GSA Annual Meeting in Seattle, Washington, USA - 2017

Paper No. 239-4
Presentation Time: 2:20 PM

ZIRCON DIVERSITY AND NUMERICAL MODELING ON DIFFERENT SCALES TO UNDERSTAND MAGMA GENESIS IN AREAS OF HOT SPOT-CRUST INTERACTION WITH EMPHASIS ON YELLOWSTONE PLUME (Invited Presentation)


BINDEMAN, Ilya N.1, COLON, Dylan P.1, GERYA, Taras2, MELNIK, Oleg3 and SIMAKIN, Alexander4, (1)Earth Sciences, University of Oregon, Eugene, OR 97403, (2)Institute of Geophysics, ETH Zentrum, Sonneggstrasse 5, Zürich, 8092, Switzerland, (3)Unstitute of Mechanics, Moscow State University, Moscow, Russian Federation, (4)Institute of Physics of the Earth, B. Gruzinskaya 10, Moscow, 123995, Russia, bindeman@uoregon.edu

Recent studies involving in situ investigation and improved single-crystal U-Pb geochronologic studies of zircon and other minerals have revealed that large volumes (1000s of km3) of low and high silica rhyolites erupt as hot, 800 to >900°C near-liquidus magmas. The estimated time between formation and eruption of the magma is recently recognized to be very short with timescales of a few 1000s of years. This presents significant challenges to heat and volume mass balances and defys conventional models of magma genesis. Additional δ18O and εHf heterogeneity within single zircons in magma products of several permil and many epsilon units suggests pre-eruptive batch assembly of (re)melts of diverse hydrothermally altered and unaltered Archean crusts on timescales faster then zircon diffusive solution-reprecipitation timescales of 10’s to a few 1000s of years. We attempt to integrate a series of numerical models that range from a millimeter scale zircon survivability study, through melting and mixing in medium 50-1000 m scale, to large scale (300x1000 km), fully coupled thermomechanical numerical models that investigate million-year timescales. We arrive to the conclusion that any significant surface rhyolitic magmatism requires crust-wide reworking and thermomechanical reorganization of the entire crustal column. Bimodality of volcanism is related to a series of thermomechanical reasons including the rheological contrasts near crustal boundaries. The crustal fertility plays an important role in magmatic productivity. Numerical experiments with rhyolite-rhyolite mixing suggest that compositional convection accompanies melting and results in effective homogenization of rhyolitic products on required timescales: to preserve strongly diverse in δ18O and εHf zircons in partially homogenized glass and assemble large volumes of eruptable magmas.