40 Ar/ 39 Ar chronology and volcanology of silicic volcanism in the Davis Mountains, Trans-Pecos Texas

Abstract

Field studies and 40 Ar/ 39 Ar dating reveal that silicic volcanism in the Davis Mountains part of the Trans-Pecos Texas volcanic field occurred in six episodes at 0.3 m.y. intervals between 36.8 and 35.3 Ma. Additionally, two groups of silicic intrusions were emplaced at 34.6 and 32.8 Ma. This episodicity is similar to that determined for volcanic fields dominated by ash-flow tuffs, yet voluminous, extensive silicic lavas are considerably more abundant than tuffs in the Davis Mountains, by number of flows and by volume. The preponderance of voluminous silicic lavas over tuffs mostly likely reflects low water contents and high temperatures of the alkalic and commonly peralkaline Davis Mountains magmas. -from Authors