Unicornis bro,

Actually I started this thread to give and get infomation about gemstones in Nepal but now it is getting into hardcore geology. You threw such a question which looks simple at general but if you start to dig more it will appear as the greatest dilemma in himalayan geology. But I don't want people over here to get into this trouble.

So in general words, MT = Mahabharat Thrust and MCT = Main Central Thrust are the large scale discontinuties in the rock that is extended over the himalaya. As all of us know that Indian contient is moving towards the north and Tibet is fixed these discontinuties were developed. It is believed that along these discontinuities rock mass moves and that will release energy created due Indian continental push. Besides MCT, and MT we have other master thrust like MBT (Main Boundary Thrust), MFT (Main Frontal Thrust) and STDS (South Tibetian Detachment System). Among all these thrusts now MFT is considered as most active along which movement of the rock masses is taking place. Unlike, MCT which is distributed along the whole length of Himalaya, MT is only found around the Kathmandu valley and there is great debate among senior Nepalese as well as international geologists whether the MT is part of MCT or separate.

And these thrusts do have implications on our daily life specially while talking about construction work. While constructing roads, bridges, dams or tunnels we try to avoid the area around these thrusts. The rock masses around these thrusts generally have several cracks and discontinuites which make rock mass weaker and our structure will be unstable. But sometimes we can't avoid these thrusts specially while constructing roads and as result we will have landslide on the road during the rainy season. Engineers usually perfom RMR (Rock Mass Rating) of the site to evaluate it for the construction.

This thrusts not only have negative role, some mineralizations may occur along these thrusts and all of our hot water springs are formed due to these thrusts.

Below here is the geological map of Nepal by BN Upreti and others, which shows the location of different thrusts as well as different types of rocks in Nepal

Map: BN Upreti and others