81-3 Using Borehole Core to Characterize Structural Features and Alteration in the Spavinaw Granite

Session: Investigating Earth’s History With Continental Scientific Drilling

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The Spavinaw Granite Group in northeastern Oklahoma, part of a Precambrian basement complex, offers insights into the interplay of tectonic and hydrothermal processes that shaped the Midcontinent's geological evolution. Periods of tectonic reactivation and hydrothermal alteration can modify the mechanical and hydrological properties of the rock with important implications. This study investigates the structural evolution and mineralogical alteration of the Spavinaw Granite using ~50ft of core, from ~1750ft measured depth, recovered from the AMAX SP-1 well located in Mayes County, OK. This research focuses on structural characterization of the core while employing petrographic analyses, X-ray diffraction (XRD), and scanning electron microscopy to identify changes in deformation styles and mineralogy. Structural and petrographic analyses revealed the presence of mineralized fractures, slickensides, mineral microfolds, and intergranular microfractures in the granite. Geochemical analyses identified multiple different hydrothermal episodes resulting in the alteration of primary minerals and textures in the Spavinaw Granite. This alteration resulted in the formation of clay-rich phases such as chlorite, kaolinite, illite, and mixed-layer of illite/smectite (I/S), along with mineral veins of quartz, chlorite, and carbonates. Hydrothermal fluid-rock interactions, structural reactivation, and the mineralization of fractures would create zones of mechanical weakness, contributing to fault instability and potentially increasing seismic susceptibility. This is particularly relevant for regions like Oklahoma, where fluid injection activities interact with pre-existing fault systems hydraulically connected to altered basement rocks, a dynamic closely linked to the state's recent history of induced seismicity driven by anthropogenic fluid circulation. This work highlights the importance of integrating thermal, mechanical, and chemical data, collected from relevant material from the subsurface, to assess the stability and behavior of basement faults in regions with active fluid injection practices.

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

doi: 10.1130/abs/2025AM-9842

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