Origin and interaction of some alkalic and silicic plutons in the Vermilion Granitic Complex, NE Minnesota
Alkalic gabbros and tonalites comprise a significant portion of the Archaean crust in the Vermilion Granitic Complex of NE Minnesota. The origin of these and associated rocks has been modeled using major and trace element approaches. Samples of the alkalic gabbro collected from three different intrusions have similar major element, REE, and transition metal concentrations. The REE patterns of these rocks can be modeled as the result of 1% to 3% melting of an undepleted garnet herzolite mantle with REE concentrations three times that of chondrites. However, their Al/sub 2/O/sub 3//CaO ratios of 2 - 3, Sr content of 900-1400 ppm and Ba of 100 - 1600 ppm suggest that the source may have been an enriched, metasomatized mantle. The hornblendites associated with these alkalic rocks have REE patterns which are consistent with crystallization and accumulation from the gabbroic magma. Major and trace element modeling suggest that the granitic dikes which are common throughout the area may be residual liquids formed by 60% crystallization of plagioclase, biotite, hornblende and apatite from the nearby tonalites such as the Burntside of Wakemup Bay plutons. Porphyritic hornblende monzonites composed of centimeter sized hornblende crystals floating in a granitic matrix occur locally. The field relations as well as the major and trace element data are consistent with the formation of these monzonitic rocks by mixing of the granite with partially consolidated hornblendite. These results suggest a complex interaction between alkalic gabbros and tonalites involving fractionation and mixing during the development of the Archaean crust of NE Minnesota.
- Research Organization:
- Univ. of Missouri, Columbia (USA)
- OSTI ID:
- 6453087
- Report Number(s):
- CONF-8510489-
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
MINNESOTA
PLUTONIC ROCKS
PETROCHEMISTRY
PETROGENESIS
BIOTITE
CHEMICAL COMPOSITION
EARTH CRUST
FELDSPARS
GEOLOGIC MODELS
HORNBLENDE
MINERALOGY
PETROLOGY
PRECAMBRIAN ERA
RARE EARTHS
AMPHIBOLE
ELEMENTS
FEDERAL REGION V
GEOLOGIC AGES
GEOLOGY
IGNEOUS ROCKS
METALS
MICA
MINERALS
NORTH AMERICA
ROCKS
SILICATE MINERALS
USA
580400* - Geochemistry- (-1989)
580300 - Mineralogy
Petrology
& Rock Mechanics- (-1989)