New in situ U-Pb zircon geochronology delineates a series of rock suites with distinct ages and compositions making up the Idaho batholith. The early metaluminous suite (98 to 87 Ma) and border zone suite (~90 Ma) are volumetrically minor in their present exposure but compositionally diverse and form the eastern and western margins of much of the batholith. The Atlanta peraluminous suite (83 to 67 Ma) represents the largest single component of the batholith and is compositionally homogeneous. The late metaluminous suite (~70 Ma) is geographically restricted but compositionally diverse. The Bitterroot peraluminous suite (66 to 54 Ma) is quite similar to the Atlanta peraluminous suite in terms of lithology but is smaller and temporally distinct. All of these units are cut by plutons of the Challis intrusive province (51 to 43), which show a great diversity of compositions. New Sr, Nd, Pb, and Hf (whole-rock and zircon) isotopic data suggest an increase and then decrease in crustal melting with time. The early metaluminous and border zone suite are hybrids of mantle-derived arc basalts and supracrustal rocks. Crustal thickening led to a shift to almost pure crustal melting, leading to the formation of the Atlanta peraluminous suite from Neoproterozoic and Archean components. Limited sampling of the late metaluminous suite makes its origin enigmatic. The Bitterroot peraluminous suite, although lithologically similar to the Atlanta peraluminous suite, is isotopically distinct and the result of melting of Paleoproterozoic basement and assimilation of small amounts of Mesoproterozoic sediments. The Challis intrusions formed after a switch to extensional tectonics, allowing mantle melts to enter and interact with the crust, leading to a wide range of magmatic products. The ages of inherited zircon components are fundamentally different between the southern Atlanta lobe and northern Bitterroot lobe of the batholith. The Atlanta lobe is dominated by two sharp age peaks at ~670 and 2.55 Ga, which are consistent with known local metaigneous sources, whereas the Bitterroot lobe shows a continuum of the ages, ranging from ~1.4 to 1.9 Ga and remarkably similar to the detrital zircon spectrum of large portions of the Belt Supergroup
