Origin & Eruptive History of Quaternary Volcanism in Nosy Be and Itasy-Ankaratra, Madagascar

Miami University, Oxford OH

Investigators

Abstract

Madagascar, the fourth largest island in the world, has experienced a complex history related to continent assembly and breakup, associated with a prolonged history of volcanism. Despite growing evidence for young volcanism in Madagascar, as well as highly active tectonics and associated seismicity, there has been very limited study of the recent volcanism. Nosy Be, a popular tourist destination, is considered to be the youngest of the volcanic fields in northern Madagascar, and is characterized by active geothermal systems and seismic activity with earthquakes as large as Richter magnitude 6. The Istasy-Ankaratra region, located in very close proximity to the capital city, Antananarivo, has been active as recently as 8,500 years ago and has a history of explosive volcanism, and should therefore be considered a volcanically active and potentially hazardous area. This study will utilize geochemical techniques to evaluate the sources and causes of volcanism in these two volcanic regions, and will establish baseline age data for evaluating the prevalence of recent volcanism - and likelihood of future volcanism - in these regions. Fundamental questions still remain about the cause(s) and source(s) of recent volcanism in Madagascar, as well as the likelihood of future eruptive activity. Key questions range widely in scope and include: Does the ancient, metasomatized subcontinental lithospheric mantle contribute significantly as a magma source, either in situ or as isolated blocks destabilized during events associated with the assembly and/or subsequent rifting of Gondwana?; What are the relative roles of Indian MORB mantle versus other potential asthenospheric sources in the Quaternary volcanism?; and How prevalent is Pleistocene and Holocene volcanism in Madgascar, and what are the recurrence intervals and potential hazards associated with this recent volcanism? This project will involve comprehensive field sampling of mafic lavas and mantle xenoliths, radiometric dating (Ar-Ar and 14C), and geochemical and isotopic analyses (Sr-Nd-Pb-Hf-Os and U-series disequilibria) of the youngest Quaternary eruptive products in these volcanic regions in order to resolve the nature and age of the underlying lithospheric mantle, to distinguish between lithospheric and asthenospheric mantle sources contributing to the Quaternary magmatism, and to provide constraints on the scope and frequency of recent eruptive events.