PALEOSTRESS ANALYSIS OF MESOZOIC RIFTING, GREAT GULF, NEW HAMPSHIRE

A brittle structural analysis was done in the Great Gulf and Mt. Clay area of the Presidential Range, NH, in an effort to complete an understanding of the deformational history of the region, relating prominent fractures and dikes to their regional tectonic context. Large-scale analysis of brittle structures in the field illuminates local differences in the geometry, allowing for refinement of regional deformational models. GPS and GIS-based mapping of basalts and joints in the Silurian Rangeley Fm. migmatites and Devonian Littleton Fm. schist and quartzite was done in this alpine region due to excellent outcropping and steep relief. Three basalt dikes were mapped, all of which strike approximately 55º and dip 65-75ºSE. Four different extensional joint sets were defined using Kamb's contour method. The oldest, dominant, basalt parallel set strikes 55º and dip 75ºSE. This set is best defined in the Rangeley Fm., and dips near vertical in the Littleton Fm. The other joint sets, in order of decreasing age, are: a set striking 100º and dipping 65ºN; a set striking 170º and dipping 65ºW; and a sheeted joint set striking 60º and dipping 20ºW. The sheeted joint set is not statistically apparent in the Littleton Fm. due to subvertical bedding anisotropy. More subtle differences in joint set orientations between the Rangeley and Littleton Fms. also reflect the influence of bedding plane anisotropy in the latter. The multiple joint set orientations suggest that more than one paleostress field existed in the Mesozoic. These results confirm regional studies in New England and Quebec that show a NW-SE extensional stress related to rifting of Pangea, and local N-S and E-W extensional stresses related to activity of New England-Quebec igneous province intrusions, White Mountain Magmatic Series intrusions, and later rift events. Geochemical analyses will be performed on basalt samples from the Great Gulf Wilderness to define their relations to igneous provinces affecting the area.