Plagioclase compositions and non-anatectic origin of migmatitic gneisses in Northern Cascade mountains of Washington State

Misch, Peter

doi:10.1007/bf00371809

Cited by 80 publications

(69 citation statements)

References 21 publications

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“…Where present, they have sharp contacts with leucosomes, and consist of biotite f garnet f sillimanite in pelitic rocks, biotite f garnet f cummingtonite in biotite schists, hornblende in amphibolites, and biotite f hornblende in orthogneisses. Misch (1968) and Yardley (1978) noted that some migmatites lack melanosomes entirely while others have well-developed selvages. In many migmatites that lack melanosomes, leucosomes appear to grade into adjacent mesosomes.…”

Section: T H E S K a G I T M L G M A T L T E Smentioning

confidence: 99%

“…It has been proposed that the Skagit migmatites formed by subsolidus processes-metasomatism (Misch, 1968) or metamorphic differentiation (Yardley , 1978)-because the rocks do not conform to criteria generally attributed to anatectic migmatites. For example, Misch (1968) concluded that the migmatites had a subsolidus origin because (1) leucosome and mesosome plagioclase have essentially the same composition in all lithologies, (2) all leucosomes lack major K-feldspar even though metasedimentary mesosomes contain biotite, (3) leucosome plagioclase is not as sodic as predicted by experimental work on simple granitic systems (Bowen, 1913;Tuttle & Bowen, 1958), and (4) qualitative estimates of metamorphic temperatures were considered to be too low for anatexis to have occurred (i.e.…”

Section: Origin Of the Skagit Rnigrnatites: Previous Workmentioning

confidence: 99%

“…For example, Misch (1968) concluded that the migmatites had a subsolidus origin because (1) leucosome and mesosome plagioclase have essentially the same composition in all lithologies, (2) all leucosomes lack major K-feldspar even though metasedimentary mesosomes contain biotite, (3) leucosome plagioclase is not as sodic as predicted by experimental work on simple granitic systems (Bowen, 1913;Tuttle & Bowen, 1958), and (4) qualitative estimates of metamorphic temperatures were considered to be too low for anatexis to have occurred (i.e. temperatures were estimated at 600" C at intermediate pressures; Misch, 1968). Babcock & Misch (1989) concluded from mass-balance relations among associated leucosomes, melanosomes and mesosomes in Skagit biotite schist, amphibolite and orthogneiss that leucosomes formed primarily by metasomatic replacement of the country rock (accompanied by metamorphic differentiation), as a result of influx of a fluid.…”

Section: Origin Of the Skagit Rnigrnatites: Previous Workmentioning

confidence: 99%

“…Misch, 1968;Touret & Dietvorst, 1983;Olsen, 1984Olsen, , 1987Touret & Olsen, 1985). Subsolidus migmatites may be generated by stress-induced mass transfer (Sawyer & Robin, 1986) or by an influx of externally derived (metasomatic) fluid under subsolidus conditions (Misch, 1968;Babcock & Misch, 1989). For a given rock and P-T conditions, the amount, nature (free or structurally bound) and composition of the fluid determines whether partial melting can occur, and whether partial melting is by fluid-absent (dehydration melting) or fluid-present reactions.…”

Section: Introductionmentioning

confidence: 99%

“…The Skagit migmatites of the North Cascades, Washington, USA, have been cited as an example of a large-scale subsolidus migmatite complex (Misch, 1968;Yardley, 1978;Babcock & Misch, 1989), but it has also been argued that anatexis cannot be rejected as a migmatite-forming process for the Skagit migmatites (Ashworth, 1979;Whitney, 1991a). This report contains the results and conclusions of a fluid inclusion investigation of migmatitic and non-migmatitic metasedimentary (pelite, biotite schist) and meta-igneous (amphibolite, orthogneiss) rocks from the Skagit Gneiss, and combines microthermometric data with thermobarometric estimates (Whitney & McGroder, 1989;Whitney, 1992).…”

Section: Introductionmentioning

confidence: 99%

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Origin of CO₂‐rich fluid inclusions in leucosomes from the Skagit migmatites, North Cascades, Washington, USA

