354
W. L. Watney· J. Kruger· J. c. Davis· J. Harff . R. A. Olea,' G. C. Bohling
the SARs correspond to Precambrian terranes classified by lithology, geochronology, and structure. Further resolution can be provided by examination
of the magnetics and gravity information in this area and comparing trends and
patterns to basement geology and SARs. Two maps were selected to examine potential fields and SAR relationships. The first map is the residual Bouguer gravity map of Kansas with second-order regional trend removed and vertical sunshading (Fig. 3). This map is based on a previously published contour map from
data points every 1 x 1 km in eastern Kansas and every 1 x 2 km in western Kansas (Xia et al.1995). The other map is the residual aeromagnetic map of Kansas,
reduced to pole and with vertical sun-shading (Fig. 4). This map is based on a 1
x l-km grid constructed for a previously published contour map from E-W
flight lines flown 2 km apart (Xia et.al. 1995). The first part of the discussion is
referenced to SAR boundaries A through G encountered along the northwest to
southeast cross-section, beginning on the west side with SAR boundary A. The
second part of the gravity and magnetic map discussion includes three additional SAR boundaries from western Kansas, X, Y, and Z.
Boundary A is located at the edge of the northeast-northwest Midcontinent
Rift deformation and roughly associated with a northeast-southwest gravity
high. Sun-shading suggests northeast-southwest structural trends that are subparallel to boundary A. The trends may represent Precambrian faults and mafic
dikes. The magnetics map shows a similar correlation of the trends suggesting
that they are shallow Precambrian features. Both maps suggest that boundary A
is part of a major structural and compositional change in the basement.
Boundary B has similar gravity and magnetic trends as boundary A. The
northern part of the boundary roughly corresponds to the eastern margin of a
large gravity high mentioned previously. The trend of the boundary is also subparallel to magnetic and gravity lineaments probably associated with faulting
and intrusive activity related to Midcontinent rifting.
Boundary C, like boundaries A and B, follows the same northeast -southwest
orientations of the Midcontinent rifting. Boundary C is oblique to the eastern
margin of the gravity high, but appears to follow a strong northeast -southwest
magnetic lineament toward the middle of the boundary. The northern portion of
boundary C, although oblique to the eastern margin of the gravity high, appears
to follow a more subtle lineation that cross-cuts a flanking gravity low. Although
the previous boundaries A, B, and C are slightly oblique to the major magnetic and
gravity lineaments between them, NE-SW-trending segments of this boundary
appear to correlate roughly with the trend of individual lineaments. These northeast-southwest-trending segments seem to be offset from one another along
northwest-southeast-trending magnetic and gravity lineaments. The NW-SEtrending offsets may correlate with faults or shear zones associated with the Central Plains orogen, or extension related the Southern Granite-Rhyolite Province.
SAR boundary D follows the northeast-southwest-trending gravity and magnetic lineaments slightly better than A, B, or C. The curvature in the northeast
portion of the boundary appears to follow similar curvature of the axial gravity
high interpreted as gabbros and/or basalts of the Midcontinent Rift System. Re-
W. L. Watney· J. Kruger· J. c. Davis· J. Harff . R. A. Olea,' G. C. Bohling
the SARs correspond to Precambrian terranes classified by lithology, geochronology, and structure. Further resolution can be provided by examination
of the magnetics and gravity information in this area and comparing trends and
patterns to basement geology and SARs. Two maps were selected to examine potential fields and SAR relationships. The first map is the residual Bouguer gravity map of Kansas with second-order regional trend removed and vertical sunshading (Fig. 3). This map is based on a previously published contour map from
data points every 1 x 1 km in eastern Kansas and every 1 x 2 km in western Kansas (Xia et al.1995). The other map is the residual aeromagnetic map of Kansas,
reduced to pole and with vertical sun-shading (Fig. 4). This map is based on a 1
x l-km grid constructed for a previously published contour map from E-W
flight lines flown 2 km apart (Xia et.al. 1995). The first part of the discussion is
referenced to SAR boundaries A through G encountered along the northwest to
southeast cross-section, beginning on the west side with SAR boundary A. The
second part of the gravity and magnetic map discussion includes three additional SAR boundaries from western Kansas, X, Y, and Z.
Boundary A is located at the edge of the northeast-northwest Midcontinent
Rift deformation and roughly associated with a northeast-southwest gravity
high. Sun-shading suggests northeast-southwest structural trends that are subparallel to boundary A. The trends may represent Precambrian faults and mafic
dikes. The magnetics map shows a similar correlation of the trends suggesting
that they are shallow Precambrian features. Both maps suggest that boundary A
is part of a major structural and compositional change in the basement.
Boundary B has similar gravity and magnetic trends as boundary A. The
northern part of the boundary roughly corresponds to the eastern margin of a
large gravity high mentioned previously. The trend of the boundary is also subparallel to magnetic and gravity lineaments probably associated with faulting
and intrusive activity related to Midcontinent rifting.
Boundary C, like boundaries A and B, follows the same northeast -southwest
orientations of the Midcontinent rifting. Boundary C is oblique to the eastern
margin of the gravity high, but appears to follow a strong northeast -southwest
magnetic lineament toward the middle of the boundary. The northern portion of
boundary C, although oblique to the eastern margin of the gravity high, appears
to follow a more subtle lineation that cross-cuts a flanking gravity low. Although
the previous boundaries A, B, and C are slightly oblique to the major magnetic and
gravity lineaments between them, NE-SW-trending segments of this boundary
appear to correlate roughly with the trend of individual lineaments. These northeast-southwest-trending segments seem to be offset from one another along
northwest-southeast-trending magnetic and gravity lineaments. The NW-SEtrending offsets may correlate with faults or shear zones associated with the Central Plains orogen, or extension related the Southern Granite-Rhyolite Province.
SAR boundary D follows the northeast-southwest-trending gravity and magnetic lineaments slightly better than A, B, or C. The curvature in the northeast
portion of the boundary appears to follow similar curvature of the axial gravity
high interpreted as gabbros and/or basalts of the Midcontinent Rift System. Re-