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ABSTRACT

The Sierra Nevada batholith of California represents the intrusive footprint of composite Mesozoic Cordilleran arcs built through pre-Mesozoic strata exposed in isolated pendants. Neoproterozoic to Permian strata, which formed the prebatholithic framework of the Sierran arc, were emplaced against the tectonically reorganized SW Laurentian continental margin in the late Paleozoic, culminating with final collapse of the fringing McCloud arc against SW Laurentia. Synthesis of 22 new and 135 existing detrital zircon U/Pb geochronology sample analyses clarifies the provenance, affinity, and history of Sierra Nevada framework rocks.

Framework strata comprise terranes with distinct postdepositional histories and detrital zircon provenance that form three broad groups: allochthonous Neoproterozoic to lower Paleozoic strata with interpreted sediment sources from Idaho to northern British Columbia; Neoproterozoic to Permian strata parautochthonous to SW Laurentia; and middle to upper Paleozoic deposits related to the fringing McCloud arc. Only three sedimentary packages potentially contain detritus from rocks exotic to western Laurentia: the Sierra City mélange, chert-argillite unit, and Twin Lakes assemblage. We reject previous correlations of eastern Sierra Nevada strata with the Roberts Mountains and Golconda allochthons and find no evidence that these allochthons ever extended westward across Owens Valley. Snow Lake terrane detrital ages are consistent with interpreted provenance over a wide range from the Mojave Desert to central Idaho.

The composite detrital zircon population of all analyses from pre-Mesozoic Sierran framework rocks is indistinguishable from that of the Neoproterozoic to Permian SW Laurentian margin, providing a strong link, in aggregate, between these strata and western Laurentia. These findings support interpretations that the Sierran arc was built into thick sediments underpinned by transitional to continental western Laurentian lithosphere. Thus, the Mesozoic Sierra Nevada arc is native to the SW Cordilleran margin, with the Sierran framework emplaced along SW Laurentia prior to Permian–Triassic initiation of Cordilleran arc activity.

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