Do seamounts on fossil oceanic spreading centers record triple-junction migration or mantle-plume activity? Guadalupe Island, Mexico as an archetype

地球上的火山活动通常集中在构造板块之间的边界附近。这种情况发生在大洋中部扩张中心或板块下沉的俯冲带。然而，在某些情况下，火山活动发生在构造板块内。虽然一些板块内火山活动可以用地幔柱的上涌来解释，但地球上大多数板块内火山可能与地幔柱无关，尽管这类火山分布广泛。一种可能的起源可能涉及不同类型板块之间发生的过渡。这个项目调查了加利福尼亚边缘地带近海的板内火山活动。该地区具有复杂的板块边缘历史和不寻常的火山活动类型。研究小组将在下加利福尼亚州近海的瓜达卢佩岛进行实地考察并录制视频。这个岛位于一个失败的海洋中部扩散中心系统。这是一个理想的地点来测试有关非羽流、板内火山作用形成的想法。本项目资助博士后1人，博士生1人。与墨西哥合作伙伴一起，该项目将为美国和墨西哥学生提供教育机会、指导和职业发展。这个项目研究了沿失败的海洋扩张中心的海山的发展，作为它们与收敛边缘相互作用的一个症状。当大洋扩张中心靠近俯冲带时，俯冲洋板块停止并细分为更小的微板块，而会聚边缘演化为以迁移三联结为界的转换边缘。当微孔板的会聚边缘变成变换边缘时，微孔板最终被捕获。这终止了贫地幔沿原辐散边缘的减压部分熔融作用，而开始了富地幔的碱性低程度部分熔融作用的发展，并沿化石扩张中心边缘形成海山。地幔柱可以产生具有类似化学性质的海山，也必须被认为是海底山轨迹的潜在起源，例如与化石扩张中心相交的Fieberling-Guadalupe海山链。该项目旨在确定海洋瓜达卢佩岛（Guadalupe Island）的起源，瓜达卢佩岛是一个碱性海山，位于下加利福尼亚州（墨西哥）离岸约270公里的海平面以上，位于加利福尼亚边缘地区晚期发育的一个失败的海洋裂谷系统沿线。该项目将测试四种假设，预测从拉斑岩、中洋脊玄武岩（MORB）岩浆作用到碱性、化石扩散中心海山岩浆作用（由于三重结不稳定或地幔柱岩浆作用）转变的不同时间和地球化学模式。方法是综合野外地质、40Ar/39Ar地质年代学、主要微量元素和同位素地球化学以及岩石学建模。因此，在区域构造框架内对海山岩石学和时间的研究可以揭示地幔流动、地幔熔融、三结迁移、微板块捕获和/或地幔柱活动之间的地球动力学关系，从而提高我们对晚新生代北美西部演化的认识。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Volcanism on Earth is usually focused near boundaries between tectonic plates. This occurs at mid-ocean spreading centers or at subduction zones where plates sink. In some cases, though, volcanism occurs within a tectonic plate. While some intraplate volcanism can be explained by upwelling of a mantle plume, most of Earth's intraplate volcanoes are probably not related to a plume despite such volcanoes being widespread. One possible origin may involve transitions occurring between different types of plates. This project investigates intraplate volcanism offshore of the California Borderlands. This region has a complex plate margin history and unusual types of volcanism. The research team will conduct and video-blog fieldwork on Guadalupe Island offshore Baja California. This island is located along a system of failed mid-ocean spreading centers. It is an ideal location to test ideas related to the formation of non-plume, intraplate volcanism. This project will support a postdoctoral scholar and a PhD student. Together with Mexican collaborators, this project will provide educational opportunities, mentoring, and career development for USA and Mexican students. This project investigates the development of seamounts along failed oceanic spreading centers as a symptom of their interaction with convergent margins. When oceanic spreading centers approach subduction zones, the subducting oceanic plate stalls and subdivides into smaller microplates while the convergent margin evolves into a transform margin bounded by migrating triple junctions. The microplates are eventually captured when their convergent margins become transform margins. This terminates decompression partial melting of depleted mantle along their former divergent margins and initiates the development of alkaline, low-degree partial melting of enriched mantle that produces seamounts along their fossil spreading-center margins. Mantle plumes can produce seamounts with similar chemistry and must also be considered as a potential origin for seamount trails such as the Fieberling–Guadalupe seamount chain that intersect fossil spreading centers. The project intends to determine the origin of oceanic Guadalupe Island, which is an alkaline seamount that emerged above sea level ~270 km offshore of Baja California (Mexico) and is situated along a system of failed oceanic rifts that developed offshore of the California borderlands during the late Cenozoic. The project will test four hypotheses that predict different temporal and geochemical patterns for the transition from tholeiitic, mid-ocean-ridge-basalt (MORB) magmatism to alkaline, fossil-spreading-center-seamount magmatism due to triple-junction instability or mantle-plume magmatism. The approach is to integrate field geology, 40Ar/39Ar geochronology, major–trace-element and isotope geochemistry, and petrological modelling. Investigation of seamount petrology and timing within a regional-tectonic framework may therefore reveal geodynamic relationships among mantle flow, mantle melting, triple-junction migration, microplate capture, and/or mantle-plume activity, in addition to improving our understanding of the evolution of western North America during the late Cenozoic.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.