EAGER: Genesis of Continental Crust in Costa Rica and Origin of the Talamanca Range

哥斯达黎加南部的塔拉曼卡山脉位于科科斯海脊目前正在俯冲的内侧。活动弧火山作用发生在距今约10 Ma以前。火山活动停止的年龄是由钙碱性侵入岩确定的，钙碱性侵入岩是被侵蚀的火山的裸露根部。这些侵入体沿着山脉的轴线露头，海拔高达4000米，因此发生了实质性的隆升和侵蚀。火山活动停止和随后隆起的构造原因尚不清楚，也存在争议。塔拉曼卡山脉也很有趣，因为该地区具有许多陆壳的地球物理和地球化学特征，但它是在一个完全大洋的基底上形成的，很可能是在一个海洋大火成岩省上形成的。由于岩石的大陆性和快速的隆起，塔拉曼卡山脉可能能够帮助地质学家了解陆壳的形成过程，这是地质学中一个长期悬而未决的问题。在这个迫切的项目中，PI将采样塔拉曼卡侵入岩，并应用热年代学来推断剥离和隆起的时间和速度。取样工作是一项初步研究，目的是确定将热年代学应用于构成塔拉曼卡山脉主干的侵入岩的可行性。显然，试点研究不足以解决在哪里、何时和多少抬升的问题，但它应该允许设定限度，界定当地的主要陷阱，并指导完整的研究。获取磷灰石(U-Th)/He数据将提供必要的关键低温历史，以便更全面地破译该地区去顶和隆起的演化。

The Talamanca range of southern Costa Rica lies inboard of where the Cocos Ridge is currently subducting. Active arc-volcanism occurred until about 10 Ma before the present. The age of cessation of volcanism is determined from calc-alkaline intrusives, the exposed roots of eroded volcanoes. These intrusives outcrop along the axis of the range, at elevations as high as 4000 m, so substantial uplift and erosion has occurred. The tectonic causes for the cessation of volcanism and subsequent uplift are not understood and are controversial. The Talamanca range is also interesting because this region has many of the geophysical and geochemical characteristics of continental crust, yet it formed on an entirely oceanic basement, most likely on an oceanic large igneous province. Because of the continental character of the rocks and the rapid uplift, the Talamanca mountains may be able to help geologists understand the process that forms continental crust, a long-standing open problem in geology.In this EAGER project, the PIs will sample Talamanca intrusives and apply thermochronology to infer the timing and rate of unroofing and uplift. The sampling effort is a pilot study to establish the feasibility of applying thermochronology to the intrusive rocks that comprise the backbone of the Talamanca range. Obviously, a pilot study is not aggressive enough to solve the problem of where, when and how much uplift, but it should allow the setting of limits, the definition of the major local pitfalls and guide a complete study. The acquisition of apatite (U-Th)/He data will provide access to the crucial lower temperature history necessary to more fully decipher the evolution of unroofing and uplift in the region.