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Degree

MS, Kent State University, College of Arts and Sciences / Department of Geology, 2009.

Abstract

The eastern margin of the Archean Wyoming craton (Black Hills, SD) records a complex history of Precambrian thermotectonism and magmatism associated with convergence, rifting, and supercontinent cycles. U-Pb isotopic spot-analysis by ion-microprobe of zircon, monazite, and xenotime in six rocks from here provides new insights into part of this history. Firstly, quartzite and metapelite xenoliths in the 2560 Ma Little Elk Granite (LEG) record 207Pb/206Pb upper-intercept ages of 2554 ± 15 Ma (2σ, MSWD = 18) and 2552 ± 14 Ma (2σ, MSWD = 3.2), indicating that older, pre-LEG zircon was reconstituted during LEG reheating. Secondly, nine populations of detrital zircon were found within the 2560-2480 Ma Boxelder Creek metaconglomerate, which range in age from 2590 to 3370 Ma and thereby indicate Wyoming cratonic provenance. Thirdly, zircon from the Bogus Jim mafic sill (BJS) has yielded a 207Pb/206Pb upper-intercept age of 2011.8 ± 3.5 Ma (2σ, MSWD = 1.8), which constrains the time of magmatism, represents a maximum age for deposition of the Homestake iron formation and its associated gold deposit, and indicates that the eastern Wyoming craton was actively rifting at this time (probably from the southern Superior craton). Fourthly, magmatic zircon, monazite, and xenotime in the Harney Peak Granite (HPG) have yielded precise 207Pb/206Pb ages of 1716.8 ± 9.3 Ma (2σ, MSWD = 0.95); 1703.2 ± 2.2 Ma (2σ, MSWD = 2.1); and 1695.9 ± 2.9 Ma (2σ, MSWD = 1.8), respectively. Within error, these results appear to indicate that the HPG magmatic event lasted for 9-33 (or 23 +10 -12) Myr.

Subject Headings

Geochemistry; Geology

Keywords

Precambrian; Black Hills; geochronology; provenance; ion-microprobe; zircon; monazite; xenotime

Committee / Advisors

Peter S. Dahl, PhD (Advisor)
Abdul Shakoor, PhD (Committee Member)
Donna Witter, PhD (Committee Member)

Pages

153p.

Document number: kent1247685629
Permalink: http://rave.ohiolink.edu/etdc/view?acc_num=kent1247685629

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