Early Proterozoic magmatism and tectonism related to southward-dipping subduction and microcontinental accretion in central Wisconsin

Conference · Wed Jan 01 04:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5936368

Maass, R S; Brown, B A ^[1]

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1. Wisconsin Geological and Natural History Survey, Madison, WI (United States)

A polydeformed and polymetamorphosed terrane of Archean and lower Proterozoic volcanic, plutonic, and sedimentary rocks is exposed in central Wisconsin. The central Wisconsin terrane (CWT) consists primarily of 2,800 and 2,500 Ma gneisses and 1,820-1,890 Ma igneous rocks emplaced into these gneisses during the Penokean orogeny. North of a poorly define northwest-trending suture zone is the 1,8180-1,890 Ma Penokean island-arc terrane of northern Wisconsin, which lacks Archean rocks. Archean and Penokean metamorphism of the CWT each ranged from lower greenschist to upper amphibolite facies. Grade was typically lower to upper amphibolite facies at 2,800 Ma and lower amphibolite facies during the Penokean orogeny. Locally, a third metamorphic event, possibly 2,500 Ma, has been recognized. The grade of Penokean metamorphism is spatially related to plutons in some areas, but not in others. Most of the CWT underwent one or more phases of deformation during the Penokean orogeny, but at least part of the CWT escaped deformation at this time. A well developed subvertical mineral lineation attributed to diapirism is present in and around many Penokean plutons. The spatial and temporal pattern of igneous activity suggests that the Penokean orogeny involved two simultaneously operating southward-dipping subduction zones. The northern zone produced the island-arc terrane. The southern zone dipped under the CWT microcontinent, producing a continental arc. Petrographic and isotopic data from subsurface samples suggest that the CWT does not extend into southern Wisconsin.

• OSTI ID: 5936368
• Report Number(s): CONF-921058--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 24:7
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
DEVELOPED COUNTRIES
GEOLOGIC AGES
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
GEOLOGY
IGNEOUS ROCKS
ISOTOPE RATIO
MAGMATISM
METAMORPHISM
NORTH AMERICA
OROGENESIS
PETROGRAPHY
PLUTONIC ROCKS
PRECAMBRIAN ERA
ROCKS
SUBDUCTION ZONES
TECTONICS
USA
WISCONSIN