Cordilleran Subduction Initiation: Retroarc Timing and Basinal Response in the Inyo Mountains, Eastern California

Abstract

Subduction zones drive plate tectonics on Earth, yet subduction initiation and the related upper plate depositional and structural kinematics remain poorly understood because upper plate records are rare and often strongly overprinted by magmatism and deformation. During the late Paleozoic time, Laurentia’s western margin was truncated by a sinistral strike-slip fault that transformed into a subduction zone. Thick Permian strata in the Inyo Mountains of central-eastern California record this transition. Two basins that were separated by a transpressional antiform contain sedimentary lithofacies that record distinct patterns of shoaling and deepening conditions before and during tectonism associated with subduction initiation. Sandstone petrography and lithofacies analysis show that rocks in a southeastern basin are dominated by carbonate grains derived from adjacent carbonate shelves, whereas sandstones in a northwestern basin are predominantly quartzose with likely derivation from distant ergs or underlying strata. Detrital zircon spectra from all but the youngest strata in both basins are typical of Laurentian continent spectra with prominent peaks that indicate ultimate sources in Appalachia, Grenville, Yavapai/Mazatzal, and the Wyoming or Superior cratons. The first Cordilleran arc-derived detrital zircon grains appear in the uppermost strata of the northwestern basin and record Late Permian (ca. 260 Ma) Cordilleran arc magmatism at this approximate latitude, and a possible source area is suggested by geochemical similarities between these detrital zircons and broadly coeval magmatic zircons in the El Paso Mountains to the southwest. Deformation responsible for basin partitioning is consistent with sinistrally oblique contraction in the earliest Permian time. The data presented from the Inyo Mountains shed more light on the nature of Cordilleran subduction initiation and the upper-crustal response to this transition.

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.…”

Using discordant U-Pb zircon data to re-evaluate the El Paso terrane: Late Paleozoic tectonomagmatic evolution of east-central California (USA) and intense hydrothermal activity in the Jurassic Sierra Nevada arc

“…260 Ma andesites of the Goler Formation that were deposited in proximity to the nascent Sierra-Mojave arc (e.g., metasedimentary rocks of Holland Camp; Martin and Walker, 1995;Carr et al, 1997;Rains et al, 2012;Macdonald, 2016). Inboard of the nascent arc, locally derived carbonate and siliciclastic detritus was deposited in the Darwin and Lone Pine Basins, which developed in response to transpressional tectonics (Stevens et al, 2015;Lodes et al, 2020). Particularly relevant to this tectonic discussion is the regional juxtaposition of lower Paleozoic, relatively deep-water strata of the central and southern El Paso terrane against Neoproterozoic-lower Paleozoic, shallow-water, passive-margin strata, because the deposition of the Devonian and younger rocks in the El Paso terrane may have postdated terrane emplacement (Poole et al, 1992).…”

“…The Lone Pine and Darwin basins formed in response to this thrusting, which we attribute to interplay between the waning sinistral transpressive regime extending from the north and the waxing subduction zone developing to the south. Siliciclastic turbidites of the Lone Pine Formation may have received siliciclastic debris from the adjacent Conglomerate Mesa Uplift, a SW-NE-trending transpressional antiform formed in response to sinistral-oblique convergence (Stevens et al, 2015;Lodes et al, 2020). Southeast of Conglomerate Mesa, the Darwin Basin also received debris from the Bird Spring carbonate shelf located immediately to the east.…”