MESOZOIC EXTENSION IN THE PRESIDENTIAL RANGE: HUNTINGTON RAVINE, NH

Mesozoic extensional structures were examined in Huntington Ravine in the Presidential Range, New Hampshire to determine their relative ages, distribution, and paleostress fields. The bedrock geology of the ravine consists of schist and quartzite couplets of the Devonian Littleton Formation that exhibit a strong bedding/foliation parallel joint fabric. The dominant joint sets in the ravine are not parallel to these fabrics and over 1,000 such fractures were measured. A map of the major fracture traces and associated basalt dikes was made in the field and completed in ArcGIS. Four systematic fracture sets were identified and assigned relative ages based on field relations. The oldest fractures in the Ravine have a NE strike (~036, 74 SE) and are sub-parallel to the Pinnacle dike (~045, 58 SE). This joint set and the Pinnacle dike are likely coeval and are interpreted to be part of a regional set of joints and parallel basalts that formed in the Early Jurassic as part of the Eastern North American (ENA) igneous province during the rifting of North America from Africa causing NE-SW extension (Mchone & Butler, 1984). The next youngest and most prominent fracture set in the ravine has an E-W strike (~284, 71 N), and is parallel to the Upper Trail (~270, 89.5 N) and Escape Hatch (~263, 59 N) basalt dikes. Structures with similar E-W strikes are found throughout New England and Quebec as part of the Middle Cretaceous New England-Quebec (NEQ) province associated with N-S extension (Faure et al. 2006). These are interpreted to have formed as Newfoundland rifted from Iberia and Ireland. The third youngest fracture set is characterized by NW-SE striking joints (~162, 85 SW) which are found throughout the ravine. Correlations of these joints to others in the New England region are uncertain suggesting a localized event. The youngest fracture set is shallow dipping (~203, 17 NW), sub-parallel to bedding/foliation, and are thought to have formed from glacial unloading at the end of the Last Glacial Maximum. Geochemical analysis of trace and abundant minerals were done for all three dikes using and XRF, and results will be presented.