31-2 Preliminary geology of the northern half of the Loveland Pass 7.5 Minute Quadrangle, central Colorado Front Range

Session: Best Student Geologic Map Competition (Posters)

Presenting Author:

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Abstract:

A preliminary 1:24,000 scale bedrock and surficial geologic map was created of the northern half of the Loveland Pass 7.5’ quadrangle. The mapping area straddles the continental divide immediately north of the Eisenhower tunnel, between Silver Plume and Dillon, Colorado. The main objective of the project is to investigate structures associated with the ~1.8-1.6 Ga Yavapai/Mazatzal and the ~1.4 Ga Picuris orogenies. This work builds on previously completed EDMAP and related projects where increasing evidence has been found for ~1.4 Ga deformation and metamorphism in the central Colorado Front Range. The main lithologies are Paleoproterozoic biotite-sillimanite gneiss, magnetite-feldspar-amphibole heterogeneous gneiss, quartzite, the Mesoproterozoic Silver Plume granite, pegmatite of various ages, and NNE-trending 3-5 meter-wide Cretaceous-Paleogene porphyritic dikes.

Foliation, lineation and fold orientations were mainly recorded in the biotite-sillimanite gneiss, which occurs along, and as xenoliths within, the Silver Plume granite. Foliations mostly dip steeply NW or SE, and fold hinges plunge shallowly NE and SW, indicating NE-trending folds. Numerous lineaments are visible in LiDAR imagery, and at least six show fault rock including breccia. These faults generally trend NE or WNW, with some trending N. Regionally, the ~170-120 ka Bull Lake and ~30-12 ka Pinedale tills are the most prominent glacial deposits, although in the northern half of the Loveland quadrangle only Pinedale till deposits have been mapped. Some surficial lineaments along or parallel to mapped brecciated bedrock zones show apparent recent to late Pleistocene fault displacement of Pinedale Till deposits. Rock glaciers are present on north-facing slopes where they are protected from the Sun, pro-talus ramparts and landslides are also common in the area.

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

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