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Degree

MS, Kent State University, College of Arts and Sciences / Department of Geology, 2012.

Abstract

The Animikie Basin in north-eastern Minnesota is usually interpreted as a Penokean (1875-1835 Ma) foredeep deposit consisting mainly of 2 to 5 km thick turbidite sequences underlain by banded iron formations and quartzite conglomerates, all deposited in a foreland basin north of the accreted Penokean arc terrain. Much of the Animikie basin sequence is non-metamorphosed and only mildly deformed. However, along its southern margin in Carlton County, east-central Minnesota, the sedimentary sequence is strongly deformed into refolded nappes. The twice deformed sequence occurs south of a similar sedimentary sequence that has undergone a single deformation. The contact between these sequences, although nowhere exposed, was interpreted by Holst (1985) as a Penokean thrust fault and all of the deformation assumed to be Penokean in age. This contact is commonly referred to at Holst’s Line. A wealth of new data collected over the last ~15 years document Yavapai-age magmatism, metamorphism, sedimentation and deformation overprinting the Penokean orogen. Metamorphic ages post-date the Penokean orogeny and detrital zircon ages indicate that some of the Paleoproterozoic sedimentary rocks may be younger than previously thought. Based on this new evidence, I propose Holst’s Line to represent an unconformity separating sedimentary foredeep packages of different ages and test this hypothesis using geochemical and Sm/Nd isotopic data. Geochemical analyses were obtained on 10 samples divided into two groups based upon location north or south of Holst’s Line. Relative proportions of major elements varied little within and across these groups. Trace element ratio plots of La/Sc vs Ti/Zr, Sc/Cr vs La/Y, Th vs Zr and Sc vs V were created with the hope of distinguishing between different tectonic settings. The results show a concentrated grouping of data from the southern samples and a much larger spread from northern samples, suggesting a more variable source for the northern sedimentary sequence. Neither Sm nor Nd are significantly fractionated compared to each other during surficial processes, and therefore, Nd isotopes are frequently used in sedimentary rocks as an indicator of provenance. Four samples were analyzed, two from north of Holst’s Line and two to the south. Using detrital zircon and stratigraphic relationships, ages of 1770 Ma and 1850 Ma were assigned to the northern and southern rocks respectively. ƐNd (T) was then calculated for each sample with the results indicating the northern rocks were derived from an older Archean crustal source whereas the southern rocks were derived from a younger, possibly arc source. The differences documented here argue against Holst’s Line being a tectonic contact. Instead, Holst’s Line is reinterpreted as an unconformity separating Penokean foredeep and Yavapai foredeep Paleoproterozoic deposits. This reinterpretation has important ramifications for interpreting structures throughout the upper Great Lakes region. Lastly a new tectonic sequence model for the formation and deformation of the Animikie Basin is proposed.

Subject Headings

Geology

Keywords

Paleoproterozoic; Animikie Basin; Thomson Formation; Holst's Line; Carlton County; Yavapai Orogeny; Penokean Orogeny

Committee / Advisors

Daniel Holm, PhD (Advisor)
David Hacker, PhD (Committee Member)
Donald Palmer, PhD (Committee Member)

Pages

69p.

Document number: kent1350923963
Permalink: http://rave.ohiolink.edu/etdc/view?acc_num=kent1350923963

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