Equal-area Plots Research Articles

Factors Influencing the Grain of the Topography Along the Willoughby Arch in Northeastern Vermont

Equal-area plots of maximum slope linears from each of three study areas along the Willoughby Arch in northeastern Vermont are analyzed and compared with the bedrock joint system and evidence of glacial ice movement within the respective areas. These analyses reveal a correspondence of the topographic fabric to the bedrock fracture pattern and a supplementary relationship between the movement of glacial ice and the topography. This information indicates that the topography adjusted to the orientation of bedrock fractures before the Pleistocene. Chemical erosion is suggested as the major process effecting this relationship. The fracture-pattern-oriented topography prevails today with only slight modification by glaciation. This is confirmed by the linear data on the direction of glacial ice flow and the areal distribution of Pleistocene deposits on the three

Paleomagnetic study of the Sudbury Basin

A reconnaissance paleomagnetic study has been carried out on the Precambrian nickel irruptive of the Sudbury basin. A total of 60 oriented samples was collected along a single traverse across the northern range and along four traverses across the southern range of the basin. The remanent magnetism (RM) vectors of the 266 specimen cubes cut from the samples were subsequently measured with a ‘spinner’ magnetometer. The RM directions for the south range are closely grouped on the Schmidt equal-area plot, and this fact indicates that there has been negligible relative rotary movement along the 16 miles of the south range sampled since the irruptive last cooled through the Curie point of its magnetic constituents. It was also found that the RM directions for the N and S ranges differ by approximately 40°, and this may be explained by assuming that there has been 40° of relative tilting about an E-W axis through the middle of the basin. In three of the S range traverses the susceptibility (κ) of the collected samples was higher on the S end of the traverse than on the N end, and in general the κ's obtained for the N range were much higher than those obtained on the S range. It would appear that the magnetic anomalies observed over the norite sections of the N and S ranges are mainly due to the presence of RM and to a lesser extent to an induced magnetization. The pole position calculated from the RM directions is dependent on the amount of assumed relative tilting. However if the rotation is equally divided between the two ranges, the resultant pole position is 38.4°N, 99.4°W, which is in the central U.S.