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The North American Cordilleran Orogen is the result of a two-stage process: (a) Triassic-Jurassic accretion within Panthalassa forming SAYBIA, a composite ribbon continent, and (b) Late Cretaceous collision of SAYBIA with North America. This model requires that a large portion of the continental foreland of the orogen is exotic. The exotic continental component of SAYBIA, Cassiar Platform, is distinguished from the autochthon on the basis of its (a) Triassic Eurasian fauna; (b) involvement in a major Late Triassic-Early Jurassic orogenic event; and (c) young, in part Grenvillian basement and mantle. A mid-Cretaceous magmatic arc records west-dipping subduction beneath the east-margin of SAYBIA. The related accretionary prism consists of imbricated shale, chert, and deep-water limestones (the Medial Basin) and overlies an isotopically juvenile mantle domain. Carbonatite complexes delineate the cryptic suture separating SAYBIA and the autochthon. Paleomagnetic and paleobotanical data place SAYBIA 2000 km to the south relative to the autochthon at 80 Ma. Late Cretaceous thrust belt development records transpression between the north-moving ribbon continent and the autochthon. Pinning against the Okhotsk-Chukotka arc in Siberia buckled SAYBIA, giving rise to the Alaskan promontory.

The central Jiangnan Orogen, genetically formed by the Proterozoic Yangtze‐Cathaysia collision, presents as a composite structural feature in the Phanerozoic with multiple ductile and brittle fabrics whose geometries, kinematics, and ages are crucial to decipher the tectonic evolution of south China. New structural observations coupled with thermochronological and geochronological studies of these fabrics document four main stages of deformation. The earliest stage in early Paleozoic time (460–420 Ma) corresponds to combined E‐trending dextral and northwest directed thrust shearing that was variably partitioned in anastomosing high‐strain zones under greenschist‐facies conditions (~400–500°C), related to the continued Yangtze‐Cathaysia convergence externally driven by the suturing of south China with Australia. This event was heterogeneously overprinted by the second stage characterized by ~E‐oriented folding in middle Triassic time, geodynamically resulting from the continental collision of south China with Indochina and North China. The third stage was locally developed by northwest and southeast vergent thrusts that truncated ~E‐oriented folds in the Late Jurassic, due to northwestward subduction of the Paleo‐Pacific plate. The latest stage involved normal faulting and tectonic unroofing in Cretaceous time, which resulted in basin opening and reset footwall 40Ar/39Ar ages in proximity to the Hengshan detachment fault, associated with roll‐back of the subducting Paleo‐Pacific plate.

[1] U-Pb (zircon) crystallization ages of 52 late-Variscan granitoid intrusions from NW Iberia (19 from new data, 33 from previous studies) constrain the lithospheric evolution of this realm of the Variscan belt of Western Europe and allow assessment of the relationship between oroclinal development and magmatism in late-Carboniferous-early Permian times. The U-Pb ages, in conjunction with a range of geological observations, are consistent with the following sequence of events: (i) oroclinal bending starts at 310-305 Ma producing lithospheric thinning and asthenospheric upwelling in the outer arc of the orocline accompanied by production of mantle and lower crustal melts; (ii) between 305 and 300 Ma, melting continues under the outer arc of the orocline (Central Iberian Zone of the Iberian Variscan belt) and mid-crustal melting is initiated. Coevally, the lithospheric root beneath the inner arc of the orocline thickened due to progressive arc closure; (iii) between 300 and 292 Ma, foundering of the lithospheric root followed by melting in the lithospheric mantle and the lower crust beneath the inner arc due to upwelling of asthenospheric mantle; (iv) cooling of the lithosphere between 292 and 286 Ma resulting in a drastic attenuation of lower crustal high-temperature melting. By 285 Ma, the thermal engine generated by orocline-driven lithospheric thinning/ delamination had cooled down beyond its capability to produce significant amounts of mantle or crustal melts. The model proposed explains the genesis of voluminous amounts of granitoid magmas in post-orogenic conditions and suggests that oroclines and similar post-orogenic granitoids, common constituents of numerous orogenic belts, may be similarly related elsewhere.Citation:

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