10 Advancements in the Proterozoic tectonics of western North America (Posters)

This session highlights recent developments in understanding of the Proterozoic tectonic record of western Laurentia, particularly its relation to critical mineral resources. Insights derived from all disciplines and approaches are welcome.

Monday, 18 May 2026
8:00 AM - 5:30 PM
Alvarado D/E

U-Pb Geochronologic Constraints on Proterozoic Magmatism, Sedimentation, and Metamorphism in Southern New Mexico with a focus on the San Andres Mountains

Paper number: 10-2
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

We have conducted an extensive mapping, geochemical, and geochronological study of the Proterozoic rocks of the San Andres Mountains in south-central New Mexico. The rocks are exposed largely within the White Sands Missile Range and encompass the lowest exposures of a westward-tilted normal fault block extending over 100 km. Limited prior geochronology consists of a three low-precision U-Pb dates (1.7–1.4 Ga) and three argon dates (1.45–1.40 Ga). We present ~25 new igneous U-Pb zircon ages, three U-Pb baddeleyite cooling ages, and U-Pb detrital zircon ages from eleven metasedimentary rocks. The main rock types and their ages include: strongly foliated felsic gneiss with ages from 1674±10 Ma to 1647±12 Ma, and deformed amphibolite, some of which is undated and interlayered at a meter scale with orthogneiss, and another exposure ~75 km to the south which is 1634±18 Ma. Largely undeformed granites range from 1670±16 Ma to 1639±10 Ma. Many of these granites are dikes cross-cutting the gneiss. The apparent overlap in ages between deformed and undeformed rocks is baffling. Another group of granites are 1477±21 Ma to 1446±38 Ma, and three titanite ages are 1489–1459 Ma.

The ages here are broadly comparable to our other studies in the region, primarily the Burro Mountains of southwest New Mexico. We previously suggested that many of the undeformed granites of ~1650 Ma were post-collisional crustal melts following the Mazatzal orogeny. The timing of Mazatzal metamorphism is easier to determine in the San Andres, where ~1.45 Ga magmatism is less intense. We note that the 1639±10 Ma Strawberry Peak pluton has a contact aureole in phyllitic rocks in which garnet growth is enhanced near the intrusion. We use this relationship to suggest Mazatzal heating was moderate and that post-collisional plutons overprinted metamorphic rocks at ~1640 Ma. Clear evidence of heating from ~1.45 Ga granites may have reset U-Pb titanite and Ar-Ar mica systems, despite only minor exposures of coeval granites, but no deformation associated with the Picuris orogeny is observed.

Detrital zircons from quartzite, phyllite, and schist have MDA ranging from ~1680–1640 Ma. We suspect that along-range variations in timing of sedimentation, lithology, magmatism and metamorphism indicate a more complicated history possibly involving tectonic boundaries over the 100 km length of the San Andres Mountains.

Geological Society of America Abstracts with Programs. Vol. 58, No. 4

doi: 10.1130/abs/2026RM-410550

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