Geological Society of America

T13 Volcanic and Landscape Evolution of the Jemez Mountains Volcanic Field

Sunday, 31 October 2010
8:00 AM - 12:00 PM
Mile High Ballroom 4AB

SINGLE CRYSTAL ISOTOPE VARIATIONS IN RHYOLITES AT VALLES CALDERA, NEW MEXICO

Paper number: T13-6
Program: Technical Sessions
Time: 9:15 AM – 9:30 AM

Authors

Frank C. Ramos Presenting Author
New Mexico State University, Las Cruces, NM
J.a. Wolff
Washington State University, Pullman, WA
Corey A. Dimond
New Mexico State University, Las Cruces, NM
Ryan Mulhall
New Mexico State University, Las Cruces, NM
Darren L. Tollstrup
University of California Davis, Davis, CA

Abstract

Single crystal isotope analyses offer insights into identifying the sources and processes generating volcanism across a range of magma compositions. At Valles caldera, we focus on single potassium feldspar and clinopyroxene crystal analyses, in addition to, pumice fragments reflecting the host magma composition at eruption. Results suggest a complex interplay between sources characterized by potassium feldspar and clinopyroxene crystals with different ⁸⁷Sr/⁸⁶Sr and ²⁰⁶Pb/²⁰⁴Pb isotope signatures which, once age-corrected, do not overlap those of the host magma as reflected by pumice fragments. These age corrected isotope signatures do not overlap those of each other either (potassium feldspar vs. clinopyroxene). These relationships are seen in both the Otowi and Tshirege super-eruption deposits (Bandelier Tuff) and undermine the postulation that all crystals were derived from the same magmas.

In addition to Valles super-eruptions, single crystal isotope signatures from intervening Cerro Toledo eruptions are also evaluated to determine whether crystals were remobilized from pre-existing eruptions. Cerro Toledo magma compositions are variable with a range of crystal and pumice isotope signatures. As such, we will address crystal sources and processes associated with crystal remobilization and subsequent eruption at Valles caldera.