PERMIAN HIGH-TEMPERATURE HYDROTHERMAL VEINS AND AMPHIBOLITE METASOMATISM IN SOUTHWESTERN CONNECTICUT – EVIDENCE FOR THEIR ASSOCIATION WITH ALLEGHENIAN INTRUSIVES
Approximately 100 m.y. later, undeformed fluorite-bearing Permian granitoids, including Trumbull’s Pinewood Adamellite (291 ± 4 Ma, Sevigny & Hanson, 1993), were intruded along a 320º trend (Crowley, 1968) that intersects the OMP. The mineralization at the park takes two forms: (1) the veins themselves and (2) alteration of rocks adjacent to the veins. Undeformed, 1 m thick topaz veins are coarse-grained, compositionally zoned, and contain primarily quartz in cores, and intermediate and border zones of muscovite, topaz and/or albite and fluorite (a rare few contain primarily calcite). They probably crystallized above 400°C, well before a new 267 Ma 40Ar/39Ar closure age of muscovite from one vein. Alteration around the veins includes metasomatic replacement of host amphibolite to phlogopite, scapolite and albite, with minor scheelite. This mineralization is similar to, and apparently related to, discontinuous zones of metasomatically altered amphibolite characterized by very coarse-grained quartz, clinozoisite, scapolite, albite ± scheelite. The undeformed nature of the mineralized rocks, the occurrence of fluorite in the granitoids and the veins, and the 320º trend of the steep veins shared with the trend of the granitoids suggests that metasomatism is associated with another Permian intrusive a few m below the surface. Fluids rising from it invaded fractures associated with its 320º emplacement trend, bringing late mineralizing fluids to the park area.