U-Pb dating of magnetite from the Kinsman Quartz Monzonite, New Hampshire, USA: Implications for dating natural remnant magnetization

We have studied the U P b systematics of magnetites separated from the Acadian Kinsman Quartz Monzonite (KQM) in the northern Appalachians, USA. The main objective of the present study was to investigate the U P b geochronology of magnetite and to evaluate its potential for constraining the timing of magnetic acquisition in rocks. This may prove to be helpful in the reconstruction of apparent polar wander paths (APWP) for use in plate tectonic reconstruction (e.g., van der Voo, 1993) and may also shed light on the nature of remagnetization events. A few attempts have been made recently to date metamorphic and ultramafic magnetite directly using the 4~ method (e.g., (>zdemir and York, 1990; 1992) and Pb isotopes (Garitpy et al., 1990). Previous studies have identified two major episodes of plutonism during the Acadian Orogeny in New Hampshire. The KQM belongs to the earliest phase of the plutonism and has been dated at ~,410 Ma (Lyons and Livingston, 1977; Barreiro and Aleinkoff, 1985), whereas the second phase of plutonism (the Concord-type) took place at ~ 355 Ma (Harrison et al., 1987). It has been suggested that the KQM is the product of syntectonic anatexis of metasediments at midcrustal levels (Lathrop et al., 1994).