大地构造学_4课件.ppt

Tectonics Chapter 4Metamorphism,deformationandTectonics 1. MetamorphismandTectonics * Inner Zone Outer Zone MTL ISTL Introduction of general geology Ryoke belt: a Cretaceous low-pressure regional metamorphic belt Sanbagawa belt: consists of Oboke (lower) and Besshi (upper) nappe complexes with M-H meta. Chichibu belt: subdivided into the Northern, Middle (Kurosegawa) and Southern sub-belts that consist of low-grade Jurassic accretionary complexes. Shimanto belt: unmeta- or weak metamorphosed late Cretaceous-Miocene accretionary complex. 2. DeformationandTectonics Location of next fig. * * * High T and low P = Buchan type (contact metamorphism); Normal P-T = Barrovian type (regional meta.); High P and low T = Blueschist type (subduction meta.). The blueschist meta. Of 70-85 Ma age is overprinted by the 15-25 Ma Barrovian regional meta. Although the isograds do cut across the nappe boundaries, they share in the two gentle foldings of the tectonic units, suggesting that deformation of the nappes ceased before or during peak metamorphism and that later the nappes and isograds were both gently folded. Pmax is before Tmax. If it is uplifted immediately, it might follow a path of C with the surface exposure of blueschist meta. If the rock is uplifted more slowly, it might follow paths D with blueschist overprinted by Barrovian meta. And E with Barrovian meta.