PALEOSTRESS FIELDS OF MESOZOIC DIKES AND JOINTS IN GREAT GULF, TUCKERMAN RAVINE, AND HUNTINGTON RAVINE, NEW HAMPSHIRE

Mesozoic extensional structures were mapped in Great Gulf, Tuckerman Ravine, and Huntington Ravine in the Presidential Range, NH, to determine their relative ages, distribution, and paleostress fields. Over 3000 joints and 7 major dikes were measured within the folded Devonian Littleton Formation schist and quartzite with a bedding parallel anisotropy, and massive migmatites of the Silurian Rangeley Formation. One dike was found in Tuckerman Ravine, three in Huntington Ravine (Pinnacle Gully, Diagonal Gully, and Escape Hatch dikes), and three in Great Gulf (Pipeline Gully, Airplane Gully, and Oblique Gully dikes). All dikes are 1-3 meters wide, extend for several 100's of meters, exhibit composite dike textures, are often vesicular, are not significantly influenced by bedding plane anisotropies, and mostly classified as alkaline dolerites. Only common joints and no shear or conjugate joints were observed suggesting near surface conditions (<3 km?) under low lithostatic pressure. Four joint sets were identified and assigned relative ages based on field relations. The oldest and most abundant joints have a NE strike and sub-vertical dip, are most abundant near and sub-parallel to the principal NE striking dikes in each ravine (the Tuckerman Ravine, Pinnacle, Pipeline, Airplane, and Oblique Gully dikes), and likely formed during regional NW-SE extension associated with the Late Triassic and Jurassic rifting of Pangea. The second oldest joint set has a E-W strike, is sub-parallel with the Diagonal Gully and Escape Hatch dikes in Huntington, and interpreted to be part of regional N-S extension associated with the Middle Cretaceous New England-Quebec province. The third youngest fracture set strikes N-NW, has no correlative basalt dikes, and may correlate to the regional trend of the White Mountain Magma Series. The youngest joint set has shallow W-NW dipping sheeted joints thought to have formed from Quaternary glacial, and/or Late Cretaceous tectonic, unloading.