The three stages according from the oldest to the youngest formation are granite, basalt and lastly andesite formation. This will discuss about the formation, composition, type of intrusion and cooling history of each stages. The granite formation is the oldest stage since granite is formed usually beneath the crust about 1. 5 km up to 50 km depth. Primarily, granite is composed of silicon and alumina about 72. 04% and 14. 42%, respectively. The formation of granite occurs through extreme metasomatism.
Through metasomatism, elements are brought out by fluids like potassium and calcium to convert the metamorphic rock to granite. According to Himanshu K. Sachan (1999), granite in the northern Himalaya starts its cooling history at 705 °C and continued up to 650 °C in the range of 1. 2–2. 8 kbar. The next stage is the basalt formation. Basalt is composed of magnesium oxide, calcium oxide and low amount of silicon, sodium oxide and potassium oxide. The formation of basalt occurs when there is a volcanic eruption either under or above the. Mostly the formation of basalt occurs underneath the sea.
Through the introduction of water the magma hardens to form the basalt. Basalt forms between 50km up to 100 km depth within the mantle and 150 km up to 200 km for some high-alumina basalt. The next stage will be andesite. The youngest of the formation is the perpendicular andesite. After basalt, the most common volcanic rock would be he andesite. The main composition of andesite is silica about 57%. Andesite is formed either by frictional crystallization or magma mixing with felsic rhyolitic. Melting and assimilation of rock fragments by rising magma to the surface form andesite.