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Nature and timing of Late Devonian-early Mississippian island-arc magmatism in the Northern Sierra terrane and implications for regional Paleozoic plate tectonics
Powerman, Vladislav Hanson, Richard E. Nosova, Anna Girty, Gary H. Hourigan, Jeremy Tretiakov, Andrei
Powerman, Vladislav
Hanson, Richard E.
Nosova, Anna
Girty, Gary H.
Hourigan, Jeremy
Tretiakov, Andrei
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GeoScienceWorld
Date
2020-02-01
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Abstract
The Northern Sierra terrane is one of a series of Paleozoic terranes outboard of the western Laurentian margin that contain lithotectonic elements generally considered to have originated in settings far removed from their present relative locations. The Lower to Middle Paleozoic Shoo Fly Complex makes up the oldest rocks in the terrane and consists partly of thrust-imbricated deep-marine sedimentary strata having detrital zircon age signatures consistent with derivation from the northwestern Laurentian margin. The thrust package is structurally overlain by the Sierra City melange, which formed within a mid-Paleozoic subduction zone and contains tectonic blocks of Ediacaran tonalite and sandstone with Proterozoic to early Paleozoic detrital zircon populations having age spectra pointing to a non-western Laurentian source. Island-arc volcanic rocks of the Upper Devonian Sierra Buttes Formation unconformably overlie the Shoo Fly Complex and are spatially associated with the Bowman Lake batholith, Wolf Creek granite stock, and smaller hypabyssal felsic bodies that intrude the Shoo Fly Complex. Here, we report new results from U-Pb sensitive high-resolution ion microprobe-reverse geometry (SHRIMP-RG) dating of 15 samples of the volcanic and intrusive rocks, along with geochemical studies of the dated units. In addition, we report U-Pb laser ablation-inductively coupled plasma-mass spectrometry ages for 50 detrital zircons from a feldspathic sandstone block in the Sierra City melange, which yielded abundant Ordovician to Early Devonian (ca. 480-390 Ma) ages. Ten samples from the composite Bowman Lake batholith, which cuts some of the main thrusts in the Shoo Fly Complex, yielded an age range of 371 ± 9 Ma to 353 ± 3 Ma; felsic tuff in the Sierra Buttes Formation yielded an age of 363 ± 7 Ma; and three felsic hypabyssal bodies intruded into the Sierra City melange yielded ages of 369 ± 4 Ma to 358 ± 3 Ma. These data provide a younger age limit for assembly of the Shoo Fly Complex and indicate that arc magmatism in the Northern Sierra terrane began with a major pulse of Late Devonian (Famennian) igneous activity. The Wolf Creek stock yielded an age of 352 ± 3 Ma, showing that the felsic magmatism extended into the early Mississippian. All of these rocks have similar geochemical features with arc-type trace-element signatures, consistent with the interpretation that they constitute a petrogenetically linked volcano-plutonic system. Field evidence shows that the felsic hypabyssal intrusions in the Sierra City melange were intruded while parts of it were still unlithified, indicating that a relatively narrow time span separated subduction-related deformation in the Shoo Fly Complex and onset of Late Devonian arc magmatism. Following recent models for Paleozoic terrane assembly in the western Cordillera, we infer that the Shoo Fly Complex together with strata in the Roberts Mountains allochthon in Nevada migrated south along a sinistral transform boundary prior to the onset of arc magmatism in the Northern Sierra terrane. We suggest that the Shoo Fly Complex arrived close to the western Laurentian margin at the same time as the Roberts Mountains allochthon was thrust over the passive margin during the Late Devonian-early Mississippian Antler orogeny. This led to a change in plate kinematics that caused development of a west-facing Late Devonian island arc on the Shoo Fly Complex. Due to slab rollback, the arc front migrated onto parts of the Sierra City melange that had only recently been incorporated into the accretionary complex. In the melange, blocks of Ediacaran tonalite, as well as sandstones having detrital zircon populations with non-western Laurentian sources, may have been derived from the Yreka and Trinity terranes in the eastern Klamath Mountains, where similar rock types occur. If so, this suggests that these Klamath terranes were in close proximity to the developing accretionary complex in the Northern Sierra terrane in the Late Devonian.
Contents
Subject
absolute age
California
Carboniferous
dates
Devonian
geochemistry
igneous rocks
island arcs
Laurentiav
lithostratigraphy
Lower Mississippian
magmatism
major elements
Mississippian
nesosilicates
Northern California
orthosilicates
Paleozoic
plate tectonics
plutonic rocks
sedimentary rocks
Shoo Fly Complex
Sierra Nevada
silicates
stratigraphic units
trace elements
U/Pb
United States
volcanic rocks
zircon
zircon group
northern Sierra Nevada
Taylorsville Sequence
California
Carboniferous
dates
Devonian
geochemistry
igneous rocks
island arcs
Laurentiav
lithostratigraphy
Lower Mississippian
magmatism
major elements
Mississippian
nesosilicates
Northern California
orthosilicates
Paleozoic
plate tectonics
plutonic rocks
sedimentary rocks
Shoo Fly Complex
Sierra Nevada
silicates
stratigraphic units
trace elements
U/Pb
United States
volcanic rocks
zircon
zircon group
northern Sierra Nevada
Taylorsville Sequence
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Research Projects
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Journal Issue
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Department
Geological Sciences