonic Evolution of Oman: Insights from Clastic Provenance Data and Implications for the Structural Evolution of Arabia

AAPG Middle East Region Geoscience Technology Workshop

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Early Tectonic Evolution of Oman: Insights from Clastic Provenance Data and Implications for the Structural Evolution of Arabia

Abstract

Clastic sediment provenance studies (heavy minerals and zircon geochronology) of Huqf and base Haima Supergroup sandstones from Oman, integrated with sedimentological data, have allowed for a new understanding of basin paleogeography and plate tectonic setting and evolution during the Neoproterozoic-Early Paleozoic. Heavy minerals ratios offer information on the nature of the terranes exposed in the clastic sediment source areas, while detrital zircon geochronology offers information on their age, as well as the magmatic events in a basin. Integrated with other datasets can be applied to tectonics. Provenance of Neoproterozoic sandstones from Oman indicates the sand was derived from local basement sources, as well as other exotic sources from terranes exotic to Oman. The signal changes in the Early Cambrian, when new clastic sediment sources were incorporated into the system. The results have been compared to equivalent data from the Precambrian-Cambrian successions of west Arabia, India, Pakistan and Iran, to understand geographical provenance changes and paleogeography, and changes in geological time. The Ediacaran signal of Oman is comparable to that of Precambrian sandstones in India and eastern Afghanistan, supporting an East Gondwana affinity. It strongly differs from Ediacaran sandstones from west Oman and Arabia. The Cambrian signal is different from the Cryogenian-Ediacaran signal from East Oman, but resembles Ediacaran samples from West Oman and the UAE. Regionally, comparison with Cambrian-Ordovician samples from Pakistan, Iran, and west Arabia, shows similarities and the same pattern of strongly intermixed sediment sources. Based on these observations, and integration with hardrock and paleomagnetic studies in the literature, we support that the Neoproterozoic terranes of Oman formed at the edge of the Indian Shield in the Tonian, along with the Seychelles and northern Madagascar. The Neoproterozoic succession (Abu Mahara and Nafun Groups) was then deposited in a rift to passive margin setting (overprinted by oblique-slip tectonics). Simultaneously, a convergent or oblique transform margin occurred along west Oman and Saudi Arabia. A sequence of gradual basin closure is reflected in the Ara evaporites and Nimr continental clastics, while the base Haima clastics are post-tectonic sediments. We propose that collision of Oman and Arabia occurred only in the Early Cambrian, at the time of Gondwana consolidation, and that the final East-West Gondwana suture occurs along the Western (Angudan) Deformation Front, a Cambrian orogenic belt now buried in the subsurface of Oman. This was a narrow fold and thrust belt which formed a regional high during the Early Paleozoic, and supplied clastic sediments to the retro-and pro-foreland basins of Oman, Saudi Arabia and the UAE. Branches of this Cambrian deformation belt occur in the Huqf and Oman Mts outcrops. This has important implications for the understanding of the structural styles in the basins of Oman, and the petroleum systems of Oman and Arabia. The main structural lineaments in Oman are related to basement and early rift trends, reactivated during the Early Cambrian Orogeny and younger events. They differ from the trends of Arabia, formed during Ediacaran events of juvenile crust amalgamation along an active margin at the western margin of the Mozambique Ocean (Najd event).