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

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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.