Constraints on duration, age and migration of the feeder systems of the Madagascan Flood Basalt Province from high-precision 40Ar/39Ar chronology

The Late Cretaceous magmatism in Madagascar is correlated with the break-up between Madagascar and Greater India, with a presumed track of a hotspot from Madagascar towards the Marion Island and with an anoxic event in the Late Cretaceous. The lava succession and associated dyke swarms and sills of western Madagascar (Mailaka area) represent a volumetrically important area of the igneous province, where dykes with random orientation, several igneous intrusions and a flood basalt to rhyodacite sequence do occur. The magmas have a tholeiitic and weakly alkaline affinity. Using plagioclase separates, we obtained two plateau 40Ar/39Ar ages, and an inverse isochron age statistically indistinguishable, ranging from 92.9 ± 3.8 to 91.2 ± 1.3 Ma (2σ). These ages indicate that tholeiitic and alkaline rocks were erupted in the same age span. In addition, these ages are close to the Cenomanian–Turonian (C–T; 93.9 ± 0.2 Ma) boundary and are indistinguishable from the U–Pb ages available for the capping rhyodacitic unit of the Mailaka lava succession. A filtered compilation of eight ages for northern and central-western Madagascar rocks suggests a duration for the magmatic activity in this part of Madagascar province of the order of c. 3 Ma. If the western Madagascar magmatism is plume related, the plume head would need to have been located near the Mailaka area at c. 93 Ma. The geochemistry of the mafic lavas and dykes of western Madagascar is barely distinguishable from mid-ocean ridge basalt (MORB), with an increasing crustal contamination towards the evolved rocks, and does not constrain input of typical components derived by plume magmatism.