Based on a new map of the western end of the Tso Morari Culmination (Ladakh, India), stratigraphy and tectonics of an internal sector of the NW-Himalaya are discussed. This large regional structure, adjacent to the lndus-Yarlung Suture, forms the northern margin of the Indian continent.
Two paleogeographic domains can be distinguished: 1. A "classical" sequence of Cambrian to Paleocene sediments and an Ordovician granite builds up the Tethys Himalaya. The main part of the detritic Cambrian formations has been deposited on a shallow-water platform, very similar to the coeval series of Zanskar, 70 km further SW.
2. The continental rise sediments (Markha Unit) are divided into five formations: amongst them, the 2nd, 4th and 5th have been paleontologically dated as middle Trias, middle Jurassic and uppermost Cretaceous. Isolated fossil occurrences prove marine conditions already at the end of the lower Permian. The lateral evolution within the Triassic formations allows to argue in favour of a preserved paleogeography in the area of the continental shelf break.
During the post-lower Eocene suturation between the Indian and Ladakh-Kohistan blocks, the ductile Langthang Fold Nappe (LFN) has been emplaced in a S to SW direction, in the roof of a pre-Himalayan contact aureole. Km-scale recumbent folds within the LFN hold for the crustal thickening, leading to greenschist-metamorphic conditions. In a structurally low level, close to the root zone, the overturned limb of a large fold of Permian metasediments indicates a maximum translation ( > 10 km): at higher levels, we suggest that the nappe may terminate in a thin-skinned manner, by one of several ramps (with translation values of a few km), cutting through the Jurassic platform limestones in the Zanskar synclinorium.
These tangential tectonics are blocked by a regional-scale, post-metamorphic antiform which refolds both the fold-nappe (LFN) and its basement (Nyimaling Unit). This antiform was overturned to the NE, then detached along the deformed Paleozoic granite, while being backthrusted towards the north and escaping laterally in a corridor along the vertical suture surface. The compressional evolution ends with the formation of a tectonic dome, though the area continues to rise (morphogenetic phase).