The Permian Monos Formation: Stratigraphic and detrital zircon evidence for Permian Cordilleran arc development along the southwestern margin of Laurentia (northwestern Sonora, Mexico)

Abstract

The southwestern margin of Laurentia transitioned from a left-lateral transform margin to a convergent margin by middle Permian time, which initiated the development of a subduction zone and subsequent Cordilleran arc along western Laurentia. The displaced Caborca block was translated several hundred kilometers from southern California, USA, to modern Sonora, Mexico, beginning in Pennsylvanian time (ca. 305 Ma). The Monos Formation, a ~600-m-thick assemblage of mixed bioclastic and volcaniclastic units exposed in northwestern Sonora, provides lithostratigraphic, petrographic, and geochronologic evidence for magmatic arc development associated with subduction by middle Permian time (ca. 275 Ma). The Monos Formation was deposited in a forearc basin adjacent to a magmatic arc forming along the southwestern Laurentian margin. Detrital zircon U-Pb geochronology suggests that Permian volcanic centers were the primary source for the Monos Formation. These grains mixed with far-traveled zircons from both Laurentia and Gondwana. Zircon age spectra in the Monos Formation are dominated by a ca. 274 Ma population that makes up 65% of all analyzed grains. The remaining 35% of grains range from 3.3 Ga to 0.3 Ma, similar to age spectra from Permian strata deposited in the Paleozoic sequences in the western continental interior. An abundance of Paleozoic through early Neoproterozoic ages suggests that marginal Gondwanan sources from Mexico and Central America also supplied material to the basin. The Monos Formation was deposited within tropical to subtropical latitudes, yet faunal assemblages are biosiliceous and heterotrophic. The lack of photozoan assemblages suggests that cold-water coastal upwelling combined with sedimentation from the Cordilleran arc and Laurentian continent promoted conditions more suitable for fauna resilient to biogeochemically stressed environments. We propose that transform faulting and displacement of the Caborca block ceased by middle Permian time and a subduction zone developed along the southwestern margin of Laurentia as early as early Permian time. The Monos basin developed along the leading edge of the continent as a magmatic arc developed, and facies indicate a consistent shoaling trend over the span of deposition.

A Lower Devonian age for the Corvock Granite and its significance for the structural history of South Mayo and the Laurentian margin of western Ireland

“…Analyses that are >10% normally discordant or 5% reversely discordant or are spuriously young are listed in Table 1 as "rejected grains" and are not used in the overall age determinations (cf. Lodes et al 2020;Dobbs et al 2021). We used the TuffZirc algorithm in Isoplot (Ludwig, 2003) to assess likely crystallisation ages for the two units (Figs.…”

Sedimentary Record of the middle Cretaceous uplift across the Gangdese magmatic arc system in Southern Tibet

“…Sedimentary basins adjacent to subduction‐related continental arcs record the intricate history of convergent plate margins (Figure 1; Ingersoll, 1988; Dickinson, 1995; Einsele, 2000). Subduction related basins can (1) act as archives for the magmatic, tectonic, and topographic evolution of the arc (Barth et al., 2013; Capaldi et al., 2021; de Silva et al., 2015; Ingersoll, 1979; Wu et al., 2010; Zhu et al., 2023), (2) inform paleogeographic reconstructions and regional drainage patterns between the arc and forearc/retroarc basin (Finzel et al., 2016; Hao et al., 2022; Sharman et al., 2015), and (3) make up for the lack of records in the arc area caused by topographic uplift and denudation, or the destruction of records by younger magmatism and metamorphism (Dobbs et al., 2021; Schwartz et al., 2021; Surpless, 2015). Furthermore, active marginal settings are commonly characterized by narrow shelves that effectively transport sediments to deep‐water forearc basins (Sømme et al., 2009).…”