The Paleocene Kodiak batholith, part of the Sanak–Baranof belt of Tertiary near-trench intrusive rocks, forms an elongate body (~ 150 km long) that transects Kodiak Island from SW to NE. The batholith consists of three zones (Southern, Central, and Northern) of kyanite-, muscovite-, and garnet-bearing biotite tonalite and granodiorite and less abundant granite that intruded an accretionary prism (Kodiak Formation, and Ghost Rocks Formation). Small and likely coeval bodies (Northern, Western, and Eastern satellite groups) of quartz gabbro, diorite, tonalite, granodiorite, and leucogranite flank the batholith. The batholith is calc-alkalic, has an aluminum saturation index of > 1.1, FeO_t/(FeO_t + MgO) ~ 0.65 (at SiO₂ = 65 wt.%), and increases in SiO₂ (~ 61 wt.%–73 wt.%) and decreases in TiO₂ (~ 0.9 wt.%–0.3 wt.%) from SW to NE. As a group, the granitic rocks have light REE-enriched chondrite-normalized patterns with small or no negative Eu anomalies, primitive mantle-normalized negative anomalies for Nb and Ti, and positive anomalies for Pb. Small to large negative anomalies for Th are also distinctive. The quartz gabbros and diorites are generally characterized by generally flat to light REE chondrite-normalized patterns (no Eu anomalies), and mantle-normalized negative anomalies for Nb, Ti, and P. Pb isotopic compositions (²⁰⁶Pb/²⁰⁴Pb = 18.850–18.960; ²⁰⁷Pb/²⁰⁴Pb = 15.575–15.694; ²⁰⁸Pb/²⁰⁴Pb = 38.350–39.039) are intermediate between depleted mantle and average continental crust. The Southern zone and a portion of the Central zone are characterized by negative ε_Nd values of − 3.7 to − 0.3 and T_DM ages ranging from ~ 838 Ma to 1011 Ma. Other granitic rocks from the Central and Northern zones have higher ε_Nd values of − 0.4 to + 4.7 and younger T_DM ages of ~ 450 to 797 Ma. Granitic and mafic plutons from the Eastern satellites show a wide range of ε_Ndvalues of − 2.7 to + 6.4, and T_DM ages from 204 Ma to 2124 Ma. ⁸⁷Sr/⁸⁶Sr values of the Southern and Central zones overlap and tend to be slightly more radiogenic (⁸⁷Sr/⁸⁶Sr > 0.70426) than the Northern zone (⁸⁷Sr/⁸⁶Sr < 0.70472). ²⁰⁶Pb/²⁰⁴Pb values increase slightly from the Southern and Central zones toward the Northern zone. There is no clear correlation of the major or trace elements with ε_Nd, Pb or Sr isotopic values. Kodiak Formation and the Ghost Rocks Formation overlap the isotopic compositions (e.g., ²⁰⁶Pb/²⁰⁴Pb = 18.978 to 19.165, ⁸⁷Sr/⁸⁶Sr of 0.705715 to 0.707118, and ε_Nd of − 6.7 to − 1.5 at 59 Ma) and T_DM values (959 to 1489 Ma) of the batholith. Production of large volumes of granitic rocks in the Sanak–Baranof belt, and particularly on Kodiak Island, reflects a sequence of processes that includes underplating of mantle-derived mafic (possibly from the mantle wedge) and intermediate rocks under the accretionary flysch, interlayering of mantle-derived and flyschoid rocks, and partial melting of the mixed lithologic assemblages. Limited degrees of fractional crystallization or assimilation and fractional crystallization influenced compositions of the granitic rocks. The contribution of mantle-derived rocks that resided in the accretionary prism for only a short period of time prior to partial melting likely exceeds 40% (up to 80%). The balance (60 to 20%) is from a recently recycled crustal component represented by the Kodiak Formation. This type of progressive intracrustal melting from mixed sources controlled the geochemical character of the batholith and is most consistent with the hypothesis that the granitic rocks are associated with a slab-window produced by collision of a spreading oceanic center and a subduction zone and migration beneath the accretionary prism.