WHITNEY

1992

Journal Metamorphic Geology

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C0,-CH, fluid inclusions are present in anatectic layer-parallel leucosomes from graphite-bearing metasedimentary rocks in the Skagit migmatite complex, North Cascades, Washington. Petrological evidence and additional fluid inclusion observations indicate, however, that the Skagit Gneiss was infiltrated by a water-rich fluid during high-temperature metamorphism and migmatization.C0,-rich fluid inclusions have not been observed in Skagit metasedimentary mesosomes or melanosomes, meta-igneous migmatites, or unmigmatized rocks, and are absent from subsolidus leucosomes in metasedimentary migmatites. The observation that C0,-rich inclusions are present only in leucosomes interpreted to be anatectic based on independent mineralogical and chemical criteria suggests that their formation is related to migmatization by partial melting. Although some post-entrapment modification of fluid inclusion composition may have occurred during decompression and deformation, the generation of the C0,-rich fluid is attributed to water-saturated partial melting of graphitic metasedimentary rocks by a reaction such as biotite + plagioclase + quartz + graphite f AI,SiO, + water-rich fluid = garnet + melt + C0,-CH,. The presence of C0,-rich fluid inclusions in leucosomes may therefore be an indication that these leucosomes formed by anatexis., Based on the inferences that (1) an influx of fluid triggered partial melting, and (2) some episodes of fluid inclusion trapping are related to migmatization by anatexis, it is concluded that a free fluid was present at some time during high-temperature metamorphism. The infiltrating fluid was a water-rich fluid that may have been derived from nearby crystallizing plutons. Because partial melting took place at pressures of at least 5 kbar, abundant free fluid may have been present in the crust during orogenesis at depths of at least 15 km.

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Section: T H E S K a G I T M L G M A T L T E Smentioning

confidence: 99%

Section: Origin Of the Skagit Rnigrnatites: Previous Workmentioning

confidence: 99%

Section: Origin Of the Skagit Rnigrnatites: Previous Workmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Origin of CO₂‐rich fluid inclusions in leucosomes from the Skagit migmatites, North Cascades, Washington, USA

WHITNEY

1992

Journal Metamorphic Geology

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Transfer of Metasupracrustal Rocks to Midcrustal Depths in the North Cascades Continental Magmatic Arc, Skagit Gneiss Complex, Washington

et al. 2017

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The metasupracrustal units within the north central Chelan block of the North Cascades Range, Washington, are investigated to determine mechanisms and timescales of supracrustal rock incorporation into the deep crust of continental magmatic arcs. Zircon U‐Pb and Hf‐isotope analyses were used to characterize the protoliths of metasedimentary and metaigneous rocks from the Skagit Gneiss Complex, metasupracrustal rocks from the Cascade River Schist, and metavolcanic rocks from the Napeequa Schist. Skagit Gneiss Complex metasedimentary rocks have (1) a wide range of zircon U‐Pb dates from Proterozoic to latest Cretaceous and (2) a more limited range of dates, from Late Triassic to latest Cretaceous, and a lack of Proterozoic dates. Two samples from the Cascade River Schist are characterized by Late Cretaceous protoliths. Amphibolites from the Napeequa Schist have Late Triassic protoliths. Similarities between the Skagit Gneiss metasediments and accretionary wedge and forearc sediments in northwestern Washington and Southern California indicate that the protolith for these units was likely deposited in a forearc basin and/or accretionary wedge in the Early to Late Cretaceous (circa 134–79 Ma). Sediment was likely underthrust into the active arc by circa 74–65 Ma, as soon as 7 Ma after deposition, and intruded by voluminous magmas. The incorporation of metasupracrustal units aligns with the timing of major arc magmatism in the North Cascades (circa 79–60 Ma) and may indicate a link between the burial of sediments and pluton emplacement.

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Introduction

Ashworth

1985

Migmatites

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Plagioclase compositions and non-anatectic origin of migmatitic gneisses in Northern Cascade mountains of Washington State

Cited by 80 publications

References 21 publications

Origin of CO₂‐rich fluid inclusions in leucosomes from the Skagit migmatites, North Cascades, Washington, USA

Origin of CO₂‐rich fluid inclusions in leucosomes from the Skagit migmatites, North Cascades, Washington, USA

Transfer of Metasupracrustal Rocks to Midcrustal Depths in the North Cascades Continental Magmatic Arc, Skagit Gneiss Complex, Washington

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Plagioclase compositions and non-anatectic origin of migmatitic gneisses in Northern Cascade mountains of Washington State

Cited by 80 publications

References 21 publications

Origin of CO2‐rich fluid inclusions in leucosomes from the Skagit migmatites, North Cascades, Washington, USA

Origin of CO2‐rich fluid inclusions in leucosomes from the Skagit migmatites, North Cascades, Washington, USA

Transfer of Metasupracrustal Rocks to Midcrustal Depths in the North Cascades Continental Magmatic Arc, Skagit Gneiss Complex, Washington

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Origin of CO₂‐rich fluid inclusions in leucosomes from the Skagit migmatites, North Cascades, Washington, USA

Origin of CO₂‐rich fluid inclusions in leucosomes from the Skagit migmatites, North Cascades, Washington, USA