Transtensional rifting in the proto-Gulf of California near Bahia Kino, Sonora, Mexico

Research Article| November 01, 2013 Transtensional rifting in the proto–Gulf of California near Bahía Kino, Sonora, México Scott E.K. Bennett; Scott E.K. Bennett 1Department of Geological Sciences, University of North Carolina, Chapel Hill, North Carolina 27599-3315, USA2Department of Earth and Planetary Sciences, University of California–Davis, Davis, California 95616, USA †Current address: U.S. Geological Survey, Geologic Hazards Science Center, 1711 Illinois Street, Golden, Colorado 80401, USA; e-mail: sekbennett@usgs.gov Search for other works by this author on: GSW Google Scholar Michael E. Oskin; Michael E. Oskin 2Department of Earth and Planetary Sciences, University of California–Davis, Davis, California 95616, USA Search for other works by this author on: GSW Google Scholar Alexander Iriondo Alexander Iriondo 3Centro de Geociencias, Universidad Nacional Autónoma de México, Juriquilla, No. 3001, Querétaro 76230, México4Department of Geological Sciences, The University of Texas at Austin, Austin, Texas 78712, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Scott E.K. Bennett †Current address: U.S. Geological Survey, Geologic Hazards Science Center, 1711 Illinois Street, Golden, Colorado 80401, USA; e-mail: sekbennett@usgs.gov 1Department of Geological Sciences, University of North Carolina, Chapel Hill, North Carolina 27599-3315, USA2Department of Earth and Planetary Sciences, University of California–Davis, Davis, California 95616, USA Michael E. Oskin 2Department of Earth and Planetary Sciences, University of California–Davis, Davis, California 95616, USA Alexander Iriondo 3Centro de Geociencias, Universidad Nacional Autónoma de México, Juriquilla, No. 3001, Querétaro 76230, México4Department of Geological Sciences, The University of Texas at Austin, Austin, Texas 78712, USA Publisher: Geological Society of America Received: 20 Jan 2012 Revision Received: 11 Jun 2013 Accepted: 12 Aug 2013 First Online: 08 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 © 2013 Geological Society of America GSA Bulletin (2013) 125 (11-12): 1752–1782. https://doi.org/10.1130/B30676.1 Article history Received: 20 Jan 2012 Revision Received: 11 Jun 2013 Accepted: 12 Aug 2013 First Online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Scott E.K. Bennett, Michael E. Oskin, Alexander Iriondo; Transtensional rifting in the proto–Gulf of California near Bahía Kino, Sonora, México. GSA Bulletin 2013;; 125 (11-12): 1752–1782. doi: https://doi.org/10.1130/B30676.1 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 Continental rifts require focused strain to rupture and form an ocean basin. In oblique rifts, such as the Gulf of California, focused transtensional strain associated with strike-slip faulting may serve as a catalyst for rupture. To test this hypothesis, we analyzed structural mapping, geochronology, paleomagnetism, and fault kinematics of pre- and synrift rocks exposed in an ∼200 km2 coastal mountain belt flanking the eastern rift margin of the northern Gulf of California. This coastal Sonora region hosts the onshore portion of the transform boundary between the Upper Tiburón and Adair-Tepoca marine basins—two early-formed oblique rift segments. Extension commenced here between 11.5 Ma and 7 Ma, resulting in 25°–40° of E-NE tilting, initiation of clockwise vertical-axis rotation of fault-bounded blocks, and minor basin sedimentation. Rates of deformation prior to 7 Ma are unconstrained due to a lack of exposed syntectonic deposits. Deformation after 7 Ma was associated with rapid tilting and the majority of observed clockwise vertical-axis rotation and strike-slip faulting. Nonmarine sedimentary basins accumulated coarse sediments above an unconformity eroded across older, tilted strata. By 5–6 Ma, deformation in coastal Sonora must have largely ceased and migrated westward into the Upper Tiburón marine basin. We document up to 120% total extension and total clockwise block rotations up to 53°. In portions of the study area, extension and rotation were supplanted by strike-slip faulting as deformation proceeded. We develop a tectonic model for this Coastal Sonora fault zone, which is bounded by major NW-striking transform faults with >10 km of displacement. Internal to the Coastal Sonora fault zone, the majority of an estimated 6.2 ± 1.1 km of dextral deformation, associated with up to 5.7 km of WNW-directed extension, occurred over the final 1–2 m.y. of its life span, at a strain rate approaching 10–14 s–1. This activity occurred as the plate boundary localized along nascent pull-apart basins in the northern Gulf of California, consistent with the hypothesis that late proto–Gulf of California dextral shear zones, such as the Coastal Sonora fault zone, acted to focus lithospheric-scale strain and promoted continental rupture in the wide-rift setting of the Mexican Basin and Range. 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