A Pliocene ignimbrite flare-up along the Tepic-Zacoalco Rift; evidencefor the initial stages of rifting between the Jalisco Block (Mexico)and North America

Abstract

The Tepic-Zacoalco rift, a NW-trending corridor approximately 50Xapproximately 250 km, is one arm of a triple-rift system in westernMexico. Together with the Colima rift and the Middle America Trench,it bounds the Jalisco block, a portion of western Mexico that may bemoving independently of North America. The predominant basement rocktypes in the Tepic-Zacoalco rift are rhyolitic ash-flow tuffs andlavas, which were previously assumed to be Oligocene-Miocene in age,related to the Sierra Madre Occidental volcanic province, or older.New (super 40) Ar/ (super 39) Ar dates on 41 volcanic samples reveal apreviously unrecognized, voluminous flare-up of rhyolitic ignimbritesbetween 5 and 3 Ma throughout the entire corridor of theTepic-Zacoalco rift; they are often associated with Pliocene high-Tibasalts. The eruption rate during this Pliocene time period was anorder of magnitude higher (hundreds of m/m.y.) than that documented inthe Tepic-Zacoalco rift over the last 1 m.y. The P!

41 samples from this reference