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Geological Society of America Bulletin Downloaded from gsabulletin.gsapubs.org on January 15, 2014 Geological Society of America Bulletin Oceanic magmatism in sedimentary basins of the northern Gulf of California rift Axel K. Schmitt, Arturo Martín, Bodo Weber, Daniel F. Stockli, Haibo Zou and Chuan-Chou Shen Geological Society of America Bulletin 2013;125, no. 11-12;1833-1850 doi: 10.1130/B30787.1 Email alerting services click www.gsapubs.org/cgi/alerts to receive free e-mail alerts when new articles cite this article Subscribe click www.gsapubs.org/subscriptions/ to subscribe to Geological Society of America Bulletin Permission request click http://www.geosociety.org/pubs/copyrt.htm#gsa to contact GSA Copyright not claimed on content prepared wholly by U.S. government employees within scope of their employment. Individual scientists are hereby granted permission, without fees or further requests to GSA, to use a single figure, a single table, and/or a brief paragraph of text in subsequent works and to make unlimited copies of items in GSA's journals for noncommercial use in classrooms to further education and science. This file may not be posted to any Web site, but authors may post the abstracts only of their articles on their own or their organization's Web site providing the posting includes a reference to the article's full citation. GSA provides this and other forums for the presentation of diverse opinions and positions by scientists worldwide, regardless of their race, citizenship, gender, religion, or political viewpoint. Opinions presented in this publication do not reflect official positions of the Society. Notes © 2013 Geological Society of America Downloaded from gsabulletin.gsapubs.org on January 15, 2014 Oceanic magmatism in sedimentary basins of the northern Gulf of California rift Axel K. Schmitt1,†, Arturo Martín2, Bodo Weber2, Daniel F. Stockli3, Haibo Zou4, and Chuan-Chou Shen5 1Department of Earth and Space Sciences, University of California–Los Angeles, Los Angeles, California 90095-1567, USA 2Departamento de Geología, Centro de Investigación Científi ca y de Educación Superior de Ensenada (CICESE), Carretera Ensenada–Tijuana No. 3918, Zona Playitas, Ensenada, B.C., C.P. 22800, México 3Department of Geological Sciences, University of Texas at Austin, EPS RM 1.130, 1 University Station C9000, Austin, Texas 78712-0254, USA 4Department of Geology and Geography, Auburn University, 210 Petrie Hall, Auburn, Alabama 36849-5305, USA 5High-Precision Mass Spectrometry and Environment Change Laboratory (HISPEC), Department of Geosciences, National Taiwan University, Taipei 10617, Taiwan, R.O.C. ABSTRACT value implies minor (<20%) assimilation of margins is due to decompression melting in the continental crustal rocks, which, however, is mantle, which ultimately produces composition- Rift-related magmatism in the northern- an upper limit because of crystal-scale evi- ally uniform, nearly anhydrous mid-ocean-ridge most Gulf of California and the adjacent sub- dence for magma contamination by uncon- basalts (MORB). First-order compositional dif- aerial Salton Trough and Cerro Prieto basins solidated sediment at the time of eruption. ferences often result from the transition between comprises intermediate to rhyolitic surfi cial Zircon crystals in felsic rocks (rhyolite lavas, these two magmatic regimes, where subduction and buried lava fl ows and domes, including intrusive microgranites, and granophyre xe- is associated with predominantly intermedi- their xenolith cargo. In addition, geothermal noliths) have trace-element and submantle ate compositions, whereas bimodal suites are a drill wells frequently penetrate subsurface δ18O compositions that are robust indicators hallmark of continental rifting (e.g., Bryan and gabbroic to granitic sills and dikes, which for a mafi c source that has exchanged oxygen Ernst, 2008). During incipient rifting, the prox- intruded into Colorado River delta fl uviatile by interacting with meteoric hydrothermal imity to sources of continent-derived detritus and lacustrine sediments. Combined single- fl uids. Collectively, these data imply that oce- shed into rift basins can also exert strong con- crystal U-Th-Pb and (U-Th)/He zircon ages anic rifting has initiated in the Salton Trough trol on the compositional diversity of mag- reveal late Pleistocene to Holocene eruption and Cerro Prieto basins. There, MORB-type mas and their representation in the geological ages for three volcanic centers in adjacent magmas formed mafi c intrusions within thick record. These controls include (1) density fi lter- rift basins (from N to S): Salton Buttes (erup- sedimentary basin fi ll, where they became ex- ing of magmas where negatively buoyant mafi c tion age: 2.48 ± 0.47 ka; 95% confi dence), posed to deep-reaching hydrothermal fl