THE AMARGOSA SURFACE IN DEATH VALLEY, CALIFORNIA: ONE FAULT OR MANY?

The Amargosa Chaos, in the southeastern portion of Death Valley National Park, is defined by a disorderly assemblage of Proterozoic sedimentary rock faulted over crystalline basement. The Chaos plays an important role in many tectonic reconstructions of the area, some of which require northwest movement along a single detachment fault that separates the basement from the overlying sedimentary rock. To test the continuity of the fault, I determined the structural evolution and predominant slip direction at three field sites within the Amargosa Chaos. Significant differences between the three sites suggest that the Amargosa surface consists of several distinct faults, rather than a singular fault.

Each site revealed a slightly different history. At the mouth of Virgin Spring Canyon, movement on the Amargosa Fault between the basement and Crystal Springs preceded faulting between the Crystal Springs quartzite and Crystal Springs cherty dolomite, faulting between the Noonday Dolomite and the Kingston Peak Formation, and a set of high angle faults that cut through the entire outcrop. Three kilometers to the north of that site, in a side canyon off Virgin Spring Canyon, we see evidence of Mesozoic shortening, followed by movement along the Amargosa Fault, and then secondary extensional faulting post-dating the movement along the Amargosa Fault. The third field site, along Jubilee Pass Road and informally named Exclamation Point, displays strike-slip faulting within the Noonday Dolomite, which preceded movement along the Amargosa Fault. These events were then followed by faulting between the Crystal Springs and Noonday Dolomite, and faulting between the Noonday Dolomite and the Johnnie.

We observed that in all three locations, the Amargosa Fault displays movement in different directions. P-foliation, Riedel Shears, slickenlines, and separation indicate transport to the southeast at the mouth of Virgin Spring Canyon. Similar evidence shows transport to the northwest in the side canyon and to the southwest at Exclamation Point. These differing movement directions contradict the tectonic models that require northwest transport and suggest that the rhombochasm model, first advocated by Wright and Troxel (1984), might explain deformation in the area better.