Deformation and hydrofracture in a subduction thrust at seismogenic depths: The Rodeo Cove thrust zone, Marin Headlands, California

Abstract

Research Article| January 01, 2007 Deformation and hydrofracture in a subduction thrust at seismogenic depths: The Rodeo Cove thrust zone, Marin Headlands, California Francesca Meneghini; Francesca Meneghini 1Dipartimento di Scienze della Terra, Università di Pisa, 53 Via S. Maria, Pisa 56126, Italy Search for other works by this author on: GSW Google Scholar J. Casey Moore J. Casey Moore 2Earth and Planetary Sciences Department, University of California, 1156 High Street, Santa Cruz, California 96054, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2007) 119 (1-2): 174–183. https://doi.org/10.1130/B25807.1 Article history received: 11 Feb 2005 rev-recd: 14 Apr 2006 accepted: 02 Jun 2006 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Francesca Meneghini, J. Casey Moore; Deformation and hydrofracture in a subduction thrust at seismogenic depths: The Rodeo Cove thrust zone, Marin Headlands, California. GSA Bulletin 2007;; 119 (1-2): 174–183. doi: https://doi.org/10.1130/B25807.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract We have investigated the fabric and the deformational processes of an exhumed subduction zone thrust active at seismogenic depths. The Rodeo Cove thrust zone, which outcrops north of the Golden Gate Bridge of San Francisco, imbricates two basalt-chert-sandstone sequences belonging to the Marin Headlands terrane (Franciscan Complex). The thrust outcrop is a 200-m-thick complex zone that displays a range of stratal disruption from incipient deformation to a broken formation in the central part of the outcrop, dominated by basaltic lithologies, where zones of concentration of deformation have been mapped. Disruption is made by variably dense discrete fault systems synthetic to the main thrust (R and P fractures). These faults are marked by cataclasites with a shaly matrix that shows a scaly foliation defined by chlorite and pumpellyite, which also constrain the depth of faulting (8–10 km, T = 200–250 °C) within the seismogenic zone.The central part of the fault also features the densest system of carbonate-filled veins. Veins occur in the broken formation matrix and fragments, in both cases parallel to the foliation. The veins are either folded, truncated, or pressure-solved along the cleavage. Cementation and hardening of shear surfaces of the fault core may have caused the distribution, as opposed to localization, of subsequent slip events. The fault core may have developed in basaltic rocks because of their inherently high permeability and propensity to transmit overpressure from deeper levels of the subduction zone.Our analysis has shown that accretionary deformation is strongly controlled by injection of overpressured fluids occurring through systems of multiple dilatant fractures grossly parallel to the décollement zone. The crosscutting relationships between veining and foliation suggest that fluid injection is cyclic and, consequently, that large transient variations in permeability and cohesion may occur. The repeated injection of veins parallel to the fault zone may be explained by cyclic changes of the stress, or by difference in tensional strength parallel to and perpendicular to the foliation, both of which would require extremely high fluid pressure.We interpret the features of the Rodeo Cove thrust zone as evidence of the seismic cycle and hypothesize a compressional stress field in the interseismic phase and an extensional stress field in the immediately postseismic phase. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.