Permo‐Triassic tectonism in volcanic arc sequences of the western U.S. Cordillera and implications for the Sonoma orogeny

Abstract

The Permo-Triassic Sonoma orogeny, western U.S. Cordillera, involved fight folding and imbricate thrust faulting of basinal strata of the Golconda allochthon. This event is generally interpreted in terms of accretion of upper Paleozoic volcanic arc rocks of the western U.S. Cordillera ("McCloud arc") to the North American continent, either via back arc basin closure or arc-continent collision. The structural history of the McCloud arc during the Sonoma orogeny is poorly understood, however, as are the implications of this history for tectonic models. This paper presents a synthesis of the Permian to Triassic stratigraphic and structural evolution of the McCloud arc, incorporating new data from the Pine Forest Range, northwest Nevada. The synthesis indicates that, on a regional scale, the arc was affected by widespread uplift but only local tilting, folding and faulting in the Late Permian to Early Triassic. The timing of Permo-Triassic tectonic activity in the McCloud arc is thus similar to the middle Permian to Early Triassic age of deformation in the Golconda allochthon but the structures produced in the two groups of rocks differ markedly. The significance of this contrasting structural response to Sonoma age tectonism can be evaluated by comparison with other better understood examples of arc-continent accretion (back arc basin closure in the southern Andes, "compressional" arc-continent collision in New Guinea and "extensional" arccontinent collision in the Mediterranean). This comparison indicates that the contrasting structural history of the McCloud arc and Golconda allochthon is entirely compatible with an arccontinent accretion model for the Sonoma orogeny and cannot be used as a basis for concluding that the McCloud arc was not involved in the orogenic event. The comparison further indicates that either back arc basin closure or "compressional" arc-continent collision are the most likely settings for the Sonoma orogeny. In contrast, an "extensional" Mediterraneanstyle arc-continent collision, as has been recently proposed for the earlier (middle Paleozoic) Antler orogeny, is probably not an appropriate analogue for the Sonoma orogeny. The weak structural response of the McCloud arc during Sonoman compression also provides new constraints on the specific processes involved in arc accretion, either via arc-continent collision or back arc basin closure. These constraints suggest that there may be few fundamental differences between the two models during the final stages of arc accretion. Regardless of tectonic setting, Permo-Triassic uplift and associated deformation in the McCloud arc should be considered as much a response to the Sonoma orogeny as is fight folding and imbricate faulting in the Golconda allochthon. A second model interprets the arc to have been east facing, and suggests that the Havallah sequence and related rocks were deformed as they were offscraped from the subducting edge of the North American plate and incorporated into a growing accretionary prism east of the arc [Speed, 1979; Snyd...

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“…In this study we extend the work of Kistler (1993) and Lahren (1999, 2006) by describing the petrogenesis of felsic volcanic rocks associated with batholithic magmatism in the earliest stages of evolution of the arc in the east-central Sierra Nevada and adjacent parts of eastern California. These data for the early Mesozoic batholithic rock suite and Origin and Evolution of the Sierra Nevada and Walker Lane themed issue Geosphere, August 2011 its contemporaneous and spatially associated volcanic cover provide a baseline for comparison to older accreted arcs (Wyld, 1991;Miller et al, 1992), contemporaneous parts of the arc constructed on much older crustal substrates in southern California (Miller et al, 1995;Barth et al, 1997), and younger plutonic and volcanic parts of the Mesozoic Cordilleran arc.…”

Provenance and paleogeography of the Black Rock Terrane, northwestern Nevada: Implications of U-Pb detrital zircon geochronology

“…This sequence consists mostly of shallow-marine, fossiliferous limestone and clastic rocks containing sedimentary and volcanic detritus. Collectively, these Permian units and the intervening unconformity appear to reflect shoaling, uplift, erosion, and then subsidence in the region during the late Paleozoic (Wyld, 1990(Wyld, , 1991.…”

“…to Upper Triassic strata across a slightly angular unconformity that is interpreted to reflect uplift and erosion related to the Permian-Triassic Sonoma orogeny (Wyld, 1991;Figs. 2 and 3).…”

The timing and provenance record of the Late Permian Klondike orogeny in northwestern Canada and arc‐continent collision along western North America

“…Emplacement of the Golconda allochthon is generally thought to have resulted from either: (1) arc-continent collision related to westward subduction of Golconda ocean lithosphere beneath east-facing arc terranes [Speed, 1979]; or (2) noncollisional collapse of the Golconda ocean basin due to changes in plate motions within a west-facing subduction system [e.g., Burchfiel and Davis, 1975]. Sub-Triassic angular unconformities observed on arc terranes to the west of the Golconda allochthon are interpreted to reflect widespread uplift, along with local folding and faulting, during Late Permian to Early Triassic time [Wyld, 1991].…”

“…One of the more popular tectonic scenarios considers the Sonoman orogeny as the product of terrane accretion [e.g., Speed, 1979], whereby the Golconda allochthon was thrust onto the ancestral North American continental margin during east-propagating arccontinent collision. Volcanic sequences in arc terranes west of the Golconda allochthon that were deformed and uplifted during the Late Permian-Early Triassic support this collisional model [Wyld, 1991]. Significant challenges for understanding the actual age of this late Paleozoic-early Mesozoic tectonism include a profound absence of geological elements typical of arc-continent collision, such as blueschist and eclogite paired with arc successions and collision-related foreland basin sequences along the ancestral North American continental margin [Dickinson, 2006].…”