ANTLER OROGENY

The Late Devonian/Early Mississippian Antler Orogeny has been interpreted in terms of a collision between either an east or west facing arc with the continental margin resulting in the emplacement of deep water marine facies (Roberts Mountains Allochthon; RMA) over the shelf terrane. These models assume a margin parallel arc terrane(s). Paleozoic arc and subduction complex terranes within the Klamath Mountains and Sierra Nevada are often interpreted as vestiges of this arc. Recent detrital zircon studies have revealed the presence of ca. 1.5 Ga detrital zircon (DZ) indicating that the arc terrane is exotic to western Laurentia. This exotic signature is also found in the Sierra City melange of the Sierra Nevada foothills belt; in addition, Late Devonian DZ have been found in a sandstone block in the melange indicating that melange formation was ongoing in Late Devonian or younger times. The Sierra City melange is subduction complex for the exotic arc. DZ from the Yreka terrane of the eastern Klamath Mountains also contain the 1.5 Ga zircon component as well as Late Devonian DZ indicating a Late Devonian or younger assembly of the Yreka terrane thrust system. Relatively recent paleontologic finds within the coarse immature clastics of the Harmony formation of the RMA indicate a Late Devonian/Early Mississippian age and thus is probably a synorogenic Antler deposit. DZ from the Harmony are very similar to that of the British Columbia miogeocline, as well as other strata contained within the bulk of the RMA. The Harmony also contains another sandstone facies with a bimodal Neoproterozoic/Grenville age DZ population not likely derived from western Laurentia but potentially sourced by the exotic arc and its basement. We suggest that a north facing (in current corrdinates) exotic Caribbean style arc collided with a fragment of continental crust left behind following Rodinia breakup. Collision resulted in uplift of the crustal fragment leading to development of submarine fan deposits of the Harmony as well as similar deposits of the Shoo Fly in the Sierra Nevada. Lateral tectonic escape from the collision zone resulted in the emplacement of the RMA and Shoo Fly, formation of the Antler Fordeep, and formation of the Yreka terrane thrust belt and its foredeep, the Late Devonian/Early Mississippian Bragdon Formation of the Klamath Mountains.