Population-wide garnet growth zoning revealed by LA-ICP-MS mapping: implications for trace element equilibration and syn-kinematic deformation during crystallisation

George, Freya; Gaidies, Fred; Boucher, Brandon

doi:10.1007/s00410-018-1503-0

Cited by 42 publications

(46 citation statements)

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“…A spatial change to the grain boundary transport efficiency might have resulted in the piling-up of relatively mobile major element components at boundaries between micaceous and quartzofelspathic domains, where clusters of Type A and B cores seem to concentrate. There is some evidence in George et al (2018) that variations in the concentration of immobile HREE might create sites of relative nucleation preference, such that sites of elevated HREE facilitate early nucleation. Previous assessment of trace element distributions in metapelites have indicated that they are unlikely to be equilibrated across the scale of a hand sample (e.g.…”

Section: Chemical Heterogeneitiesmentioning

confidence: 99%

“…Airaghi, Lanari, de Sigoyer, & Guillot, 2017;Carlson, 1989;Chernoff & Carlson, 1997;Jamtveit & Andersen, 1992;Tracy & McLellan, 1985) and deformation histories and strain rates (e.g. Biermeier & Stüwe, 2003;George, Gaidies, & Boucher, 2018;Spiess & Bell, 1996;Stöckhert, Massonne, & Nowlan, 1997). Often, garnet is used for such studies, as it incorporates a record of the pressure-temperature (P-T) conditions of crystallization that is preserved in the case of inefficient diffusional homogenization, and forms porphyroblastic populations that are conducive to 2D and 3D textural and microstructural characterization.…”

Section: Introductionmentioning

confidence: 99%

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Simultaneous operation of opposing reaction mechanisms: The influence of matrix heterogeneity on post‐kinematic garnet crystallization in an inverted metamorphic sequence

George

Gaidies

2020

Journal Metamorphic Geology

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Metapelites from the inverted Barrovian sequence in the Sikkim Himalaya (northeast India) are shown to be largely continuous with respect to their bulk rock compositions, microstructures and pressure–temperature–time–deformation (P–T–t–D) histories. However, the upper garnet–lower staurolite zone demarcates a region of microstructurally anomalous post‐kinematic garnet populations contained within strongly segregated matrices. The different microstructures within samples from this region cannot be attributed to differences in their thermobarometric histories or bulk compositions, but are instead interpreted to represent an otherwise unexposed level of the Daling Group that is now exposed along a post‐metamorphic thrust splay. These heterogeneous samples contain several discrete garnet populations that progressively crystallized with increasing P–T. Garnet populations that experienced the most protracted growth now form complex polycrystals that exhibit crystallographically controlled and morphologically irregular interfaces adjacent to micaceous and quartzofeldspathic domains respectively. Electron backscatter diffraction indicates that these polycrystalline garnet structures contain numerous coalesced porphyroblasts that are structurally uncorrelated across their grain boundaries. However, a crystallographically preferred orientation at the polycrystal scale is interpreted to derive from epitaxial crystallization of early‐formed garnet porphyroblasts on precursor mica. Later‐nucleated porphyroblasts within polycrystals preferentially concentrated towards quartzofeldspathic domains, with the overall nucleation distribution likely controlled by a complex interplay between chemical heterogeneities, strain partitioning and epitaxial crystallization. The subsequent growth of these polycrystals was equally spatially heterogeneous; it was moderated by differences in the efficiency of grain boundary transfer between quartzofeldspathic and micaceous domains that precluded thin section‐scale chemical equilibration. In contrast to samples from Sikkim containing more typical porphyroblastic populations in continuous and disseminated matrices, heterogeneous availability of garnet‐forming components within this strongly layered matrix is shown to have resulted in grain‐scale variations in growth rates and the spatial juxtapositioning of interface‐controlled microstructures and locally equilibrated chemical compositions with those that were transport controlled.

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Section: Chemical Heterogeneitiesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Simultaneous operation of opposing reaction mechanisms: The influence of matrix heterogeneity on post‐kinematic garnet crystallization in an inverted metamorphic sequence

George

Gaidies

2020

Journal Metamorphic Geology

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“…Dasgupta et al 2009;Anczkiewicz et al 2014;Gaidies et al 2015;George and Gaidies 2017;George et al 2018). Previous work suggests that the P-T of garnet nucleation (determined by garnet core isopleths) occurred at the garnet-in curve,(Gaidies et al 2015) and subsequent calculations of the P-T of garnet nucleation using the parallel tangent method determined an overstep of <10ºC and 0.4 kbar(George and Gaidies 2017), indicating that the departure from equilibrium during garnet nucleation was negligible.…”

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confidence: 93%

The (chemical) potential for understanding overstepped garnet nucleation and growth

Nagurney

Caddick

Dragovic

et al. 2021

American Mineralogist

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Overstepping of porphyroblast-forming reactions has been shown to occur in regional, contact, and subduction zone metamorphism, calling into question the paradigm that metamorphic mineral reactions occur at or very close to thermodynamic equilibrium. These overstepped reactions result from the fact that nucleation and growth of new phases requires a thermodynamic driving force, or a departure from equilibrium. We use phase equilibria modeling to elucidate the energetic consequences of overstepped garnet nucleation and growth by comparing the chemical potentials of garnet-forming oxide components (MnO, CaO, FeO, MgO, Al 2 O 3) in two sets of calculations: one in which Gibbs free energy is minimized and one in which the minimization proceeds under identical conditions but in the forced absence of garnet. We focus on twelve examples from the literature which have previously described garnet nucleation as minimally overstepped (garnet nucleation at the P-T of initial garnet stability) or garnet nucleation as more substantially overstepped (garnet nucleation at P-T conditions greater than initial garnet stability). For a small P-T interval above nominal garnet-in reactions, differences in the chemical potentials between the two calculations are commonly minimal. In all 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.

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“…Further work is required to develop our understanding of the likely myriad (and sample‐specific) controls on HREE distribution within a sample, with accessory and precursor phases likely playing an important role (Catlos, 2013), and leucosome dynamics feasibly influential, but LA‐ICP‐MS mapping studies of a range of phases are providing important insights (e.g. George, Gaidies, & Boucher, 2018).…”

Section: Discussionmentioning

confidence: 99%

Quantitative elemental mapping of granulite‐facies monazite: Textural insights and implications for petrochronology

Weller

Jackson

Miller

et al. 2020

Journal Metamorphic Geology

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Population-wide garnet growth zoning revealed by LA-ICP-MS mapping: implications for trace element equilibration and syn-kinematic deformation during crystallisation

Cited by 42 publications

References 94 publications

Simultaneous operation of opposing reaction mechanisms: The influence of matrix heterogeneity on post‐kinematic garnet crystallization in an inverted metamorphic sequence

Simultaneous operation of opposing reaction mechanisms: The influence of matrix heterogeneity on post‐kinematic garnet crystallization in an inverted metamorphic sequence

The (chemical) potential for understanding overstepped garnet nucleation and growth

Quantitative elemental mapping of granulite‐facies monazite: Textural insights and implications for petrochronology

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