6 Structural Geology: Recent Advances in Structural Geology

Sunday, 9 October 2011
8:00 AM - 12:00 PM
Room 200A-C

INITIATION AND SLIP HISTORY OF THE CENTRAL SEGMENT OF THE GARLOCK FAULT, CALIFORNIA

Paper number: 6-5
Program: Technical Sessions
Time: 8:50 AM – 9:05 AM

Authors

Abstract

New mapping and geochronology for the Lava Mountains and Summit Range (LMSR), California, lead us to present new data and interpretations for the structure and timing of initiation and slip history of the central Garlock fault (segment from El Paso Mountains to the southern Panamint Valley fault zone). This history includes not only the slip on the sinistral Garlock fault zone, but also interaction with a major fault in the Eastern California Shear Zone (ECSZ). Key to this interpretation is better understanding of late Miocene volcanic rocks and Miocene dikes. These rocks are offset across the Garlock fault from the El Paso Mountains/southern Sierra Nevada to the west as well as within the LMSR. Miocene rocks are divided into older and younger sequences. The older igneous sequence is an ~11 Ma set of mostly silicic rocks present in all areas. Offset of these rocks gives about 44 km of net slip on the trace of the central Garlock fault, well short of the ~64 km demonstrated by other markers. The difference is accounted for by two additional faults in the LMSR – the Browns Ranch and Savoy faults. These faults are sub-parallel to the Garlock and have ~20 km of sinistral slip. Collectively the three faults make up the Garlock fault zone. A later set of ~8 to 6 Ma volcanic rocks also serve as slip markers. These rocks are used to interpret slip on the sinistral faults as well as the dextral Blackwater fault of the ECSZ.

Using these rocks to understand the slip history of the Garlock, Savoy, Browns Ranch, and Blackwater faults leads us to the following interpretations. Early movement on the Garlock fault zone was synchronous with 10-11 Ma rapid exhumation on nearby Basin and Range detachment faults. Slip was concentrated on the Savoy fault and was probably around 11 km. A second, more complex slip episode of the Garlock fault zone results from interaction with the ECSZ. During this phase slip continued on the Savoy, and initiated on the Browns Ranch and Garlock fault (present trace). During this deformation, the LMSR accommodated 8-11 km dextral slip of the Blackwater fault via local tectonic escape, contraction, extension, vertical axis rotation, and by transfer of material across the Garlock fault. Our model requires that 80% of the 64 km slip of the Garlock fault is younger than ~6 Ma.