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，经历了一段与大陆组装和分裂有关的复杂历史，并伴随着漫长的火山历史。尽管越来越多的证据表明马达加斯加存在年轻的火山活动，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。诺西贝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，其特点是地热系统活跃，地震活动，地震强度可达里氏6级。伊斯塔希-安卡拉特拉地区距离首都塔那利佛非常近，直到8500年前才开始活动，有爆发火山活动的历史，因此应被视为火山活动和潜在危险地区。这项研究将利用地球化学技术来评估这两个火山地区的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盛行--以及未来火山活动的可能性。马达加斯加最近火山活动的原因(S)和来源(S)以及未来喷发活动的可能性仍是基本问题。关键问题涉及的范围很广，包括：古老的、交代的次大陆岩石圈地幔是否作为岩浆来源做出了重大贡献，无论是原地还是作为孤立的地块，在与冈瓦那的组装和/或随后的裂谷相关的事件中被破坏了稳定性？印度MORB地幔与其他潜在的软流圈来源在第四纪火山活动中的相对作用是什么？更新世和全新世火山活动在马德加斯卡的普遍程度，以及与最近的火山活动相关的重复间隔和潜在危险是什么？该项目将涉及对这些火山区最年轻的第四纪喷发产物进行全面的野外镁铁质熔岩和地幔包体采样、放射性测年(Ar-Ar和14C)、地球化学和同位素分析(锶-钕-铅-Hf-Os和U系列不平衡)，以确定下伏岩石圈地幔的性质和年龄，区分有助于第四纪岩浆活动的岩石圈和软流圈地幔来源，并对最近喷发事件的范围和频率提供限制。

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.