IMPLICATIONS OF THE CALEF MEMBER OF THE ELIOT FORMATION, EPPING QUADRANGLE, SOUTHEAST NEW HAMPSHIRE

Detailed EDMAP-supported bedrock mapping of the Epping 7.5 minute quadrangle, southeast New Hampshire, extends the Calef Member of the Eliot Formation southwest into the adjacent Kingston quadrangle. Previous speculation that the Calef Member marks a fault contact between the Eliot Formation and Berwick Formation within the quadrangle is supported by this study.

Structurally (and perhaps stratigraphically) the Calef Member bounds two metasedimentary units of the Silurian-Ordovician Merrimack Group. Gray calcareous interlayered metasiltstone and phyllite of the Eliot Formation crop out in the east, and the dark gray to purple quartz, biotite, and calc-silicate granofels of the Berwick Formation dominate the west. Devonian intrusions of diorite and granite crop out in the southeast and northwest corners of the quadrangle, respectively. The Calef Member has previously been described as a black phyllite and is here redefined as a well-crenulated, rusty-maroon weathering, gray graphitic phyllonite with discontinuous quartz stringers. Preliminary petrographic data show the composition of the Calef Member to be mostly quartz, muscovite, and chlorite, with fibrolite preserved locally in the southern part of the quadrangle. The presence of fibrolite indicates a higher metamorphic grade than at least the adjacent Eliot Formation.

Structural and petrographic analysis of the Calef Member and Gove Member of the Berwick Formation, in particular, indicate a polydeformational history. Garnet? and staurolite? pseudomorphs in these units indicate a polymetamorphic history as well. Shear fabric suggests early ductile deformation, followed by brittle faulting marked by slickensides. Kinematic indicators such as asymmetric grains and slickensides suggest west-side-up movement as the most recent motion. The extent of this high strain zone within the Merrimack Group and the distribution of isograds across it are important remaining questions.