Comparative petrogenesis of anorthositic and troctolitic series rocks of the Duluth Complex, Minnesota
Results of new mapping in the NW part of the Middle Proterozoic Duluth Complex in NE Minnesota reinforces the view that the Complex consists dominantly of two major lithostratigraphic units: an Anorthositic Series (AS) and a Troctolitic Series (TS) dominated by troctolite and olivine gabbro. Consistent intrusive and inclusive relationships confirm that AS rocks are older than TS. Interpretations of field, petrographic, and petrochemical data imply that the petrogenesis of the two rock series differed in at least four significant ways: 1) While parent magmas to both rock series could have been derived from high-Al olivine tholeiite primary magmas by fractional crystallization of Pl+Ol+Cpx+Sp in lower to intermediate crustal (40-15 km) chambers, AS parent magmas were generally more evolved than TS magmas upon their introduction into the Duluth Complex. 2) As magmas were intruded as plagioclase crystal muses (less than or equal to50% crystals), whereas later TS intrusions contained rare or minor intratelluric plagioclase and olivine. Periodic intrusions of viscous AS mushes probably caused much of the structural complexity ubiquitous to these rocks. 3) Although parent magmas to both rock series were saturated in plagioclase upon intrusion, AS magmas were less often saturated in olivine than were TS magmas. 4) TS rocks record fractional crystallization within Duluth Complex chambers; however, the extent and pattern of differentiation often reflects repeated replenishment of more primitive magmas.
- Research Organization:
- Univ. of Minnesota, Minneapolis (USA)
- OSTI ID:
- 6454024
- 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
ANORTHOSITES
PETROCHEMISTRY
PETROGRAPHY
GABBROS
MINNESOTA
CHEMICAL COMPOSITION
COMPARATIVE EVALUATIONS
CRYSTALLIZATION
FELDSPARS
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
MAGMA
MAGMATISM
MINERALOGY
OLIVINE
PETROGENESIS
PRECAMBRIAN ERA
ALKALINE EARTH METAL COMPOUNDS
FEDERAL REGION V
GEOLOGIC AGES
IGNEOUS ROCKS
IRON COMPOUNDS
IRON SILICATES
MAGNESIUM COMPOUNDS
MAGNESIUM SILICATES
MINERALS
NORTH AMERICA
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
PLUTONIC ROCKS
ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
USA
580300* - Mineralogy
Petrology
& Rock Mechanics- (-1989)
580400 - Geochemistry- (-1989)