a Ford Granodiorite source for the leucogranites (Saito et al., 2007) at T, P conditions of 820-870°C and 6.5-7.5 kbar determined from mineral equilibria modeling (Korhonen et al., 2007a,b). There is evidence of metamorphic zircon growth as early as ca. 140 Ma. A summary of U-Pb SHRIMP analyses of igneous and metamorphic zircon from Fosdick Mountains migmatites (Figure 6) reveals that there is a bimodal distribution of ages. Whereas HT metamorphism and zircon growth is recorded as early as 150 Ma, a majority of points analyzed thus far fall within the interval of 120-100 Ma. Anatectic leucosomes from sites in MBL’s Amundsen Province, the Demas Range (Figure 2) yield ages of 128 Ma to 113 Ma for igneous zircon (Mukasa and Dalziel, 2000). The MBL data fall within the 126-107 Ma age range of the youngest arc-related intrusions identifid in NZ by Muir et al. (1997, 1998), those of the Separation Point and Rahu suites in the Western Province and the deeper level Fiordland Orthogneiss in Fiordland. The Rahu suite granites are interpreted to derive from crustal melting of preexisting rocks (Ireland and Gibson, 1998). Thus, the conditions for HT metamorphism and granite genesis in the Fosdick Mountains were attained and overlapped in time with arc plutonism in the Median Batholith and in the Amundsen Province.
By contrast, the alkaline plutonism attributed to back-arc extension occurred in eastern MBL (Figure 5) at 105-102 Ma (Weaver et al., 1992, 1994; Mukasa and Dalziel, 2000), distinctly later than onset of high temperature metamorphism. In western MBL the Ford Ranges experienced alkalic plutonism at 105-103 Ma and ca. 99 Ma (Richard et al., 1994) and in Edward VII Peninsula at 103-98 Ma (Mukasa and Dalziel,