Petrology and Geochemistry of Metamorphosed Cambrian-Ordovician Volcanic Rocks of the St. Croix Belt, Western Penobscot Bay, Maine, Poster 39

The northern Appalachians contain several geologic terranes that were accreted onto the margin of Laurentia during the Paleozoic. Preserved within these terranes are metamorphosed volcanic rocks that contain information... [ view full abstract ]

The northern Appalachians contain several geologic terranes that were accreted onto the margin of Laurentia during the Paleozoic. Preserved within these terranes are metamorphosed volcanic rocks that contain information important in determining tectonic environment of formation. The purpose of this contribution is to present new petrologic and geochemical data from the St. Croix and Jam Brook belts located in the Penobscot Bay region of Maine. Within the St. Croix Belt, metamorphosed volcanic rocks are found at the base of the Penobscot Formation extending from Union to Belfast, ME. Bulk-rock geochemistry of the Gushee meta-volcanics (n=21) yields a range of compositions from 44 - 76 wt. % SiO2. Preliminary trace element geochemistry displays flat REE patterns with a distinct niobium anomaly suggestive of a source region influenced by subduction. Immediately west of the St. Croix Belt are metamorphosed volcanics within the Jam Brook complex. Limited chemistry from these volcanics (n=7) yields chemical compositions from 49 - 76 wt. % SiO2. Trace element geochemistry displays flat REE patterns, also with distinct niobium anomalies. Analysis of these volcanics is on-going, and the data collected will be compared with volcanic rocks of similar age and integrated into tectonic models of the area.