NEW DETAILS OF THE THERMO-DEFORMATIONAL SEQUENCE IN CENTRAL-COASTAL MAINE FROM INCLUSION TRAILS IN PORPHYROBLASTS

New microstructural analysis of inclusion trails preserved in metamorphic porphyroblasts in rocks of central-coastal Maine reveals at least a four-stage Siluro-Devonian history of regional fabric-forming events contemporaneous with regional and pluton-related metamorphism. This detailed regional thermal-deformational sequence was established on the basis of textural relationships between inclusion trails in metamorphic phases and also with matrix foliations from rocks from the Central Maine sequence, the Liberty-Orrington belt, and the Fredericton trough. The order of appearance of metamorphic phases was also used to distinguish between similar inclusion trails in phases with differing pressure-temperature stability ranges. Comparison of the thermal-deformational sequence to inclusion trails across regional strike indicates that metamorphism was experienced somewhat later in the northwestern portion of the study area where late Devonian plutons occur, and that relatively high temperatures were maintained in the central and eastern portions through at least the beginning of significant dextral shearing. In addition, the microstructures suggest that dextral shearing was focused where the higher temperatures were maintained before, during, and after pluton emplacement to the west. The inclusion-trail sequence is correlated with the three regional folding and dextral shear phases of deformation, and adds one and possibly two phases of deformation that are only preserved as porphyroblast inclusion trails. As well as adding detail to it's tectonic history, this work has implications for the spatial and temporal thermal-structural evolution of this transpressive northeastern portion of the Appalachian orogen.