28 Geologic Mapping in the West (Posters)

This poster session highlights geologic mapping in the western Cordillera and Rocky Mountains. We encourage submissions that explore bedrock and surficial geology, geophysics, hydrology, hazards, and more. Both professional and student submissions are welcome.

Tuesday, 19 May 2026
8:00 AM - 5:30 PM
Alvarado D/E

Resolving Late Archean to Earliest Paleoproterozoic Evolution on the Southern Margin of the Wyoming Craton with High-resolution Geological Mapping and U-Pb Geochronology

Paper number: 28-6
Program: Technical Sessions
Time: 8:15 AM – 8:15 AM

Authors

Abstract

The Sierra Madre in SE Wyoming contains metasedimentary and igneous rocks representing the Archean-Paleoproterozoic transition with stratigraphic studies indicating strong similarities between supracrustal units developed on the southern margins of the Superior and Wyoming cratons and their deposition in the same sedimentary basin. Despite these similarities, a thick sequence of 2.45 Ga volcanic rocks in the basal Huronian Supergroup appeared to have no corollary volcanic succession on the southern margin of the Wyoming Craton until recent dating of a 2450 Ma volcanic unit and a detrital zircon study revealed that the volcanosedimentary Phantom Lake Metamorphic Suite (PLMS) has a statistically significant population of detrital zircon at ca. 2450 Ma (Mammone et al., 2022), further supporting the Paleoproterozoic correlation between the basal Huronian Supergroup in Canada with the PLMS in Wyoming. While these recent geochronologic results have tightened the correlation between these Paleoproterozoic successions, inconsistencies arose between relative ages established with previous geological mapping in the Sierra Madre with absolute ages established by U-Pb dates. The 2710±10 Ma Spring Lake Granodiorite (Premo and Van Schmus, 1989) is older than the ca. 2450 Ma Paleoproterozoic PLMS. However, mapped relationships between units were used to infer that the PLMS is intruded by the Spring Lake Granodiorite. We address these inconsistencies in relative vs absolute ages of the PLMS and the Spring Lake Granodiorite, by presenting detailed geologic maps for the Sierra Madre that resolve contact relationships between the Spring Lake Granodiorite and PLMS. In addition, new U-Pb isotope data reveal that the Spring Lake Granodiorite is a polygenetic unit, containing a series of lithologies, including early Archean basement granitoids, ca. 2.71 Ga granitoids of the same age as the Vulcan Mountain Metavolcanics that underlies the PLMS, and ca. 2.68 Ga and 2.65 Ga granitoids. While ca. 2.65 Ga granitoids intrude the Vulcan Mountain Metavolcanics, which bear carbonates, the PLMS has no stratigraphic or igneous contacts with these granitoids nor host any carbonates. U-Pb geochronology potentially indicates a correlative to the 2.45 Ga Baggot Rock comingled felsic and mafic intrusion, extending felsic magmatism of this age to the Sierra Madre. Our study highlights a complex tectonic evolution along the southern margin of the Wyoming Craton with multiple magmatic events spanning the Archean-Paleoproterozoic transition.

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

doi: 10.1130/abs/2026RM-410578

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