Evidence for an Early and Sustained Mode of Diffuse Lithospheric Extension in the Central Arabian Flank of the Red Sea Rift System: Implications for Margin Structural Kinematics and Basin Development

The Red Sea rift (RSR) exhibits dissimilar rift character along-strike; sea-floor spreading has operated in the southern Red Sea since ~5 Ma while the continental lithosphere has not ruptured in the central and northern sections. To explore this contrast, we use apatite and zircon (U-Th)/He thermochronology and MATLAB-based modeling techniques to establish the time-temperature (t-T) history of extended continental lithosphere within the central Arabian rift flank (CARF). Trends in our (U-Th)/He age database identify multi-scale structural domains that accommodated diffuse extension within the CARF and controlled rift flank architecture with progressive rifting. Thermal modeling reveals a three-stage thermotectonic t-T history for the region. The Arabian-Nubian Shield experienced a Paleo-Mesozoic cooling event that brought the CARF terrane to a mid-to-upper crustal structural level where it remained thermally stable through the Mesozoic. With the onset of rifting, the CARF terrane was dissected and exhumed along numerous rift-parallel fault blocks from pre-rift flank depths of ~1.5 - 3.9 km. Minimal reheating paths in our models indicate the absence of common reheating mechanisms such as burial by significant accumulations of pre-rift volcanic or Paleo-Mesozoic sedimentary overburden thicknesses and / or increased heat flow in mid-to-upper-crustal levels from active rifting processes. Rifting in the CARF began with the onset of major extension ca. 23 Ma. This rift signal is mirrored elsewhere along the Red Sea Nubian margin and the southern Arabian rift flank in Saudi Arabia and Yemen, confirming that Red Sea rifting began concomitantly along the near-full length of the Red Sea - Gulf of Suez system. Since this time, block faulting, as opposed to rigid, regional flank uplift has been the dominant structural style in the CARF. Highly segmented rift flank dissection and widespread fault block exhumation, including synchronous development of the intra-marginal Hamd and Jizil half-grabens, created a ~200 km-wide zone of diffuse extension that endured for ~8 million years. Inboard RSR deformation begins near the coincident intersection of the Makkah-Medina-Nafud volcanic line with the Red Sea axial trough at 21 °N latitude and expands to the NW where it encompasses pre- and syn-rift grabens (e.g., Azlam and Tabuk) and defines a “deformed wedge” of diffuse continental lithosphere extension, altogether different from the relatively rigid southern Arabian margin.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California