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A summary of ODP leg 141 hydrogeologic, geochemical and thermal results

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  • The subduction of the oceanic spreading center at the Chile Triple Junction is marked by a substantial thermal perturbation and marked changes in the hydrogeologic and aqueous geochemical regimes in the overthrust plate. Ridge subduction substantially changes the fluid chemistry in the wedge through variably hydrating the oceanic basement, accretionary wedge, and continental backstop. This generates positive anomalies in salinity and chloride values with respect to sea water. The wedge immediately above the subducted ridge also experiences greatly enhance diagenesis and cementation together with the influx of primordial mantle derived ⁴He. Linear temperature and pore fluid chemistry profiles suggest a predominantly diffusive/conductive regime predominates in the interior eastern portion of the wedge and continental backstop region. In contrast, a vigorous and transient hydrogeolgic system within 5 km of the toe of the wedge at both Sites 859 and 863 generates spatially narrow, large, and complex anomalies in temperature and fluid chemistry. At the toe the vigorous hydrogeologic system may be variably influenced by the episodic expulsion of fluid from both the deeper parts of the wedge and oceanic basement driven convection systems. Structural and diagenetic observations are also consistent with a hydrogeologic regime that both evolves with time and that is dominated by episodic processes. In particular, studies of cements, mineralized veins, deformation bands, and Fe sulfide distribution suggest that above the subducting ridge (i.e., Site 863) the lithification in the wedge is greatly enhanced and that and periods of enhanced fluid expulsion are associated with local hydrofracture and dilation episodes.
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  • Brown, K., Bangs, N., Froelich, P., Zheng, Y., Didyk, B., Prior, D., et al. (1995). A summary of ODP leg 141 hydrogeologic, geochemical and thermal results. Proceedings of the Ocean Drilling Program, Scientific Results, 141, 363-372.
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  • 141
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