Volcanic Markers of the Post-Subduction Evolution of Baja California and Sonora, Mexico: Slab Tearing Versus Lithospheric Rupture of the Gulf of California

Abstract

The study of the geochemical compositions and K-Ar or Ar-Ar ages of ca. 350Neogene and Quaternary lavas from Baja California, the Gulf of California and Sonora allows us to discuss the nature of their mantle or crustal sources, the conditions of their melting and the tectonic regime prevailing during their genesis and emplacement. Nine petrographic/geochemical groups are distinguished: "regular" calc-alkaline lavas; adakites; magnesian andesites and related basalts and basaltic andesites; niobium-enriched basalts; alkali basalts and trachybasalts; oceanic (MORB-type) basalts; tholeiitic/transitional basalts and basaltic andesites; peralkaline rhyolites (comendites); and icelandites. We show that the spatial and temporal distribution of these lava types provides constraints on their sources and the geodynamic setting controlling their partial melting. Three successive stages are distinguished. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 3 mantle of the Gulf area, generating calc-alkaline lavas as well as adakites derived from slivers of oceanic crust incorporated within this mantle.

Seismic structure beneath the Gulf of California: a contribution from group velocity measurements

“…More importantly, the timing of melt production from these numerical models matches geochemical observations. Calmus et al (2011) suggest that the spatial and temporal distribution of volcanism in Baja is consistent with the development of a slab-tear evolving into a 200-km wide slab window parallel to the trench extending from the Pacific coast across Baja to coastal Sonora. Tholeiites and alkali basalts of subslab origin rose through this window, while the adakites were derived from the partial melting of its upper lip, close to the trench.…”

“…We give here a brief description of the main lavas in the study region following Calmus et al (2011). Among mafic rocks, regular calc-alkaline lavas are evident mostly from 32 • to 24 • N in eastern Baja, in the Gulf beneath Isla Tiburon and also close to the coast of central Sonora (Fig.…”

“…The focus of this study is to compare our seismic velocity structure, which is determined at a map resolution of approximately 10 × 10 km to the gross lithospheric structure based on regional volcanism suggested from geological and geochemical studies (e.g. Castillo 2008;Calmus et al 2011).…”

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“…Stretching of the continental lithosphere preceded direct interaction of the Pacifi c and North America plates and produced the Basin and Range composite extensional province (Dickinson, 2002). In Mexico, the Basin and Range episode of extension is recognized across a wide region north of the Trans-Mexican Volcanic Belt (e.g., Henry, 1989;Henry andAranda-Gomez, 1992, 2000;Calmus et al, 2010) (Fig. 1), although the western limit of this extension has been poorly defi ned.…”

“…Separating young extension of the GEP from that of the older Basin and Range is particularly challenging in the northern part of the SMO (Fig. 1) (see discussion in Calmus et al, 2010). In Sonora and Chihuahua, extension has affected the entire volcanically active region, and appears spatially contiguous and temporally continuous, leading to different interpretations on the location of the boundary between the two extensional provinces (Fig.…”