Discussion on Mesozoic extensional structures of the Fangshan tectonic dome and their subsequent reworking during collisional accretion of the North China Block Journal , Vol. 163 , 2006, 127–142

Abstract

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 …