2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 18
Presentation Time: 8:00 AM-12:00 PM


PETRONIS, Michael Seth, Earth and Planetary Sciences, Univ of New Mexico, Albuquerque, NM 87131, GEISSMAN, John, Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131 and OLDOW, John, Geological Sciences, University of Idaho, Moscow, 83844-3022, mspetro@unm.edu

We are attempting to estimate the magnitude of permanent Neogene strain in the Mina Deflection area, west central Nevada and, based on paleomagnetic data, propose a mechanism by which a component of deformation is accommodated. The Mina Deflection links the NW-trending faults of the central Walker Lane to the NW-trending faults of the Owens Valley - Fish Lake Valley fault system by transferring displacement in an extensional right-step along a system of E-W striking faults. Paleomagnetic data from three regionally extensive Oligocene ignimbrites that cover the area reveal spatially variable components of vertical axis rotation. The ignimbrites provide a datum to evaluate components of rotation and tilting as the sheets were fragmented into many structural blocks during extension and paleomagnetic data from individual blocks allow for an assessment of the magnitude and sense of deformation between blocks. To quantify relative if not absolute rotation, we have selected a section along the SW side of Huntoon Valley where the ignimbrites crop out in order on the same structural block. These are the westernmost exposures of the ignimbrites and, importantly, the area is characterized by NW-SE striking faults. We assume that this area has experienced little if any vertical axis rotation. All paleomagnetic data, following correction for tilt based on compaction fabrics, are compared to data from this "reference" section. Each ignimbrite has a unique characteristic remanent magnetization (ChRM) and any deviation from that ChRM at individual sites compared to the reference section suggests a vertical axis rotation. The reference paleomagnetic directions (Candelaria Junction (CJ), Belleville, and Metallic City) are 249.5°, -53.5°, a95= 1.9°; 044.3°, 30.5°, a95= 3.6°; and 355.3, -32.2°, a95= 2.6°, respectively. We recognize variable magnitude and sense vertical axis rotations across the area with rotations between 0° to 40° (average ~ 20°), but locally > 50°. In the western Candelaria Hills, the CJ is rotated clockwise 15°, while in the northern Volcanic Hills it is rotated counterclockwise by 12°. We interpret the non uniform magnitude and sense of vertical axis rotation across the Mina Deflection to reflect strain partitioning between normal and strike slip faults with some structures accommodating more strain than others.