A discussion on the structure and evolution of the Red Sea and the nature of the Red Sea, Gulf of Aden and Ethiopia rift junction - The shear along the Dead Sea rift (original) (raw)

1970, Philosophical transactions of the Royal Society of London

Recent surface and subsurface geological investigations in Israel and Jordan provide new data for the re-examination of Dubertret's (1932) hypothesis of the left-hand shear along the Dead Sea rift. It is found that while none of the pre-Tertiary sedimentary or igneous rock units extend right across the rift, all of them resume a reasonable palaeographical configuration once the east side of the rift is placed 105 km south of its present position. It is therefore concluded that the 105 km post-Cretaceous, left-hand shear along the Dead Sea rift is well established. The 40 to 45 km offset of Miocene rocks and smaller offsets of younger features indicate an average shear movement rate of 0.4 to 0.6 cm a-1 during the last 7 to 10 Ma. Unfortunately, the 60 km pre-Miocene movement cannot be dated yet. Along the Arava and Gulf of Aqaba and in Lebanon the shear is divided over a wide fault zone within and outside the rift. H istorical r e v ie w The verse '.. . and the Mount of Olives shall cleave in the midst thereof towards the east and towards the west,.. . and half of the mountain shall remove towards the north, and half of it towards the south' (Zechariah, xiv. 4), can probably be regarded as a description of left-hand shear by an ingenious observer who lacked the professional terms. One century ago Lartet (1869) noticed that Arabia and Africa might have drifted apart in an oblique left-hand direction to open up the Red Sea. About 60 years later Dubertret (1932), following Lartet's idea, advocated also by Bogolepov (1930) and von Seidlitz (1931), suggested that a 160 km left-hand shear along the Dead Sea rift, associated with a 6° rotation between Arabia and Africa, might explain several structural relations in the Levant. Wellings (in Willis 1938) realized that this hypothesis corresponds to the offset of the marine Cambrian and Jurassic beds across the rift south of the Dead Sea. Willis, however, rejected this hypothesis, and during the following 20 years it was completely neglected in papers about the geology of the Levant (e.g. Picard 1943; Dubertret 1947). It was not mentioned even in papers which discussed other strike slip faults in this region (Bentor & Vroman 1954; Renouard 1955; Vroman 1957). Quennell (1958, 1959) revived Dubertret's hypothesis, though to his opinion the shear amounts to 107 km as indicated by the offsets across the rift of a Precambrian porphyry body, of Cambrian limestone, copper and manganese sandstone, of marine Triassic and Jurassic beds, of the southern extent of the marine Albian and the Upper Cretaceous transgressions, of Senonian bituminous chalk, and of three pairs of transverse faults. Quennell suggested that a Pleistocene movement of 45 km explains several geomorphic features, the most prominent of which is the shape of the deep depression of the Dead Sea. The remaining 62 km shear was in his opinion of Miocene age.