CAPE ELIZABETH FORMATION: RETROSPECTIVE AND NEW INSIGHTS

Originally recognized in the greater Casco Bay region of the southwest coast in the first quarter of the 20^th century, the Middle Ordovician age Cape Elizabeth Formation was extended into south – central Maine, along with other components of the Casco Bay Group by the 1970s. Recent 7.5’ scale mapping over the last decade has refined its distribution, structure, metamorphism and migmatization in south – central and central Maine. While recognized as conformable and interbedded with the underlying Cushing Formation and conformable with the overlying Spring Point Formation in the southern Casco Bay area, contacts in south – central and central Maine are now largely confirmed as faults. Mylonite of varying width along with local pseudotachylyte are present along contacts with other members of the Casco Bay Group, the Falmouth – Brunswick and the Silurian Central Maine sequences on the northwest and Fredericton sequence or Passagassawaukeag Gneiss on the southeast. Locally, faults or fault zone rocks such as the Sand Hill Corner Fault are enclosed within the unit.

The Cape Elizabeth Formation is a dominant member of the Casco Bay Group, and comprises an outcrop belt of varying width that extends northeasterly from Casco Bay in southwestern Maine approximately 200 km to central Maine. The Cape Elizabeth is comprised of thin to very thinly bedded, quartzo – feldspathic granofels and metapelite. Thin map scale calcsilicate, amphibolite, quartzite, and rusty weathering units are locally present. The degree of metamorphism varies along the outcrop belt ranging from biotite through sillimanite K-feldspar zones. The unit is locally migmatized and/or intruded with granitoid dikes and sills. Structural deformation such as complex polyphase folding together with multiple schistosities or cleavages are locally present. Such complex deformation varies along the outcrop belt.