33-7 Paleomagnetic Analysis Suggests Synrift Emplacement of Diabase Dikes in the Scottsville Basin, VA

Session: Going with the Shear - New Insights into Lithospheric Extensional and Strike-Slip Systems (Posters)

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This study investigates the emplacement history of a diabase dike in the Scottsville Basin in Virginia just southwest of Charlottesville. This small half-graben (130 km²) developed as part of the normal fault systems that formed along the rifted margin of North America during the breakup of Pangea. Rift related sediments are tilted and consist primarily of siltstone and sandstone which are crosscut by diabase dikes. Forty samples were cored from an orientated hand sample of diabase dike and subjected to gradual thermal demagnetization to a maximum of 700˚C. Excluding those samples that exhibited incomplete demagnetization, irregular demagnetization, and those with southward trends and negative inclinations, the high temperature thermal remanent magnetization is characterized by a northward declination with a moderate downward inclination (n = 21, D = 356, I = 47, a₉₅ = 6.7).  The virtual geographic pole position (VGP) suggested by this in situ remanent magnetization is inconsistent with the North American Apparent Polar Wander curve of Torsvik et al. (2012).  However, if the surrounding tilted sedimentary rocks are restored to horizontal the resulting tilt corrected remanent magnetization (D = 343, I = 31) yields a VGP that falls directly on the apparent polar wander curve at approximately 160 Ma.  This is consistent with recent dating of rift related dikes in the mid-Atlantic and yielded ages clustering around ~201 Ma, ~180 Ma, and ~155 Ma. (Foster-Baril et al., 2025).  Together, these results suggest that a diabase dike was emplaced into the Scottsville Basin ~160 Ma. Extension continued after emplacement resulting in tilting of both the rift fill sediments and the diabase dike.

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

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