T136 Tectonic Controls on Volcanism: Geologic Perspectives

Monday, 1 November 2010
1:30 PM - 5:30 PM
Mile High Ballroom 4AB

LATEST TRIASSIC-MIDDLE JURASSIC AGE OF CORDILLERAN-NAZAS ARC IN MEXICO INDICATED BY U-PB DETRITAL ZIRCON AND VOLCANIC-ROCK AGES

Paper number: T136-15
Program: Technical Sessions
Time: 5:05 PM – 5:20 PM

Authors

Abstract

The Jurassic Cordilleran-Nazas volcanic arc of the southwestern United States and Mexico followed a general southeastward trend from the Mojave Desert region to the northern extent of the Sierra Madre Oriental and then turned southward to pass through what is now eastern Mexico. Jurassic magmatism succeeded Early Permian-Middle Triassic magmatism that took place along a roughly parallel trend and preceded extensive Cretaceous continental magmatism that began generally to the west of the Jurassic trend. Genetic relationships and temporal continuity of Jurassic igneous activity with the older and younger magmatic events remain debated.

A compilation of U-Pb detrital zircon ages from Upper Jurassic and Lower Cretaceous strata overlying the Jurassic arc rocks and ages on pyroclastic and volcanic rocks from the arc section itself from all border states except Chihuahua across northern Mexico, as well as San Luis Potosí and Chiapas indicate that magmatism was continuous at all localities from ~200-164 Ma, but began about 215 Ma in NE Mexico and Chiapas, and continued to ~145 Ma in Sonora. At all sites except near Saltillo, Coahuila, there is a marked gap in zircon ages in the Middle-Late Triassic (~241-215 Ma). In Chiapas, a thick section of andesite and dacite with a U-Pb age of 191 Ma directly overlies the Permo-Triassic batholith. In Nuevo León, pyroclastic strata dated at 194 Ma (U-Pb) directly overlie Paleozoic schist. Welded eutaxitic tuffs in the upper part of the type Nazas Formation near Torreón have ages of 172 and 169 Ma (U-Pb). Ages from ash fall and ash flow tuffs in Lower and Middle Jurassic strata of north-central Sonora range 189-151 Ma. Late Jurassic ages in Sonora are from reworked air-fall tuffs in a rift basin and probably represent magmatism associated with crustal extension rather than Cordilleran-Nazas arc magmatism. A post-Jurassic gap recorded in zircon ages from Lower Cretaceous strata in Sonora (~145-128 Ma) indicates temporal separation of the Jurassic arc system from the Cretaceous continental-margin arc. Our age compilation thus indicates that Jurassic arc magmatism was separated in time from earlier Permian-Triassic and later Cretaceous igneous activity.