A growing body of evidence indicates that Middle Jurassic to Early Cretaceous plutons recorded changing sources during tectonic evolution of the Klamath Mountain province. The data set now includes U-Pb zircon ages and zircon trace element compositions determined by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Thirteen rock samples were dated, and these data refine thermal ionization mass spectrometry (TIMS) data where inheritance was problematic, or provide new U-Pb ages. Individual plutonic suites, previously defined on the basis of crystallization age, isotope and elemental compositions, and petrogenetic style, show characteristic inherited zircon age ranges and zircon trace element patterns. Moreover, ages of inherited zircons in these suites are distinct and, in at least three suites, indicate the presence of cryptic (unexposed) source rocks. The zircon data complement oxygen, Nd, and Sr isotope whole-rock data that, when taken together, suggest a number of major changes in the crustal column with time. Middle Jurassic magmatism began with the oceanic(?) arc-related western Hayfork terrane comprising volcanic, volcaniclastic, and plutonic components. After regional thrusting on the ca. 170-Ma Wilson Point thrust, the Ironside Mountain batholith and Wooley Creek suite of plutons were emplaced. The former shows little evidence of interaction with the crust, but the latter contains Middle Jurassic inheritance and Sr, Nd, and oxygen isotope signatures suggestive of interaction with metasedimentary crustal rocks. Following Nevadan thrusting (ca. 153–150 Ma), emplacement of western Klamath suite plutons in the western Klamath Mountains province involved significant assimilation of Galice Formation metasedimentary rocks. This activity was followed by emplacement of tonalite-trondhjemite-granodiorite (ttg) plutons in the eastern Klamath Mountains province, which were derived by partial melting of metabasic rocks. Their zircon trace element signatures indicate diverse magma histories and, at least locally, multiple magma sources. Inherited zircons in ttg plutons suggest late Middle Jurassic to Late Jurassic sources, younger than the Josephine ophiolite. The youngest magmatism in the Klamath Mountains province consists of broadly granodioritic plutons, which, on the basis of limited data, show variable petrogenesis and zircon inheritance. At least one of these plutons (136-Ma Yellow Butte pluton) contains a ca. 150-Ma inheritance that indicates the presence of Late Jurassic crustal rocks beneath the eastern Klamath terrane.

A distinctive set of andesitic dikes crops out in the Klamath Mountains province south of ∼41°15′. These dikes are characterized by phenocrysts of Al-rich amphibole, Ca-rich almandine-pyrope garnet, plagioclase, and, commonly, quartz, set in a fine-grained groundmass of plagioclase, quartz, alkali feldspar, and amphibole. Conspicuous microphenocryst/accessory phases are allanite/epidote, zircon, and apatite. A variety of thermobarometric methods plus comparison with published experimental data indicates the phenocryst assemblage was stable at pressure >7 kb and at temperatures between 850 °C and the solidus. The best estimate of pressure of phenocryst equilibration is 8–9 kb and ∼800 °C, which corresponds to depths of 25–30 km. Emplacement pressure was probably 3–4 kb, and the lack of low-pressure equilibration features suggests that the dike magmas rose and cooled quickly. Rare earth element (REE) patterns for zircon are distinct from regional zircon compositions (samples in Klamath River sand) but are consistent with crystallization in equilibrium with garnet. Moreover, the zircons have strongly depleted light REE patterns, which is consistent with co-precipitation of allanite/epidote. A U-Pb (zircon) age of 160.5 ± 1.9 Ma was determined for one of the dike samples. This age is coeval with emplacement of the voluminous Wooley Creek plutonic suite in the central and northern parts of the province (north of latitude 41°15′). It is not clear why sparse dikes with high-pressure assemblages crop out in the southern Klamath Mountains province and voluminous coeval plutons are present in the central and northern parts. This distribution may reflect distinct tectonic regimes in the north (extension) versus the south (contraction), differences in melt productivity, or differences in the composition of deep crustal rocks.

Ore element ratios in intrusion-related mineralisation are in part a function of the relative oxidation state and degree of fractionation of the associated granite suite. A continuum from Cu–Au through W to Mo dominated mineralisation related to progressively more fractionated, oxidised I-type magmas can be traced within single suites and supersuites. Such systematic relationships provide strong evidence for the magmatic source of ore elements in granite-related mineral deposits and for the production of the observed ore element ratios dominantly through magmatic processes. The distribution of mineralised intrusive suites can be used to define a series of igneous metallogenic provinces in eastern Australia. In general, there is a correlated evolution in the observed metallogeny (as modelled based on the compatibility of ore elements during fractionation) with increasing degree of chemical evolution of the associated magmatic suite. This is from Cu–Au associated with chemically relatively unevolved magmas, through to Sn and Mo-rich mineralisation associated with highly evolved magmas that had undergone fractional crystallisation. Provinces recognised in that way do not necessarily correlate with the tectonostratigraphic boundaries defined by the near-surface geology, indicating that the areal distribution of some granite source regions in the deep crust is unrelated to upper crustal geology.

Most zoned plutons described in the geological literature have mafic rims and felsic cores and are referred to as “normally zoned”, whereas relatively few “reversely zoned” intrusions (felsic rims and mafic cores) have been described. That unusual zonation pattern has been variously attributed to in situ processes or to the reordering of an underlying, vertically stratified, magma chamber either by intrusion through an orifice or by emplacement of composite diapirs. The Turtle Pluton is an early Cretaceous, reversely zoned, intrusion that is divided into four facies: a Rim Sequence that is graditionally zoned from bt + ilm + musc monzogranite to hb + bt + mt + sph granodiorite; a Core Facies of more homogeneous hb + bt + mt + sph granodiorite to quartz monzodiorite; between these two facies, a structural discontinuity termed the Schlieren Zone; and an Eastern Facies of monzogranite to granodiorite. Field relationships, distribution of strain, and geochemical and isotopic studies (including a range of initial 87 Sr/ 86 Sr from 0.7085–0.7065) suggest that the reverse zonation of the Turtle Pluton is the result of sequential emplacement of two diapirs each derived from the same underlying, vertically stratified, magma chamber, and that the Rim Sequence zonation is chiefly the result of mixing of intermediate and felsic magmas from distinct sources accompanied by minor fractional crystallisation.