Fold test, Methow, Redbeds, Remagnetization, Synfolding
The palaeomagnetism of folded Cretaceous redbeds in the Methow-Pasayten belt of Washington was studied in an attempt to resolve the tilt versus translation origin of shallow inclinations found in most Cretaceous plutonic rocks of the Pacific Northwest. After elimination of results from apparently strained, overturned beds, correction to palaeohorizontal of the high-temperature, dominant components produced two distinct directions, one from each of two areas. Treated separately, the magnetizations from these two areas appear to pass the fold test. Both directions are anomalously shallow which is typical of the region, but the discrepancy between them casts doubt that both could have been acquired when the strata were horizontal. Instead we propose that they date from at least two episodes of remagnetization after the planar strata were tilted but before development of the tighter folds observed today. Our caution is that a positive fold test only establishes that a magnetization likely was acquired when strata in an area were planar. Other arguments are required to demonstrate that this planar surface was in fact horizontal during magnetization.
Geophysical Journal International
Required Publisher's Statement
Oxford Journals, Oxford University Press
Geophys. J. Int. (1990) 102 (2):455-463.doi: 10.1111/j.1365-246X.1990.tb04477.x
Burmester, Russ R.; Beck Jr., Myrl E.; and Bazard, D. R., "Postfolding Remagnetization that Passes the Fold Test" (1990). Geology Faculty Publications. 22.