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The mid-Miocene Aztec Wash pluton is divisible into a relatively homogeneous portion entirely comprising granites (the G zone, or GZ), and an extremely heterogeneous zone (HZ) that includes the products of the mingling, mixing and fractional crystallisation of mafic and felsic magmas. Though far less variable than the HZ, the GZ nonetheless records a dynamic history characterised by cyclic deposition of the solidifying products of the felsic portion of a recharging, open-system magma chamber. Tilting has exposed a 5-km section through the GZ and adjacent portions of the HZ. A porphyry is interpreted as a remnant of a chilled roof zone that marks the first stage of felsic GZ intrusion. Subsequent recharging by felsic and mafic magma, reflected by repeated cycles of crystal accumulation and melt segregation in the GZ and emplacement of mafic flows in the HZ, rejuvenated and maintained the chamber. Kilometre-scale lobes of mafic HZ material were deposited as prograding tongues into the GZ during periods of increased mafic input. Thus, they are lateral equivalents of the cumulate GZ granites with which they interfinger. Conglomerate-like units comprising rounded, matrix-supported intermediate clasts in cumulate granite are located immediately above the lobes. These 'conglomerates' appear to represent debris flows shed from sloping upper surfaces of the lobes. Thus, the GZ can be viewed as comprising distal facies, remote from the site of mafic recharging in the HZ, and the HZ as comprising proximal facies.Elemental chemistry suggests that the GZ cumulate granites represent a second-stage accumulation from an already evolved melt, and that coarse, more mafic, feldspar+biotite+accessory mineral hornblende rocks trapped between mafic sheets in the HZ are the initial cumulates. Fractionated melt accumulated roofward and laterally, and was the direct parent of the 'evolved' GZ cumulates. The most highly fractionated, fluid-rich melts accumulated at the roof.

Field observations from an exposed section of deep continental crust, the Athabasca granulite terrane (AGT), Saskatchewan, Canada, provide a view of granite genesis and a mechanism for deep-seated contamination of felsic and mafi c magmas. The 1.9 Ga Chipman mafi c dike swarm was emplaced into the Chipman Tonalite (ca. 3.3 Ga) and the megacrystic Fehr granite (ca. 2.6 Ga) at a crustal depth of ~40 km. The Fehr granite shows evidence for extensive partial melting and generation of granitic leucosome. Mafi c dikes and granitic leucosome display magma mingling and mixing textures similar to those widely described from shallow crustal exposures. The AGT provides a view of a dynamic, heterogeneous, and locally fertile deep crust. Mantle-derived mafi c magma promotes extensive partial melting of fertile granitoids, which in turn fi lter and entrap later mafi c dikes and sills. The result is almost inevitable mingling and hybridization (i.e., contamination) of mafi c and felsic end members. This interaction of magmas in the deep crustal environment may account for the isotopic and compositional signatures of igneous rocks at shallower crustal levels that typically record contamination of crustal melts by mantle material and vice versa.

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