Deducing Source Lithologies in Microtektites from the Chicxulub Impact

The Chicxulub Impact on the Yucatan Peninsula at the Cretaceous-Paleogene boundary produced microtektites that were distributed over a large region centered on the Caribbean basin. The tektites are generally altered in most localities, but a recently discovered deposit at Gorgonilla Island, Columbia yields a large percentage of fresh glassy microtektites up to ~2 mm in dimension. Previous work on these and the well-preserved tektites from Beloc, Haiti reveal heterogenous compositions between and even within individual tektites at scales down to a few microns. To a first order, compositions by EPMA reveal that the tektites are binary mixtures of granitic and Ca-S-rich components. However, there is significant variation from a simple mixing line and additional components are clearly implicated. Recent data from the Chicxulub drilling project provide a variety of additional possible components. The Chicxulub impactor itself has been assumed to have been fully vaporized during the event, and subsequent hydrothermal alteration has altered many of the terrestrial target rocks. Thus tektites have long been speculated as a possible source for identifying pre-impact target lithologies and possibly that of the impactor. Using pristine glassy Gorgonilla Island microtektites, this study aims to better quantify the number and compositions of Chicxulub target lithologies and ideally, insight into the lithology of the impactor itself. We are using microbeam techniques to produce a large geochemical data set for ~100 microtektites selected for the broadest range of colors and other characteristics. To these data we apply principal component analysis (PCA) and multivariate curve resolution-alternating least squares (MCR-ALS) techniques to identify the optimal components that explain the diversity of compositions which represent mixtures at various scales. Special attention is given to misfit elements such as volatiles, whose anomalies can reveal fractionation during vaporization or condensation- thus enhancing knowledge of the formation mechanism for these objects.