Zvi Garfunkel

Internal structure of the Dead Sea leaky transform (rift) in relation to plate kinematics

Abstract The structures along the Dead Sea transform (rift) are related to the motions of the Sinai and Arabia plates which border it, and to the irregularities of their boundaries. The total slip was 105 km left-lateral, but the present structures were formed mainly during the last 40 km of slip, which probably occurred in the Plio-Pleistocene. Along the southern half of the transform the strike-slip motion takes place on en-echelon faults. This produces rhomb-shaped grabens or pull-aparts, which are sometimes composite, and in which there is local crustal separation. Thus, much of the transform is “leaky”. These structures occur in a morpho-tectonic “rift-valley” delimited by normal faults, which express a small component of transverse extension. Along a few segments the shape of the transform is such that lateral motion produces local transverse compression. The geometric relations of the structures along the transform define an Eulerian pole of relative plate motions at 32.8° N 22.6° E ± 0.5° . The older motion was somewhat different and is described by a pole located about 5° west of the above. Then the component of transverse extension and crustal separation was much smaller than now, while local transverse compression was more important. The northern half of the Dead Sea transform has an irregular shape, and the bordering plates did not remain rigid as lateral motion continued. Here transverse compression is often important.

The Shear along the Dead Sea Rift [and Discussion]

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.Recent surface and subsurface geological investigations in Israel and Jordan provide new data for the re-examination of Dubertrets (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

Active faulting in the dead sea rift

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Plate kinematics of the circum Red Sea—a re-evaluation

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.

The structure of the Dead Sea basin

Abstract Manifestations of Late Quaternary and Holocene faulting were studied in a 500 km long segment of the Dead Sea transform (rift). Most prominent are left-slip faults, whose characteristic physiographic features are recognizable along most of the studied segment. Where these faults bend or are stepped to the left, rhomb-shaped grabens (or pull aparts) are produced, forming depressions. In the reverse situation compressional features such as pressure ridges, domes and folds form positive topographic features. Such structures are combined on a variety of scales ranging from a few hundred meters long to tens of kilometers. Normal faults, sub-parallel to the left slip faults, produce a trough-like valley along much of the Dead Sea transform, but are most prominent along the margins of the large rhomb-grabens, e.g., the Dead Sea trough. They apparently record a small component of transverse extension. Generally, their motion is slow: young slip did not occur along some segments during the last few 10 4 y. Elsewhere throws of 10–20 m at least occurred in this period. The Dead Sea transform is seismically active. The instrumental and historic records indicate a seismic slip rate of 0.15–0.35 cm/y during the last 1000–1500 y, while estimates of the average Pliocene—Pleistocene rate are 0.7–1.0 cm/y. Either much creep takes place, or the slip rate varies over periods of a few 10 3 y.

CONSTRAINS ON THE ORIGIN AND HISTORY OF THE EASTERN MEDITERRANEAN BASIN

Abstract Instantaneous and finite kinematic models of plate motions in the Red Sea area were constructed based on a re-evaluation of the plate boundaries in the Afro-Arabian rift system. The kinematic analysis is a useful way to integrate data from all parts of the system in order to better define its overall history. The most important new aspect of the models is the treatment of the Dead Sea transform as a leaky, or transtensional, feature. The detailed structure of the transform allows accurate location of the Eulerian poles of its young (0–5 Ma) and total (0–25 Ma) motion at (32.8°N, .22.6°E) ±0.5° and (32.7°N, 19.8°E) ±2°, respectively. This constrains the Red Sea opening pole to (32.5°N, 24.0°E) ±2°; only such locations predict geometries of Suez rift opening compatible with its structure. The Gulf of Aden pole is relocated at (24.5°N ± 0.5 °, 26.0 °E ± 2 °), about 5° southeast of previously accepted positions. The small differences between pole positions proposed here and previously accepted ones create significant shifts in the motions on the various rifts which are essential in the construction of self-consistent kinematic models compatible with the known geologic constraints. The kinematic analysis shows that (1) about 30 km of displacement has occurred along the Dead Sea transform in post-Miocene time, 10–15 km less than hitherto accepted, and (2) the opening of the Red Sea and Gulf of Aden has been less than their widths. Diffuse stretching and intrusional expansion amounting to about 200 km of plate separation took place in these basins prior to the initiation of centralized seafloor spreading as characterized by lineated magnetic anomalies. This suggests that the thinned continental crust and block fault structures of a mature continental margin are developed largely in an early stage of ocean evolution. The diffuse extension phase in the Red Sea has lasted longer where plate separation has been slow, but the amount of total extension prior to seafloor spreading has generally been about 250%, irrespective of the rate of plate separation.

Back arc extension and denudation of Mediterranean eclogites

Abstract The Dead Sea basin is located along the left-lateral transform boundary between the Arabian and Sinai plates. Its structure and history are known from surface geology, drilling, seismic reflection and other geophysical data. The basin comprises a large pull-apart, almost 150 km long and mostly 8–10 km wide, which is flanked by a few kilometres wide zones of normal faulting. The basin formed at about 15 Ma or earlier, close to the beginning of the transform motion, and it reached about half its present length before the end of the Miocene. A strong negative gravity anomaly records a thick sediment basin fill: > 5 km under half its length, reaching a maximum of ≥ 10 km. The fill includes a few km of salt (ca. 6-4 Ma) which forms several diapirs. At any one time large parts of the basin subsided simultaneously, but the site of fastest subsidence seems to have shifted northward. Sedimentation rates reached at least hundreds of metres per million years or more in the Miocene, and ≥ 1 km/Myr in later periods. The basin structure is dominated by longitudinal faults: intrabasinal faults which delimit the pull-apart and which are the extensions of the major strike-slip faults north and south of the basin, and normal faults which extend along the basin margins. The latter faults express a small component of extension across the basin, whereas the pull-apart resulted from the much larger lateral motion along the basin. In addition, transverse faults divide the pull-apart into several segments with somewhat different histories. The pull-apart grew by becoming longer parallel to the transform motion. At shallow levels this was probably achieved by normal slip on transverse listric faults while the fill between them was little deformed. The crust under the basin was stretched and thinned during basin lengthening, which caused its subsidence. Basin formation was accompanied by uplifting of its flanks by ≥ 1 km. Sparse igneous activity occurred along the basin and its flanks. Its presence suggests a thermal anomaly in the lower lithosphere beneath the basin and adjacent parts of the transform.

