A COMBINED U-PB, HF, AND O IN ZIRCON ISOTOPIC STUDY OF THE NORTHERN SIERRA MADRE OCCIDENTAL SILICIC LARGE IGNEOUS PROVINCE

We are undertaking a regional-scale, three-system isotope and trace element study of zircon from 38 Eocene - Oligocene silicic tuffs and lavas in the northern Sierra Madre Occidental (SMO) in Chihuahua and Durango states, northern Mexico. Our goal is to understand the timing and origin of magma genesis in the SMO, the largest Cenozoic silicic large igneous province (SLIP), including, estimating the relative contributions of crustal and mantle melting, correlating between ignimbrites, and learning about the nature of the underlying crust (e.g., buried cratons vs. terranes).

We are analyzing zircon separated from volcanic rock samples collected over a 40 year period by research groups at UT Austin, UT San Antonio, UNAM, and UCSB. We have selected samples with existing radiometric (e.g., Ar-Ar, K-Ar), geochemical, and isotopic data; and where possible, from lavas and ignimbrites with known sources - some of the ca. 40 known calderas out of the 100s that probably exist. We will analyze for dO in zircon and dO in quartz at the University of Wisconsin by SIMS and laser fluorination, respectively. U-Pb, Hf and trace element analyses will be conducted by LA-ICP-MS at Washington State University.

Here we present details of our sample suite, including location, age, and whole-rock geochemistry.