Detrital-zircon geochronology of the Sawtooth metamorphic complex, Idaho: Evidence for metamorphosed lower Paleozoic shelf strata within the Idaho batholith

Abstract

U-Pb ages of detrital zircons from metasedimentary rocks of the Sawtooth metamorphic complex (SMC) are key for identifying the stratigraphic age of metamorphosed strata within the Idaho batholith region of the Cordilleran orogen. The SMC is an exposure of medium-to high-grade metasedimentary rocks surrounded by the Idaho and Sawtooth batholiths. U-Pb ages of detrital zircons from SMC quartzites and quartzofeldspathic gneisses yield two distinctive age spectra consisting of primary 2900-2510 Ma and 1990-1760 Ma zircons for one group and 1870-1670 Ma, 1490-1330 Ma, and 1220-1020 Ma zircons for the other group. The suite of samples also yields a small number of zircons with concordant Cambrian and Neoproterozoic ages. Statistical and visual comparisons of age spectra with detrital-zircon data from Proterozoic and Paleozoic strata deposited on the western passive margin of Laurentia suggest that the SMC rocks were deposited in the Cambrian and Middle Ordovician. The identification of lower Paleozoic shelf strata in the SMC, along with similar sections recently identified in the Stibnite and Gospel Peaks inliers of the Idaho batholith, suggest that the Cordilleran passive margin sequence was continuous along the western margin of Laurentia, including the area occupied by the Idaho batholith. 2016, Detrital-zircon geochronology of the Sawtooth metamorphic complex, Idaho: Evidence for metamorphosed lower Paleozoic shelf strata within the

Provenance analysis of the Ochoco basin, central Oregon: A window into the Late Cretaceous paleogeography of the northern U.S. Cordillera

“…The detrital-zircon age signature of the Goose Rock Conglomerate quartzite cobble closely resembles that of Ordovician quartzite found in the North American Cordillera from Canada to Mexico (Fig. 8; Gehrels and Stewart, 1998;Baar, 2009;Wulf, 2011;Workman, 2012;Gehrels and Pecha, 2014;Ma et al, 2015;Linde et al, 2016). Although the overall uniformity of detrital-zircon age signatures in these Ordovician quartzites precludes confi dent identifi cation of a unique source, subtle differences in proportion, such as a prominent ca.…”

500–490 Ma detrital zircons in Upper Cambrian Worm Creek and correlative sandstones, Idaho, Montana, and Wyoming: Magmatism and tectonism within the passive margin

“…West of this fault, Neoproterozoic and Cambrian strata, not present on the Lemhi arch to the east, are recognized at Edwardsburg, Stibnite, and in the Sawtooth Mountains ( Fig. 1) (Hobbs et al, 1991;Lund et al, 2003;Lewis et al, 2012Lewis et al, , 2014Ma et al, 2016).…”

“…In the Sawtooth Mountains (Fig. 11) it is group B of Ma et al (2016). In Cambrian strata of the northern Canadian Cordillera, it is provenance type I of Hadlari et al (2012).…”

Magma‐facilitated transpressional strain partitioning within the Sawtooth metamorphic complex, Idaho: A zone accommodating Cretaceous orogen‐parallel translation in the Idaho batholith

“…The metapsammites from highly sheared units often contain abundant zircon with Archean to early Paleozoic detrital cores and wide (>30 µm) overgrowths that give Cretaceous ages of ca. 92–89 Ma [ Bergeron , ; Ma et al, ]. The consistence of age between the detrital zircon overgrowths and magmatic zircons from the magmatically foliated intrusive sheets, along with the compatible fabrics between the metapsammites and those other metasedimentary/intrusive rocks, suggests that the metamorphic or hydrothermal overgrowths on detrital zircons are contemporaneous with and probably genetically related to the SMC transpressional deformation.…”

“…The SMC is bounded on the east side by a buried east‐dipping normal fault (Figure b) [ Reid , ; Fisher et al, ; Dutrow et al, ]. The SMC metasedimentary rocks are mostly composed of intermediate‐ to high‐grade siliciclastic and carbonate materials (Figure ) [ Dutrow et al, ; Metz , ; Fukai , ; Ma , ], the protoliths of which were likely deposited in the Cambrian and Middle Ordovician [ Ma et al, ]. These metasedimentary rocks are intruded by gabbroic, granitic, and leucogranitic sheets, pods, and dikes, along with Eocene Challis rhyolitic and basaltic dikes [e.g., Ma , ].…”