Ph.D. RESEARCH SEMINAR - Peteris Rozenbaks
P膿teris Rozenbaks
Ph.D. Candidate
Department of Earth and Environmental Sciences
鲍鱼tv University
Title: Redox-sensitive trace element partitioning between apatite, biotite, and melt: Implications for oxygen barometry in evolved crustal rock
Abstract: Apatite and biotite, ubiquitous minerals in a multitude of igneous crustal assemblages, host a variety of trace elements, including heterovalent elements, whose valence state and hence ionic radius and charge can vary over the oxygen fugacity (fO2) of natural magmatic systems. In high-temperature environments, the oxidation state (quantified as fO2) through redox reactions wields a strong control on magma and ore genesis by defining or representing the composition of carbon, oxygen, hydrogen, sulfur, and iron species, which subsequently influence the phase stability, rock solidus, and melt production. In many crystalline, Fe-poor systems, fO2 remains poorly constrained thus hampering our understanding and modelling of their magmatic evolution and development of economic mineralization.
The existing knowledge gap can be filled by using the redox-sensitivity of heterovalent element partitioning between coeval apatite and biotite. This is being carried out in the three projects of my Ph.D. thesis by analyzing natural rock samples and using experimental methods. In the first project, I assess the feasibility of employing the redox-sensitivity of several heterovalent elements (V, As, Eu, Mo, Sn, W) by analyzing their partitioning in a suite of rocks of diverse fO2. The second project focuses on the evolution of the strongly peraluminous Macusani subvolcanic system (Peru) - a unique hypabyssal/volcanic peraluminous system. The final project experimentally determines the influence of fO2 and other intensive variables to develop an oxybarometer.
Results of the initial project show that with increasing melt oxidation, vanadium (V) partitioning in apatite increases by approximately an order of magnitude, while V partitioning in biotite decreases by more than an order of magnitude. This contrasting partitioning behaviour results in a change of almost three orders of magnitude in V partitioning between apatite and biotite, thus identifying it as a promising oxybarometer. A preliminary vanadium partitioning model that considers changes in the proportion of vanadium species with fO2 and estimated behavior of each vanadium species is used to assess the fO2 of the peraluminous South Mountain Batholith (Nova Scotia) and Palabora carbonatite (South Africa). In addition, the mineral lattice strain models suggest that vanadium intermineral partitioning is likely influenced by temperature (T), and biotite composition.
The second project investigates mineral and melt compositions to constrain the intensive variables (T, fO2, fH2O etc.) in the Macusani subvolcanic system. The current results reveal evidence of phase disequilibrium thus providing an opportunity to study the changes in the physical conditions and the phase composition prior and during the intrusion of these peraluminous bodies. The current hypothesis of thermal perturbation and mafic admixture will be tested by employing chemical mapping of the biotite and apatite crystals.
The final project is focused on developing a vanadium partitioning-based oxybarometer by using experiments to calibrate the effect of intensive variables that were identified as important during the first project. The developed high-T, high-P piston-cylinder- based experimental method is tested on synthetic apatite- and biotite-saturated, V-spiked carbonate melts. The synthesized phase compositions will be analyzed to assess the influence of fO2, T, P, melt and mineral composition on vanadium intermineral partitioning and calibrate the oxybarometer.
Biography: P膿teris received his B.Sc. and M.Sc. in Geology from the University of Latvia in 2013 and 2016, respectively. In addition, he obtained training and lab experience during his ERASMUS semester at the University of Innsbruck (Austria) and exchange studies at the University of Wisconsin-Eau Claire (USA). His undergraduate research project, conducted in collaboration with Latvia's national energy company, Latvenergo, focused on tracking the source of the P募avi艈as hydro-power plant regression well clastic output by analyzing its heavy mineral fraction. For his master鈥檚 thesis, P膿teris investigated the emplacement conditions of the Kurzeme batholith in the crystalline foundation of Western Latvia. He further developed his expertise in microanalytical techniques and igneous oxybarometry during his Master of Earth Sciences (Advanced) degree at the Australian National University, which he completed in 2018. His current research focuses on the redox sensitivity of heterovalent element partitioning between apatite and biotite, with the goal of developing a novel oxybarometry method for evolved crustal rocks.
Time
Location
Milligan Room - 8007 LSC