Relationship of faults in basin sediments to the gravity and magnetic expression of their underlying fault systems

Time-domain electromagnetic signatures of polymetallic vein deposits in Cottonwood Canyon area, Santa Cruz County, Arizona

“…Because CDTs based on airborne TEM data do not see into bedrock below basin fill, the occurrence of mineralization in the bedrock concealed by basin fill cannot be ascertained. A comparison of the basin-fill/bedrock contact between Baldyga's (2001) cross section and CDT 8 in figure A2-2 shows several differences. First, the depth to bedrock is overestimated on the CDTs.…”

“…The same fault appears in CDT 8, and the bedrock is offset in the same direction as in the cross section, but the offset in the CDT is less than 100 m and the upthrown bedrock block is about 400 m deep. Two lines (A2-4a and A2-4b) in figure A2-4 are drawn between Baldyga's (2001) cross section and the CDT. Just east of line A2-4a in Baldyga's cross section is an upthrown bedrock block at about 250 m depth; the same feature is visible in CDT 11 at about 400 m depth.…”

“…In the CDT, the basinfill/bedrock contact tends to remain at a constant depth. The interpretation of the CDT indicates that exposed bedrock (which may be covered with very thin alluvium, a few meters thick or less) is reached when a major decrease in conductivity occurs at the surface, at approximately the same point where the basin-fill/bedrock contact reaches its shallowest in Baldyga's (2001) cross section. Thus, as the basin shallows, the CDT drastically overestimates depth to bedrock but still accurately indicates the location of the mapped basin-fill/bedrock contact on the surface.…”

“…A recent study by Baldyga (2001) uses gravity data to model geologic cross sections in the Cottonwood Canyon area (pl. 1; fig.…”

“…A recent study by Baldyga (2001) analyzed the relation of faults in basin fill to the magnetic and gravity expression of their underlying (bedrock) fault systems. Baldyga acquired closely spaced gravity and magnetic data along two profiles in the Cottonwood Canyon, Ariz. area, named the northern and southern profiles.…”