ORIGIN OF DAGGETT'S ROCK: MAINE'S LARGEST KNOWN GLACIAL ERRATIC

Daggett's rock, located in Phillips, Maine, is one of Maine's largest glacially transported erratics, at 7.6m tall, 24m long, 9m wide, and weighing ~ 7,200 metric tons. It is composed of a two-mica granite, rests upon Devonian metasedimentary bedrock locally overlain by glacial till. Based on regional ice flow data indicating ice flow from the WNW in Phillips, two granitic plutons are considered potential sources of the erratic - the Redington pluton (RP) located ~20km to the NW, and the Lexington pluton (LP), located ~60km to the north. We present the results of a petrographic and geochemical study, the first of its kind for sourcing erratics in Maine.

Daggett's rock is a two-mica granite with a light brown color and equigranular texture although some phenocrysts are evident. The RP and LP are texturally and compositionally variable, requiring widespread sampling to assess the heterogeneity ofeach pluton. Samples were collected across the RP from Orbeton stream in the SE, Spaulding Mtn. to the NE, Saddleback Mtn. in the NW, and a displaced boulder located between Mt. Abraham and Farmer Hill in the eastern arm of the pluton. The RP samples ranged from equigranular granite (Orbeton stream) to porphyritic granite containing feldspars up to 2cm (the Mt. Abraham boulder) and severely weathered granite/schist (Spaulding mountain). However, the Saddleback Mtn. sample, a two-mica equigranular granite, is the closest petrographically to the Daggett's rock erratic. The LP varies from a bt + hb granodiorite to a megacrystic two mica granite which becomes finer grained toward the southerly margin of this pluton. It is therefore petrographically distinct from the erratic.

Samples of Daggett's rock and the RP were analysed for major and trace elements using XRF spectrometry. These data when combined with published data for the RP (Tomascak et al., 2004) and data for the LP (Gibson, unpublished data) provide a robust data set to geochemically “fingerprint” the Daggett's rock erratic. Preliminary data for the levels of MgO, TiO₂, and CaO, reveal that the closest correlation exists between the erratic and samples from Saddleback Mtn.. The combination of petrographic and geochemical similarities are consistent with the striation data indicating that Daggett's rock originated 20 km to the WNW in the Saddleback Mtn. range.