Chemical trends in massif anorthosites: comparison with Stillwater trends
Conference
·
· Geol. Soc. Am., Abstr. Programs; (United States)
OSTI ID:6596423
Formation of massif anorthosites may begin with equilibrium crystallization of suspended plagioclase and sinking mafic minerals. Thick Stillwater anorthosites formed that way and show two chemical trends. In one, all elements are strongly correlated or anticorrelated with MgO and can be modeled precisely as mixtures of cumulus plagioclase, adcumulus plagioclase and pyroxene, magnetite, and trapped liquid. Layers developed from meter-sized packets of crystal mush, each slightly unique in composition, without chemical gradients across thick units ANI or ANII. In the other trend, SiO/sub 2/ and Al/sub 2/O/sub 3/ are deficient, a result of dilution by FeO, TiO/sub 2/, volatiles, and trace elements, all apparently introduced from brines. Marcy anorthosites retain no evidence of a cumulus or adcumulus mafic component. Most samples fall within an envelope of two chemical trends, perhaps indicating two trapped liquids. Neither liquid was necessarily parental to the plagioclase; both may have been carrier liquids that mobilized the feldspar during development of the massif. Metamorphism has altered the composition of some plagioclase and may have extended the range for elemental migration beyond the scale of hand specimens, so trends are evident only when data for many samples are examined.
- Research Organization:
- Washington Univ., St. Louis, MO (USA)
- OSTI ID:
- 6596423
- 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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Conference
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· Geol. Soc. Am., Abstr. Programs; (United States)
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Related Subjects
58 GEOSCIENCES
580300* -- Mineralogy
Petrology
& Rock Mechanics-- (-1989)
580400 -- Geochemistry-- (-1989)
ALKALINE EARTH METAL COMPOUNDS
ANORTHOSITES
BRINES
CHALCOGENIDES
CHEMICAL ANALYSIS
CHEMICAL COMPOSITION
CHEMISTRY
COMPARATIVE EVALUATIONS
CRYSTALLIZATION
GABBROS
GEOCHEMISTRY
IGNEOUS ROCKS
IRON COMPOUNDS
IRON ORES
IRON OXIDES
MAGNESIUM COMPOUNDS
MAGNESIUM OXIDES
MAGNETITE
METAMORPHISM
MINERALIZATION
MINERALOGY
MINERALS
ORES
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PETROGENESIS
PHASE TRANSFORMATIONS
PLUTONIC ROCKS
PYROXENES
ROCKS
SILICATES
SILICON COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
580300* -- Mineralogy
Petrology
& Rock Mechanics-- (-1989)
580400 -- Geochemistry-- (-1989)
ALKALINE EARTH METAL COMPOUNDS
ANORTHOSITES
BRINES
CHALCOGENIDES
CHEMICAL ANALYSIS
CHEMICAL COMPOSITION
CHEMISTRY
COMPARATIVE EVALUATIONS
CRYSTALLIZATION
GABBROS
GEOCHEMISTRY
IGNEOUS ROCKS
IRON COMPOUNDS
IRON ORES
IRON OXIDES
MAGNESIUM COMPOUNDS
MAGNESIUM OXIDES
MAGNETITE
METAMORPHISM
MINERALIZATION
MINERALOGY
MINERALS
ORES
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PETROGENESIS
PHASE TRANSFORMATIONS
PLUTONIC ROCKS
PYROXENES
ROCKS
SILICATES
SILICON COMPOUNDS
TRANSITION ELEMENT COMPOUNDS