Lineament analysis and inference of geologic structure: examples from the Balcones Ouachita trend of Texas
Lineaments perceived in remotely sensed images are reliable indicators of geologic structure. Lineaments on ten Landsat multispectral scanner images (band 5; 1:250,000 scale) were mapped covering the Ouachita/Balcones-Luling-Mexia-Talco structural trend between the Rio Grande and Red river in Texas. More than 5,000 lineaments were perceived in these images. Maps depicting the lineaments (individually and in various combinations) were compared with maps of structural/ tectonic features and geothermal gradient contours, noting instances of apparent correlation among these themes. Lineaments are correlative with the individual faults and the aggregate fault patterns of the Baicones, Luling, Mexia, and Talco fault zones, Transverse lineaments, which trend almost perpendicular to these fault zones, mark the northernmost extent of the Balcones fault system and outline carbonate piatforms, such as the Belton High/Moffat Mound trend and the San Marcos arch. Transverse lineaments are coincident also with the axes of the buried Chittim and Preston anticlines and with the flanks of the Sherman and Round Rock synclines. Numerous salt domes occur at depth in the western part of the east Texas basin near the trend; many of these domes, particularly those in Henderson, Anderson, and Freestone Counties, are found along and at the intersection of major lineament zones where the concentration of individuai lineaments is greatest. Most of the buried Late Crelaceocs volcanoes of central Texas near Austin lie along northeast southwest- trending lineament zones; the altered pyroclastic rocks and associated beachrock facies at many of these volcanoes are hydrocarbon reservoirs. The orientation and spacing of geothermal gradient contour lines ("isograds") also correspond to major structures and thus, to the pattern of lineaments throughout the region. Correlation of (1)individual lineaments, zones of cortiguous or nearly parallel lineaments, and areas of homogeneous lineament density and orientation to (2) surface and subsurface structure and (3) geothermal,'isograd" patterns indicates that lineament analysis has many potential applications to regional mineral resource assessment.