This is a continuing project in which detailed, integrated studies have already been conducted of the younger, mantle- derived basanites of San Luis Potosi, including measurement of Sr and Nd isotope ratios. These data indicate at least three mantle source components. This award will enable the PIs to perform Pb isotopic analyses on the same samples, and to expand field based investigations to include the Durango area and the older, magacryst-rich basenites from both areas. They will also attempt to deduce total Nd and Sr budgets in the xenoliths. It should then be possible to trace the history of mantle melting for a 500-km transect across the southernmost Basin and Range Province throughout the period of extreme tectonism. Age dating by both K-Ar and Ar-Ar methods will be done at Cal-Berkeley. Probe studies and leaching of clinopyroxenes from lherzolites will be carried out prior to isotopic analysis.
