Ophitic olivine diabase (Beaver River Diabase, Beaver Bay Complex, Mesoproterozoic, ~1096 Ma; Split Rock Lighthouse, Minnesota, USA) 2

            Diabase in the Precambrian of Minnesota, USA.

The lake shoreline cliff shown above is below Split Rock Lighthouse.  The rocks are diabase (Beaver River Diabase of the Beaver Bay Complex), a mafic, intrusive igneous rock that is essentially identical to basalt, but with slightly larger crystals.  Diabase (and basalt) are principally composed of the minerals plagioclase feldspar and pyroxene.  This particular diabase unit also has some olivine.

Description of the Beaver Bay Complex from Miller et al. (2001): “Multiphase intrusive complex of mostly hypabyssal intrusions emplaced in the central part of the North Shore Volcanic Group.  Consistent normal magnetic polarity and two U-Pb ages (about 1096 Ma) suggest emplacement generally after Duluth Complex intrusions."

Description of the Beaver River Diabase from Miller et al. (2001): “Extensive mafic dike and sill complex extending from Split Rock Point to Lutsen on the shore of Lake Superior; multiple composite phases present locally.”

Geologic unit & age: Beaver River Diabase, main phase of the Beaver Bay Complex, Midcontinent Rift Intrusive Supersuite, late Mesoproterozoic, ~1096 Ma

Locality: Split Rock Lighthouse, Stony Point, northern shore of western Lake Superior, northeastern Minnesota, USA (47° 12' 00.01” North latitude, 91° 21’ 59.78” West longitude)
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Reference cited:
Miller et al. (2001) - Geologic map of the Duluth Complex and related rocks, northeastern Minnesota.  Minnesota Geological Survey Miscellaneous Map Series Map M-119.

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Taken on: June 8, 2015

Tags:

ophitic

olivine

Beaver

River

Bay

Complex

Midcontinent

Rift

Intrusive

Supersuite

Precambrian

Proterozoic

Mesoproterozoic

igneous

rock

Split

Lighthouse

Stony

Point

Minnesota « less

Sets appears in: • Minnesota Rocks & Minerals • Mesoproterozoic Rocks, Minerals, Fossils more » • Beaver Bay Complex (Mesoproterozoic, ~1096 Ma; Split Rock Lighthouse, Minnesota, USA) « less

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