Hensen, Christian (2012) Geochemistry of (forearc) fluids. [Talk] In: The Lübeck Retreat, Collaborative Research SFB 574 Volatiles and Fluids in Subduction Zones: Climate Feedback and Trigger Mechanisms for Natural Disasters. , 23.05.-25.05.2012, Lübeck . The Lübeck Retreat: final colloquium of SFB 574; May 23-25, 2012: program & abstracts. ; p. 12 .

Abstract

Emanation of fluids at cold seeps, mud volcanoes, and other types of submarine seepage structures is a typical phenomenon occurring at continental margins worldwide. Cold seeps represent pathways along which volatiles and solutes are sometimes recycled from deeply buried sediments into the global ocean, and hence they may be considered as a potentially important link in global geochemical cycles. In forearcs of active margins they may help to further our understanding of exchange processes, and hence the coupling between subducting and overriding plate. Over the past decade SFB 574 has undertaken considerable efforts to study the Central American and the Chilean forearcs as well as other areas of interest such as the Gulf of Cadiz, the Mediterranean Ridge, or the active margin off New Zealand. The results have helped to understand and systemize processes of fluid formation and alteration in different geological and tectonic environments. In this contribution we will summarize findings from the major working areas and show how these relate to forearcs of other subduction zones and seepage areas. In general, clay-mineral dewatering plays a central role in terms of fluid-mobilization from greater depth, however, resulting cold seep fluids are typically very different from each other and cover a large range of geochemical signatures. This is mainly due to variations in control parameters such as the type of sediment input or thickness of the sediment cover, thermal conditions, distribution of fluid pathways, and the potential of secondary overprinting. For example, freshened fluids emanating at cold seeps off Costa Rica indicate dewatering and related geochemical reactions in subducting sediments, while fluids sampled at mud volcanoes in the Gulf of Cadiz indicate a fluid source originating in the underlying oceanic basement and as such a hydrological connection between buried oceanic crust and the water column at high crustal ages. The latter finding is a clear spin-off of the work conducted within SFB 574 and illustrates a challenging new perspective on future cold seep research.

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