Sources of clasts in terrestrial impact melts - Clues to the origin of LKFMLow-K Fra Mauro (LKFM) 'basalt', which is found exclusively as an impact melt rock, cannot be modeled geochemically from its clast population or from any combination of known pristine lunar rock types. To clarify clast/melt relationships, a study was made of impact melt rocks from Mistastin Lake crater, Labrador, where there are only three target rocks: anorthosite, quartz monzonite, and granodiorite. Feldspar compositions in these rocks define distinct fields on the An-Ab-Or ternary diagram, making it possible to identify the source of each feldspar clast. Clasts in the Mistastin impact melts do not reflect the abundance of target rocks melted during the impact. The abundance of anorthosite in the clast population varies from 34 to 100 percent compared to a relatively constant value of 65 percent calculated to be in the melt matrix. Therefore the clasts appear to be derived predominantly from material relatively far removed from the zone of impact melting. Melt-matrix composition is dictated strictly by the composition of the target materials within a small radius around and below the point of impact. This suggests that the LKFM composition was derived from a lower crustal source.
Document ID
19890049177
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Mccormick, K. A. (New Mexico Univ. Albuquerque, NM, United States)
Taylor, G. J. (New Mexico Univ. Albuquerque, NM, United States)
Keil, K. (New Mexico, University Albuquerque, United States)
Spudis, P. D. (USGS Flagstaff, AZ, United States)
Grieve, R. A. F. (Geological Survey of Canada Geophysics Div., Ottawa, United States)