uids. magmas stall within sequences of low-density Cerro Prieto (maximum eruption age: 73 ± Diverse intermediate- to high-silica rhyolitic sediments so that the record of surfi cial vol- 7 ka), and Roca Consag (eruption age: 43 ± magmas that are prevalent at the surface canic rocks is not representative of magma fl ux 6 ka). U-Th zircon and allanite crystalliza- are produced by fractional crystallization of at depth (e.g., Fuis et al., 1984); (2) rapid sub- tion ages are close to the eruption ages, with mafi c parental magmas with minor assimila- sidence and burial, which conceal earlier phases the exception of Roca Consag lava, the zir- tion of sediments or pre-rift basement rocks, of magmatism (e.g., Herzig, 1990; Hurtado- con population of which is dominated by and by partial melting of hydrothermally al- Brito, 2012); (3) contamination of magmas dur- zircon with ca. 1 Ma crystallization ages, a tered mafi c intrusions. ing ascent through thick sequences of sedimen- population interpreted to be recycled from tary basin fi ll (through melting and assimilation, an unknown crustal source underlying the INTRODUCTION or mingling between magma and sediment; e.g., Wagner basin. Nd isotopic ratios for sub- Gibson et al., 1997); and (4) metamorphism and surface micro gabbros from Cerro Prieto The southwestern North American conti- hydrothermal alteration caused by fl uid circu- (εNd = +8.9) overlap with values for mid- nental margin evolved from a convergent plate lation through porous sediments in magmati- oceanic-ridge basalts (MORB) from the East boundary into a series of rift basins and embry- cally active rift zones (e.g., Einsele et al., 1980; Pacifi c Rise, adjacent to the southern Gulf onic oceanic spreading centers interconnected McKibben et al., 1988). of California. Cerro Prieto microgranites by NW-SE–oriented transform fault systems In order to better constrain the origins of and Salton Sea basaltic xenoliths have simi- during the late Cenozoic (Lonsdale, 1989; Oskin rift-related magmatism and the interaction larly elevated εNd values. The lowest εNd value and Stock, 2003). This plate boundary reconfi g- between magma and sediment during conti- for late Pleistocene–Holo cene igneous rocks uration encompasses a transition between fun- nental breakup, we studied a comprehensive from the northern Gulf of California is for damentally different magma production mecha- suite of surface and subsurface magmatic rocks Cerro Prieto dacitic lava (εNd = +0.6). This nisms: during subduction, melting is triggered from the northern Gulf of California, consist- by hydration of the mantle wedge, whereas ing of samples from two subaerial rift basins †E-mail: [email protected] magmatism in continental rifts and divergent (Salton Trough, Cerro Prieto) and the submarine GSA Bulletin; November/December 2013; v. 125; no. 11/12; p. 1833–1850; doi: 10.1130/B30787.1; 14 fi gures; 3 tables; Data Repository item 2013358. For permission to copy, contact [email protected] 1833 © 2013 Geological Society of America Downloaded from gsabulletin.gsapubs.org on January 15, 2014 Schmitt et al. Wagner basin (Fig. 1). In addition to whole- rock geochemical analysis, we also focused on single-crystal geochemical and geochrono- SAF logical analysis of zircon as a robust indicator 1 mineral. Single-crystal zircon geochronology IF permits us to constrain magmatic crystallization U.S.A. Mexico 2 and eruption ages at high temporal resolution, . ........................................................................................ ............................................................................... .......................CPF............................................................................................................................................... ...................................................................................................................................................................... even for subsurface rocks highly altered by geo- . ...................................................................................................................................................................... ............................................................................................................................................................. .......... ...................................................................................................................................................................... thermal activity. Alteration-resistant geochemi- . ...................................................................................................................................................................... ..................................................................................................
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