Muscovite breakdown above the sillimanite isograd, Cortlandt Complex, NY

Conference · Tue Jan 01 04:00:00 EST 1985 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:6322373

Waldron, K

Textural and mineral chemical data reveal that the metamorphic aureole of the Cortlandt Complex (southeast NY) has experienced T/P conditions exceeding those of the second sillimanite (sill) isograd. The intrusion crosscuts Taconian structures and metamorphic isograds. The aureole is superimposed upon regional metamorphic assemblages and consists of a well-exposed 100m wide band of sill-bearing schists. Though the country rock contains abundant muscovite (mus), it is absent in rocks within 25m of the contact. K-bearing phases (except biotite) are absent within 10m of the contact. K-spar appears beyond 10m and mus is present as rare small laths beyond 25m. Beyond 30m, mus dominates samples as large poikiloblasts, formed during the contact event, that grow across foliation and enclose all other mineral phases. Near the contact sill occurs both as mats of fibrolite oriented parallel to foliation, and as randomly oriented prismatic crystals. Garnet-biotite pairs yield temperature estimates of 650-725 C. Pressures of 6-7 kb are obtained using QGAP. The assemblage gnt + sill + bio + ksp + corundum + sta (qtz absent) occurs 10m from the contact. Quartz was exhausted in this reaction and/or by mus + qtz = ksp + sill + H20. Corundum most likely formed by the breakdown of mus after the depletion of qtz. These observations suggest that muscovite was present in the country rocks prior to intrusion. Mus breakdown is responsible for the formation of a second generation of sill, and in the absence of quartz, for the production of corundum. Bulk chemical analyses of samples may determine whether migration of K-rich fluids from muscovite breakdown explains the distribution of K-bearing phases.

• Research Organization: Yale Univ., New Haven, CT (USA)
• OSTI ID: 6322373
• Report Number(s): CONF-8510489-
• Conference Information: Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Journal Volume: 17
• Country of Publication: United States
• Language: English

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15 GEOTHERMAL ENERGY
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58 GEOSCIENCES
580300* -- Mineralogy
Petrology
& Rock Mechanics-- (-1989)
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
BIOTITE
CHALCOGENIDES
CHEMICAL COMPOSITION
CHEMISTRY
CORUNDUM
CRYSTALLOGRAPHY
FEDERAL REGION II
FLUIDS
GARNETS
GEOBAROMETRY
GEOCHEMISTRY
GEOLOGIC HISTORY
GEOTHERMAL FLUIDS
GEOTHERMOMETRY
METAMORPHIC ROCKS
METAMORPHISM
MICA
MINERALOGY
MINERALS
MUSCOVITE
NEW YORK
NORTH AMERICA
ORIENTATION
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PETROGENESIS
PRESSURE MEASUREMENT
QUARTZ
ROCK-FLUID INTERACTIONS
ROCKS
SCHISTS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SILICON OXIDES
TEMPERATURE MEASUREMENT
USA