River Valley pluton, Ontario: A late-Archean/early-Proterozoic anorthositic intrusion in the Grenville Province

Journal Article · Wed Mar 01 00:00:00 EST 1989 · Geochimica et Cosmochimica Acta; (USA)

DOI:https://doi.org/10.1016/0016-7037(89)90006-9· OSTI ID:5127594

Ashwal, L D ^[1]; Wooden, J L ^[2]

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1. Lunar and Planetary Institute, Houston, TX (USA)
2. Geological Survey, Menlo Park, CA (USA)

The River Valley pluton is a ca. 100 km{sup 2} body of anorthositic and gabbroic rocks located about 50 km northeast of Sudbury, Ontario. The pluton is situated entirely within the Grenville Province, but its western margin is a series of imbricate thrust faults associated with the Grenville Front Tectonic Zone. It is dominated by coarse leuconorite and leucogabbro, with lesser anorthosite, gabbro, and rare ultramafics. Igneous textured rocks are abundant and consist of plagioclase (An{sub 60-70}) charged with Fe-Ti oxide inclusions, low Ca pyroxene (orthopyroxene and/or inverted pigeonite) and augite. The most unfractionated rocks are minor olivine gabbros with Fo{sub 70-80}. A variety of deformed and recrystallized equivalents of the igneous-textured rocks is also present, and these are composed largely of calcic plagioclase and hornblende. An Sm-Nd isochron from 3 igneous-textured leucogabbros and an augite mineral separate gives 2,377 {plus minus} 68 Ma, implying slight disturbance of the Sm-Nd whole-rock-mineral system during later metamorphism. The Rb-Sr system has been substantially disturbed, giving an age of 2,185 {plus minus} 105 Ma, which is similar to internal Pb-Pb isochron ages of 2,165 {plus minus} 130 Ma and 2,100 {plus minus} 35 Ma for two igneous-textured rocks. Initial isotopic ratios for the River Valley pluton correspond to single-stage model parameters of {mu} = 8.06, {epsilon}{sub Nd} = O to {minus}3, and I{sub Sr} = 0.7015 to 0.7021. Collectively, these suggest either an enriched mantle source or crustal contamination of a mantle-derived magma. The crustal component involved must have been older and more radiogenic than the majority of rocks exposed at the surface in the nearby Superior Province.

• OSTI ID: 5127594
• Journal Information: Geochimica et Cosmochimica Acta; (USA), Vol. 53:3; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
GABBROS
CHEMICAL COMPOSITION
ISOTOPE DATING
MINERALOGY
PETROGENESIS
PETROLOGY
ONTARIO
FELDSPARS
GEOCHEMISTRY
GEOLOGIC FAULTS
GEOLOGIC HISTORY
HORNBLENDE
INCLUSIONS
IRON OXIDES
LEAD ISOTOPES
NEODYMIUM ISOTOPES
PRECAMBRIAN ERA
SAMARIUM ISOTOPES
TITANIUM OXIDES
AGE ESTIMATION
AMPHIBOLE
CANADA
CHALCOGENIDES
CHEMISTRY
GEOLOGIC AGES
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
GEOLOGY
IGNEOUS ROCKS
IRON COMPOUNDS
ISOTOPES
MINERALS
NORTH AMERICA
OXIDES
OXYGEN COMPOUNDS
PLUTONIC ROCKS
RARE EARTH ISOTOPES
ROCKS
SILICATE MINERALS
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
580000* - Geosciences