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Volcanic Markers of the Post-Subduction

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Volcanic Markers of the Post-Subduction Volcanic Markers of the Post-Subduction Evolution of Baja California and Sonora, Mexico: Slab Tearing Versus Lithospheric Rupture of the Gulf of California Thierry Calmus, Carlos Pallares, René Maury, Alfredo Aguillón-Robles, Hervé Bellon, Mathieu Benoit, François Michaud To cite this version: Thierry Calmus, Carlos Pallares, René Maury, Alfredo Aguillón-Robles, Hervé Bellon, et al.. Volcanic Markers of the Post-Subduction Evolution of Baja California and Sonora, Mexico: Slab Tearing Versus Lithospheric Rupture of the Gulf of California. Pure and Applied Geophysics, Springer Verlag, 2011, 168 (8-9), pp.1303-1330. 10.1007/s00024-010-0204-z. insu-00543676 HAL Id: insu-00543676 https://hal-insu.archives-ouvertes.fr/insu-00543676 Submitted on 25 Feb 2011 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Manuscript Click here to download Manuscript: CALMUS et al.doc Volcanic markers of the post-subduction evolution of Baja 1 2 3 California and Sonora, Mexico: Slab tearing versus lithospheric 4 5 rupture of the Gulf of California 6 7 8 9 10 11 a, a, b b c 12 Thierry Calmus *, Carlos Pallares , René C. Maury , Alfredo Aguillón-Robles , 13 b d e 14 Hervé Bellon , Mathieu Benoit , François Michaud 15 16 17 18 19 a 20 Estación Regional del Noroeste, Instituto de Geología, Universidad Nacional 21 Autónoma de México, Hermosillo, Son., C.P. 83000, México 22 23 24 25 b 26 Université Européenne de Bretagne, Université de Brest; CNRS; UMR 6538 27 Domaines Océaniques; Institut Universitaire Européen de la Mer, Place N. Copernic, 29280 28 29 Plouzané, France. 30 31 32 33 c 34 Instituto de Geología, UASLP, Av. Dr. Manuel Nava no. 5, Zona Universitaria, San 35 Luis Potosí, S.L.P., C.P. 78250, México. 36 37 38 39 d 40 UMR 5562, OMP, Université Paul Sabatier, 14 Avenue Edouard Belin, F-31400 41 Toulouse, France 42 43 44 45 e 46 UMR 6526, Géosciences Azur, Université Pierre et Marie Curie, F-06235 47 Villefranche sur Mer, France. 48 49 50 51 52 53 * Corresponding author: e-mail: [email protected] 54 55 56 57 58 59 60 61 62 63 1 64 65 Abstract 1 2 The study of the geochemical compositions and K-Ar or Ar-Ar ages of ca. 350 3 4 Neogene and Quaternary lavas from Baja California, the Gulf of California and Sonora allows 5 us to discuss the nature of their mantle or crustal sources, the conditions of their melting and 6 7 the tectonic regime prevailing during their genesis and emplacement. Nine 8 9 petrographic/geochemical groups are distinguished: “regular” calc-alkaline lavas; adakites; 10 11 magnesian andesites and related basalts and basaltic andesites; niobium-enriched basalts; alkali 12 13 basalts and trachybasalts; oceanic (MORB-type) basalts; tholeiitic/transitional basalts and 14 15 basaltic andesites; peralkaline rhyolites (comendites); and icelandites. We show that the spatial 16 17 and temporal distribution of these lava types provides constraints on their sources and the 18 19 geodynamic setting controlling their partial melting. Three successive stages are distinguished. 20 Between 23 and 13 Ma, calc-alkaline lavas linked to the subduction of the Pacific- 21 22 Farallon plate formed the Comondú and central coast of Sonora volcanic arc. In the extensional 23 24 domain of western Sonora, lithospheric mantle-derived tholeiitic to transitional basalts and 25 26 basaltic andesites were emplaced within the southern extension of the Basin and Range 27 28 province. 29 30 The end of the Farallon subduction was marked by the emplacement of much more 31 32 complex Middle to Late Miocene volcanic associations, between 13 and 7 Ma. Calc-alkaline 33 34 activity became sporadic, and was replaced by unusual post-subduction magma types including 35 adakites, niobium-enriched basalts, magnesian andesites, comendites and icelandites. The 36 37 spatial and temporal distribution of these lavas is consistent with the development of a slab 38 39 tear, evolving into a 200 km-wide slab window sub-parallel to the trench, and extending from 40 41 the Pacific coast of Baja California to coastal Sonora. Tholeiitic, transitional and alkali basalts 42 43 of subslab origin ascended through this window, adakites derived from the partial melting of its 44 45 upper lip, relatively close to the trench, and calc-alkaline lavas, magnesian andesites and 46 47 niobium-enriched basalts formed from hydrous melting of the supraslab mantle triggered by 48 49 the uprise of hot Pacific asthenosphere through the window. 