Abstract

Lineaments of mainly short to intermediate length were mapped on eleven individual LANDSAT-1 infrared positive transparencies and color composites covering the state of Pennsylvania. Each lineament was rated subjectively on two ordinal sea es, one of degree of expression (best expressed, intermediate, and least prominent), the other of the dominant means of expression (major streams, minor streams or tonal alignments).

Lineaments with orientations near the sun azimuth or the scan line direction tend to be subdued and overlooked in the mapping, but by comparing the frequency/length data and the degree of expression with SKYLAB images, a crude correction can be applied. Plotted as rose diagrams in cells 62 × 85 kms, the lineaments exhibit a preferred orientation that parallels the regional structural grain in areas of nearly flat-lying rocks and trends obliquely to it in the folded terranes. A broad northwest trend corresponds to the direction of dip joints across the State and suggests a genetic relationship between the two. While the orientation of short to intermediate lineaments is controlled by structural and lithologic domains, the larger lineaments transgress physiographic province boundaries and appear to be independent of the age of country rocks. Base metal and barite occurrences are preferentially distributed along some of the longer lineaments.

The longest lineaments mapped are probably the surface expression of buried tear faults or romps (“Gwinn-type” lineaments) in the Paleozoic strata overlying basal Appalachian decollements. They also coincide with the terminations of 2nd and 3rd order folds and may represent domain boundaries related to basement faults, such as have been described in West Virginia and Alabama. The Everett lineament extends across the Great Valley and South Mountain, suggesting that the basal decollement extends below the Blue Ridge to the east. This lineament and the Tyrone-Mount Union and Dunmore lineaments to the north and east are radial to the Pennsylvania salient of the Appalachian orocline. Many of the shorter lineaments trending oblique to strike may be related to tear and ramp faults associated with lystric thrust faults.

The apparent structural and lineament control of water and wind gaps in the Valley and Ridge Province does not support theories of superposition of Appalachian drainage, in which the gaps are randomly located and only locally adjusted to structure. Sixteen lineaments coincide with mapped faults and Gwinn lineaments, and four others appear to be extensions of mapped faults. However, the majority of the 2200 lineaments mapped are of unknown origin or subsurface expression, and may be analogous to joints, and related to earth body forces.