Paleostress Analysis of Mesozoic Extension in Fractures and Basalt Dikes, Great Gulf, NH

A brittle structural analysis was done in the Great Gulf Wilderness and Mt. Clay area of the Presidential Range, NH, to complete an understanding of the deformational history of the region and relate brittle structures and intrusions to the broader regional tectonic context. GPS/GIS mapping of basalts and joints in the Silurian Rangeley Fm. migmatites and Devonian Littleton Fm. schist and quartzite was done where excellent outcrop abundance and steep relief dominate. Three basalt dikes were mapped, and all strike approximately 55º and dip 65-75ºSE. Four extensional joint sets were defined using Kamb\u27s contour method. The oldest, basalt parallel set strikes 50º and dips 80ºSE. This set is best defined in the Rangeley Fm., and dips near vertical in the Littleton. The other joint sets, in order of decreasing age, are: a set striking 100º and dipping 65ºN; a set striking 170º and dipping 70ºW; and a sheeted set striking 60º and dipping 20ºW. These results confirm regional studies in New England and Quebec that show a NW-SE extensional stress related to rifting of Pangea, followed by N-S extension related to the intrusion of the New England-Quebec igneous province, then E-W extensional stress related to a later uplift event