Conventional and SHRIMP U-Pb Zircon Dating of the Chor Granitoia, Himachal Himalaya

Conventional zircon U-Pb analyses of optically clear multi-grain fractions from the Chor Granitoid sample - CH 1/1:provide a comp1ex pattern with eight points yielding a reference line with an upper intercept age of c. 910 Ma and large scatter. Three zircon fractions from the more deformed sample CH 4/11 of this body define a-discordia line with an imprecise upper and lower intercept ages of 859±¹¹⁹₂₇ Ma and 460±264 Ma respectively. On the other hand, SHRIMP analyses of carefully selected core and rim of CH 1/1 zircon give magmatic rim/grain age of 823± 5 Ma with zircon cores having more than 5% discordant ²⁰⁷Pb/²⁰⁶Pb ages ranging from ∼900 Ma to ∼1560 Ma. The presence of older cores indicate that 0.9 Ga age obtained from conventional TlMS U-Pb technique is probably a mixed age of magmatic and inherited zircons.