Plagioclase population dynamics and zoning in response to changes in temperature and pressure

Abstract

Zoned plagioclase crystals are commonly interpreted as proxies for magmatic history, because the mineral occurs in most silicic magmas and has compositional sensitivity to pressure, temperature, and melt composition with slow internal diffusion that preserves zoning. Changes in growth rates and crystal dissolution complicate quantitative relation of time to particular zoning patterns. The numerical model SNGPlag uses Rhyolite MELTS to determine the equilibrium phase assemblage and compositions for a user-defined magma composition, experimentally determined instantaneous nucleation and growth rates, and reasonable dissolution rates to examine plagioclase crystallization and population dynamics through time. SNGPlag tracks the numbers, sizes, morphologies, and compositional zoning of plagioclase crystals through time in response to changes in pressure, temperature, and volume or mass inputs. Results show that significant fractions of time are missing from the crystal record because of effectively zero growth rates, or erased through dissolution; those processes can together remove >>50% of time from the crystal record. Temperature-(or pressure-) cycling alone will not produce substantial This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America. The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.

Bulk-Rock and Mineral-Scale Geochemical Evidence of Open-System Magmatic Processes in the Felsic Rocks of the Northern Part of the Ditrău Alkaline Massif (Eastern Carpathians, Romania)

“…Therefore, amphibole and clinopyroxene chemistry can be applied to unravel the igneous evolution and, ideally, the composition of the parental melt (e.g., Piwinskii 1968;Naney 1983;Schmidt 1992;Marks et al 2004;Ubide et al 2014a). Similarly, plagioclase crystallises over an extensive spectrum of magma compositions, as well as over a large range of temperature (e.g., Wiebe 1968;Anderson 1984;Blundy & Wood 1991;Putirka 2005). Although the concentration of trace elements and the type of trace elements that are incorporated by plagioclase are significantly lower than in clinopyroxene and amphibole crystals, some of the elements (e.g., Sr and Ba) are particularly useful for deciphering the igneous processes (Blundy & Shimizu 1991;Ginibre et al 2002;Grogan & Reavy 2002).…”

MGP‐1 Plagioclase: A Potential Element and Sr Isotope Reference Material for In Situ Microanalysis

“…It crystallises over a wide range of magma compositions under various P-T conditions and persists as a stable crystallising phase throughout cooling and eruption (e.g., Singer et al 1995, Tepley et al 2000, Costa et al 2008, Fedele 2015, Waters et al 2015. Plagioclase crystals are commonly used as proxies for magmatic history because of their compositional sensitivity to magmatic conditions such as pressure, temperature and composition (e.g., Anderson 1984, Ren et al 2003, Streck et al 2008, Andrews 2021). Owing to a slow CaAl-NaSi diffusion exchange, compositional and textural zoning patterns are often preserved in plagioclase during primary growth (Grove et al 1984), preserving records of the chemical and physical evolution of magma chambers (e.g., Blundy andShimizu 1991, Singer et al 1995).…”

“…Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is well established for determination of trace elements in geological samples, and the coupling of multi-collector (MC) ICP-MS with a LA system has made in situ Sr isotopic measurements possible (Kimura et al 2013(Kimura et al , 2015. Glass reference materials (e.g., BHVO-2G, MPI-DING, BCR-2G, ARM and NIST SRM 610) are commonly used for calibration and quality control of elemental and isotopic compositions, and play major roles in ensuring LA-(MC)-ICP-MS measurement accuracy (e.g., Elburg et al 2005, Weis et al 2005, Jochum et al 2000, 2009, 2011, 2021. However, major element compositions of synthetic glasses are very different to those of plagioclase, which may lead to severe analytical problems due to matrix effects (e.g., Hinton 1995, Jochum et al 2000.…”

“…2015). Plagioclase crystals are commonly used as proxies for magmatic history because of their compositional sensitivity to magmatic conditions such as pressure, temperature and composition (e.g., Anderson 1984, Ren et al . 2003, Streck et al .…”

“…2003, Streck et al . 2008, Andrews 2021). Owing to a slow CaAl–NaSi diffusion exchange, compositional and textural zoning patterns are often preserved in plagioclase during primary growth (Grove et al .…”