THE GARLOCK FAULT ZONE AS A WIDE ZONE OF ACCOMMODATION, A LONG-LIVED PASSIVE STRUCTURE EMBEDDED IN THE EVOLVING EXTENSIONAL TO DEXTRAL SHEAR DEFORMATION SYSTEMS OF EASTERN CALIFORNIA

The significance and evolution of the large-magnitude sinistral slip Garlock fault is a critical component to understanding the Miocene to Recent deformation systems of the combined Death Valley-Walker Lane belt-Eastern California shear zone. The Garlock fault is anomalously oriented transverse to adjoining dextral-slip and transtensional slip faults. We seek to understand the detailed slip history of the Garlock fault and it’s interaction through time with the adjacent fault systems.

We have investigated numerous areas along the central and eastern parts of the fault including access-controlled military base areas. We are evaluating the idea that the Garlock fault is a passive structure embedded in a complex deformation system; its tectonic history is intimately associated with these other deformation systems. We combined the results of seven field projects (involving detailed geologic mapping, structural analysis, and geochronology) that we have accomplished to assemble a relatively complete dataset of observations along the central Garlock fault. We then identified as many fault slip offset markers along the Garlock fault and adjoining structures, examining markers of different ages from before and during the ~11 m.y. history the Garlock fault and regional deformation.

The Garlock fault is a 5 to 20 km wide zone of deformation, which accommodates the slip of the transversely oriented incoming fault systems, which do not cut the Garlock fault except at its eastern end in Death Valley. Numerous mechanisms of accommodation are found within the Garlock fault zone, including: paired contraction and extensional corners, block rotation, tectonic expulsion, orogenic bending, and side-stepping of the main active slip surface. One key result is the identification of the Marine Gate fault which has 19 km of the total Garlock fault zone slip of 60-70 km since ~11 Ma. The Marine Gate fault was the locus of sinistral slip until ~3 Ma and is now reactivated as a dip slip fault as the main locus of Garlock fault zone slip has stepped southward. The evolution and mechanism of accommodation in the Garlock fault zone are critical for evaluating the seismicity and hazards of not only of the Garlock fault itself but also for the adjacent active dextral faults.