HR: 1340h
AN: GP33A-0100    [Abstracts]
TI: Timing and Origin of Chemical Remagnetization(s) in the Mississippian Madison Group, Sawtooth Range, Montana
AU: * O'Brien, V J
EM: obrienvj@ou.edu
AF: School of Geology and Geophysics, The University of Oklahoma, 100 East Boyd Street, Norman, OK 73019 United States
AU: Moreland, K M
EM: kmmorel@sbcglobal.net
AF: School of Geology and Geophysics, The University of Oklahoma, 100 East Boyd Street, Norman, OK 73019 United States
AU: Elmore, R D
EM: delmore@ou.edu
AF: School of Geology and Geophysics, The University of Oklahoma, 100 East Boyd Street, Norman, OK 73019 United States
AU: Engel, M H
EM: ab1635@ou.edu
AF: School of Geology and Geophysics, The University of Oklahoma, 100 East Boyd Street, Norman, OK 73019 United States
AB: Paleomagnetic and geochemical results are presented from Mississippian Madison Group carbonates in the Sawtooth Range, northwestern Montana. Sites were collected from two east-west trending transects perpendicular to the thrust faults in the Sun River Canyon and in the South Fork of the Teton River and from several anticlines associated with thrust activity. Paleomagnetic and rock magnetic data indicate that the Madison Group contains a widespread characteristic remanent magnetization (ChRM) that resides in magnetite with southerly declinations and moderately steep up inclinations. The ChRM cannot be explained by a thermoviscous remagnetization mechanism, because burial temperatures (~150^oC) are too low to explain the maximum unblocking temperatures of 520^oC. The ChRM is interpreted as a chemical remanent magnetization (CRM). Tilt test results suggest that the CRM is syn- to pretilting in the thrust faults, pretilting in the Teton Anticline, and syntilting in a small fold to the west of the Teton Anticline in the North fork of the Teton River. The tilt test results, which are similar to results reported by other workers from equivalent units in the southern Canadian Cordillera, suggest that the CRM is coeval with Laramide deformation during the Early Tertiary. To date, a remagnetization trend perpendicular to the thrust faults as reported from the southern Canadian Cordillera has not been found in the study area. Geochemical studies (⁸⁷Sr/⁸⁶Sr) indicate that the Mississippian carbonates that contain the CRMs were altered by radiogenic fluids, and petrographic analysis indicates that hydrocarbons migrated through the carbonates. The CRM is interpreted to be related to alteration by either or both of these fluids. Additional paleomagnetic and geochemical studies will investigate the origin of the CRM and resolve other issues such as the differences in tilt test results and the possibility of a remagnetization trend across the thrust faults.
DE: 1533 Remagnetization
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005