Geochemistry and petrogenesis of the mafic flow units within the Chisos Formation, Big Bend National Park, Texas.

Abstract

The Tertiary Chisos Formation, located in the eastern alkalic belt, Trans-Pecos magmatic province is divided into the Alamo Creek Basalt, Ash Spring Basalt, Bee Mountain Basalt, Mule Ear Spring Tuff, and Tule Mountain Trachyandesite. Major and trace element modeling, combined with petrographic and field evidence suggest a complex petrogenesis. Varying degrees of partial melting of a metasomatically veined mantle produced compositionally different enriched primary liquids. Varying evolutionary paths of these liquids, caused by fractionation, assimilation, and replenishment, have given rise to chemically independent magmas and evolved products. Several distinct chemical groupings exist within the Chisos Formation. Additionally, some Alamo Creek samples are chemically similar to Ash Spring samples, suggesting a replication of magmatic processes through time. K-Ar age determinations indicate that the Ash Spring Basalt had a long eruption period 34-43 ma, or several Alamo Creek outcrops were previously incorrectly mapped as Ash Spring Basalt.

43 samples from this reference