Structure and stratigraphy of the Antelope Mountain Quartzite, Klamath Mountains, Northern California
Previously, the Antelope Mountain Quartzite has been interpreted as a nappe over the Duzel Phyllite, however, field mapping and regional data indicates it is a km-scale block in melange, and that the Duzel Phyllite is thrust over it. The Antelope Mountain has been subjected to polyphase deformation including mid-Paleozoic thrust faulting responsible for an overturned anticline, high-angle normal faulting, and younger, previously unrecognized, Cretaceous high-angle normal faulting. The Antelope Mountain Quartzite contains a mappable stratigraphy including black chert, red argillite, and resistant quartzite beds that are used to document these younger extensional deformations; East-west oriented high-angle normal faults with minor displacement are probably products of mid-Paleozoic forearc accommodation. These faults are recognizable by offset of both the thrust contact and chert marker beds in the Antelope Mountain Quartzite. North-south oriented high-angle faults occur throughout the study area. Evidence for these faults includes offset of the early high-angle faults, and repetition of resistant quartzite marker beds. These later normal faults cut Middle Albian conglomerate in the southern part of the field area, and are overlapped by Coniacian to Maastrichtian sandstone of the Hornbrook Formation, thus tightly bracketing deformation to the mid- to Late Cretaceous. This deformation provides an ancient example of intra-arc extension expressed solely in the pre-extensional metasedimentary rocks, rather than in the syn-extensional igneous rocks themselves. Cretaceous crustal extension, along with Cenozoic erosion appears to be responsible for much of the present-day topography.
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