Orogen-scale L tectonite domain in the Tongbai orogenic belt, central China: Geological setting and origin

L tectonite is well developed and widely distributed in the Tongbai orogenic belt in central China. The orogenic belt as a whole has an antiformal geometry and the hinge of the antiform is subhorizontal and trends NW-SE. The L tectonite occurs in the core of the antiform, in a zone that is 10-30 km wide and over 100 km long. Lineations in the L tectonite are sub-horizontal, parallel to the hinge of the antiform. Sheath folds are also well developed associated with the L tectonite, with the hinges parallel to the lineations. Migmatite occurs in the core and structurally below the L tectonite and has a gradational relationship with the L tectonite. The domain of L tectonite is bounded by three ductile shear zones, on the north, at the top and on the south, respectively. Well-developed shear sense indicators indicate that the southern, the overlying and the northern shear zones have a dextral, top-to-NW and sinistral sense of shear, respectively. These geometrical and kinematic data indicate that the three shear zones are likely part of a single shear zone that wraps around the L-tectonite domain. The L-tectonite zone in the core moves southeast relative to the hanging wall. The development of the tectonite is interpreted to be a result of this special geometry and kinematics and reflects a post-collisional orogen-parallel extension synchronous with migmatization and the continuing convergence between the Yangtze Block and the North China Block in the Early Cretaceous.