Collaborative Research: Geochemistry and Tectonics of Cretaceous Gateway Closure in the Central American Isthmus

地球在很深的地方被分为三层：地核、地幔和地壳。地幔的动力学对地壳的演化具有重要的控制作用，而地壳的演化反过来又塑造了我们今天看到的地表形态。虽然很少，但在剧烈的构造事件（如大陆碰撞）发生的地方发现了暴露的地幔，这些地方基本上是我们了解地球的窗口。这项研究将集中在哥斯达黎加的圣埃琳娜半岛，这是一个几乎未被探索的裸露地幔部分。对地表的观测将提供有关导致火山活动的过程的宝贵信息。一个目标是将中美洲的地质历史同影响全球环流、气候和生态演变的陆桥和海道封闭的发展联系起来。这些研究人员将通过对哥斯达黎加圣埃琳娜半岛地幔和伴生火山岩的地球化学、岩石学和结构分析，探索该地区的古地理和构造演化。这将是第一次用现代分析技术研究圣埃琳娜地幔剖面。目的是限定该地块形成和固结的时间和构造环境。为了解决这些问题，研究人员将绘制不同的岩性图并进行详细的结构分析。选定的地幔橄榄岩和其他超镁质岩性样品将使用电子显微探针和原位激光烧蚀ICP-MS进行研究。将对火山单元的样品进行主要、微量元素和放射性成因同位素组成分析。这些分析将限制不同岩性的年龄，以及合并圣埃琳娜复合体的构造事件。该复合体与弧前、弧后或洋中脊构造背景的识别将有助于限制导致白垩纪第一中美洲门户关闭的大规模构造几何。

Planet Earth is divided in three main layers at great depth, the core, the mantle and the crust. The dynamics of the mantle exerts significant control over the evolution of the crust, which in turn shapes the morphology of the surface we see today. Although rare, exposed mantle is found where dramatic tectonic events such as continental collisions have taken place, and these places are essentially windows into our planet. This study will focus on the Santa Elena Peninsula, Costa Rica, a practically unexplored segment of exposed mantle. The observations on the surface will provide valuable information about processes that result in volcanic activity. One goal is to link the Central American geologic history to the development of land-bridges and seaway closures that affected the evolution of global circulation, climate and ecology. These researchers will explore the paleogeography and tectonic evolution of the region through geochemical, petrologic and structural analysis of mantle and associated volcanic rocks of the Santa Elena Peninsula, Costa Rica. This will be the first time the Santa Elena mantle section will be studied with modern analytical techniques. The objectives are to constrain the timing and tectonic environment of formation and consolidation of this terrane. To address these questions the investigators will map the different lithologies and conduct detailed structural analysis. Selected samples of mantle peridotites and other ultramafic lithologies will be studied with electron-microprobe and in-situ laser ablation ICP-MS. Samples from the volcanic units will be analyzed for major, trace element and radiogenic isotope compositions. The analyses will constrain the age of the different lithologies and also the tectonic events that amalgamated the Santa Elena complex. The identification of the complex with a fore-arc, back-arc or mid-ocean ridge tectonic setting will help constrain the large-scale tectonic geometry that led to the closure of the first Central American Gateway during the Cretaceous.