The central portion of San Luis Potos¿ State, Mexico, contains many isolated basic alkalic volcanic centers of Quaternary age, including seven large maar complexes. These vents are divided into two geographically distinct groups, Ventura to the southwest and Santo Domingo to the northeast. The maars and other volcanic centers contain xenoliths of mantle-derived spinel lherzolite and lower crustal granulites. The Santo Domingo maars also contian kaersutite megacrysts derived from kaersutite-rich veins in spinel lherzolite. Basic volcanic rocks form a well-defined petrologic series from strongly silicatundsersaturated olivine nephelinites and basanites rich in spinel-lherzolite xenoliths and xenocrysts which, are dominant at Ventura, through alkali olivine basalts and basalts having little to no lherzolitic debris, which are dominant at Santo Domingo.

All rocks have olivine phenocrysts with Cr-Al spidnel inclusions, titanaugite-augit phenocrysts or micropnocrysts, and groundmass crystals of one or both Fe-Ti oxide series. Plagioclase decreases in abundance with increasing normative ne+lc and is absent or restricted to the groundmass in the most undersaturated rocks. Normative ne+lc is also strongly correlated with the abundances of incompatible elements, among which the degree of enrichment in the suite decreases in the sequence Nb, Ta, P, La, Th, Ce, Sm, Sr, Ba, Zr, Eu, Hf, K, Ti, yb, and Na. Based on experimental analogs and major and trace element abundances, the entire volcanic suite dfrom San Luis Potosi can be modeled by progressive degrees of partial melting of a garnet periodtite mantle source. In this scheme, the Santo Domingo magmas were produced by relatively larger degrees of partial melting. Equally plausible, however, is formation of the San Luis Potosi magmas as mixtures of melts from two different mantle sources. In this scenario, the Ventura-type mantle is enriched in Nb, Ta, P, La, and related elements compared with the Santo Domingo-type mantle. In the Pier et al we describe Sr and Nd isotopic data for these samples that demand multisource models. ¿ American Geophysical Union 1989