50 During the Plio-Quaternary, the “no-slab” regime following the sinking of the old 51 52 part of the Farallon plate within the deep mantle allowed the emplacement of alkali and 53 54 tholeiitic/transitional basalts of deep asthenospheric origin in Baja California and Sonora. The 55 56 lithospheric rupture connected with the opening of the Gulf of California generated a high 57 58 thermal regime associated to asthenospheric uprise, and emplaced Quaternary depleted MORB- 59 60 type tholeiites. This thermal regime also induced partial melting of the thinned lithospheric 61 62 63 2 64 65 mantle of the Gulf area, generating calc-alkaline lavas as well as adakites derived from slivers 1 2 of oceanic crust incorporated within this mantle. 3 4 5 6 7 Keywords: slab tearing, slab melting, ridge-trench collision, adakite, basalt, comendite, 8 9 magnesian andesite, asthenospheric window, Basin and Range, Gulf of California, Baja 10 11 California, Sonora, México 12 13 14 15 16 17 1. Introduction 18 19 20 The geochemical (major, trace elements and isotopic) compositions of fresh magmatic 21 22 rocks are mostly inherited from those of their source materials during partial melting, although 23 24 they may have been modified later by intracrustal petrogenetic processes such as fractional 25 26 crystallization coupled or not with assimilation of host rocks, or magma mixing. On one hand, 27 28 experimental studies allow the petrologist to take into account the geochemical effects linked 29 30 to variable source mineralogy, temperature, pressure, and melting rate on the composition of 31 32 the melts. On the other hand, the presence of a given source at depth and the physical 33 34 conditions governing its partial melting are controlled by the regional geodynamic setting. 35 Magmatic rocks are thus potential markers of the tectonic regime prevailing during their 36 37 emplacement. 38 39 The Neogene and Quaternary geological history of Baja California, Sonora and Gulf of 40 41 California has been marked by the almost continuous emplacement of volcanic rocks showing 42 43 an exceptional geochemical diversity (Gastil et al., 1979; Sawlan, 1991; Benoit et al., 2002). 44 45 Mafic lavas encompass the whole range of basaltic compositions, from depleted mid-oceanic 46 47 ridge basalts (MORB) to plume-type alkali basalts, through various kinds of tholeiitic, 48 49 transitional and calc-alkaline basalts and the very rare niobium-enriched basalts (NEB: 50 Aguillón-Robles et al., 2001). Intermediate and evolved lavas are also highly diversified. In 51 52 addition to the types commonly found in calc-alkaline series, they include unusual rocks such 53 54 as magnesian andesites (Saunders et al., 1987; Calmus et al., 2003), adakites (Aguillón-Robles 55 56 et al., 2001; Calmus et al., 2008), icelandites and peralkaline rhyolites (Vidal-Solano et al., 57 58 2008a, b). 59 60 61 62 63 3 64 65 A majority of authors have considered this geochemical diversity as resulting from the 1 2 partial melting of contrasted mantle and crustal sources, during the complex tectonic evolution 3 4 of the Pacific margin, which followed the end of the subduction of the Farallon oceanic plate 5 around 12.5 Ma. In Baja California, the wide range of erupted magmas is generally attributed 6 7 to the opening of an asthenospheric window, although the details of the process are debated: 8 9 for instance, the source of adakites is thought to be either the subducted Farallon crust or the 10 11 mafic base of the continental crust (see Pallares et al., 2007, 2008; Castillo, 2008, 2009; Maury 12 13 et al., 2009, and references therein). In Sonora, the association of tholeiitic to transitional 14 15 basalts (temporally evolving towards alkali basalts) with icelandites and peralkaline rhyolites is 16 17 linked to the transition from a typical Basin and Range regime to rift opening in the nearby 18 19 Gulf of California (Vidal-Solano et al., 2008a, b). 20 However, a rather different point of view has been developed in two recent articles. 21 22 Negrete-Aranda and Cañón-Tapia (2008) consider that a stalled Farallon slab is still present 23 24 beneath Baja California, and that the post-subduction magmas originated from sources located 25 26 in the mantle wedge or the overlying continental crust. These authors claim that the partial 27 28 melting of these sources was due to the thermal rebound following the end of subduction, and 29 30 that the temporal and spatial distribution of post-subduction lavas resulted from local tectonic 31 32 features like the stress field and the tensile strength of the Baja California crustal rocks. Till et 33 34 al. (2009) consider all the Miocene volcanism in Sonora as subduction-related (continental arc 35 type), and find only subtle geochemical changes (slight variations of incompatible element 36 37 ratios, e.g.
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