The Minnesota River valley subprovince (MRV) is a fragment of Mesoarchean
continental crust that was sutured to the southern margin of the Superior craton about
2,600 m.y. ago. The suturing event induced widespread regional metamorphism and
local anatexis in a dominantly orthogneissic crust and ended with the emplacement of
numerous granite plutons. In the Paleoproterozoic era the MRV was a tectonically rigid
part of the cratonic foreland with respect to Penokean (geon 18), Yavapai (geon 17), and
Mazatzal (geon 16) accretionary events. As such, it was affected by crustal extension and the
emplacement of mafic dikes associated with the ca. 2,070 Ma opening of the pre-Penokean
ocean. Subsequently, internal shear zones that had formed during Neoarchean docking
of the MRV crustal block were reactivated in response to stresses applied during cycles of
Paleoproterozoic stretching and subsequent compression from the south and southeast.
Most of this reactivation is inferred to have taken place between 2,000 and 1,750 Ma. The
Minnesota segment of the Great Lakes tectonic zone, the Neoarchean suture, was not
significantly reactivated, whereas the Appleton shear zone and the Yellow Medicine shear
zone both were. Six sets of mafic dikes were emplaced in the interval between 2,070 and
ca. 1,750 Ma. Two sets that were emplaced early in the interval are the southwesternmost
members of the pre-Penokean Kenora–Kabetogama/Fort Frances dike swarm. Two and
perhaps four younger dike sets were emplaced during a period of vigorous crustal heating
and magmatic activity that affected much of the MRV in early- to mid-geon 17. Numerous
plugs and small plutons also were emplaced in early- to mid-geon 17. These intrusions
range in composition from peridotite to granite and are comparable to rock types within
and satellitic to the East-Central Minnesota batholith; they are most abundant in the
eastern and southern parts of the MRV, relatively near the inferred Penokean and Yavapai
tectonic fronts. Transtensional stress during the extensional stage of the Mazatzal orogenic
cycle generated differential subsidence of crust south of the Yellow Medicine shear zone
and produced en echelon fault-bounded depressions that became depocenters filled by
supermature clastic sediment ancestral to the Sioux Quartzite. The Sioux Quartzite was
deposited, lithified, and hydrothermally altered over a prolonged time interval that may
have begun as early as ca. 1,730 and ended as recently as ca. 1,280 Ma.
RI-69 Reexamination of the Minnesota River Valley Subprovince with Emphasis on Neoarchean and Paleoproterozoic Events.
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