A Pliocene ignimbrite flare-up along the Tepic-Zacoalco rift: Evidence for the initial stages of rifting between the Jalisco block (Mexico) and North America

Abstract

The Tepic-Zacoalco rift, a NW-trending corridor ~50 × ~250 km, is one arm of a triple-rift system in western Mexico. Together with the Colima rift and the Middle America Trench, it bounds the Jalisco block, a portion of western Mexico that may be moving independently of North America. The predominant basement rock types in the TepicZacoalco rift are rhyolitic ash-fl ow tuffs and lavas, which were previously assumed to be Oligocene-Miocene in age, related to the Sierra Madre Occidental volcanic province, or older. New 40 Ar/ 39 Ar dates on 41 volcanic samples reveal a previously unrecognized, voluminous fl are-up of rhyolitic ignimbrites between 5 and 3 Ma throughout the entire corridor of the Tepic-Zacoalco rift; they are often associated with Pliocene high-Ti basalts. The eruption rate during this Pliocene time period was an order of magnitude higher (hundreds of m/m.y.) than that documented in the Tepic-Zacoalco rift over the last 1 m.y. The Pliocene ash-fl ow tuffs have been faulted along NW-trending lineaments, producing vertical offsets up to at least 500 m. The voluminous ignimbrite fl are-up in the TepicZacoalco rift at 5-3 Ma may refl ect the initial stages of rifting of the Jalisco block away from North America, analogous to what occurred in the proto-gulf region at 12-6 Ma, prior to the transfer of Baja California from North America to the Pacifi c plate. Additionally, new 40 Ar/ 39 Ar dates show that the Sierra Madre Occidental volcanic province extends across the entire width of the Tepic-Zacoalco rift and terminates abruptly at the northern boundary of the Jalisco block near the Rio Ameca. In contrast, PaleoceneEocene basement from the Jalisco block extends northward into the Tepic-Zacoalco rift, where it is locally overlain by Sierra Madre Occidental rhyolites.

Geochemical evidence of mantle reservoir evolution during progressive rifting along the western Afar margin

“…Fresh matrix chips (0.2 g) were carefully handpicked under a binocular microscope and Ar analysis was undertaken using standard procedures outlined in Frey et al (2007). Samples were wrapped in pure Al foil packets and irradiated in location 5C of the McMaster Nuclear Reactor.…”

Present state of knowledge and new geochemical constraints on the central part of the Mexican Volcanic Belt and comparison with the Central American Volcanic Arc in terms of near and far trench magmas

“…In fact, in the western part of the MVB a well-defined triple junction with three intersecting rifts has been proposed (Tepic-Zacoalco rift, Colima rift, and Chapala rift; e.g., Allan, 1986;Garduño-Monroy et al, 1993;Frey et al, 2007), which is widely accepted by all researchers. In the remaining parts of the MVB (the C-MVB and the eastern part of the MVB-E-MVB; Figure 1) also, such extensional features have been documented in numerous studies (Negendank et al, 1985;Harrison, 1989, 1990;Ferrari et al, 1990;Suter et al, 1992Suter et al, , 1995aSuter et al, , 1995bSuter et al, , 2001Mooser et al, 1996;Alaniz-Álvarez et al, 1998;García-Palomo et al, 2000, 2002a, 2002bAnguita et al, 2001;Márquez et al, 2001;Wassmer et al, 2004;Norini et al, 2006;CamposEnríquez et al, 2013CamposEnríquez et al, , 2014.…”

Description of the Geology of the Tecolotlan Graben, Jalisco, Mexico

“…Previous work by Wallace and Carmichael (1989), Righter and Rosas-Elguera (2001);and Frey et al (2007) have also examined the Cretaceous volcanic rocks near the Tecolotlan graben. Righter and Rosas-Elguera (2001) described an older "greenish to violet colored andesite breccia" that they called the Jalisco breccia.…”

“…Between ca. 5 Ma and the present, mafi c to intermediate composition lavas were accompanied by a second generation of alkaline magmas (Allan, 1986;Moore et al, 1994;Frey et al, 2007;Ferrari et al, 2012).…”

“…Age probability diagram for dated volcanic rocks in the Tepic-Zacoalco and Colima grabens. Data from Allan (1986), Moore et al (1994), Nieto-Samaniego et al (1999), Ferrari et al ( , 2013Ferrari et al ( , 2014, Frey et al (2004Frey et al ( , 2007, Centeno-García et al (2011), Valencia et al (2013, Duque-Trujillo et al (2015).…”