37-11 Basaltic Detectives: Determining Source Regions and Paleodrainage Across the Southern High Plains, North America by Petrographic Analysis of Ogallala Basalt Cobbles

Session: Geoscience Research Poster Showcase by 2YC and 4YCU Undergraduate Students

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Abstract:

Petrographic analysis of basaltic samples collected from the Miocene Ogallala Formation at Caprock Canyons, Janes Quarry, and Southeastern Colorado shows data that lead to inferences of these samples’ source regions and transport histories.

Several different populations have been observed via petrographic analysis to be in various conditions of weathering and alteration: hardly any weathering - and fresh olivine glomerocrysts - occur in one population; partial weathering and olivine alteration occur in another population; and, in another population, most to all olivine has completely altered to iddingsite, and/or the population is extremely weathered. Populations are also either vesicular or non-vesicular, with calcite and/or barite forming in and around the vesicles in the vesicular basalts. Other phenocrysts (e.g., feldspar, biotite) in the samples also range from fresh to completely altered. Magma mixing is suspected in some samples due to present rims around phenocrysts, dissolution of phenocrysts, and present xenocrysts. Other populations of note show zoning, indicating they underwent fractional crystallization. There are two possible source regions: a northerly source originating in the lava flows of northern New Mexico/southern Colorado, and a southerly source originating in the Trans-Pecos region. By collecting and comparing data from both formations and possible source regions, the latter can be deduced, and paleodrainage systems can be traced, both of which give a more complete understanding of the southwestern United States’ geology during the Cenozoic.

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