EXPERIMENTAL ALTERATION OF IMPACT GLASSES FROM THE CHESAPEAKE BAY IMPACT — EYREVILLE AND CAPE CHARLES CORES

During meteorite impact events, impact-melt glasses are commonly produced as melt particles and spherules, as coherent melt sheets and breccias, or as melt clasts in a clastic matrix of suevite breccia. The alteration or transformation of impact-melt glasses to clay minerals, particularly smectite, has been recognized in several impacts. In this project we have studied the alteration of both artificially produced glass as well as melt-rock clasts from the suevites in drill cores (ICDP-USGS Eyreville-B core and USGS Cape Charles test hole) from the Chesapeake Bay impact structure.

The artificial glasses were specifically designed to mimic their alter ego from an impact into a wet target in the Chesapeake Bay region. The melt samples were crushed in an opal mortar prior to any experimental alteration, then processed in a 450 ml ParrTM mixed-flow reactor without using the stirring equipment. The reactor was half filled with artificial seawater, and the samples were altered for one week. In order to speed up the reactions, we used reactor temperatures of both 200°C and 300°C.

The alteration experiments formed clay minerals on the surfaces of the melt particles as well as fine-grained material in suspension in the solutions. Smectite and vermiculite have been identified.

The experiments showed that the impact glasses follow the same dissolution mechanism as the natural glasses, following the rate equation previously described for basaltic glass. This equation has been used to model the dissolution of the impact glasses in this experiment.