Texas lineament revisited
— William R. Muehlberger

The type locality of the Texas Lineament and for the Texas direction of wrench faulting includes the corridor between Van Horn and Sierra Blanca, Texas (Albritton and Smith, 1957; Moody and Hill, 1956). This corridor has been the principal route of travel across this region from time immemorial: it includes the route of the Butterfield Stage Coach Line, two railroads and the main highway between Van Horn and El Paso. Across this corridor the difference in geology is profound: a stable platform on the north (thin shelf carbonates of Permian and Lower Cretaceous age on Precambrian rocks in the Diablo Plateau) and a mobile subsiding trough on the south (thick Cretaceous carbonates and clastics on Mesozoic evaporites of the Chihuahua Tectonic Belt, which have been thrust northeastward against the margin of the platform). Albritton and Smith (1965) found no evidence for strike-slip movement at Sierra Blanca or eastward, and because they found no continuation eastward beyond the Carrizo Mountains they doubted that large strike-slip movement had occurred along this segment of the zone. A gravity and magnetic study of this region by Wiley (1970, 1972) showed that the major geophysical anomalies in Eagle Flat turned southward along the south edge of the Carrizo Mountain and became coincident with the exposed Rim Rock fault that extends southward for 96 km nearly to Presidio. These faults mark the northeastern margin of the Chihuahua tectonic trough, structures that have been active since mid-Mesozoic time. An equivalent Late Paleozoic border must lie in this same zone (probably to the southwest) but its exact location is uncertain. For the rest of the Paleozoic there are no stratigraphic data to support any movement along this zone (horizontal or vertical; Wiley and Muehlberger, 1971). Because recurrent deformation, metamorphism and intrusion along this zone suggests that there is a fundamental crustal discontinuity, it will continue to be studied by many in an effort to unscramble the successive effects and true history of this region.

LANDSAT imagery has given new impetus to the study of lineaments with a consequent rash of papers showing lines all over maps; some of these lines are geologically meaningful, for others the meaning is obscure to unknown. LANDSAT images show a band of linear features, 16 km wide at most, that extends from El Paso, through Sierra Blanca, Marfa, Persimmon Gap and into northern Coahuila through the Pico Etereo igneous area to Valle el Infante. This band can be identified on Figures 4 and 5; parts are readily found on Figures 2 and 3. It includes the type area of the Texas Lineament; thus, this remarkably straight band of linear features must constitute the trace of the Texas Lineament across Trans-Pecos Texas. A parallel line 80 km to the south in northern Mexico, which includes the west-northwest-trending segment of the Rio Grande downstream from Presidio, forms the boundary between nearly north-trending elements on the south and westnorthwest-trending elements on the north. This 80-km-wide band includes virtually the entire zone of west-northwest trending structures in this region. Albritton and Smith (1957) defined the Texas Lineament as a zone and described its appearance west from Van Horn, Texas. LANDSAT views suggest that the Texas Lineament across Trans-Pecos Texas is this 80-km-wide band. Possible extensions in either direction are beyond the scope of this paper.

This paper will focus on tectonic features and events of Trans-Pecos Texas with forays into the surrounding region as necessary to indicate the relationships and larger implications of this restricted area.

The set of maps accompanying this paper shows the orientation and type of structure known to have been active during each orogenic period that has affected Trans-Pecos Texas. This set of maps should be considered a progress report, because many of the faults identified in the field cannot be uniquely assigned to a specific deformational episode and, thus, are shown for only the latest movement for which stratigraphic evidence is available; others have been active in virtually every phase of deformation. I have attempted to show only data (observable field relations) on these maps. Thus, they are sparse because interpreted structures that seem necessary because of the regional pattern are not included (as is usually the case). The text is mainly explanatory material for the maps.

The overriding theme is that the Texas Lineament is a zone of recurrent movement that separates more stable crust on the north from less stable crust on the south. Dip-slip (normal, steep reverse, or thrust) movements are widely demonstrable. Strike-slip movement can be documented for episodes but the amount of slip necessary to produce the observed effects is in miles rather than in hundreds of miles. This paper discusses the region from its probable birth about 1.4 b.y. ago to the present.