Partial melting under conditions of filter pressing: field and geochemical evidence from the migmatites of NE Minnesota

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

OSTI ID:6070457

Sheehan, T J; Bauer, R L; Nabelek, P I; Glascock, M D

Amphibolite-grade Archean migmatites in the southern Vermilion Granitic Complex with well-defined paleosome-melanosome and melanosome-leucosome boundaries and with exceptionally wide melanosomes (on the order of centimeters) were studied to elucidate granite-forming processes during high-grade metamorphism. Metagreywacke paleosomes containing 50% plag, 28% qtz, 20% biot and minor hbld, and apat, have (Ce/Yb)/sub N/ = 13.5 to 21 with 650-960 ppm Ba, 42-110 ppm Rb, and 982-1159 ppm Sr. Melanosomes containing 45% plag, 35% biot, 20% hbld and minor qtz and apat, have (Ce/Yb)/sub N/ = 6.8 to 9.3 and have 950-1750 ppm Ba, 41-194 ppm Rb, and 1020-1926 ppm Sr. Leucosomes containing 82% plag, 13% qtz, 5% biot and minor hbld and apat, have overall depleted REE patterns with positive Eu anomalies and 460-750 ppm Ba, 41-43 ppm Rb, and 1876-2106 ppm Sr, suggesting cumulate plagioclase. Mass balance calculations preclude formation of the melanosome from mixing the paleosomes and leucosomes. However, major and trace element modeling suggest that the leucosome formed by in situ partial melting followed by fractional crystallization and filter pressing which resulted in the removal of the residual liquid. Model REE patterns for the melt drive off by this process are REE enriched with a negative Eu anomaly. Such patterns which have been found in some low Sr granites are difficult to produce by simple belting models. Partial melting under conditions of tectonic stress may thus provide an explanation for such granites.

• Research Organization: Univ. of Missouri, Columbia (USA)
• OSTI ID: 6070457
• 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

Related Subjects

58 GEOSCIENCES
580300* -- Mineralogy
Petrology
& Rock Mechanics-- (-1989)
580400 -- Geochemistry-- (-1989)
AMPHIBOLE
AMPHIBOLITES
APATITES
BIOTITE
CHALCOGENIDES
CHEMICAL COMPOSITION
CHEMISTRY
ELEMENTS
FEDERAL REGION V
FELDSPARS
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC MODELS
GEOLOGY
GRANITES
HORNBLENDE
IGNEOUS ROCKS
METALS
METAMORPHIC ROCKS
METAMORPHISM
MICA
MINERALOGY
MINERALS
MINNESOTA
NORTH AMERICA
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PETROGENESIS
PETROLOGY
PHOSPHATE MINERALS
PLUTONIC ROCKS
PRECAMBRIAN ERA
QUARTZ
RARE EARTHS
ROCKS
SILICATE MINERALS
SILICON COMPOUNDS
SILICON OXIDES
USA