PETROLOGY OF IMPACT-MELT ROCKS AT THE CHICXULUB MULTIRING BASIN, YUCATAN, MEXICO

Compositions and textures of melt rocks from the upper part of the Chi cxulub structure are typical of melt rocks at other large terrestrial impact structures. Apart from variably elevated iridium concentrations (<1.5 to 13.5 +/- 0.9 ppb) indicating nonuniform dissemination of a m eteoritic component, bulk rock and phenocryst compositions imply that these melt rocks were derived exclusively from continental crust and p latform-sediment target lithologies. Modest differences in bulk chemis try among samples from wells located approximately 40 km apart suggest minor variations in relative contributions of these target lithologie s to the melts. Subtle variations in the compositions of early-formed pyroxene and plagioclase also support minor primary differences in che mistry between the melts. Evidence for pervasive hydrothermal alterati on of the porous mesostasis includes albite, K-feldspar, quartz, epido te, chlorite, and other phyllosilicates, as well as siderophile elemen t-enriched sulfides, suggesting the possibility that Chicxulub, like S udbury, may host important ore deposits.