Leucosome distribution in migmatitic paragneisses and orthogneisses: A record of self-organized melt migration and entrapment in a heterogeneous partially-molten crust

Yakymchuk, Chris; Brown, Michael; Ivanic, Tim J.; Korhonen, Fawna J.

doi:10.1016/j.tecto.2013.05.022

Cited by 37 publications

(45 citation statements)

References 107 publications

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“…The amount of melt chosen to be integrated should be guided by the critical threshold deemed to apply for melt loss in rocks (i.e. approximately 7 mol% melt; Rosenberg and Handy, 2005;Brown and Korhonen, 2009;Brown, 2010a;Yakymchuk et al, 2013;Yakymchuk and Brown, 2014b) as well as by how abundant evidence for 'late' melt is in the terrane (Greenfield et al, 1996;Anderson et al, 2013;Morfin et al, 2013;Morrissey et al, 2014). The TeM melt section method provides an estimation of H 2 O in the context of the full NCKFMASH composition of silicate melt and also allows for quantitative appraisal of the effect of the abundance of melt on the temperature location of the solidus (Anderson et al, 2013;Morrissey et al, 2013).…”

Section: Estimating the H 2 O Content Of Compositionmentioning

confidence: 99%

On ultrahigh temperature crustal metamorphism: Phase equilibria, trace element thermometry, bulk composition, heat sources, timescales and tectonic settings

Kelsey

Hand

2015

Geoscience Frontiers

377

285

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a b s t r a c tUltrahigh temperature (UHT) metamorphism is the most thermally extreme form of regional crustal metamorphism, with temperatures exceeding 900 C. UHT crustal metamorphism is recognised in more than 50 localities globally in the metamorphic rock record and is accepted as 'normal' in the spectrum of regional crustal processes. UHT metamorphism is typically identified on the basis of diagnostic mineral assemblages such as sapphirine þ quartz, orthopyroxene þ sillimanite AE quartz and osumilite in MgeAlrich rock compositions, now usually coupled with pseudosection-based thermobarometry using internally-consistent thermodynamic data sets and/or Al-in-Orthopyroxene and ternary feldspar thermobarometry. Significant progress in the understanding of regional UHT metamorphism in recent years includes: (1) development of a ferric iron activityecomposition thermodynamic model for sapphirine, allowing phase diagram calculations for oxidised rock compositions; (2) quantification of UHT conditions via trace element thermometry, with Zr-in-rutile more commonly recording higher temperatures than Ti-in-zircon. Rutile is likely to be stable at peak UHT conditions whereas zircon may only grow as UHT rocks are cooling. In addition, the extent to which Zr diffuses out of rutile is controlled by chemical communication with zircon; (3) more fully recognising and utilising temperature-dependent thermal properties of the crust, and the possible range of heat sources causing metamorphism in geodynamic modelling studies; (4) recognising that crust partially melted either in a previous event or earlier in a long-duration event has greater capacity than fertile, unmelted crust to achieve UHT conditions due to the heat energy consumed by partial melting reactions; (5) more strongly linking UePb geochronological data from zircon and monazite to PeT points or path segments through using Y þ REE partitioning between accessory and major phases, as well as phase diagrams incorporating Zr and REE; and (6) improved insight into the settings and factors responsible for UHT metamorphism via geodynamic forward models. These models suggest that regional UHT metamorphism is, principally, geodynamically related to subduction, coupled with elevated crustal radiogenic heat generation rates.Ó 2014, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

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Section: Estimating the H 2 O Content Of Compositionmentioning

confidence: 99%

On ultrahigh temperature crustal metamorphism: Phase equilibria, trace element thermometry, bulk composition, heat sources, timescales and tectonic settings

