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The Mesozoic and Cenozoic deformations of the North Qiangtang terrane reflect a portion of the collisional tectonics of the Tethys Ocean, involving Late Triassic, Early Cretaceous and Cenozoic intraplate structures of shallow to superficial tectonic levels. The structural mapping of the Permian–Triassic structural layer indicates that the Mesozoic structural style is dominated by Early Cretaceous horizontal contractional deformations characterized by NW–SE-trending thrust faults and flexural-slip folds. These folds and thrusts were superimposed on Late Triassic buckle folds. Structural analysis of deformations of the Neogene and Quaternary sedimentary layers indicates that there was an obvious transition in the Cenozoic tectonic evolution of the North Qiangtang terrane, which can be divided into two deformation stages. In episode I (50–40 to 18 Ma), the crust experienced large-scale north–south horizontal shortening and vertical thickening shown by buckle folds and thrust faults. In episode II (18 Ma–present day), east–west passive extension formed conjugate strike-slip fault systems and pull-apart basins. During episode II, the Qiangtang basin was extruded eastwards, and a number of superficial north–south-trending buckle folds were formed. Supplementary material: Supplementary material is available at http://www.geolsoc.org.uk/SUP18787.

Yu Wang writes: On the basis of descriptions of the stratigraphic sequences and structural features in the field, and interpretations of published data, Yan et al . (2006 a ) reach the surprising conclusion that early Mesozoic (early–middle Triassic) ESE-oriented extension resulted in formation of the Fangshan metamorphic core complex. If correct, the authors have made an important contribution to understanding of the tectonic evolution of North China. However, the way in which they cite previously published work to support their model, and discrepancies between their findings in the field and those of other workers raise a number of problems that will be discussed below. ### Citing of published work. Yan et al . (2006 a ) cited many references (e.g. Lei et al . 1994; Niu et al . 1994; Yu & Zhang 1996; Chen 1999; Fu 1999; Meng et al . 2003) in support of their conclusions about early Triassic extension and formation of metamorphic core complexes, as well as Late Cretaceous normal faulting. In many cases, however, the cited references do not lend support to their interpretations. For example, the Du Shan granite and surrounding Archaean and Proterozoic metamorphic rocks (Yu & Zhang 1996) contain no evidence for extension or development of metamorphic core complex features, but instead record NE-trending, strike-slip ductile shearing, not top-to-the-SE extension. The Malanyu dome is an old metamorphic sequence (Chen 1999), and no one has previously interpreted it as an extensional dome associated with SE-directed extensional shear. Zhang et al . (1991) did not examine any aspect of the geology in the area of the so-called Yuerya metamorphic core complex. Furthermore, no dome has been identified here by any previous geologists; instead, it is a c . 175–174 Ma (U–Pb sensitive high-resolution ion microprobe ages, Luo et al . 2001) granitic sheet-like …

The Fangshan area, SW of Beijing, lies at the junction of the NNE-trending Taihang mountain range and the southeastern portion of the Yanshan intraplate orogenic belt and has undergone at least five stages of deformation. Mid- to late Triassic extensional deformation (D 1 ) is represented by the formation of the Fangshan tectonic dome during SE-directed extensional tectonics. This deformation was later modified by NNW-directed thrusting in the late Triassic (D 2 ) and WNW-directed thrusting in the late Jurassic (D 3 ). These D 1 –D 3 structures were deformed by the arcuate Beiling syncline (D 4 ), which formed during the intrusion of the 133–128 Ma Fangshan pluton. D 5 deformation is represented by Cretaceous to Quaternary NNE-striking high-angle normal faults. The ages of these events demonstrate that the principal ENE-trending tectonic framework of the Yanshan intraplate orogenic belt was established mainly in the mid- to late Triassic (the Indosinian event). The Jurassic to Cretaceous Yanshanian deformation with thick-skinned thrusting was associated with intrusion of numerous plutons, and strongly modified the older structures. The tectonic evolution of the Fangshan tectonic dome was linked genetically with the collision of the North China Block and the Siberian Craton, and the later collision of the North and South China blocks.