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1 Bureau of Economic Geology, John A. and Katherine G. Jackson School of Geosciences, University of Texas at Austin, Austin, TX 78713, USA
2 Department of Petroleum and Geosystems Engineering, University of Texas at Austin, Austin, TX 78713, USA Steve.Laubach{at}beg.utexas.edu
3 Geocosm L.L.C., 3311 San Mateo, Austin, TX 78729, USA
High-resolution scanning electron microscope (SEM)-based cathodoluminescence images were used to reconstruct incremental fracture opening in regional opening-mode fractures in sandstone. Opening is recorded by crack-seal texture in isolated mineral bridges that span opening-mode fractures formed in sandstone at moderate-great depth (c. 1000–6000 m). We restored opening histories of nine representative fractures with apertures of millimetres in five sandstones from five sedimentary basins. Gaps created by fracture widening in 11 bridges range from less than 1 µm to more than 1 mm, but nearly all are less than 20 µm and most are less than 5 µm. These are the opening amounts that could be spanned by cement growth in these diagenetic environments. Our observations are the first evidence of opening amounts from mostly porous, opening-mode (joint-like) fractures formed in diagenetic environments. Patterns are consistent with a new structural diagenetic model of bridge growth that can use opening patterns to indicate rate of fracture opening as a function of time.
