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Stamatakos, J.A., 1990

Paleomagnetism applied to tectonic problems in south-central Alaska and in the central Appalachian Valley and Ridge Province

Bibliographic Reference

Stamatakos, J.A., 1990, Paleomagnetism applied to tectonic problems in south-central Alaska and in the central Appalachian Valley and Ridge Province: Bethlehem, Pennsylvania, Lehigh University, Ph.D. dissertation, 172 p.


Paleomagnetic, rock magnetic, finite strain, and rock fabric analyses have been used to investigate the role of the Castle Mountain fault in the accretion history of southern Alaska, the relationship between penetrative strain and synfolding magnetizations in the Mississippian Mauch Chunk Formation, and the effects of grain-scale strains on the Silurian Bloomsburg Formation paleomagnetic pole. Paleomagnetic and rock magnetic analyses from the Arkose Ridge and Chickaloon formations in southern Alaska indicate that these rocks contain a pre-folding magnetization which yields a paleomagnetic pole for the Chickaloon Formation at 50.5°N, 277.2°E, dm = 12.2°, dp = 7.7°, and a paleomagnetic pole for the Arkose Ridge Formation at 60.4°N, 138.6°E, dm = 11.6°, dp = 6.4°. These results suggest that there is no paleomagnetically discernible latitudinal offset across the Castle Mountain Fault since Paleocene time, but that both the Chickaloon and Arkose Ridge rocks, as part of the Peninsular terrane, originated approximately 1,600 - 1,200 km south of their present position with respect to North America. Paleomagnetic results from Mauch Chunk Formation sites on both limbs of the Frackville Anticline reveals a two polarity characteristic magnetization that appears synfolding at 75% unfolding (I = 27.3°, D = 184.0°). Rock fabric analysis indicates a complex strain history that includes layer-parallel shortening overprinted by flexural slip/flow folding. Inclination varies systematically with the magnitude of finite strain and suggests that a prefolding magnetization has been rotated by penetrative bedding-parallel shear to appear synfolding. Remanence rotation is consistent with rigid particle behavior of the ferromagnetic grains in a viscously deforming medium. The relationship between the strain geometry and remanence around three central Appalachian Valley and Ridge folds indicates that penetrative deformation has also rotated the characteristic magnetization in the Bloomsburg formation from a prefolding, Silurian magnetization to an apparent synfolding, Devonian configuration. Based on the low-strained sites from this study, a new Bloomsburg Formation paleomagnetic pole is calculated at 18.5°N, 107.6°E (k = 61.2, A95 = 8.0°) which falls between the Silurian Wabash Reef pole (McCabe et al., 1985) and the Siluro-Devonian Andreas pole (Miller and Kent, 1988).

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