Abstract
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.
Highlights
Sedimentary records of subduction initiation are generally poorly preserved because of erosion, deformation, and overprinting by later magmatism, but preserved records can provide valuable insight into the timing and mechanisms of the transition from a previous tectonic regime to subduction [1,2,3,4]
Arc magmatism was previously thought to have begun in the early Triassic time at ca. 250 Ma, due to exposure of arc plutons of that age in eastern California [7,8,9], and at ca. 255 Ma Sm/Nd age from the Kings Kaweah ophiolite that is interpreted to represent metamorphism along the subduction interface during early subduction [6]
The Inyo Mountains in eastern California are a rare location in which Permian strata contain detrital zircon that crystallized in the early Cordilleran arc ([14]; Figure 1)
Summary
Sedimentary records of subduction initiation are generally poorly preserved because of erosion, deformation, and overprinting by later magmatism, but preserved records can provide valuable insight into the timing and mechanisms of the transition from a previous tectonic regime to subduction [1,2,3,4]. The western margin of Laurentia transitioned from a transform to a convergent boundary with an offshore subduction zone in the early Permian time (e.g., [5, 6]; Figure 1). 250 Ma, due to exposure of arc plutons of that age in eastern California [7,8,9], and at ca. More recent ages from plutons in Sonora, Mexico, and the El Paso terrane in southeastern California record local earliest arc magmatism at ca. The Inyo Mountains in eastern California are a rare location in which Permian strata contain detrital zircon that crystallized in the early Cordilleran arc ([14]; Figure 1).
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