The Relationship between Metamorphic Charnockite and Marble near Speculator, Central Adirondack Mountains, New York

Abstract

Granites and charaockites with similar bulk compositions are exposed in a series of roadcuts along Rt. 8-3 east of the central Adirondack town of Speculator. The mineralogy of these rocks is correlated with their associated rock types, with the orthopyroxene-bearing varieties occurring in the marble-rich portion of the sequence. Mineral assemblages in a charnockite boudin enclosed in marble appear to be consistent with equilibration with a $$CO_{2}$$-rich fluid under high-grade (T = 700°C, P = 7 kb) conditions, while high density, $$CO_{2}$$-rich fluid inclusions occur in a quartz vein enclosed within the boudin. It is suggested that small amounts of charnockite may have been produced in this area by the influx of $$CO_{2}$$ produced by devolatilization reactions in the marble. However, carbonic metamorphism in the Adirondacks appears to have been, at most, a minor local process and did not operate on the regional scale that has been suggested for some other granulite terranes. Thus, the presence of abund...