CORRELATION OF PALEOMAGNETISM AND MAGNETIC MINERALOGY OF GRENVILLE METAMORPHIC AND IGNEOUS ROCKS, ADIRONDACK HIGHLANDS, USA INDICATE A COUNTER-CLOCKWISE LOOP FROM 990 TO 960 MA

An east-west traverse of the Adirondacks Highlands, northern New York, USA, sampled rocks metamorphosed to granulite facies (T>650°C) at ~1050 Ma during the Grenville Orogeny. Fourteen sites of microcline gneiss give a mean direction of -62.8°, 289.2° with a₉₅ = 7.6° and a corresponding pole at 18.6°S, 150.6°E. Metamorphosed anorthosites and associated rocks (N = 14) give a direction of -67.3°, 283.9° with a₉₅ = 7.7° and a pole at 25.1°S, 149.0°E. Post-metamorphic fayalite granites (N = 8) give a statistically different direction of -75.8°, 297.0° with a₉₅ = 3.9°, and a pole of 28.6°S, 132.3°E. Both normal and reversed polarities are recorded, with reversed sites occurring on the eastern and western ends of the traverse, and normal polarities restricted to the central part. The remanence in the microcline gneisses is carried by ilmeno-hematite, while in the metamorphosed anorthosites and fayalite granites, magnetite is the predominant oxide. Using local cooling curves, and blocking temperatures determined for ilmeno-hematite (< 520°C) and magnetite (~ 570°C), the age of remanence is ~990 Ma for the granites, ~970 Ma for the metamorphosed anorthosites, and ~960 Ma for the microcline gneisses. Selected studies in the Grenville Province, with age control and known magnetic mineralogy, yielded poles centered on 30°S and 140°E. By comparison, the mean pole positions of the three units studied here support counterclockwise motion on the Grenville loop, with this part of Laurentia moving northward to mid-southern latitudes in the waning stages of the Grenville Orogeny.