Geometrical and Kinematic Setting of L-tectonites in the Tongbai Orogenic Belt, Central China

English Abstract:

L-tectonites are 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 west-east. The L-tectonites occur in the core of the antiform, in a zone that is ~20-40 km wide and over 100 km long. Lineations in the L-tectonites are subhorizontal, parallel to the hinge of the antiform. Sheath folds are also well developed associated with the L-tectonites, with the hinges parallel to the lineations.

The L-tectonite zone is bounded by two ductile shear zones, on the north and south side, respectively. Well-developed shear sense indicators indicate that the southern and northern shear zones have a dextral and sinistral sense of shear, respectively. The L-tectonite zone is capped by a sub-horizontal shear zone with the hanging wall moving west relative to the footwall. 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 zone. The L-tectonite zone in the core moves east relative to the hanging wall. The development of the tectonites is interpreted to be a result of this special geometry and kinematics. Available geological and geochronological data indicate that this took place in Early Cretaceous. Magmatism in late Cretaceous affected but did not significantly change the overall geometry.