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doi:10.2204/iodp.proc.344.208.2019 IntroductionA primary objective of Integrated Ocean Drilling Program (IODP) Expeditions 334 and 344 was to understand the processes that generate earthquakes along the subduction plate boundary at erosive margins. Fundamental to this objective is determining the nature of the upper plate seaward of the seismogenic zone. Current models suggest that at erosive margins, such as those proposed for Costa Rica, fluids migrate from the plate interface and react little with the framework wedge material as they ascend and vent at the seafloor (e.g., Ranero and von Huene, 2000; Hensen et al., 2004; Sahling et al., 2008). Carbonate formation in the Costa Rica forearc was thus expected to result solely from anaerobic oxidation of the discharging methane-rich fluids, forming carbonate mounds that punctuate the margin. However, IODP drilling during the Costa Rica Seismogenesis Project (CRISP) revealed that significant fluid-rock reactions occur in the margin framework, including extensive carbonate cementation at depth. Here, we report on the chemical and isotopic composition of the carbonates recovered from Site U1380 and on isotopic composition of the dissolved inorganic carbon and water at Site U1378, which may aid in unraveling fluid sources and the processes that led to formation of the carbonate cements in the wedge framework of the margin. |
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