Lower crustal source for massif anorthosites

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

OSTI ID:6169693

Taylor, S R

Proterozoic massif anorthosites have very low Rb/Sr ratios, variable commonly unsupported /sup 87/Sr//sup 86/Sr ratios, positive Eu anomalies, and a wide range in element of/sub Nd/ (+4 to -6) which show a correlation with the crustal provinces in which the anorthosites occur, suggestive of a crustal source. Typical models for the development of the continental crust include a massive episodic growth from the mantle in the Late Archean followed 100-200 m.y. later by intracrustal melting to produce upper crustal granites, leaving an Eu and Al-rich lower crust, depleted in Rb, with increased Sm/Nd ratios. Melting of this lower crust in the Proterozoic can produce dry plagioclase-rich melts, enriched in Eu, with low Rb/Sr ratios, unsupported /sup 87/Sr//sup 86/Sr ratios (inherited from the precursor history) and variable Sm/Nd (and element of/sub Nd/) reflecting previous complex crustal history. Since the granite melting episode removed the heat-producing elements into the upper crust, a separate heat source is required. Movement of the crust over a mantle plume of mid-ocean ridge type could account for the linear distribution of anorthosites, and their association with failed rift environments.

• Research Organization: Australian National Univ., Canberra
• OSTI ID: 6169693
• 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)
ALKALI METAL ISOTOPES
ALKALINE EARTH ISOTOPES
ANORTHOSITES
CHEMICAL COMPOSITION
CHEMISTRY
CONTINENTAL CRUST
EARTH CRUST
GABBROS
GEOCHEMISTRY
GEOLOGIC STRUCTURES
HEAT SOURCES
IGNEOUS ROCKS
ISOTOPE RATIO
ISOTOPES
MAGMATISM
MELTING
ORIGIN
PETROGENESIS
PHASE TRANSFORMATIONS
PLUTONIC ROCKS
RIFT ZONES
ROCKS
RUBIDIUM ISOTOPES
STRONTIUM ISOTOPES