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。这发生在大洋中部的扩张中心或板块下沉的俯冲区。然而，在某些情况下，火山活动发生在构造板块内。虽然一些板内火山活动可以用地幔热柱上涌来解释，但地球上的大多数板内火山可能与热柱无关，尽管这种火山很普遍。一种可能的起源可能涉及不同类型的板块之间发生的转变。这个项目调查的是加州边界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和视频博客。这座岛位于一个由失败的大洋中扩张中心组成的系统中。它是检验与无羽流、板内火山作用形成有关的想法的理想地点。该项目将支持一名博士后学者和一名博士生。与墨西哥的合作者一起，该项目将为美国和墨西哥的学生提供教育机会、指导和职业发展。这个项目调查了沿着失败的海洋扩张中心的海山的发展，作为它们与汇聚边缘相互作用的症状。当大洋扩张中心接近俯冲带时，俯冲的大洋板块停滞并细分为较小的微板块，而会聚边缘演化为由迁移的三个结点包围的变换边缘。当它们的汇聚边缘变成变换边缘时，微板最终被捕获。这终止了沿其以前的分叉边缘的贫化地幔的减压部分熔融，并启动了富集地幔的碱性、低程度部分熔融的发展，从而沿着其化石扩张中心边缘产生了海山。地幔羽流可以产生具有类似化学成分的海山，也必须被认为是海山踪迹的潜在来源，例如与化石扩散中心相交的费伯林-瓜达卢佩海山链。该项目旨在确定大洋瓜达卢佩岛的起源，瓜达卢佩岛是一座碱性海山，位于下加利福尼亚州(墨西哥)近海约270公里的海平面以上，位于晚新生代期间在加利福尼亚州边界近海发育的一个破裂的海洋裂谷系统中。该项目将检验四种假说，这些假说预测由于三重结不稳定或地幔-岩浆作用而从拉斑玄武岩(MORB)岩浆作用向碱性、化石扩张中心-海山岩浆作用转变的不同时间和地球化学模式。该方法综合了野外地质、40Ar/39Ar年代学、常量元素和同位素地球化学以及岩石学模拟。因此，在区域构造框架内调查海山岩石学和计时可能揭示地幔流动、地幔熔融、三交界处迁移、微板块捕获和/或地幔羽流活动之间的地球动力学关系，此外还可以提高我们对北美西部在晚更新世的演化的理解。这一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智力优势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.