ASSESSING BRITTLE VOLUME-GAIN AND PRESSURE SOLUTION VOLUME-LOSS PROCESSES IN QUARTZ ARENITE

Quartz arenite of the Tuscarora Sandstone has been deformed by disloca tion flow, pressure solution and microfracturing of which the last two are most important. Pressure solution involved shortening with no ext ension. Most samples have approximately 20% shortening normal to beddi ng interpreted to be compaction, and a few have up to 20% layer-parall el shortening of tectonic origin. Because there is no extension, these shortenings resulted in an equivalent amount of bulk volume loss, Mul tiple sets of microfractures in the form of fluid inclusion planes and microveins account for up to 10% extension and bulk volume increases up to 17%. When both microfracture volume gains and pressure solution volume losses arc considered together, all samples show a net bulk vol ume loss ranging from 14 to 35%. Changes in material volume are differ ent than bulk volume because of the presence of porosity at the time o f pressure solution. Whereas all samples show bulk volume losses, most samples show net material volume gains of up to 16% with only those h aving experienced both compactional and tectonic pressure solution sho wing material volume losses. Pressure solution during compaction can a ccount for most but not all cement. Compactional pressure solution sur faces do not extend into pore-filling cement suggesting that much of t he cement was externally derived after compaction. Therefore, the flux of material may have been considerably greater than the material volu me changes would indicate.