![]() ![]() Samples GOM-46 and GOM-76 were collected in westcentral Arkansas near the western margin of the Mississippi embayment (Blum and Pecha, 2014 Blum et al., 2017). Fortunately, the principal magmatic provinces that constitute the North American Cordillera (i.e., Coast Mountains batholith, North Cascades Range, Idaho batholith, Sierra Nevada batholith, Peninsular Ranges batholith, Transverse Ranges, Sierra Madre Occidental, and Laramide porphyry copper province) are characterized in terms of their zircon Hf isotopic signature to a degree that is sufficient to provide a robust reference data set for comparisons with newly generated detrital Hf results (Arvizu and Iriondo, 2011 Cecil et al., 2011 Gaschnig et al., 2011 Lackey et al., 2012 Shaw et al., 2014 Barth et al., 2016 Mahar et al., 2016 Fisher et al., 2017 Homan, 2017 Sauer et al., 2017 Chapman et al., 2018 Dafov et al., 2020 Garcia et al., 2021). In addition to crustal evolution information, Hf isotope measurements in zircon provide an additional diagnostic tool for detrital zircon provenance evaluation (Gehrels and Pecha, 2014) however, this also requires knowledge of the U-Pb age and Hf isotopic signature(s) of the potential source terranes. We propose that the PTGs from NW Sonora formed in a continental arc setting likely derived from the heat-fluxed melting of crustal material induced by mafic (basaltic?) underplating, thus the PTGs record the initiation of subduction and the generation of the early magmas in the nascent Late Paleozoic Cordilleran arc in SW Laurentia. Crustal contamination is supported by field evidence, including xenoliths, stoped blocks, and roof pendants of Proterozoic basement rocks (Yavapai-type? crust). All these geochemical features imply that crustal assimilation did play a major role in magma genesis. ![]() Trace-element ratios of Ba/Ta≫1000, Th/Yb > 1, and Th/Ta>6–20 also support a setting in an active continental margin. The enrichment in LILE (such as K, Rb, Ba, Sr, and Pb) and LREE over HFSE and HREE, respectively, together with negative Nb, Ta, P, and Ti anomalies, suggest derivation from a crustal source in a continental arc setting. PTGs are petrologically and geochemically classified as granodiorites, granites, and quartz monzonites, with medium-to high-K calc-alkaline affinity, and volcanic-arc granite (VAG) signatures. PAS cut both granitoid suites and local Paleoproterozoic banded gneisses. MS is slightly older than LS based upon field relations and age dating. PAS is composed of garnet-bearing pegmatite-aplite dikes of Permo-Triassic age. MS has I-type signatures (mostly metaluminous: biotite and hornblende), while LS is weakly peraluminous with biotite, muscovite, and garnet. Based on mineralogical and geochemical characteristics, the PTGs are subdivided into three main suites: melanocratic (MS), leucocratic (LS) and pegmatitic-aplitic (PAS) suites. Permo-Triassic granitoids (PTGs) (284–224 Ma) crop out in Sierra Los Tanques (SLT) and surrounding areas in NW Sonora, Mexico.
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