Complete deformation history of the transition zone between oblique and orthogonal collision belts of the SE Tibetan Plateau: Crustal shortening and rotation caused by the indentation of India into Eurasia

Abstract

The successive indentation of India into Eurasia generated the orthogonal collisional E–W Himalaya–Tibet and the oblique collisional N–S SE Tibetan Plateau along the frontal and eastern edges of the indenter, respectively. An understanding of the complete crustal deformation history of both regions is needed to reconstruct the processes involved in this indentation. Geological mapping and structural analysis of the transitional zone between these collisional belts reveal two stages of structures with different geometries. The earlier of these stages involves structures with an unusual structural association consisting of en échelon aligned overturned dome-and-thrust pairs within a background of open folding, most likely representing the early development of a fold-and-thrust system. The later structures consist of an association of N–S-trending thrust-and-tear-faults and open folds. Combining stratigraphic data from this region with the results of previous research indicates that the earlier structures formed at 60−48 Ma, whereas the later structures formed between the early Miocene and ca. 5 Ma. This information combined with geological and paleomagnetic data for the region allows reconstruction of the complete crustal deformation history of the oblique collisional belt, which consists of early and late stages of crustal shortening separated by a middle stage involving the ∼80° clockwise rotation of the crust. The spatiotemporally variable crustal deformation of the oblique collision belt combined with the long-lived N–S crustal shortening of the orthogonal belt outline a consistent tectonic scenario within a single geodynamic system that enables the reconstruction of the indentation of India into Eurasia.