The origin of the Bir Zreir rhomb‐shaped graben, eastern Sinai

Abstract

The Bir Zreir Graben, a rhomb‐shaped depression located in eastern Sinai is well exposed in three dimensions. A nearly horizontal nonconformity between Precambrian crystalline basement and overlying Phanerozoic sediments, contacts of basement plutons and a system of early Miocene basaltic dikes permit very precise mapping of the local structures and the determination of vertical and horizontal displacements along faults. Applying the standard “pull‐apart model” to the Bir Zreir rhomb‐shaped graben predicts greater vertical separations, 3 to 6 times larger, than those observed. An alternative model, based on a rotational movement of the Bir Zreir block, agrees more closely with field evidence. It is concluded that the shape and size of the graben was determined by the original fault pattern, and that its final shape was changed relatively little by later movements. The rotation of the Bir Zreir block resulted from a combination of sinistral displacement along N‐S faults, a change of their trend to NNE, and a regional E‐W extension. The model proposed here does not require the presence of large, deep gaps along the diagonal faults as in “pull‐aparts”.