A PHYSICAL ANALOG MODEL OF EXTENSIONAL DEFORMATION IN THE YUCCA MOUNTAIN REGION, NEVADA

The structural geology of the Crater Flat (CF) basin, including Yucca Mountain, consists of west-dipping extensional faults that trend between 000^° and 030^°, with subsidiary strike-slip and reverse faults. Faulting developed in response to E-W or NW-SE extension coeval with deposition of Miocene tuffs. We consider CF as the deformed hanging wall of the east-dipping and listric-shaped Bare Mountain Fault (BMF). To simulate extensional deformation of CF, we developed a 1:100,000 scale model of the CF basin. The analog model consisted of a layered sandpack above a rigid wood and clay footwall. The BMF décollement was simulated by a plastic sheet that separated the sandpack from the footwall. Balanced cross sections drawn across northern and southern CF were used to define the shape of the BMF. In the northern section, the thickness of the hanging wall above the modeled BMF was 6 cm [2.4 in]. In the southern section, the hanging wall thickened to 12 cm [4.7 in]. An E-W lateral ramp connects the deeper southern and shallower northern hanging walls. This lateral ramp is interpreted to lie beneath a zone of NW trending strike-slip and oblique slip faults within Yucca Mountain and coincident with major displacement transfer from the Solitario Canyon fault in the east to the Fatigue Wash and Northern Windy Wash faults in the west. The analog model was deformed by E-W extension. Results show that the deformed model closely reproduces the pattern of faults observed within CF. At the southern end of the model, deformation of the hanging wall is characterized by large NS trending antithetic normal faults. At the northern end of the model, these faults transfer displacement to a set of smaller antithetic normal faults that lie much closer to the BMF. Above the lateral ramp an array of NW trending oblique to strike slip faults formed. Sequential sections cut through the model after completion resemble the balanced cross sections drawn through CF. These observations support tectonic interpretations in which faults in CF were produced by E-W or NW-SE extension of the CF hanging wall above an irregular-shaped BMF.

[This abstract is an independent product of the CNWRA and does not necessarily reflect the views or regulatory positions of the U.S. Nuclear Regulatory Commission.]