Olivine- and pyroxene-bearing Fe-enriched dioritic rocks in the 1434 Ma Laramie anorthosite complex are interpreted to represent variably fractionated and contaminated magmas residual after the crystallization of anorthosite. Geochemical characteristics of this suite include the following: high contents of TiO₂, , and P₂O₅; high incompatible trace element contents; rare earth element patterns with a large range of Eu anomalies; and isotopic compositions that reflect the geographic location of individual samples, with I_Sr increasing and ∈_Nd decreasing from south to north. After extraction from anorthosite, fractionation of ferrodioritic residual magmas resulted in secondary residual monzodioritic melts and complementary oxide-rich ferrodiorite cumulates. Geographic trends in isotopic composition reflect an increasing Archean crustal component from south to north. Dioritic dikes and cumulates with isotopic compositions similar to associated anorthosites were derived locally. Large isotopic discrepancies between some diorites and their hosting anorthosites reflect preferential contamination of residual magma during ascent and emplacement of mantle-derived plagioclase-rich diapirs, followed by subsequent extraction and isolation of Fe-enriched interstitial melt. Strong isotopic contrasts between anorthosite and associated Fe-enriched rocks in anorthosite complexes do not preclude a direct relationship between them and reflect the diversity and complexity of processes during their petrogenesis.

Zirconium and Hf are nearly identical geochemically, and therefore most of the crust maintains near-chondritic Zr/Hf ratios of ∼35–40. By contrast, many high-silica rhyolites and granites have anomalously low Zr/Hf (15–30). As zircon is the primary reservoir for both Zr and Hf and preferentially incorporates Zr, crystallization of zircon controls Zr/Hf, imprinting low Zr/Hf on coexisting melt. Thus, low Zr/Hf is a unique fingerprint of effective magmatic fractionation in the crust. Age and compositional zonation in zircons themselves provide a record of the thermal and compositional histories of magmatic systems. High Hf (low Zr/Hf) in zircon zones demonstrates growth from fractionated melt, and Ti provides an estimate of temperature of crystallization (T_TiZ) (Watson and Harrison, 2005). Whole-rock Zr/Hf and zircon zonation in the Spirit Mountain batholith, Nevada, document repeated fractionation and thermal fluctuations. Ratios of Zr/Hf are ∼307–40 for cumulates and 18–30 for high-SiO₂ granites. In zircons, Hf (and U) are inversely correlated with Ti, and concentrations indicate large fluctuations in melt composition and T_TiZ (>100°C) for individual zircons. Such variations are consistent with field relations and ion-probe zircon geochronology that indicate a >1 million year history of repeated replenishment, fractionation, and extraction of melt from crystal mush to form the low Zr/Hf high-SiO₂ zone.