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TitleDiagenetic, metamorphic, and hydrogeologic consequences of hydrothermal circulation in subducting crust
AuthorSpinelli, G; Wada, I; Wang, KORCID logo; He, J; Harris, R; Underwood, M
SourceSubduction top to bottom 2; Geosphere vol. 14, no. 6, 2018 p. 1-18, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20180142
PublisherGeological Society of America
Mediapaper; on-line; digital
File formatpdf
Subjectstectonics; igneous and metamorphic petrology; hydrogeology; tectonic environments; subduction zones; downgoing slab; hydrothermal systems; diagenesis; metamorphism; deformation; groundwater; aquifers; fluid dynamics; fluid flow; thermal analyses; anomalies; hydrothermal alteration; permeability; viscosity; models; modelling
Illustrationsschematic cross-sections; location maps; geoscientific sketch maps; time series; profiles; phase diagrams; models; tables
ProgramPublic Safety Geoscience Assessing Earthquake Geohazards
Released2018 10 24
AbstractThe redistribution of heat by fluid circulation in subducting igneous crust generates thermal anomalies that can affect the alteration of material both within a subduction zone and in the incoming plate prior to subduction. This hydrothermal circulation mines heat from subducted crust and transports it seaward, resulting in anomalously high temperatures in material seaward of the trench and anomalously low temperatures in the subduction zone. Anomalously high temperatures on the incoming plate are spatially limited; for example, on the Nankai margin of southern Japan, a zone of high temperatures is within ~30 km of the accretionary prism deformation front. The incoming plate (Shikoku Basin) undergoes the high-temperature anomaly for less than 2 million years; so the alteration of clay minerals in Shikoku basin sediments advances only slightly because of the thermal anomaly. In contrast, subducted material is cooled by hydrothermal circulation, and therefore alteration of subducted sediment and igneous rock is shifted farther landward (i.e., delayed); in the Cascadia and Nankai margins, this includes the seismically inferred locations of the basalt-to-eclogite transition in the subducting crust. In very hot margins, hydrothermal circulation cools the subducting slab and affects where, and if, subducting material may melt. In southern Chile, this cooling helps explain the lack of a basaltic melt signature in arc lavas despite the young subducting lithosphere. Finally, the cooling of the subducting slab via hydrothermal circulation shifts fluid sources from dehydration reactions farther landward, delays metamorphic reactions that tend to reduce permeability, and increases fluid viscosity. The responses to hydrothermal circulation in subducting crust are most pronounced in the hottest subduction zones, where the lateral heat exchange in the subducting basement aquifer is greatest.
Summary(Plain Language Summary, not published)
Temperature controls rock properties and hence earthquake generation. In a subduction zones with young and warm subducting plate, the temperature of the shallow part of subduction zones can be significantly affected by hydrothermal circulation of fluids in the subducting crust. This paper reviews recent studies of the role of such circulation in affecting sediment and rock properties that affect earthquake generation along the plate interface and within the subducting plate. Cascadia is included in the discussion as an end-member warm subduction zone.

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