GEOLOGY OF THE EXETER AND HAMPTON 7-1/2' QUADRANGLES, SE NEW HAMPSHIRE

New exposures of rocks within the Siluro-Ordovician Merrimack Group (MG) and older Rye Complex (RC) identified in recent EDMAP efforts in the Exeter and Hampton 7-1/2' quadrangles help to constrain the deformation history and boundary conditions between them. In areas of poor exposure abundant well data provide a picture of the underlying bedrock surface and shed some light on lithologic distribution through this region, particularly satellitic bodies of the Exeter Pluton.

Intercalated dark brown quartzite and pelitic rocks of the MG preserve at least two clear deformation events that predate the 406 Ma Exeter Pluton. Refolded shallow, NE plunging, isoclinal folds and associated obliquely plunging ribby lineations represent the older event. A larger antiformal structure with associated minor folds and crenulation lineation parallel to the main hinge represents the younger event. Similar structures are found beyond the limits of the Exeter and Hampton quadrangles, particularly the Great Bay area.

Higher grade (garnet to sillimanite) rocks of the RC, and the younger Breakfast Hill granite (BH), are variably mylonitized and preserve a more complex deformation history. These include at least three foliations and kinematic indicators (augen and sigma-delta grains) typically record dextral slip motion. Present data indicate that the BH and RC share a concordant boundary parallel to foliation and that the boundary between the RC and MG is folded. Both Acadian and Alleghanian deformations are inferred in this area.