The petrogenesis of Early–Middle Jurassic magmatism in southern and central Mexico and its role during the break-up of Western Pangaea

Abstract

Central and southern Mexico represents a strategic place to understand the dynamics of Pangaea break-up and its influences on the evolution of the Pacific margin of North America. Lower–Middle Jurassic volcano-sedimentary successions, and scarce magmatic rocks, crop out discontinuously across this region and have been interpreted either as a vestige of a continental arc or as several deposits of syn-rift magmatism. At present, their origin is controversial. Available geochemical data on these igneous rocks suggest that they represent almost pure crustal melts produced in a rift environment rather than in an arc. In fact, the studied rocks exhibit the high silica contents and moderate to strong peraluminous character typical of sediment melts. The enriched isotopic composition (high 86Sr/87Sr and low 143Nd/144Nd) and the age distributions of inherited zircon grains readily identify the widespread Upper Triassic metasedimentary sequences presently exposed in southwestern and central Mexico as the most likely crustal source of these Jurassic igneous rocks. Accordingly, we argue that these Early–Middle Jurassic magmas originated in a syn-rift igneous province associated with extensional-driven crustal attenuation in the context of Pangaea fragmentation. Our findings also constrain post-Pangaea subduction initiation to be younger than Middle Jurassic time in central and southern Mexico.

La Unión Monzogranite: geochronology and significance of the Jurassic arc in the Sula Terrane, Guatemala

“…Normalized to: P mantle (Sun and McDonough, 1989) Normalized to: Cl chondrite (Sun and McDonough, 1989) for LUP samples with a database of modern (Trans Mexican Volcanic Belt) and Mesozoic (Alisitos and NW) arcs in Mexico, as well as to the NIP Jurassic samples reported by Parolari et al (2022), it is possible to observe that LUP samples fit with the NIP ones, being equally depleted in Sr, high in Rb and with low, but variable, Nb contents (Figure 11).…”

“…While in northwestern Mexico the Jurassic continental magmatism is seen as the southern continuation of the Cordilleran system (see Martini and Ortega-Gutierrez, 2018, for a complete synthesis), in northeastern, central and southern Mexico Jurassic magmatism belonging to the Nazas Igneous Province (NIP) has been recently reinterpreted as crustally derived by partial melting of continental rocks during the extensional tectonics that accompanied the opening of the Gulf of Mexico, based upon a strict reinterpretation of its geochemical character (Parolari et al, 2022). The model proposed by Parolari et al (2022) also applies to isolated Jurassic rocks of southwestern Mexico, such as: (a) a Middle Jurassic pluton with an age of 165 Ma reported by Guerrero-García et al (1978) from the Acapulco -Tierra Colorada transect of the Xolapa Complex; (b) a ~158 Ma orthogneiss reported by Ducea et al (2004) from north of Puerto Escondido; and (c) the Early Jurassic Tizapa metagranite (186.5 ± 7.4 Ma, lower intercept of discordant data) in the eastern Guerrero Terrane, Teloloapan subterrane (Elías-Herrera et al 2000); (d) Jurassic, two-mica granites exposed E of the Puerto Vallarta batholith (Valencia et al, 2013;Schaaf et al, 2020). In southern Mexico a migmatization event is known in the eastern Acatlán complex (Magdalena migmatite, 175±3 and 171±1 Ma) and associated with a thermal unroofing during the breakup of Pangea (Keppie et al, 2004), thus it can be clearly ascribed to the same extensional event.…”

“…While the obtained ages sit the LUP magmatism in the Middle Jurassic, two regimes contributed to the generation of this magmatism for this time span: 1) the magmatism related to the subduction of the Farallon and Cocos plates, which were active at least since the beginning of Mesozoic, as the widespread magmatism since the Early Jurassic testifies (e.g., Spikings et al, 2015;Martini and Ortega-Gutiérrez, 2018, and Figure 12); together with 2) the extensional processes that produced several rift basins associated to the onset of the Gulf of Mexico opening (e.g., Engebretson et al, 1985;Pindell and Kennan, 2009;Martini and Ortega-Gutiérrez, 2018;Parolari et al, 2022, and references therein), the breakup of Pangea (e.g., Martini et al, 2022) with the relative migration of Gondwana toward SE and the formation of several NS and WNW-oriented lateral faults in southern Mexico (#1 to 5 in Figure 12, see also Zepeda-Martínez et al, 2021). The NS-trending lateral faults are subparallel to the Tamaulipas-Chiapas Transform zone, which corresponds to the main trace of the Yucatán displacement during the opening of the Gulf of Mexico (Figure 12).…”

“…crustal thinning that accompanied the initial stages of Pangea breakup. Such process is represented, in Mexico, by the Nazas Igneous Province (e.g., Parolari et al, 2022) whose emplacement accompanied the breakup of Pangea and opening of the Gulf of Mexico.…”

Detecting the Laramide event in southern Mexico by means of apatite fission-track thermochronology

“…During the Mesozoic period, the continental extensional tectonics was controlled by two important geodynamic processes: the subduction of the Farallon Plate beneath the western margin of North America and the rupture of Pangaea during Late Triassic-Middle Jurassic time (e.g. Martini & Ortega-Gutiérrez, 2018;Parolari et al 2022). Martini suggested that the Late Jurassic to Early Cretaceous back-arc spreading of the Arperos Basin separated the Guerrero terrane from the Mexican mainland.…”