Wausau And Stettin

The Wausau complex is much larger than the adjacent and coeval Stettin intrusion but is less alkaline. Wausau comprises northern and southern segments, both cored by younger quartz monzonites of the Ninemile granite, the southern segment overlapping the northern. Syenitized xenoliths are abundant throughout Wausau, the large quartzite xenolith forming Rib Mountain being 3.2 km long; other rock types represented among the xenoliths include sillimanite schist and diverse meta-volcanics. Around the quartz monzonite cores lie intermediate zones of quartz syenite which in turn are enveloped, particularly in the southern segment, by pyroxene and amphibole syenites. The syenites contain barkevikite, sodic pyroxene, fayalite and biotite and sodic amphiboles occur in late pegmatites. The Stettin intrusion is emplaced principally into volcanics which are extensively fenitized at the contacts. Along the eastern and southern margins are complex areas of screens and pendants of volcanics within various contaminated phases of the pluton including nepheline syenite. The intrusion is concentrically zoned from an outer zone of nepheline syenite passing inwards to tabular syenite, followed by an intermediate zone of highly variable amphibole and pyroxene syenites, to a core, situated asymmetrically in the north of the pluton, of nepheline syenite surrounding pyroxene syenite. The outer nepheline syenite is a banded rock of perthite, nepheline, cancrinite, aegirine, sodic amphibole, olivine and accessory sodalite, pyrochlore and fluorite, cut by tabular syenite of a similar mineralogy but lacking nepheline. The intermediate zone syenites contain a little quartz, augite rimmed by arfvedsonite-riebeckite and some fayalite. The nepheline syenite of the core is a laminated rock of microperthite, up to 25% nepheline partially altered to cancrinite and 20-30% of pyroxene and amphibole. The innermost core rock is an augite-arfvedsonite syenite. Accounts of the field relationships, mineralogy and rock chemistry will be found in Myers (1980, 1983) and of the mineral assemblages of the pegmatites in Falster (1983).