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

马达加斯加是世界第四大岛，经历了与大陆合并和分裂有关的复杂历史，并与长期的火山活动历史有关。尽管越来越多的证据表明马达加斯加有年轻的火山活动，以及高度活跃的构造和相关的地震活动，但对最近的火山活动的研究非常有限。Nosy Be是一个受欢迎的旅游目的地，被认为是马达加斯加北部最年轻的火山田，其特点是活跃的地热系统和地震活动，地震强度高达里氏6级。伊斯塔西-安卡拉特拉地区非常靠近首都塔那那利佛，最近在8 500年前一直很活跃，有爆炸性火山活动的历史，因此应被视为火山活跃和具有潜在危险的地区。这项研究将利用地球化学技术来评估这两个火山区火山活动的来源和原因，并将建立基线年龄数据，以评估这些地区最近火山活动的流行程度和未来火山活动的可能性。关于马达加斯加最近火山活动的原因和来源，以及未来爆发活动的可能性，仍然存在一些基本问题。关键问题的范围很广，包括：古老的、交代的次大陆岩石圈地幔是否作为岩浆源做出了重大贡献，无论是原位的还是在冈瓦纳板块组合和/或随后的裂谷相关事件中不稳定的孤立块体？在第四纪火山活动中，印度MORB地幔与其他潜在软流圈源的相对作用是什么？以及马达加斯加的更新世和全新世火山活动有多普遍，以及与最近的火山活动相关的复发间隔和潜在危险是什么？该项目将包括对这些火山区最年轻的第四纪喷发产物进行全面的基性熔岩和地幔捕虏体野外取样、放射性定年（Ar-Ar和14C）以及地球化学和同位素分析（Sr-Nd-Pb-Hf-Os和u系列不平衡），以确定岩石圈地幔的性质和年龄，区分对第四纪岩浆作用有贡献的岩石圈和软流圈地幔源。并限制最近火山喷发的范围和频率。

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.