Abstract

New geologic mapping and Ar-Ar geochronology of the late Cenozoic volcanic-sedimentary units in central and southern Panamint Valley, California, provide the first known Miocene palinspastic reconstruction vectors for Panamint Valley. Panamint Valley contains active faulting and potentially accommodates a significant percentage of the slip of the Walker Lane at this latitude. Volcanism in Panamint Valley occurred during two time intervals, one ca. 15–13.5 Ma ago and a second ca. 4.5–4 Ma ago. The reconstruction vectors are based on unique relationships of sedimentary source areas and the only known Miocene intrusive zones to determine the displacement across Panamint Valley since ca. 15 Ma ago. The Argus Range was displaced ~17 km to the west-northwest, and the southern Slate Range was displaced 10.5 km to the north-northwest relative to the Panamint Range. Our displacement vector for reconstructing the past ~15 Ma of slip across Panamint Valley is 14 km shorter than previously published reconstruction models. We interpret this smaller slip value to be a function of the previous studies using displacement vectors that included a component of pre–15 Ma ago slip. The Harrisburg fault of the Tucki Mountain detachment system is a likely candidate for an earlier slip, possibly during the regionally observed extension during Late Cretaceous and Eocene. We created a model of the ca. 0–15 Ma ago displacement history of Panamint Valley using our new slip vectors and the slip vector for the Hunter Mountain fault. The Miocene extension begins with or slightly before ca. 15 Ma ago volcanism and may have continued to <~13.5 Ma ago. We interpreted the slip during Miocene extension to have occurred on one master detachment fault. Pliocene and younger extension is oblique to the Miocene extension, and the detachment fault was then cut up into discrete segments, the Emigrant, Panamint, and Slate Range detachment faults. The Panamint detachment was reactivated in an oblique normal sense, while slip on the other two detachment faults ceased; slip now occurs on nearby steeper normal faults. The Panamint detachment ends to the north and south in triple junctions: at the north end, slip is partitioned onto the Hunter Mountain and Towne Pass faults, and at the south end, slip is partitioned onto the Manly Pass and Southern Panamint Valley faults. The southern triple junction has an unstable geometry and it must migrate northward, lengthening the Southern Panamint Valley fault at the expense of the Panamint detachment. The continued slip on the unfavorably oriented low-angle Panamint detachment may be explained by the presence of weak fault gouge along it or by a regional pattern of slip partitioning. Major regional strike-slip faults, the Northern Death Valley and Garlock faults, are proximal to the northern and southern triple junctions. These two large faults may drag the two ends of the Panamint detachment with them, creating the triple junctions. The modern complex geometries and kinematics of Panamint Valley may therefore be a function of older structures being reactivated and interference with nearby faults.

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