Bulgarmarsh Granite of southeastern RI and adjacent MA south of Fall River has been dated as early Paleozoic (Galloway (1970), but it cannot be readily separated from granite north of Fall River from which R.E. Zartman (1978, written commun.) obtained Proterozoic Z age, an age similar to others in southeastern MA batholith (Kovach and others, 1977). Bulgarmarsh is therefore assigned a Proterozoic Z age.

Source: GNU records (USGS DDS-6; Reston GNULEX).

Included in rocks mapped as granite of Fall River pluton of Proterozoic Z age.

Source: GNU records (USGS DDS-6; Reston GNULEX).

Fall River pluton of the MA State map (Zen, 1983) is here referred to as the Fall River Granite. According to the authors, the change in name is meant to indicate the heterogeneous nature of the granite and the fact that it may consist of more than a single pluton. Included in this unit is the Bulgarmarsh Granite of Fall River and a mass of alaskitic gneiss shown on the State map south of Fall River. No type section is designated. Geologic map shows the Fall River present in the New Bedford area of MA and RI and bounded on the west by the Narragansett Bay Group. The Fall River was dated by Zartman and Naylor (1984) at about 600 Ma (U-Th-Pb zircon) and the Bulgarmarsh at 516+/-13 Ma (Rb-Sr whole-rock) by Galloway (1973). Authors state that it is not unusual for Rb-Sr ages to be younger than U-Pb ages for the same rocks.

Source: GNU records (USGS DDS-6; Reston GNULEX).

Bulgarmarsh Granite, within the Fall River pluton, has been described by Zen (1983) as a "brittlely deformed granitic terrane." Affinity to Dedham Plutonic Complex long recognized. Isotopic data from Zartman and Naylor (1984) indicate Late Proterozoic age (650-600 Ma). Described as coarse-grained pink to white, massive to foliated, granite to quartz-monzonite, commonly alaskitic. Microcline, microperthite, albite, quartz, biotite and chlorite are principal minerals.

Source: GNU records (USGS DDS-6; Reston GNULEX).