Water-rich bending faults at the Middle America Trench

TitleWater-rich bending faults at the Middle America Trench
Publication TypeJournal Article
Year of Publication2015
AuthorsNaif S, Key K, Constable S, Evans RL
JournalGeochemistry Geophysics Geosystems
Volume16
Pagination2582-2597
Date Published2015/09
Type of ArticleArticle
ISBN Number1525-2027
Accession NumberWOS:000362365600008
Keywordsarc lavas; bulk porosity; data; east pacific rise; electrical-resistivity; Magnetotelluric; mantle wedge hydration; regional-variations; slow earthquakes; subduction zones; young oceanic-crust
Abstract

The portion of the Central American margin that encompasses Nicaragua is considered to represent an end-member system where multiple lines of evidence point to a substantial flux of subducted fluids. The seafloor spreading fabric of the incoming Cocos plate is oriented parallel to the trench such that flexural bending at the outer rise optimally reactivates a dense network of normal faults that extend several kilometers into the upper mantle. Bending faults are thought to provide fluid pathways that lead to serpentinization of the upper mantle. While geophysical anomalies detected beneath the outer rise have been interpreted as broad crustal and upper mantle hydration, no observational evidence exists to confirm that bending faults behave as fluid pathways. Here we use seafloor electromagnetic data collected across the Middle America Trench (MAT) offshore of Nicaragua to create a comprehensive electrical resistivity image that illuminates the infiltration of seawater along bending faults. We quantify porosity from the resistivity with Archie's law and find that our estimates for the abyssal plain oceanic crust are in good agreement with independent observations. As the Cocos crust traverses the outer rise, the porosity of the dikes and gabbros progressively increase from 2.7% and 0.7% to 4.8% and 1.7%, peaking within 20 km of the trench axis. We conclude that the intrusive crust subducts twice as much pore water as previously thought, significantly raising the flux of fluid to the seismogenic zone and the mantle wedge.

DOI10.1002/2015gc005927
Short TitleGeochem. Geophys. Geosyst.
Student Publication: 
No