ABSTRACT In this paper, we present a comprehensive review of literature data (~2600 analyses), including major and trace elements and Sr-Nd isotopes, on continental flood basalts from the Ethiopia-Yemen, Deccan (India), and Karoo (southern Africa) volcanic provinces in order to evaluate whether they can be attributable to similar tectonomagmatic processes that occurred during the past 200 m.y. in central Gondwana. Results indicate that the three investigated provinces share fundamental features, such as the following: (1) Major and trace element compositions are closely comparable, in terms of parental magmas and fractionation trends, for the various continental flood basalt suites recognized in the provinces, namely, low Ti (LT, TiO 2 0.5–3 wt%), high Ti (HT1, TiO 2 1–4 wt%), and very high Ti (HT2, TiO 2 2.5–7 wt%). (2) There is a clear zonal arrangement of continental flood basalts, with the hottest (potential temperature T p up to ~1600 °C) and deepest (up to 5 GPa) HT picrite-basalt magmas in the central area and cooler and shallower LT basalts (T p down to 1450 °C, pressure [ P ] = 2–3 GPa) at the periphery, corresponding to a maximum thermal difference of 60–110 °C from the inner to the outer zones in each province. This conforms to continental flood basalt generation from a lenticular melting region, plausibly reflecting thermo-compositionally zoned plume heads, with maximum excess temperature T ex = 250–300 °C with respect to the notional mid-ocean-ridge basalt (MORB) ambient mantle. (3) The central area of all provinces is characterized by the nearly exclusive occurrence of superheated HT picrite-basalt (and nearly coeval alkaline-carbonatite complexes) at the intersection of multiple extensional lineaments (faulting, rifting, and dike swarms), reflecting the focus of the tectonomagmatic activities. (4) The common occurrence of rhyolitic differentiates at the top of picrite-basalt lavas (e.g., Lalibela suite, northern Ethiopia; Pavagadh suite, Deccan; Lebombo suite, African Karoo) has to be considered an effect of the inversion of the stress regime, from generalized regional extension (continental flood basalt eruption) to localized continental rifting accompanying magma differentiation to rhyolites; activity at some of these rift and dike systems, e.g., the Western Afar Escarpment, the coastal dikes of Western Deccan, and the Rooi Rand dikes, was protracted until continental breakup and the opening of new oceanic branches of the Red Sea, the central Indian Ocean, and southwestern Indian Ocean, respectively. (5) The Sr-Nd isotope distributions of continental flood basalts show HT picrite-basalt magmas mostly recording mantle values unaffected by continental lithospheric signatures, and LT basalts mainly reflecting either mixed source components located at the lithosphere-asthenosphere transition or continental crust contamination, particularly in the Karoo and Deccan provinces. Overall, results from this review provide compelling evidence that hot mantle plumes impinged diachronously on the central Gondwana lithosphere, causing similar tectonomagmatic events and continental flood basalt zonal arrangements that reflect a common thermocompositional zonation of the plume head in the three investigated provinces.

Abstract Basement rocks tend to have negligible primary (rock matrix) porosity and, where present, almost all porosity is fracture-related. An insight into fracture type and distribution is therefore of importance when attempting to predict potential flow zones in hydrocarbon reservoirs. In the absence of core, borehole images provide a proven means of characterizing fractures within basement rocks. This paper will concentrate upon the classification and characterization of basement structural elements, including fractures, faults and breccias, versus lithological elements, such as foliations and intrusion boundaries from borehole images. In addition, suggestions of how to differentiate present-day in-situ stress indicators from natural fractures will be made as these features may provide important information regarding open fracture set orientations. Examples of microresistivity and acoustic borehole images acquired in fractured igneous basement rocks from oil wells in Yemen will be presented together with a suggested methodology for their interpretation. The discussion will be based on hydrocarbon reservoirs; however, the methodology outlined can potentially have wider applications in, for example, groundwater pollution prevention schemes or groundwater extraction, radioactive waste disposal, geothermal energy resources and deep-drilling research programmes.

Abstract This volume is intended to generate ideas for the future exploration of immature and mature basins across the Tethyan Region. From the Paleozoic to the Cenozoic, the Arabian Plate, North Africa and parts of Southern Eurasia, were on the margin of a series of Tethys seaways, Proto-Tethys, Paleo-Tethys, and Neo-Tethys. These areas evolved together and as a result they have numerous similarities in their tectono-stratigraphic history and petroleum systems. These similarities could be used to extrapolate proven petroleum systems to underexplored areas and lead to hydrocarbon discoveries. The back cover illustrates the countries that evolved along the Tethyan Region in their present day location. Countries covered in this volume are outlined.