Abstract
Sr, Pb, and REE data from samples from igneous rocks, metasedimentary inclusions, and intruded metasedimentary country rocks of the northeastern portion of the Idaho batholith indicate a significant contribution from a lower crustal source region to the intrusive rocks. Rb-Sr and U-Pb data indicate that the source region was depleted in Rb and U and that it was heterogeneous. Zircons separated from a sample collected from the interior of the batholith were found to have rounded cores and euhedral overgrowths. U-Pb isotopic analysis of these zircons and monazite yields a lower intercept age of 60 Ma and an upper intercept age of ~1710 Ma. This is interpreted to be a mixing line between the crystallization age of the granitic rocks (60 Ma old overgrowths) and the average age of the source (1710 Ma old cores). The zircon cores are most likely inherited from the source region of the granite, and not assimilated from the intruded country rocks.
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