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Multichannel seismic reflection profiles, gravity measurements, and bathymetric soundings, in conjunction with field geological reconnaissance and remote sensing images, reveal with unprecedented detail the morphostructure of a major segment of the South America–Scotia plate boundary in the Tierra del Fuego region. This segment, known as the Magallanes‐Fagnano fault system, is a continental transform margin arranged in an en echelon geometry, along which prominent asymmetric basins were developed. Data acquired off the Atlantic coast of Isla Grande (the main island of Tierra del Fuego), in its central and eastern part, and in the central and western Magallanes Strait image the surface and subsurface structure of the transform fault and its associated basins. The Magallanes‐Fagnano fault system is composed of distinct tectonic lineaments that are segments of the transform system and are represented by mostly near‐vertical faults. In the Atlantic sector, the fault system trends broadly N70°E and seems to be composed by a single master fault, along which a highly asymmetric basin has formed. At around 63°W, the fault terminates by splaying into secondary normal faults that dissipate the horizontal displacement along the system. In the central eastern part of Isla Grande, the fault segments have been principally identified from analyses of remote sensing images on the basis of their morphological expression. These segments are located within river valleys and are generally associated with localized gravity minima. Lago Fagnano, a 105‐km‐long, E‐W trending depression, is a large, mostly asymmetric pull‐apart basin developed within the principal displacement zone of the Magallanes‐Fagnano fault system. Restraining bends and overlapping step‐over geometry characterize the central part of the Magallanes Strait. Along the western part of the fault system, in the vicinity of the Pacific entrance of the Magallanes Strait, asymmetric sedimentary basins have also developed. The sedimentary architecture of the basins formed within the principal displacement zone of the fault, in which the thick end of the depositional wedge abuts the transform segment, suggest simultaneous strike‐slip motion and transform‐normal extension, a common feature found in other continental transtensional environments. Strike‐slip faulting in the Tierra del Fuego region is also documented along other prominent lineaments which parallel the Magallanes‐Fagnano fault system. Along at least two of these lineaments, characterized by a remarkable morphological expression, widespread Quaternary activity occurs. The present‐day motion between the South America and Scotia plates is slow (<5 mm/yr). Also the modern seismicity monitored in the Tierra del Fuego region is low (individual events <3.5 in magnitude). The low seismicity may be explained by the slow relative motion between plates and may be further affected by slip partitioning along the different segments which make up the Magallanes‐Fagnano fault array, and along the subsidiary wrench lineaments that...

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The Gulf of Elat (Aqaba) occupies the southern part of the Dead Sea rift. The rift is considered to be a plate boundary of the transform type (partially leaky) which connects seafloor spreading in the Red Sea with the Sagros‐Taurus zone of continental collision. The deep water in the Gulf of Elat, up to 1850 m, provides a rare opportunity to examine the process of continental rifting by marine geophysical techniques. The bathymetry alone provides much information about fault patterns in this area. The fragmentation of the once continuous Arabian‐African platform is a complicated process. It shapes the structure of the gulf which has developed through continuing tectonism, primarily consisting of faulting. Recent geophysical and geological studies of the Gulf of Elat including bathymetry, bottom photographs, continuous seismic profiles, seismic refraction, gravity, magnetics, heat flow, and coring provide new information about the shallow and deep crustal structure of this important segment of the world rift system. The shallow structure of the gulf is dominated by three elongated en echelon basins, which strike N20°–25°E. Undulations in the floors of the basins produce several distinct deeps. These basins are interpreted as pullaparts. The new data from the gulf suggest that classical models for the formation of these structures should be modified. Only one of the longitudinal faults of each depression is a strike‐slip fault, while the other is predominantly a normal fault. The situation with the other two sides of the basin which are supposed to be composed of normal faults may also be more complex than previously thought. At least in one case, one such boundary is composed of a strike‐slip fault while the other has no significant fault. Crustal models of the Gulf of Elat based on gravity data indicate that the basins are rather shallow and do not extend into the lower crust. The fill of the basins extends to about 5 km below the seafloor in. the northern and southern basins and less in the central basin. Most significant magnetic anomalies in the Gulf of Elat extend from land into the sea. None of them, however, extends from one coast to another across the gulf. This supports the geological evidence for a shear between the Arabia and Sinai plates. The magnetic field over the southern third of the gulf is rather smooth and markedly different from that of the other parts. The nature of the magnetics, the crustal structure of the western margin, and the heat flow values indicate a thinner crust and different tectonic processes in the southern part of the gulf. Overall, it seems that within the southern Gulf of Elat a transition occurs between crustal spreading that takes place in the Red Sea to a rifting without spreading that takes place along the Dead Sea transform. Spreading activity propagates from south to north. The most active place is the central basin which is being propagated northward into the shallow northern basin.

S U M M A R YAs part of the DEad Sea Integrated REsearch project (DESIRE) a 235 km long seismic wideangle reflection/refraction (WRR) profile was completed in spring 2006 across the Dead Sea Transform (DST) in the region of the southern Dead Sea basin (DSB). The DST with a total of about 107 km multi-stage left-lateral shear since about 18 Ma ago, accommodates the movement between the Arabian and African plates. It connects the spreading centre in the Red Sea with the Taurus collision zone in Turkey over a length of about 1 100 km. With a sedimentary infill of about 10 km in places, the southern DSB is the largest pull-apart basin along the DST and one of the largest pull-apart basins on Earth. The WRR measurements comprised 11 shots recorded by 200 three-component and 400 one-component instruments spaced 300 m to 1.2 km apart along the whole length of the E-W trending profile. Models of the P-wave velocity structure derived from the WRR data show that the sedimentary infill associated with the formation of the southern DSB is about 8.5 km thick beneath the profile. With around an additional 2 km of older sediments, the depth to the seismic basement beneath the southern DSB is about 11 km below sea level beneath the profile. Seismic refraction data from an earlier experiment suggest that the seismic basement continues to deepen to a maximum depth of about 14 km, about 10 km south of the DESIRE profile. In contrast, the interfaces below about 20 km depth, including the top of the lower crust and the Moho, probably show less than 3 km variation in depth beneath the profile as it crosses the southern DSB. Thus the Dead Sea pull-apart basin may be essentially an upper crustal feature with upper crustal extension associated with the left-lateral motion along the DST. The boundary between the upper and lower crust at about 20 km depth might act as a decoupling zone. Below this boundary the two plates move past each other in what is essentially a shearing motion. Thermo-mechanical modelling of the DSB supports such a scenario. As the DESIRE seismic profile crosses the DST about 100 km north of where the DESERT seismic profile crosses the DST, it has been possible to construct a crustal cross-section of the region before the 107 km left-lateral shear on the DST occurred.

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