Kelsey

Hand

2015

Geoscience Frontiers

377

285

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“…In general, the process of melt extraction is considered to be cyclic with pulses of melt build-up and melt drainage as the amount of melt in the system reaches the critical threshold for extraction (Handy et al 2001;Brown & Korhonen 2009;Brown 2010a;Hobbs & Ord 2010;Brown 2013;Yakymchuk et al 2013a). Accordingly, in this study the suprasolidus crust is treated as a conditionally open system, whereby it is closed during melt accumulation up to the critical threshold for extraction then open during melt drainage.…”

Section: Fluid-absent Meltingmentioning

confidence: 99%

“…Notwithstanding the discussion above, migmatites in domes commonly have >20 vol% leucosome and sometimes 40-60 vol% leucosome and/or leucogranite at outcrop, but this does not typically represent in situ melting (Brown 1994;Nyman et al 1995;Marchildon & Brown 2003;Morfin et al 2013;Yakymchuk et al 2013a). Although melt is present throughout the evolution for several of the P-T paths modelled in this study (for decompression from 1.2 GPa, the pelite paths ID750 and ID820, and the greywacke path ID820, and for decompression from 1.8 GPa for both the pelite and the greywacke), the amount of melt at any given point along these P-T paths is always low because melt is expected to escape at or before the MCT in nature.…”

Section: Implications For Buoyancy and Rheologymentioning

confidence: 99%

Consequences of open-system melting in tectonics

Yakymchuk

Brown

2013

JGS

124

139

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Partial melting and melt drainage from deep suprasolidus crust in orogens has important consequences for tectonics. Melt extraction along prograde segments of clockwise P – T paths reduces fertility and increases the density and strength of residual crust, which has implications for further melt production during decompression. Using calculated P – T phase diagrams, implications of stepwise melt loss along clockwise P – T paths for pelite and greywacke are assessed, and density of the progressively more residual source and the potential role of buoyancy in the exhumation of deep crustal rocks are evaluated. Two model P – T paths are considered: isobaric heating at 1.2 GPa followed by decompression to 0.4 GPa at 750, 820 and 890 °C, and prograde heating from the fluid-present solidus at 1.2 GPa to 860 °C at 1.8 GPa followed by isothermal decompression to 0.4 GPa. Both closed-system (undrained) and conditionally open-system (drained by intermittent melt loss) conditions are assessed. If melt is drained along clockwise P – T paths in suprasolidus crust then lower quantities of melt will be generated during decompression than sometimes inferred in tectonic models. Instead, the role of melt transfer through suprasolidus crust and melt accumulation at shallow levels in the anatectic zone should be considered rather than simply invoking the generation of large volumes of melt in decompressing crust.

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“…The amount of melt chosen to be reintegrated is guided largely by the critical melt loss threshold (i.e. approximately <7 mol% melt addition to the residual bulk composition; Brown, 2010;Brown and Korhonen, 2009;Rosenberg and Handy, 2005;Yakymchuk and Brown, 2014;Yakymchuk et al, 2013). This is assessed by contouring for melt modal abundance in the peak assemblage field.…”

Section: Phase Equilibria Modellingmentioning

confidence: 99%

A duality of timescales: Short-lived ultrahigh temperature metamorphism preserving a long-lived monazite growth history in the Grenvillian Musgrave–Albany–Fraser Orogen

Tucker

Hand

Kelsey

et al. 2015

Precambrian Research

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Leucosome distribution in migmatitic paragneisses and orthogneisses: A record of self-organized melt migration and entrapment in a heterogeneous partially-molten crust

Cited by 37 publications

References 107 publications

On ultrahigh temperature crustal metamorphism: Phase equilibria, trace element thermometry, bulk composition, heat sources, timescales and tectonic settings

On ultrahigh temperature crustal metamorphism: Phase equilibria, trace element thermometry, bulk composition, heat sources, timescales and tectonic settings

Consequences of open-system melting in tectonics

A duality of timescales: Short-lived ultrahigh temperature metamorphism preserving a long-lived monazite growth history in the Grenvillian Musgrave–Albany–Fraser Orogen

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