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Title: Diabase dikes of the Midcontinent Rift in Minnesota: a record of Keweenawan magmatism and tectonic development

Abstract

Swarms of both reversed-polarity (R, older) and normal-polarity (N, younger) basaltic dikes help to define the evolution of the Minnesota portion of the Midcontinent Rift of North America. Each swarm, representing fissure-feeders for a package of overlying plateau lavas now eroded away, shows the direction of least principal stress at that time and place in the complex evolution of this abortive but nearly-successful rift. Paleomagnetic pole determinations for Carlton county (CC) and Grand Portage (GP) R dikes are coincident along the Logan Loop of the Proterozoic track, showing essential contemporaneity, though their trends are different (N.30/sup 0/E vs. N. 70-90/sup 0/E.) and they are 250 km apart. These poles match that of the R lavas of the North Shore Volcanic Group (NSVG) and imply a younger age than the R Logan sills and dikes. The geochemistry of the dikes (71 analyses) also correlates well with NSVG flows, ranging from olivine tholeiites to transitional basalts and basaltic andesites and is similar to tholeiites of Columbia River, Parana, and Tertiary No. Atlantic provinces. Though each swarm shows a range of compositions, some are dominantly more evolved, whereas others contain more primitive dikes with higher Al, Mg/Fe, Cr and Ni and lower Fe,more » Ti, P and LIL's. An early major episode of rifting during the R polarity interval was followed by at least one major N episode in Minnesota before the final one along the present Lake Superior syncline axis. Rifting directions and mantle sources were different for each episode as shown by cross-trending dike sets, indicating complex rift development.« less

Authors:
;
Publication Date:
Research Org.:
Univ. of Minnesota, Duluth (USA)
OSTI Identifier:
6598049
Report Number(s):
CONF-8510489-
Journal ID: CODEN: GAAPB
Resource Type:
Conference
Journal Name:
Geol. Soc. Am., Abstr. Programs; (United States)
Additional Journal Information:
Journal Volume: 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; DIABASES; CHEMICAL COMPOSITION; MINNESOTA; RIFT ZONES; GEOLOGIC HISTORY; AGE ESTIMATION; GEOCHEMISTRY; MAGMATISM; PALEOMAGNETISM; PLATE TECTONICS; BASALT; CHEMISTRY; FEDERAL REGION V; GEOLOGIC STRUCTURES; IGNEOUS ROCKS; MAGNETISM; NORTH AMERICA; ROCKS; TECTONICS; USA; VOLCANIC ROCKS; 580100* - Geology & Hydrology- (-1989); 580201 - Geophysics- Seismology & Tectonics- (1980-1989); 580400 - Geochemistry- (-1989)

Citation Formats

Green, J C, and Chandler, V C. Diabase dikes of the Midcontinent Rift in Minnesota: a record of Keweenawan magmatism and tectonic development. United States: N. p., 1985. Web.
Green, J C, & Chandler, V C. Diabase dikes of the Midcontinent Rift in Minnesota: a record of Keweenawan magmatism and tectonic development. United States.
Green, J C, and Chandler, V C. 1985. "Diabase dikes of the Midcontinent Rift in Minnesota: a record of Keweenawan magmatism and tectonic development". United States.
@article{osti_6598049,
title = {Diabase dikes of the Midcontinent Rift in Minnesota: a record of Keweenawan magmatism and tectonic development},
author = {Green, J C and Chandler, V C},
abstractNote = {Swarms of both reversed-polarity (R, older) and normal-polarity (N, younger) basaltic dikes help to define the evolution of the Minnesota portion of the Midcontinent Rift of North America. Each swarm, representing fissure-feeders for a package of overlying plateau lavas now eroded away, shows the direction of least principal stress at that time and place in the complex evolution of this abortive but nearly-successful rift. Paleomagnetic pole determinations for Carlton county (CC) and Grand Portage (GP) R dikes are coincident along the Logan Loop of the Proterozoic track, showing essential contemporaneity, though their trends are different (N.30/sup 0/E vs. N. 70-90/sup 0/E.) and they are 250 km apart. These poles match that of the R lavas of the North Shore Volcanic Group (NSVG) and imply a younger age than the R Logan sills and dikes. The geochemistry of the dikes (71 analyses) also correlates well with NSVG flows, ranging from olivine tholeiites to transitional basalts and basaltic andesites and is similar to tholeiites of Columbia River, Parana, and Tertiary No. Atlantic provinces. Though each swarm shows a range of compositions, some are dominantly more evolved, whereas others contain more primitive dikes with higher Al, Mg/Fe, Cr and Ni and lower Fe, Ti, P and LIL's. An early major episode of rifting during the R polarity interval was followed by at least one major N episode in Minnesota before the final one along the present Lake Superior syncline axis. Rifting directions and mantle sources were different for each episode as shown by cross-trending dike sets, indicating complex rift development.},
doi = {},
url = {https://www.osti.gov/biblio/6598049}, journal = {Geol. Soc. Am., Abstr. Programs; (United States)},
number = ,
volume = 17,
place = {United States},
year = {Tue Jan 01 00:00:00 EST 1985},
month = {Tue Jan 01 00:00:00 EST 1985}
}

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