Origin and Evolution of the Sierra Nevada and Walker Lane themed issue Middle Miocene to early Pliocene oblique extension in the southern Gulf of California Fiona H. Sutherland1,*, Graham M. Kent2, Alistair J. Harding1, Paul J. Umhoefer3, Neal W. Driscoll1, Daniel Lizarralde4, John M. Fletcher5, Gary J. Axen6, W. Steven Holbrook7, Antonio González-Fernández5, and Peter Lonsdale1 1Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093, USA 2Nevada Seismological Laboratory, 0174, University of Nevada Reno, Reno, Nevada 89557, USA 3Department of Geology, Northern Arizona University, Flagstaff, Arizona 86011, USA 4Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 USA 5CICESE (Centro de Investigación Científi ca y de Educación Superior de Ensenada), Ensenada, Baja California, Mexico 6Department of Earth and Environmental Science, New Mexico Tech, Socorro, New Mexico 87801, USA 7Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming 82071, USA ABSTRACT a symmetrical continental rift. Two styles 1995; Dixon et al., 2000; Michaud et al., 2006; of rifted basin are observed; older basins Plattner et al., 2007). Microplate capture of A multichannel seismic (MCS) experi- (estimated as 14–11 Ma using sedimenta- this Cretaceous arc terrain resulted in a highly ment spanning 600 km across the Alarcón tion rates) show distributed extension with oblique, rifted continental margin with marked Rise and its conjugate rifted margins in the extensive basement faulting. In contrast, the differences in extensional style from north to southern Gulf of California (western North younger basins (likely post–6 Ma) are asym- south. The northern Gulf of California and America) provides insight into the spatial metrical with synrift deposits thickening into Salton Trough are buried under kilometers of and temporal evolution of extension between the basin-bounding faults. The northeast- sediment originating from the Colorado River; Baja California and the mainland (Mexico). southwest geomorphic expression of the sediment burial of these segments likely affects Stratigraphic analysis of multiple rift basins Tamayo bank and trough and other features rifting, which is typifi ed by widely distributed within the Alarcón spreading corridor indi- provides additional evidence that northwest- zones of deformation with no oceanic seafl oor cates an initial stage of oblique extension southeast oblique extension began ca. 12 Ma. spreading (Nagy and Stock, 2000; Persaud starting ca. 14–12 Ma. This initial phase of These new spatial and temporal constraints, et al., 2003; González-Fernández et al., 2005). extension was characterized by the forma- when combined with a crustal thickness In contrast, the southern gulf is poorly sedi- tion of several large basins in the center of the profi le obtained across the entire Alarcón mented and the southernmost gulf segment, the gulf and on the southeast margin with neg- corridor, suggest that signifi cant northwest- Alarcón segment, hosts an unsedimented mid- ligible synrift sedimentation. A second phase southeast oblique extension within the Gulf oceanic ridge system similar in many respects of oblique extension, likely synchronous of California started well before 6 Ma, in con- to open-ocean mid-oceanic ridge systems with large-scale basin opening in the central trast to earlier models. throughout the Pacifi c (Larson, 1972). Most of and northern Gulf of California, began ca. the present-day deformation is localized on the 8–5 Ma and was characterized by the for- INTRODUCTION main plate boundary in the central and southern mation of smaller half-grabens distributed gulf, but the width and style of rifting prior to across the conjugate margins that contain The Gulf of California formed and evolved this localization vary greatly from the mouth both synrift and postrift deposits. A key fea- over the past ~12 Ma due to a tectonic reorga- to the central gulf (Lizarralde et al., 2007). ture imaged within the MCS data is a highly nization when the Magdalena rise stalled off the The PESCADOR Experiment (Premiere refl ective, ropey layer at the top of basement, west coast of North America and a new Pacifi c– Experiment, Sea of Cortez, Addressing the interpreted to be either volcanic rocks from North America plate boundary was established Development of Oblique Rifting) was designed the 25–12 Ma Comondú Group, and/or early behind the Baja California batholith. The known to compare and contrast rifting architecture rifting volcanic rocks that are between 11 bounding points on this system are the Magda- across three different segments in the gulf, and 9 Ma, or younger. This volcanic layer lena spreading ridge stalling off the west coast including the Guaymas Basin, Alarcón Basin, is extensively faulted, suggesting that it pre- of Baja ca. 12 Ma (Stock and Hodges, 1989) and and the Cabo San Jose to Puerto Vallarta seg- dates the episode of early extension. Upper the onset of seafl oor spreading in the southern ment, with coincident two-dimensional (2D) crustal extension appears to be equally dis- Gulf of California ca. 3.5 Ma. The distribution, multichannel seismic (MCS) and ocean-bottom tributed across conjugate margins, forming both geographical and temporal, of the dex- seismometer transects oriented parallel to trans- tral and extensional components of the plate form faults (Fig. 1A) (Lizarralde et al., 2007). *Present address: BP Exploration Operating Com- motion between these two events is still debated Results from these three PESCADOR profi les pany Ltd., Sunbury-on-Thames TW16 7LN, UK. (Stock and Lee, 1994; DeMets, 1995; Lonsdale, complement an existing, coincident wide-angle Geosphere; August 2012; v. 8; no. 4; p. 752–770; doi:10.1130/GES00770.1; 15 fi gures; 2 tables. Received 27 November 2011 ♦ Revision received 24 April 2012 ♦ Accepted 25 April 2012 ♦ Published online 16 July 2012 752 For permission to copy, contact [email protected] © 2012 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/8/4/752/3341403/752.pdf by guest on 02 October 2021 Mid-Miocene to early Pliocene oblique extension –113 –112 –111 –110 –109 –108 –107 –106 –105 –104 27 27 B CARMEN B -2000ASIN NORTH AMERICAN PLATE 26 Loreto 26 Comondu FARALLON BASIN Los Mochis –500–5–50 T 50 osco-Abreojos Fault BAJA CALIFORNIA SUR 25 PESCADERO–2000 BASIN 25 –500 Sierra –2000 Madre Occidental 24 –500 La Paz ALARCÓN BASIN Ignimbrites 24 Magdalena Fan Mazatlan PACIFIC PLATE Cabo San Lucas TAM 23 AYO TRANSFORM 23 A –500 –500 SAN BEN Latitude (degrees) E –2000 22 ITO- TOSCO ABREOJOS FAULT 22 GUAYMAS Tepicc Isla Tres Marias ALARCON 21 –2000 TMVB 21 –500 CABO-P.V. EAST PACIFIC RISRIVERA PLATE Puerto Vallarta enlarged 20 20 –113 –112 –111 –110 –109 –108 –107 –106 –105 –104 Longitude (degrees) Figure 1. Southern Gulf of California map; major geologic and tectonic features are shown. (A) Three cross-gulf seismic transects (Guaymas, Alarcón, and Cabo San Jose to Puerto Vallarta, [Cabo-P.V.]) acquired during this experiment are shown in red. (B) Southern Gulf of California. The Alarcón profi le is shown in blue. Dashed line indicates entire line including refraction data, and the blue solid line shows the extent of multichannel seismic data. Major geologic provinces are the Comondú formation, Sierra Madre Occidental, and Trans-Mexican Vol- canic Belt (TMVB). The location of the Magdalena Fan is also highlighted. and refl ection profi le across the northern Gulf cón transect, combined with available geologic extension (the direction of extension is not per- of California from the CORTES Experiment information from the Baja California peninsula, pendicular to the continental margin) has been (Crustal Offshore Research Transect by Exten- mainland Mexico, several offshore islands, and ongoing since the inception of rifting within sive Seismic Profi ling) (González-Fernández rock dredge hauls. the Gulf of California, with strain partitioning et al., 2005). The two-ship PESCADOR seis- We infer that the late Comondú Group vol- varying spatially and temporally along the gulf. mic refl ection and refraction experiment using canic units (prerift), along with possible early For example, in the northern Gulf of California R/V Maurice Ewing and R/V New Horizon was synrift volcanic rocks, were deposited over much much of the extension appears to have occurred conducted in fall 2002. MCS refl ection profi les of the basement along the Alarcón transect east of the present-day gulf (e.g., Gans, 1997; collected across the Alarcón Basin, the south- before and during early stages of continental Fletcher et al., 2007). These observations differ ernmost basin in the Gulf of California (Fig. 1), rifting. Based on sediment thickness and esti- from the two-stage rifting models, where rifting are presented herein, defi ning the spatial and mated sediment depositional rates in the large switches from an east-west orientation to the temporal history of extensional deformation basins, we infer that rifting in the southern gulf oblique northwest-southeast–oriented rifting ca. across this conjugate rifted margin. The seismic may have begun as early as 14–11 Ma, as the 6 Ma (Stock and Hodges, 1989). Our conceptual refraction profi les, including the Alarcón tran- Cocos-Magdalena subduction waned west of model sees no change in rifting orientation and sect, were presented in Lizarralde et al. (2007). Baja California. This age estimate is consistent predicts that oblique northwest-southeast exten- The tectonic evolution of the southern Gulf of with evidence for an early (and controversial) sion has been the rifting style since 14–11 Ma. California is constructed from interpretation of marine incursion (McDougall, 2006). Thus, we This conclusion, when coupled with the recent a 2D refl ection seismic profi le across the Alar- infer that northwest-southeast–oriented oblique interpretation of an estimate of 425–485 km Geosphere, August 2012 753 Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/8/4/752/3341403/752.pdf by guest on 02 October 2021 Sutherland et al.