KINEMATICS OF APPARENT REVERSE FAULTS WITHIN EXTENSIONAL TECTONICS: CASE STUDY FROM THE PAHRANAGAT SHEAR ZONE (PSZ), BASIN AND RANGE, NEVADA, USA

The two end member laboratory based and theoretical concepts are simple and pure shear deformation, which commonly are applied in plane strain. However, in nature faults bend, which may lead to triaxial strain. Generally, strike-slip deformation accommodate simple shear, but the formation of duplexes, bends, or stepovers along strike-slip faults can generate internal deformation which might cause a change in the rock volume shape. A change in shape of rock volume can be associated with triaxial strain. Therefore, deformation can occur heterogeneously along strike of the strike-slip zones.

We used a case study of a duplex along a left-lateral strike-slip fault in an extensional regime, the Maynard Lake fault (MLF), southern Nevada to assess the possibility of triaxial strain. The MLF is one of the three major strike-slip faults in the Pahranagat shear zone (PSZ).

New mapping at 1:12,000 scale documents fault attitudes, cross-cutting relationships, the attitude of beds and compaction foliations from ash-flow tuffs, and folds. A duplex along the western MLF contains normal and reverse faults, and folds despite the fact that the duplex lies in a transtentional bend. In map pattern the duplex has a skewed diamond shape, wide in the center and narrow at the ends. This geometry required the rock volume within the duplex to change shape as it translated along bends in the bounding faults. Normal, reverse and oblique-slip faults, and folds within the duplex accommodated the change in shape. .

This study shows that deformation is heterogeneous within the MLF zone; triaxial deformation occurred dominantly within a restricted region (duplex zone) and simple shear deformation occurred across the MLF outside the duplex. Additionally, the origin of contractional features such as apparent reverse faults within the transtensional duplex structure is explained by progressive tilting and rotation of the early formed faults within the duplex.