Abstract The Equatorial Atlantic evolved from a transform margin to an oblique-passive margin from the early rifting to early drifting stages. The entire Equatorial region of the South Atlantic behaved as a global-scale accomodation zone linking the evolving Central and Southern Atlantic ocean basins. Lithospheric keels and the roots of thick, stable Proterozoic cratons worked as an anchor, preventing and postponing the continental rupture. The transition, from a continental transform margin to an oblique-passive margin, lasted approximatelly 10 m.y. Once oceanic lithosphere started to be created at the main transtensional segments, large offset transform faults developed. Remarkable differences are observed between adjacent basins. Deformation partitioning ocurred at the equatorial margin due to the coaxiality of the progressive deformation. Diachronous deformation occurred as a function of the degree of obliquity of each basin at a specific time. Individual segments of the margin are associated with individual strike-slip basins at early rifting stages and have different amounts of obliquity with a decrease in obliquity from south to north. Because, basement faults form and develop during rifting their geometry gets locked at the time of first emplacement of oceanic crust. Therefore, the geometry of the basement and basement faults can be used to reconstruct the geometries of the original strike-slip basins prior to oceanic spreading.

Abstract Isotopic ages in volcanic arc igneous and subduction complex rocks in Venezuela and on the offshore island of Aruba are consistent with the finding that the ages of arc igneous activity and high pressure–low temperature metamorphism in both of those areas are restricted to times between ca 150 Ma and ca 70 Ma. That age range, and the restriction of fossil ages in the subduction complexes to between mid-Jurassic (ca 170 Ma) and late Cretaceous (ca 70 Ma) times, reveals a match to the ages of volcanic arc rocks that were involved in collision with the Andean Margin of Ecuador more than 2000 km (1242.7 mi) away. The similarity of ages can be explained if the rocks in both areas are those of the Great Arc of the Caribbean, which has been considered to have collided with the west coast of South America during the late Cretaceous. Synthesizing results from Ecuador and Colombia shows that in those areas the Great Arc was involved in collisions, first with the Caribbean–Colombian Oceanic Plateau (CCOP) and then with the Andean Margin of South America. By 70 Ma a ca 200-km(124.2-mi)-wide Ribbon Continent consisting of fragments of both the Great Arc of the Caribbean and the CCOP was traveling to the north in a transpressive plate boundary zone (PBZ) along the Colombian coast. By 65 Ma, as the CCOP began to enter the Atlantic Ocean and a newly formed Caribbean plate (CARIB) separated from the Farallon plate, parts of the Ribbon Continent began to be carried in a southern CARIB transform PBZ eastward along the north coast of South America. We characterize three W–E-trending belts in that part of the Ribbon Continent: (1) a Northern Belt consisting largely of Great Arc of the Caribbean intrusions and subduction complex rocks; (2) a Central Belt, very well known in Venezuela, consisting of Great Arc of the Caribbean subduction complex rocks; and (3) a fold-and-thrust belt in the Serrania del Interior and Lara nappes of Venezuela. A receiver function (seismic) study has shown where rocks of the Great Arc of the Caribbean abut the South American continent along an E–W-trending line in Venezuela. We find that rocks of both the subduction complex of the Great Arc and rocks of the Serrania del Interior have been thrust across that boundary in secondary thrusts as the Ribbon Continent has propagated to the east in the South Caribbean transform PBZ. The structure of the north coast of South America is being radically altered by the northward movement of the Maracaibo Block as it escapes from deformation related to the collision of the Panama Arc with Colombia. Restoration of movements within that block during the past 15 My has been essential to reconstruct the structure and history of the Ribbon Continent on the north coast of South America.

