NEW, DETAILED MAPPING IN THE PALMER 1:24,000 QUADRANGLE, SOUTH-CENTRAL MASSACHUSETTS: CONSTRAINTS ON POST-ACADIAN EVOLUTION OF THE BRONSON HILL TERRANE

Monson orthogneiss and amphibolite are dominated by S>L tectonites and protomylonite, and discreet zones of mylonite/ultramylonite; foliations are sub-vertical (~000 82 W) and Qtz-Fs-Bt lineations define a bimodal population (~338 81 and 199 37) that is distributed mesoscopically; asymmetric closed to isoclinal folds and shear bands display dextral and reverse kinematics. Foliations in Glastonbury orthogneiss dip moderately to steeply and define a NE-striking, SE-dipping great circle and a NW-plunging beta axis, parallel to Qtz-Fs-Bt lineations (~305 43); isoclinal folds and distinct shear bands deform the gneiss, and the northern contact is complexly folded. The Belchertown complex is a weakly deformed diorite; although tectonite and mylonite equivalents are distributed throughout, strain is concentrated along its contacts forming orthoschist; Qtz-Fs-Bt-amphibole lineations plunge shallowly N (~017 28). The isoclinal, steeply plunging Great Hill syncline runs the length of the quadrangle. The eastern limb and portions of the western limb are dominated by tectonites and S-C mylonites with steep, W-dipping foliations (~359 72 W), SW-plunging lineations (~205 24); kinematic indicators display sinistral and normal motion; the contact with the Monson is the Mt. Dumplin high strain zone; lineations parallel those in the Belchertown at the contact. Closed to isoclinal folds and associated axial planar cleavage deform the Amonoosuc volcanics in the western limb near the eastern Glastonbury-Belchertown contact. The Central Maine terrane (CMT) consists of Rangeley Bt-Sil-Grt paragneisses, diorite, amphibolite, and leucocratic, porphyritic Coys Hill granite. Lithologies are isoclinally folded, foliations define a NW-striking, NE-dipping great circle with a shallowly SW-plunging beta axis parallel to mineral lineations (~210 43). Discreet zones of mylonite are common in the Coys Hill granite. The BHT-CMT contact is the Conant Brook shear zone defined by Bt-Sil-Grt paragneisses with steep, west-dipping foliations (mean = 001 70W) and microscopic partitioning of bimodal Qtz-Fs-Sil lineations (273 68 and 202 36) in Rangeley Fm. and Greenwich syncline (Partridge Fm.), which show dextral and reverse kinematics. Multiscale relationships are consistent with regional bulk dextral transpression.