LOW-PRESSURE EMPLACEMENT OF THE MOUNT WALDO PLUTON, NORTHERN PENOBSCOT BAY, MAINE

The Mount Waldo Pluton (371±2 Ma), at the northern terminus of the Penobscot Bay, Maine, is a medium-gray, seriate to porphyritic, biotite ± hornblende granite, which intrudes the metasedimentary country rock and imparts a 2-3 km wide contact aureole. The country rock consists of the Appleton Ridge Formation (a staurolite, garnet, andalusite, biotite, muscovite schist), that is interbedded with the Bucksport Formation (a diopside, hornblende, plagioclase, quartz granofels), and the Penobscot Formation (an andalusite bearing, iron-sulfide rich, biotite, muscovite schist). Petrography of samples from within the contact aureole in the Appleton Ridge and Penobscot Formations reveals contact metamorphic alteration of regional metamorphic assemblages. Pseudomorphs after staurolite occur in both the Appleton Ridge and Penobscot Formation samples, and consist of cordierite, biotite, and quartz. Samples taken close to the Mount Waldo Pluton contact (<100m) have little remaining garnet. Samples collected farther from the contact exhibit more garnet, but show some regression to biotite, chlorite, and chloritoid. Andalusite is present in all samples from the Mount Waldo Pluton contact aureole. These mineralogical relationships suggest a maximum emplacement pressure of less than ~2.2 Kbar and a temperature of less than 615&#61616;C. Aluminum-in-hornblende geobarometry data, as well as plagioclase-hornblende geothermometry data are in progress and will be presented with the above observations.