CAA: U-Pb Geochronology of Squantum 'Tillite' and Related Rocks Around Boston, MA: Implications for Terminal Proterozoic Glaciation and Supercontinent Breakup

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Thompson 9628520 For more than a century, geologists have congregated at the Squaw Head seacliff in Quincy, Massachusetts to argue over the possible glacial origin of the Squantum "Tillite". Although recent sedimentological opinion has finally titled toward glaciomarine deposition, much remains to be learned by dating this rock. Squantum age data, for example, will provide the first radiometric evidence for the timing of sedimentary-volcanic events post-dating the well known ca. 625-590 Ma Avalonian magmatic arc complex around Boston. The Squantum "Tillite" will be dated in the Radiogenic Isotope Laboratory at MIT using methods of high precision U-Pb zircon geochronology. Volcanic rock clasts as well as detrital zircons from Squantum diamictite will be analyzed to fix its maximum depositional age. Volcanic flows interbedded with a conglomeratic Squantum sequence farther south in Houghs Neck, Quincy will also be dated. This result will constrain the age of deposition, and thus the age glaciation in this area, more directly. A broader view of Squantum provenance will be sought via detrital zircon studies. For a Principal Investigator who has spent twenty years teaching undergraduates, the opportunity presented by this project to learn the methods of U-Pb geochronology in MIT's Radiogenic Isotope Laboratory represents a major career advancement. Much broader and more stimulating research questions will certainly arise once high precision age determinations can be integrated with existing field, petrographic and geochemical data. The results of such research will surely come full circle by returning an intellectually energized instructor to Wellesley classrooms.