The age and cooling history of the chain of ponds and big island pond plutons and the spider lake granite, west-central Maine and Quebec

Abstract

40Ar/39Ar release spectrum ages have been determined for hornblende, biotite, and K-feldspar from the Chain of Ponds pluton (CPP), Spider Lake Granite (SLG), and Big Island Pond pluton (BIPP) west-central Maine and Quebec. Mean plateau ages of 373.3 ± 2.0, 367.6 ± 1.3, and 367.7 ± 1.3 Ma for hornblendes from the CPP, SLG, and BIPP respectively are interpreted to be intrusive ages for these plutons. A best estimate biotite age of 371.5 ± 2.7 Ma for the CPP is reported. The K-feldspars from the CPP exhibit radiogenic 40Ar loss profiles resultant from an ~170 Ma thermal disturbance and have plateau or terminal ages varying from ~312 to 365 Ma. A three dimensional conductive cooling model for the CPP suggest that rapid cooling to ambient conditions occurred within ~3 Ma of intrusion. This model corresponds well with the rapid cooling suggested by the essentially concordant hornblende and biotite ages. -Authors