It has long been recognised that the deposition and deformation of the Phanerozoic cover in the Zagros Basin (mountains plus foreland) was strongly influenced by the reactivation of old tectonic fabrics in its basement. Facies boundaries and structures trending north-south and NW-SE can be attributed to the reactivation of Pan-African sutures and Najd faults which are exposed in the Nubian-Arabian Shield. However, to the east of a projection of the Oman line SWwards into the Rhub Al Khali Basin, cover structures have a NE-SW trend which is not seen in Arabia. This boundary may overlie a Pan-African suture between Arabia and India (Somalia or Pakistan). Data including magnetic intensities, geothermal gradients and isopach maps are used here to distinguish old faults which were reactivated in the basement from more recent faults formed in the cover by Zagros shortening. Old faults trending NW-SE are interpreted as having reactivated episodically since the Permo-Triassic opening of Neo-Tethys; perhaps more significantly, the basement faults that reactivated in the East Arabian Block since then trend north-south. The basement configuration is clarified by extending a modified East Arabian Block across the Zagros to an "East Arabian-Zagros block" in which the NW trend of the Zagros lies between two syntaxes. This suggests a new tectonic framework for the region. The repeated reactivation of basement faults throughout the East Arabian-Zagros Block controlled source rocks, traps and seals for the supergiant and giant oil and gas reserves which are present at various stratigraphic levels in different areas.