Abstract:
The igneous rocks from Mansehra Granitic Complex are studied for their
petrographic and geochemical characteristics. On the basis of outcrop relationships
and petrographic analyses, the rocks are divided into three categories; granites,
doleritic dykes and metamorphosed volcanic rocks (andesite). Mansehra granite has
typical mega-porphyritic texture with both fine grained and foliated varieties. During
petrographic analysis it was observed that essential minerals of granites are quartz,
perthitic and microcline alkali feldspar and plagioclase. It constitute the part of both
phenocrysts and ground mass for other minerals like biotite, muscovite, tourmaline,
quartz, apophyllite, apatite, monazite, andualsite, epidote, zircon, titanite, clay and ore
mineral (s). The doleritic dykes display sub-ophitic to ophitic texture and essentially
comprised of plagioclase and clinopyroxene while the metamorphosed volcanic rocks
have foliated and fine grained texture and comprised of amphibole, quartz and
plagioclase. On the basis of detailed geochemical analysis, the Mansehra granites are
strongly per-aluminous and calc-alkaline. The per-aluminous property confirms its
formation as S-type and collisional granite. These granites are derived from
plagioclase poor and clay rich sedimentary melt. The modal mineralogy of dykes
indicates its alkaline nature. The foliated texture of above mentioned rocks represents
low to medium grade metamorphism in these rocks. The comparison of Mansehra
granites with Utla and Ambela granites indicates it’s more resemblance with Utla
granites rather than Ambela granites. Both these granites share same type of texture,
modal mineralogy, geochemical characteristics and petrogenesis.
