5 The southern margin of the North American cordillera through time

This session deals with the geologic evolution of the southeastern Cordillera of the North American Plate, its role during ancient orogenic cycles, opening of the Gulf of Mexico, and its interaction with the Caribbean Plate.

Wednesday, 22 April 2026
8:00 AM - 12:00 PM
LMH, Meeting Room

Petrogenesis of the ~1.47–1.38 Ga intracratonic magmatism emplaced into the Paleoproterozoic provinces of the southwestern corner of Laurentia, northwestern Mexico

Paper number: 5-7
Program: Technical Sessions
Time: 10:05 AM – 10:25 AM

Authors

Abstract

During the mid-Mesoproterozoic, the recently formed intracratonic crustal provinces of Laurentia were intruded by a voluminous ~1.50−1.34 Ga granitic magmatism, commonly known as A-type or, more recently, ferroan. Traditionally, it was thought that these granites formed in an anorogenic tectonic environment, whereas the sources of their parental magmas have remained highly controversial. More recently, however, growing geological evidence, coeval with this magmatic episode, from Eastern Canada and the United States of America (USA), suggests a link to the accretionary processes along the southern margin of Laurentia. In northwestern Mexico, the southwestern corner of Laurentia’s craton, the age and petrogenesis of this inboard magmatic event remained poorly constrained.

New zircon U-Pb geochronology (LA-ICPMS and SHRIMP-RG), along with whole-rock Sm-Nd (TIMS), and zircon Lu-Hf (LA-ICPMS) isotope analyses were performed in intracratonic granite samples collected mostly from Sonora (northwestern Mexico), and a few from Arizona and New Mexico (USA). The results were compared with similar data from other ~1.40 Ga granite plutons and their host provinces from the southwestern USA.

Crystallization ages of the analyzed granitoids range from ~1470 to ~1379 Ma, with a higher frequency at the ~1420−1410 m.yr interval, supporting previous models of southwestward migration of this mid-Mesoproterozoic magmatism. Initial isotope signatures and depleted mantle model ages of granitoids from Sonora and southwestern USA indicate mixing between melts derived from the crustal reworking of the host Paleoproterozoic provinces and a depleted mantle reservoir. This interpretation is consistent with geochemical data indicating that the parental magmas of these granites were derived from mafic and sedimentary materials. These source components account for the chemical variability of this inboard magmatism, from the slightly ferroan to moderately magnesian, metaluminous to mostly peraluminous, and dominantly alkalic-calcic to calc-alkalic affinities. The majority of the studied samples plot in the continental arc fields on tectonic discrimination diagrams, with a few granite samples falling in the continental rift areas. These results are interpreted in terms of a back-arc tectonic setting, controlled by the structural features and dynamics of the subducting oceanic plate and its interactions with the overriding Laurentian craton.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3

doi: 10.1130/abs/2026CD-410912

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