Abstract: Fluvial Catskill Magnafacies of New York Dates an Acadian Event of Hydrothermal Circulation at lapetus Mid-Ocean Spreading Ridges

FRIEDMAN, GERALD M.

In fluvial meandering facies of the Gilboa Formation (Upper Givetian; uppermost Middle Devonian) within the eastern Catskill Mountains of New York, a well-rounded pebble revealed the texture and composition of metamorphosed diabase. This pebble of green-schist facies, composed for the most part of feldspar and chlorite, derived from mid-oceanic spreading ridges in the lapetus Ocean. Hydrothermal metamorphism at about 200-400 degrees C, 2-3 km below the ocean floor, transformed diabase into green-schist metamorphic rock. A K-Ar date on feldspar gave an age of 402 +/- 11 my. Zircons in the same pebble yielded ca. 400 my. These dates coincide with the early phase of Acadian orogeny. The age of the Gilboa Formation (Upper Givetian) has been dated at 385 to 370 Ma. The ca. 15-30 million-year differential between formation of the diabase body and the final settling of the pebble of metamorphosed diabase in the fluvial deposit, allowed about 15-30 my for converting mid-ocean spreading ridges into the rising Acadian Mountain ranges, and degradation of the mountains by rivers to form the fluvial wedge. Zircon dates in the pebble at around 1200 Ma confirm the Grenville basement as the initial source.

AAPG Search and Discovery Article #90939©1997 AAPG Eastern Section and TSOP, Lexington, Kentucky