Evolution of the Kerguelen LIP: Insights from Crystal Stratigraphy & Crystal Size Distributions from Site 1137, Elan Bank

University Of Notre Dame, Notre Dame IN

Investigators

Abstract

ABSTRACT (Neal - 0452102) Understanding how magmas evolve is important for knowing why volcanoes erupt. Analysis of whole-rock samples gives compositions that reflect only an average of the processes that the lava has experienced prior to eruption. Examination of individual crystals and crystal populations, however, provides better insight into the dynamics of magma evolution. This research involves researchers at the University of Notre Dame and utilizes different populations of crystals in igneous rocks (i.e., crystal size distributions) that have related nucleation and growth histories. It them combines this approach with mineral-scale compositional studies (i.e., crystal stratigraphy). This combined methodology constrains the timing and extent of differentiation processes (i.e., magma mixing, crustal contamination) that permits quantification the dynamics and timing of processes that have modified a magma body since separation from its source and can lead to identification of the source itself. The research uses samples from the Kerguelen Large Igneous Province on the Elan Bank In the Southern/South Indian Ocean to develop a new technique for reconstructing magma chamber evolution using crystal size distributions and wavelet based correlations to determine different plagioclase crystal populations in seven co-magmatic flows from Ocean Drilling Program Site 1137. Samples range in age from 107-108 Ma and encompass three distinct breaks in magmatism, which are represented by volcaniclastic interbeds. These volcaniclastic units divide the lave flow sequence into four parts. Each section will be studied from the top, middle, and base. Representative plagioclase crystals from different crystal zones will be analyzed for major, minor, and trace elements via electron microprobe, SEM, and in-situ laser ablation ICP mass spectrometry. These data will allow partition coefficients to be determined and the reconstruction of parent liquid compositions and local crystallization environments. Strontium isotope measurements will be made on a sub-set of crystals to further constrain parent magma compositions and the extent of crustal contamination. Independent estimates of crystal residence times will be obtained from the crystal size and geochemical data. Broader Impacts Broader impacts of this proposal include education of a graduate student and involvement of a K-12 teacher and students at a school in a Hispanic dominated high school in Deming, New Mexico. This effort will expose Hispanic high school students to the excitement of geochemical and petrological research. The research also involves international collaboration with researchers at the University of Durham in the UK. Results of the work will be integrated into graduate and undergraduate teaching at the University of Notre Dame. A "crystal stratigraphy" web site will also be set up to inform the public and other researchers about the technique and its potential applications.