East Asian orogenic collapse caused by oblique subduction and reduced boundary force

<p>East Asia experienced compressional deformation in the early Mesozoic, across the South China Block, North China Craton (NCC) and the part of the Central Asian Orogenic Belt to the north of the NCC. Deformation and magmatism resulted from Triassic collisions that accreted the continental blocks, and also Izanagi (Paleo-Pacific) Plate subduction from the east. We suggest that there was a single East Asian orogenic plateau by the Middle Jurassic, from NE Russia to SW China, with a length of ~4000 km. The causes and timings of the destruction of this plateau are unclear, especially loss of the lower lithosphere of the NCC. Here, we synthesize evidence for late Mesozoic and early Cenozoic crustal thinning via extension and denudation, to quantify the previous crustal thickness. We find that there was a ~50 km thick crust by the Middle Jurassic across much of the area between NE Asia and SW China, which has since undergone ~30% thinning. A force balance indicates that the buoyancy force produced by the gravitational potential energy of this thick crust drove extension from the latest Jurassic - Early Cretaceous (~145 Ma), when a rapid switch from orthogonal to oblique subduction at the Asia-Izanagi plate margin reduced the compressive boundary force by ~30%. Mantle lithosphere thinning of the NCC exceeds crustal thinning by a factor of ~2; extensional collapse cannot be the only cause of cratonic destruction, but played a major role, and potentially triggered mantle instability. Early Cretaceous extension was accompanied by a flare-up in volcanism along East Asia, which we speculate contributed to the Cretaceous hothouse climate.</p>

Architectural and Tectonic Control on the Segmentation of the Central American Volcanic Arc

Central America has a rich mix of conditions that allow comparisons of different natural experiments in the generation of arc magmas within the relatively short length of the margin. The shape of the volcanic front and this margin's architecture derive from the assemblage of exotic continental and oceanic crustal slivers, and later modification by volcanism and tectonic activity. Active tectonics of the Cocos-Caribbean plate boundary are strongly influenced by oblique subduction, resulting in a narrow volcanic front segmented by right steps occurring at ∼150-km intervals. The largest volcanic centers are located where depths to the slab are ∼90–110 km. Volcanoes that develop above deeper sections of the subducting slab are less voluminous and better record source geochemical heterogeneity. Extreme variations in isotopic and trace element ratios are derived from different components of the subducted oceanic lithosphere. However, the extent that volcanoes sample these signatures is also influenced by lithospheric structures that control the arc segmentation. ▪ The architecture of Central America derives from the assemblage of exotic continental and oceanic crustal slivers modified by arc magmatism and tectonic processes. ▪ Active tectonics in Central America are controlled by oblique subduction. ▪ The lithospheric architecture and tectonics define the segmentation of the volcanic front, and thus the depth to the slab below a volcanic center. ▪ The composition of the subducted material is the main control of the along arc geochemical variations observed in Central American volcanoes. ▪ Geochemical heterogeneity in each segment is highlighted by extreme compositions representing the smaller centers with variations up to 65% of the total observed range. Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 49 is May 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.