Magma evolution in the Nain Complex, Labrador, and implications for the origin of anorthosite

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

OSTI ID:6862820

Berg, J H

Analyses of over 50 chilled margins of plutons and contemporaneous dikes in the anorthositic Nain Complex reveal a well-defined trend of liquid evolution along a plagioclase-olivine cotectic. Fractional crystallization of olivine and plagioclase has resulted in extreme enrichment of TiO/sub 2/ and FeO/sub T/ and depletion of Al/sub 2/O/sub 3/ in the more evolved compositions. The contemporaneous Harp Dikes and Seal Lake Volcanics of southern Labrador also fall along this trend. Although rare, other dikes in the Nain complex are very olivine-rich and the olivine is quench-textured. Modeling of major and trace elements indicates that the leucotroctolitic liquids can be derived from the melatroctolites by olivine removal, and that the more evolved cotectic liquids can be derived from the leucotroctolitic liquids by removal of o1 + plag in a 25:75 ratio. If the equilibrium saturation surface of plagioclase is ignored, continued olivine removal from the leucotroctolites is capable of producing compositions very similar to compositions of hypothesized anorthositic magmas. In the Nain Complex, field evidence for supersaturation of plagioclase is abundant. Since all of the compositions discussed above are low in normative diopside, it may be that such liquids are less capable of nucleating plagioclase than liquid with more normal diopside contents, thus permitting the supersaturation.

• Research Organization: Northern Illinois Univ., DeKalb (USA)
• OSTI ID: 6862820
• 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)
ALKALINE EARTH METAL COMPOUNDS
ANORTHOSITES
CHEMICAL ANALYSIS
CHEMICAL COMPOSITION
CHEMISTRY
CRYSTALLIZATION
GABBROS
GEOCHEMISTRY
GEOLOGIC MODELS
IGNEOUS ROCKS
IRON COMPOUNDS
IRON SILICATES
MAGMATISM
MAGNESIUM COMPOUNDS
MAGNESIUM SILICATES
MINERALIZATION
MINERALS
OLIVINE
OXYGEN COMPOUNDS
PETROGENESIS
PHASE TRANSFORMATIONS
PLUTONIC ROCKS
ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
TRANSITION ELEMENT COMPOUNDS