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.

Various types of evidence, including the size and volume of the Siberian Traps, the timing and duration of eruptions, paleotectonic and paleogeographic reconstructions, lithospheric structure, heatflow, and the trace-element and radiogenic isotope compositions of lava, are reviewed in this chapter. The major evidence may be summarized as follows. The Siberian Traps erupted in a number of brief volcanic events from the Late Permian until the end of the Middle Triassic. They occupied a vast region (∼7 × 10 6 km 2 ) in a back-arc tectonic setting. The overall volume of erupted rocks was as much as ∼4 × 10 6 km 3 , with most of the volume erupted within the Tunguska syncline. This syncline experienced long-term subsidence before initiation of the volcanism, and the region is now underlain by a relatively thin lithosphere, which is ∼180 km thick. Two types of trace-element patterns are observed in the Siberian Traps: subordinate high-Ti ocean island basalt–like patterns and dominant low-Ti island arc basalt–like patterns. In radiogenic isotope and trace-element coordinates, mixing trends between these two types of magma are absent, or at least not evident. Some volcanic rocks contain primary magmatic mica. These are considered in light of different models. Each model can explain, or was thought to explain, particular observations. However, some evidence can be fatal for some models. For example, the enormous size and volume of the Siberian Traps cannot be explained in the framework of impact and edge-driven convection models and are problematic for lithospheric delamination models. Plume models face problems in explaining the uplift and subsidence pattern and the absence of mixing curves between expected high-Ti primary plume melts and contaminated low-Ti melts. Therefore, a model that relates Siberian Trap magmatism and subduction is suggested. In this model, subducting slabs brought significant amounts of water into the mantle transition zone. Consequent release of water from the transition zone lowered the solidus of the upper mantle, leading to voluminous melting. Major supporting observations for this model include (1) the tectonic position of the Siberian Traps in a back-arc setting of Permian subduction systems, (2) island arc basalt–like trace-element patterns for the majority of the erupted basalts, (3) primary mica found in volcanic rocks, and (4) experimental data on the high water capacity of the mantle transition zone and its recharging via the subduction process.

The mechanisms of magma crust accretion at large igneous provinces (LIPs) are questioned using arguments based on the north Atlantic case. Published and new data on the calculated flow vectors within dike swarms feeding the early traps and subsequent seaward-dipping reflector lavas suggest that most of the mafic magmas forming the north Atlantic LIP transited through a small number of igneous centers. The magma was injected centrifugally in dike swarms at some distance away from individual igneous centers along the trend of the maximum horizontal stress acting in the crust, feeding lava piles via dikes intersecting the ground surface. This mechanism is similar to that observed in present-day Iceland and, more generally, in mafic volcano-tectonic systems. The absence of generalized vertical magma transit in a LIP has major geodynamic consequences. We cannot link the surface extent of LIP magmas to the dimensions of the mantle melting zone as proposed in former plume head models. The distribution of LIP magmas at the surface is primarily controlled by the regional stress field acting within the upper crust, but is also affected by magma viscosity. The igneous centers feeding LIPs most likely represent the crustal expression of small-scale convective cells of the buoyant mantle naturally located beneath the mechanical lithosphere.