XENOLITH STRUCTURES IN WELDED BASALT AGGLUTINATE ASSOCIATED WITH DOTSERO CRATER, COLORADO.

The Dotsero maar volcanic crater formed through phreatomagmatic (interactions of lava with wet, unconsolidated sediment) and magmatic processes around 4,150 ± 300 years before present (B.P.) which erupted through sections of Pennsylvanian age sedimentary deposits. The field observations of the eruptive material showed various xenolith structures, or foreign rock fragments within the cooled magmatic material, which can be categorized into four specific groups based on the mineral grain size of the sediments and subtle color variation. The fieldwork focused on three sites located downslope from the southern crater rim of the Dotsero maar, accounting for all xenoliths = 1 cm in size in selected agglutinate clasts and gathering samples of the localized surface sediments and xenolith structures. The surficial sediment samples and two groups of xenolith structures were examined through X-ray powder diffraction laboratory analyses. The results of this analysis demonstrate that field classifications of xenolith structures continue to be the most accurate form of identification and present grounds for further analyses through scanning electron microscopy (SEM) and thin section observations for differentiation and determination of thermal alterations created by the lava and sediment interactions. [ABSTRACT FROM AUTHOR]