Sediments and structure of the Gulf of Elat (Aqaba)—Northern Red Sea

Abstract The basin formed along the northern passive margin of Gondwanaland as a relict of the Mesozoic Neotethys in early Mesozoic time. Though direct information from the basin itself is meagre, the geology of its passive margins and the regional framework of the Tethys evolution constrain the formation and history of the basin. The Eastern Mediterranean and its passive margins are interpreted to have formed as a result of several faulting and continental breakup phases from Early Permian to Middle Jurassic times, before Pangaeas complete disintegration. This led to the detachment of the Eratosthenes and Tauride blocks from the margins of the Levant and Herodotus basins, respectively. The latter merged in the northeast with the Cyprus basin that extended along Arabias northern margin. The main rifting probably occurred in the Triassic, leading to seafloor spreading in the Herodotus and Cyprus basins, while along the Levant margin important rifting also occurred in the Jurassic. During the initial rifting stages extension perpendicular to the Levant margin was important, but subsequently the Tauride block drifted mainly northward. The existence of the passive margins and slopes of the Eastern Mediterranean is documented at least from the end of the Middle Jurassic. Until then the basin was probably narrow (≤200–300 km?), but during the main phase of the Africa–Laurasia separation it grew to twice its present width, or more. This scenario depends critically on the interpretation that the Tauride block was originally located next to northeastern Africa on the western side of the Eratosthenes block. Plate convergence and consumption of the northern portion of the basin have taken place since mid-Cretaceous times, but the active convergent boundary on its northern side formed only in the Neogene by modification of earlier structures. Some intra-plate deformation also took place, especially in the Neogene, but it hardly changed the original configuration of the remaining portion of the basin.

Model for the Late Cenozoic Tectonic History of the Mojave Desert, California, and for Its Relation to Adjacent Regions

Eclogite-facies rocks exposed in Mediterranean back arcs are delimited from above by low-angle normal faults and detachments. Nevertheless, our work demonstrates that these extensional structures associated with back arc extension played only a limited role in removing the overburden from above the eclogites. Extension in Mediterranean back arcs began in the late Oligocene or early Miocene, but the pressure - temperature - time (P-T-t) paths of eclogite-facies rocks exposed in these areas indicate that a major part of the overburden, several tens of kilometers, has been removed from above these rocks prior to the Oligo-Miocene. We show that the time period bracketed between the peak of eclogite metamorphism (Eocene in the central Aegean, probably Upper Cretaceous in Corsica and the Betics) and the onset of back arc extension in the Oligo-Miocene was characterized by thrust faulting. In the central Aegean, Corsica, and the Betics, eclogite-bearing units were partly unroofed and then overthrusted lower-pressure units. We emphasize that, with one exception (Tinos island, Greece), the entire inventory of extensional contacts operated subsequently to the overthrusting of the eclogites above the lower-grade sequences. Thus Mediterranean back arc extension lags behind a major part of the denudation process, and is superposed on orogenic wedges that contain eclogite-facies rocks at relatively shallow structural levels. We emphasize that the mode of occurrence of eclogites in Mediterranean back arc regions involves a continuum of in-situ crustal accretion below the eclogites, widespread P-T paths that show cooling or isothermal decompression, and lower-grade rocks at the bottom of the structural pile. Thus instead of reflecting whole - crust back arc extension, the tectonic style associated with the denudation of Mediterranean eclogites better fits an active accretionary-wedge setting. This is similar to the mode of occurrence of eclogite-facies rocks in mountain belts, such as the western Alps, where decompression was synorogenic and back arc extension played no role.

Uplift and exhumation of high-pressure metamorphic terrains : the example of the Cycladic blueschist belt (Aegean Sea)

Abstract The Gulf of Elat (Aqaba), about 180 km long and 15–25 km wide, comprises the southern part of the Dead Sea rift. Its floor is up to 1850 m deep, about 4 km below the neighbouring mountains on land. The Gulf occupies a fault-controlled depression, partly filled by sediments. The structure of the Gulf is dominated by en-echelon faults which delimit three elongated basins that strike N20–25°E. Sedimentation in these basins was syn-tectonic. Their fill consists of turbidities and, pelagic deposits. The recorded thicknesses reach 2–3 km, without reaching basement. The fill extends to more than 7 km below adjacent lands when corrected for erosion. In parts of the basins deformation was fast enough relative to sedimentation as to deform the seafloor. Flexures, arches and small folds were formed. In the southern part of the Gulf sharp upright folds, which form prominent hills, may be of diapiric origin. The basins are flanked by marginal blocks, which are much wider on the western side of the Gulf of Elat than on its eastern side, which consists of a very steep slope. The marginal blocks on the west sometimes form topographic terraces. Alluvial fans and submarine cones are conspicuous on the west side of the Gulf, but are virtually absent on the east side. It seems that the present shape of the Gulf was acquired during the last stage of movement on the Dead Sea rift, when left lateral slip of about 40–50 km took place. Tectonism was strongest in the basins and on the faults which flank them, but the marginal blocks are also involved in active tectonism.