ABSTRACT
The Himalaya is the highest and largest mountain belt around the world formed after the collision between the
Indian and Eurasian plates during the Eocene.
The Nidar - Tso Morari area, in NW India, illustrates the transition between the Indian and Eurasian plates
including remnants of the Neotethys oceanic crust preserved as ophiolites in the Indus suture zone. This area is
characterized by the ultra-high pressure (UHP) metamorphic Tso Morari nappe made up of Ordovician granites
intruded in Precambrian to Cambrian sediments (Phe and Karsha Fms) and eclogite boudins. The rocks of the Tso
Morari nappe characterize the leading edge of the northern Indian passive continental margin and are overlaid by
the sediments of the Tetraogal nappe. The Tso Morari nappe records UHP metamorphism dated at ~53 m.y. ago
during the north dipping subduction of the Indian continent beneath the Eurasian plate.
The subduction of the Neotethys oceanic crust started during the Lower Cretaceous in an intra-oceanic setting
involving magmatism in the upper Eurasian plate and generated the rocks of the Nidar Ophiolite. The Nidar
Ophiolite is an almost complete ophiolitic sequence that records at least two magmatic events in a suprasubduction
zone context close to the Eurasian continental margin. The first magmatic phase generated a fore-arc oceanic
crust and the second magmatic phase is characterized by arc-related intrusive complexes and dikes intruded
into the preexisting fore-arc crust. The subduction-related magmatic activity migrated northward to form the
Ladakh Batholith between the Lower Cretaceous and the Middle Eocene. The progressive subduction of the
Neotethys oceanic crust produces an accretionary wedge that records evidence of seamount accretion before the
collision between the Indian and the Eurasian plates. These seamounts are partly preserved in the Drakkarpo
and the Karzok-Ribil nappes. The Drakkarpo nappe is also characterized by the Changlung Mélange formed in
“Piggy Back” basin developed on the accretionary wedge. This basin was fed by the erosion of the wedge and the
southern Eurasian plate. A shelf was present in the northern part of the basin between the Early Ypresian and the
Early Lutetian. It represents the youngest marine occurrence in the Indus suture zone.
Based on field work and samples collected in the Nidar - Tso Morari area, we present new lithostratigraphic,
geochronologic, biostratigraphic structural and geochemical data which allow to constrain: (1) the geology of
the Eastern part of the Tso Morari nappe through a new detailed map; (2) the age of the magmatic records and
the geodynamic context of the formation of the Nidar Ophiolite; (3) the geometry and the composition of the
accretionary wedge (Drakkarpo and the Karzok-Ribil nappes); (4) the age of the last marine occurrence in the
Neotethys Ocean; (5) the global geodynamic significance and the formation of the North Himalayan nappes (The
Tso Morari, Tetraogal and Karzok-Ribil nappes); and (6) the timing of the India-Asia collision.
We propose a kinematic reconstruction of the paleogeography between the Indian and Eurasian plates from
the initiation of the intra-oceanic subduction zone to the nappe exhumation during the collision from Lower
Cretaceous to Upper Eocene. The new data on the geometry of the north Indian margin and the accretionary
wedge, and the structure of the North Himalayan nappe stack could be integrated in exhumation models of the
ultra-high pressure Tso Morari nappe.