31-4 Preliminary Bedrock and Surficial Geological Mapping of the Southern Half of the Loveland Pass 7.5’ Quadrangle

Session: Best Student Geologic Map Competition (Posters)

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Abstract:

A 1:24,000 geologic map of the southern half of the Loveland Pass 7.5’ quadrangle was drafted as a part of the USGS EDMAP Program. The area, which is located along the 1-70 corridor approximately 60 miles west of Denver, Colorado, includes the Johnson and Eisenhower Memorial Tunnels as well as the continental divide at Loveland Pass, and the Loveland Ski Area. The primary objective of this study is to explore the structural evolution of the region throughout the Proterozoic, specifically in relation to the Paleoproterozoic Yavapai/Mazatzal (1.8-1.6 Ga) orogenies and the Mesoproterozoic Picuris Orogeny (~1.4 Ga).  

The dominant rock types in the area are Paleoproterozoic biotite-sillimanite schist and gneiss, biotite schist and gneiss, monzogranite and granite gneiss. These units, as well as minor quartzite and amphibolite gneiss, are components of a large, heterogeneous sequence of metasedimentary and metavolcanic rocks. Local migmatite and sillimanite indicate that these rocks reached upper amphibolite facies metamorphism. The Mesoproterozoic Silver Plume Granite (1424 ± 6 Ma) is predominant in the eastern and north-eastern extent of the map area. Laramide orogeny-aged pegmatitic and porphyritic dikes intrude the Proterozoic bedrock. Quaternary deposits in the map area include glacial till from the Bull Lake (170-120 Ka) and Pinedale (30-12 Ka) glacial periods.     

Based on preliminary structural data, the main structures in the area can be attributed to shallowly to moderately NNE-plunging regional F2 folding. Foliations in the heterogenous migmatitic gneiss and schist package predominantly dip moderately to steeply towards the SE and NW.  Isoclinal F1 folds have variable hinge orientations, while asymmetric folds moderately plunge NNE and SSW and are likely related to F2. Locally along the ridges in the eastern part of the area, F2 fold hinges plunge shallowly to moderately towards the WSW and ENE. Intersection and mineral lineations generally plunge steeply to moderately NE. The Silver Plume Granite locally demonstrates moderate to weak foliation that is parallel to subparallel to foliations in proximal units. Lineaments visible in LiDAR imagery have variable orientations. Lineaments oriented NNE and NNW in the SE section of the quadrangle locally correlate to brecciated zones. Cretaceous-Paleogene pegmatites and porphyry dikes do not show any evidence of deformation.  

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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