Evidence for Whole Mantle Convection Driving Cordilleran Tectonics

Abstract

Deducing mechanisms for advance and retreat of magmatic arcs is fundamental to understanding accretionary tectonics and the evolution of continents. However, first‐order explanations of large spatial and long temporal changes in magmatic arcs remain elusive. We present isotopic evidence that Cordilleran magmatic arc systems were controlled by spherical harmonic degree‐2 mantle convection and characterized by two antipodal upwellings bisected by a meridional downwelling. Once established, the meridional “subduction girdle” drives hemispheric slab rollback and remains the locus of Cordilleran oceanic arcs. Continual westward migration of the North and South American continents led to arc advancement and consumption of back‐arc basins, culminating in arc‐continent collisions and reversals of subduction polarity. Continental arcs initiated diachronously as North and South America arrived at the subduction girdle and oceanic arcs were accreted. Systematic patterns in radiogenic isotopes along the Cordilleran system support that slab dynamics are controlled, to first order, by long‐wavelength mantle convection.

Ice, Fire, or Fizzle: The Climate Footprint of Earth's Supercontinental Cycles

“…Depending on the magnitude of lateral mantle temperature variations acquired during supercontinent assembly, supercontinental breakup can involve spreading continental fragments that overrun adjacent subduction zones and drive them into compressional continental arc modes (Lee et al, ; Spencer et al, ) (Figure ). In addition to their sliding down dynamic topographic gradients, the viscous coupling of continental fragments to warm mantle material spreading into mid‐ocean ridges causes them to be drawn toward adjacent subduction zones to drive accretion.…”

“…Finally, we assume that the total lengths of active volcanic arcs remain unchanged. Rigorous observational constraints on changes in arc and/or mid‐ocean ridge lengths during Rodinia and Pangea supercontinental cycles are challenging, although recent reconstructions from varied geological data and plate kinematic models suggest increases in the total length of rifts at the times of Rodinia and Pangea assembly (Merdith et al, ) and increases on the length of continental arc at the start of the breakup of Pangea relative to present day (e.g., Lee et al, ; Müller et al, ; Spencer et al, ).…”

“…The formations of all three supercontinents reduced the global chemical weathering sink for atmospheric by concentrating the majority of topography production and erosion within the very dry interiors of these landmasses, at large distances from moisture sources (Cox et al, ; Donnadieu et al, ; Fiorella & Poulsen, ; Goddéris et al, ; Otto‐Bliesner, ; Veevers & Powell, ). During the breakups of Pangea and Rodinia, plate reconstructions and geological data suggest that disaggregating supercontinental fragments overran neighboring island arcs forming an initial perimeter (Lee et al, ; Macdonald et al, ; Merdith et al, ; Spencer et al, ). A resulting relatively rapid tectonic transition into continental arc modes is also correlated with large increases in mid‐ocean ridge and arc magmatism (Brandl et al, ; Kelemen & Holbrook, ; Van Avendonk et al, ) and continental arc magmatism (Lee et al, ; McKenzie et al, ) and also marked by extensive orogenesis and chemical weathering occurring close to oceans (e.g., Donnadieu et al, ; Goddéris et al, ; Hartmann et al, ).…”

Detrital zircon geochronology and Hf isotope geochemistry of Mesozoic sedimentary basins in south-central Alaska: Insights into regional sediment transport, basin development, and tectonics along the NW Cordilleran margin

“…The most accepted interpretation for the last several decades is that this convergent margin was the product of eastward-dipping subduction (northward-dipping from the perspective of Alaska) outboard of the Wrangellia composite terrane (McClelland et al, 1992;Plafker and Berg, 1994;Kalbas et al, 2007;Gehrels et al, 2009;Hampton et al, 2010;Pavlis et al, 2019). A new intriguing model based on seismic anomalies in the deep mantle has postulated that the margin formed due to westward-dipping subduction along the inboard margin of the Wrangellia composite terrane (Sigloch andMihalynuk, 2013, 2017;Spencer et al, 2019). Our new detrital zircon data sets from the Nutzotin and Wrangell Mountains basins, in conjunction with the regional framework from previously published detrital zircon data sets, indicate a strong provenance and temporal link between all major Mesozoic tectonic elements of the southern Alaska convergent margin.…”

Yanshanian Orogeny During North China's Drifting Away From the Trench: Implications of Numerical Models

“…Contrasts between tectonics across the Pacific Ocean since the Cretaceous support this correlation (Yang et al, 2019). South and North America moved trench‐ward rapidly after the Atlantic Ocean opening, and these continents transited from the extension‐dominated to compression‐dominated tectonics accordingly during the middle Cretaceous (Ramos, 2010; Spencer et al, 2019). On the other hand, the trench‐ward motion of Asia is limited, and East Asian tectonics since the Early Cretaceous is dominated by an extension (Yang et al, 2019).…”