Granites in Nepal Himalaya

Granites are distributed in three parallel belts in Nepal Himalaya

1.     Paleozoic Granites

·       They are Cambro-Ordovician age.

·       They are found in thrust sheets of Lesser Himalaya, Kathmandu Nappe and Dadeldhura Nappe.

·       The granites are made up of biotite-rich and tourmaline-rich varieties .

·       They are closely associated with the adjacent gneisses, which display a similar mineral composition.

·       Several concordant, tabular granite bodies, up to 200 m thick, are intruded.

·       Some well-known bodies are Palung Granite, Agra Granite, Dadeldhura Granite

 

2.     Higher Himalaya Leucogranites

·       They are of Tertiary age and occur as several plutons, very many dikes, and veins.

·       Early to Middle Miocene Leucogranites

·       These igneous rocks are mainly concentrated towards the top part of the migmatitic gneisses in the Tibetan slab

·       Tourmaline is so frequent in the granite that they are sometimes called the tourmaline granites, where the mineral is generally concentrated in veins and pegmatite margins

·       Owing to intense deformation, the granites are sometimes transformed into augen gneisses. The C/S fabric shows a top-to-north or northeast sense of shear

·       They are found in the Annapurna–Manaslu region, where the floor of these intrusives is generally concordant with the underlying rocks

 

Manaslu Granite is a well known leucogranite body in Annapurna Mansalu region. The Manaslu granite has a less than 100 m wide contact metamorphic aureole in a garnet–staurolite metamorphic assemblage. It records a pressure of about 0.4 GPa and a temperature of 550 ± 40 °C and requires a corresponding emplacement depth of about 9 to 13 km (Guillot et al. 1995). The granite was intruded around 25–18 Ma. Its roof is rather irregular and it intrudes into the Tethys Himalayan sedimentary sequence up to the Cretaceous rocks.

 

3.     North Himalayan Granites

·       North Himalayan Granites intruded in Tethys Himalya similar to Higher Himalaya Leucogranites.

·       Their composition is similar to those of the HH Leucogranites (differ from HH Leucogranites in emplacement style, younger age and higher melting temperature >750 C)

·       These plutons are located about 60 km south of and parallel to the Indus–Tsangpo suture zone.

·       There are about 20 domes, and the two well-known bodies are the Mugu and Mustang granites,

·       Most of them were intruded after the emplacement of the Higher Himalayan leucogranites and they range in age from approximately 20–10 Ma