Experimental Study of Clinopyroxene Growth and Sector Zoning

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Clinopyroxene is a major rock-forming mineral on Earth and other rocky planets, and one of the first solids crystallized by high temperature magmas and lavas. In theory, the chemical composition and the crystal shape of clinopyroxene can be used to extract information about the liquid from which the mineral formed (e.g., temperature, pressure, composition). When studying rock samples, the accuracy of such markers is critical in deciphering the dynamics of a large number of volcanic and magmatic systems, both on Earth and other planetary bodies. However, the crystallization processes of clinopyroxene are complex and still poorly understood, which hampers its potential as a tracer of magmas. The proposed work aims to refine the crystallization processes of clinopyroxene using a combination of laboratory experiments and advanced analytical methods. These results will complete previous datasets, provide new insights on the mineral at the microscopic scale, and pave the way for new research avenues. The tasks will nurture a collaboration between three academic institutes with premier experimental petrology laboratories (Brown University, the University of Hawaii, and the Universite de Lorraine), support the professional development of two early-career researchers, and provide a research opportunity for three undergraduate students. Clinopyroxene is one of the most complex igneous minerals in terms of its variability in texture and chemical zoning. Even today, its intricate complexity stands as a significant roadblock to reconstructing the history of clinopyroxene-bearing magmas. The rationale for this project stems from former characterizations of natural samples bearing complex sector zoning, and previous experiments on clinopyroxene + melt systems. This new work will exploit a trio of experimental apparatuses to address a broad range of crystallization conditions: heating stage microscope, 1-atm gas mixing furnace, and piston cylinder. The investigations will focus on major- and trace-element composition (in fine-scale detail to capture intricate zoning), growth features (habits, melt and solid inclusions, crystal defects) and the crystallization kinetics of clinopyroxene during the cooling of synthetic and natural melts. The experimental products will be analyzed using optical, electron probe, and transmission electron microscopies, and laser ablation inductively coupled mass spectrometry. The overarching goals are: to document the textural variation of clinopyroxene at various pressure, temperature, and cooling conditions; to establish the conditions (cooling rate, undercooling, melt composition) at which sector zoning occurs; and to examine major- and trace-element partitioning between clinopyroxene and melt, and between sectors in clinopyroxene. These goals are intended to advance the practical application of clinopyroxene thermobarometry, by establishing which sectors and elements faithfully record magmatic pressure-temperature conditions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.