This outline of the topographic evolution of Africa tied to the history of the African Surface illustrates how a unique geomorphic history over the past 180 million years reflects the continent's distinctive tectonics. The African Surface is a composite surface of continental extent that developed as a result of erosion following two episodes of the initiation of ocean floor accretion around Afro-Arabia ca. 180 Ma and 125 Ma, respectively. The distinctive tectonic history of the African continent since 180 Ma has been dominated by (1) roughly concentric accretion of ocean floor following those two episodes; (2) slow movement of the continent during the past 200 m.y. over one of Earth's two major large low shear wave velocity provinces (LLSVPs) immediately above the core-mantle boundary; (3) the eruption during the past 200 m.y. of deep mantle plumes that have generated large igneous provinces (LIPs) from the core-mantle boundary only at the edge of the African LLSVP; and (4) two episodes during which basin-and-swell topography developed and abundant intracontinental rifts and much intra-plate volcanism occurred. Those episodes can be attributed to shallow convection resulting from plate pinning, i.e., arrested continental motion, induced by the successive eruption of the Karroo and Afar plumes. Shallow convection during the second plate-pinning episode generated the basins and swells that dominate Africa's present relief. By the early Oligocene, Afro-Arabia was a low-elevation, low-relief land surface largely mantled by deeply weathered rock. When the Afar plume erupted ca. 31 Ma, this Oligocene land surface, defined here as the African Surface, started to be flexed upward on newly forming swells and to be buried in sedimentary basins both in the continental interior and at the continental margins. Today the African Surface has been stripped of its weathered cover and partly or completely eroded from some swells, but it also survives extensively in many areas where a lateritic or bauxitic cover has accordingly been preserved. Great Escarpments, which are best developed in the southern part of the continent, have formed on some swell flanks since the swells began to rise during the past 30 m.y. They separate the high ground on the new swells from low lying areas, and because they face the ocean at some distance from the African coastline, they mimic rift flank escarpments at younger passive margins. The youthful Great Escarpments have developed in places where the original rift flank uplifts formed at the time of continental breakup. Their appearance is therefore deceptive. The African Surface and its overlying bauxites and laterites embody a record of tectonic and environmental change, including episodes of partial flooding by the sea, during a 150-million-year long interval between 180 Ma and 30 Ma. Parts of African Surface history are well known for some areas and for some intervals. Analysis here attempts to integrate local histories and to work out how the surface of Afro-Arabia has evolved on the continental scale over the past ∼180 m.y. We hope that because major landscape development theories have been spawned in Africa, a review that embodies modern tectonic ideas may prove useful in re-evaluation of theory both for Africa itself and for other continents. We recognize that in a continental-scale synthesis such as this, smoothing of local disparities is inevitable. Our expectation is that the ambitious model constructed on the basis of our review will serve as a lightning rod for elaborating alternative views and stimulating future research.

Abstract The Red Sea—Gulf of Aden rift System provides a superb example of the formation of passive continental margins. Three phases are well represented: (1) continental rifting (Gulf of Suez); (2) rift-to-drift transition (northern Red Sea); and (3) sea-floor spreading (Gulf of Aden and southern Red Sea). Recently published radiometric and biostratigraphic ages, outcrop studies, and reflection seismic profiles more tightly constrain the evolution of this rift system. The principal driving force for separation of Arabia from Africa was slab-pull beneath the approaching Urumieh-Dokhtar volcanic arc on the north side of Neotethys. However, the rifting trigger was impingement of the Afar plume beneath northeast Africa at ~31 Ma. Rifting followed quickly thereafter, initiating in the Gulf of Aden, perhaps in the area between Socotra Island and southern Oman. Extension occurred in the central Gulf of Aden by ~29 Ma. Shortly thereafter, at ~27 Ma, rifting jumped to Eritrea, east of the Danakil region. Rifting then spread from Eritrea to Egypt at ~24 Ma, accompanied by a major dike-emplacement event that covered more than 2,000 km in possibly less than 1 Ma. At ~14 Ma, the Levant transform boundary formed, largely isolating the Gulf of Suez from later extension. Constriction of the Suez-Mediterranean and Red Sea-Aden marine connections resulted in widespread evaporite deposition at this time. Sea-floor spreading began in the eastern Gulf of Aden at ~19 Ma, the western Gulf of Aden at ~10 Ma, and in the south-central Red Sea at ~5 Ma. Propagation of the oceanic ridge has taken much longer than the propagation of its continental rift predecessor. Therefore, the rift-to-drift transition is diachronous and is not marked by a specific “breakup” unconformity. The Red Sea sub-basins are each structurally asymmetric during the syn-rift phase and this is seen in the geometries obtained when its present paired conjugate margins are palinspastically restored. During the Late Miocene and Pliocene, regional-scale, intrasalt detachment faulting, salt flowage, and mass-movement of the post-Miocene salt section toward the basin axis masked the deeper fault block geometry of most of the Red Sea basin. This young halokinesis has enormous consequences for hydrocarbon exploration.