EARLY TO LATE CRETACEOUS COOLING ACROSS NEW HAMPSHIRE BASED ON APATITE FISSION TRACK AGES

Apatite fission-track (AFT) ages were determined for 75 crystalline rock samples from eastern Vermont, throughout New Hampshire and western Maine to delineate any discontinuities across major fault boundaries. In the central and southern Connecticut River valley, AFT ages ranged from 96 to 104 Ma and showed no distinct offset across the Ammonoosuc Fault. To the north between Haverhill and Littleton, older AFT ages ranging from 128 to 140 Ma were determined. East of the Connecticut Valley, a northeast trending zone of significantly younger Late Cretaceous AFT ages, 70 to 104 Ma, extends from Unity in the south to Andover near the Maine border. In western Maine, AFT ages of 88 to 104 Ma, continue this younger age trend. Sample transects were collected across major faults in southeastern New Hampshire. AFT ages show a slight increase, ~120 – 130 Ma, southeast toward the Pinnacle Fault (PF) and decrease to 80 to 107 Ma between PF and the Campbell Hill Fault (CHF). In both the Massabesic Gneiss Complex and the Exeter pluton, AFT ages decrease to the northeast, 137 to 105 Ma (Manchester to West Nottingham) and 133 to 113 Ma (Exeter to Durham), respectively. With the exception of the AFT age discontinuity between PF and CHF, there appears to be no distinguishable offset in AFT age across major faults in New Hampshire. However, what the new data does show is a northeast trending zone of significantly younger AFT ages in central to northern New Hampshire and adjacent western Maine. Samples from the White Mountain magma series, which lie along this northeast trending Late Cretaceous AFT age zone, are being analyzed to constrain the extent of Late Cretaceous cooling ages in this region.