A PALEOMAGNETIC ANALYSIS OF VERTICAL AXIS ROTATION ALONG THE TASCOTAL MESA FAULT IN FAR WEST TEXAS

The Tascotal Mesa transfer zone (TMTZ), as described by Dickerson (1995), is an east-west trending zone expressing ~290 million years of tectonic and magmatic activity since the late Paleozoic. The Tascotal Mesa Fault (TMF) lies within the TMTZ as a right-lateral strike-slip fault expressing ~1 km of dextral offset and ~735 m of normal dip-slip motion within the last ~30 million years (Dickerson, 1995). The TMF is at the southeastern margin of the Basin and Range extensional province and functions as a transfer zone within the Rio Grande rift in west Texas (Dickerson, 2013; Henry, 1998; Henry et al., 1991). Ideal horizontal extension should cause the crust to undergo only vertical motion or rotation about a horizontal axis, but vertical-axis rotations have been documented in volcanic flows within the TMTZ, by the use of paleomagnetism (Sager et al., 1992). The methods for a detailed paleomagnetic analysis on the TMF represent a combination of techniques including large-scale geologic field mapping, paleomagnetism field core drilling, GPS point accumulation, thin-section characterization, and rock-magnetization analysis. The goal of this study is to interpret the role of the Tascotal Mesa Fault in accommodating crustal deformation through a quantitative vertical-axis rotation paleomagnetic analysis.