The behavior of zircon during partial melting in anatectic migmatites: Insights to metamorphism, deformation and tectonism in the central Santa Fe Range, northern New Mexico

Three lithologic assemblages exposed in the central Santa Fe Range, northern New Mexico include (1) a septum of Proterozoic low temperature (~700oC, 5.5 kbars), semi-pelitic anatectic migmatites surrounded by (2) deformed megacrystic biotite granite that is intruded by (3) discrete plutons of largely undeformed hornblende biotite tonalite. Metamorphic fabrics in the migmatite record three deformation events (D1 - D3); a composite S1/S2 fabric (D1 and D2) that formed contemporaneous with anatexis and is folded about a southwest plunging map-scale (D3) antiform. The megacrystic granite exhibits a pervasive S1 subsolidus foliation that parallels the S1/S2 fabric in the migmatite and is cut by discordant leucosomes. The hornblende tonalite cross-cuts both the S1 foliation of the megacrystic granite and the S1/S2 foliation of the migmatite. New U-Pb SIMS ages were collected on zircon from the two plutonic units and from a stromatic metasedimentary migmatite (leucosome-melanosome-paleosome). Megacrystic granite yielded a concordant U-Pb age of 1633 ± 12 Ma (2ó) and hornblende tonalite yielded a concordant U-Pb age of 1395 ± 7 Ma (2ó); both plutonic units have Th/U \u3e0.1. The evaluation of migmatite zircon from leucosome-melanosome-paleosome have highly variable Th/U values (\u3e0.1 to0.1 yielded two age populations: protolith cores with a Pb-Pb age = 1634 ± 16 Ma and new growth with a Pb-Pb age of 1398 ± 17 Ma. Three zircon analyses yield older Pb-Pb ages of 1791 ± 25 Ma. Migmatite zircon with Th/U value