Abstract
The Arabian plate has been converging with Eurasia for 20-30 Ma, currently at 2-3 cm/year. Convergence is manifested differently along strike, with collision and tectonic escape in the west (Anatolia) and subduction of Arabia beneath Eurasia in the east (Iran). The reason for these differences may reflect the greater density of the Arabian lithosphere in the east relative to that in the west. Five observations indicate that the eastern Arabian plate is more dense and thus easier to subduct than the western Arabia Plate: (1) the >1000 km-long, N-S trending Central Arabian Magnetic Anomaly (CAMA) marks a ~600Ma-old suture between E and W Arabia that (2) separates crustal tracts with distinct Neoproterozoic histories (850-750 Ma crust in the east, 850-570 Ma in the west); (3) E. Arabian (platform) crust is slightly thicker and more felsic than that of W. Arabia (shield) and thus more buoyant; (4) E. Arabia is underlain by thicker mantle lithosphere than W. Arabia; and (5) W. Arabia has a long history of uplift whereas E. Arabia has subsided throughout Phanerozoic time. We infer that regional variations in lithospheric thickness largely reflect the earlier stabilization (and onset of conductive cooling) of E. Arabia relative to W. Arabia, leading to the development of significantly thicker mantle lithosphere in the east relative to the west. This also explains why Arabia east of CAMA was inundated by shallow seas ~540 Ma ago and accumulated salt whereas Arabia west of CAMA did not, as well as the long history of subsidence of the Arabian Platform and uplift of the Arabian Shield. These differences in lithospheric thickness may have been further modified by thermal erosion in Cenozoic time due to Red Sea rifting and the Afar hotspot.
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