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岭俯冲的内侧。活跃的弧火山活动一直持续到距今约10万年。火山作用停止的年代是由钙碱性侵入物、侵蚀火山的暴露根确定的。这些侵入物沿着山脉的轴线露头，海拔高达4000米，因此发生了大量的隆起和侵蚀。火山活动停止和随后隆起的构造原因尚不清楚，而且存在争议。塔拉曼卡山脉也很有趣，因为这个地区具有许多大陆地壳的地球物理和地球化学特征，但它完全是在海洋基底上形成的，很可能是在一个海洋大火成岩省上。由于岩石的大陆特征和快速隆起，塔拉曼卡山脉可能能够帮助地质学家了解大陆地壳的形成过程，这是地质学中一个长期存在的开放性问题。在这个EAGER项目中，pi将对Talamanca侵入岩进行采样，并应用热年代学来推断拆顶和隆升的时间和速率。取样工作是一项试点研究，旨在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，一项初步研究不足以解决抬升的地点、时间和幅度的问题，但它应该允许设置限制，定义主要的局部陷阱，并指导完整的研究。磷灰石(U-Th)/He数据的获取将为更全面地破译该地区拆顶和隆升的演化提供关键的低温史。

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.