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

汤普森 9628520 世纪以来，地质学家们聚集在马萨诸塞州昆西的斯阔角海崖，争论斯阔角“冰碛岩”可能的冰川起源。 尽管最近的沉积学观点最终倾向于冰海沉积，但通过测定这种岩石的年代仍有许多东西有待了解。 例如，量子年龄数据将为沉积火山事件的时间提供第一个放射性证据。625-590 Ma波士顿周围的阿瓦隆岩浆弧杂岩。 将在麻省理工学院放射性同位素实验室使用高精度U-Pb锆石地质年代学方法对Scquantum“Tillite”进行定年。 将分析火山岩碎屑以及来自Squantum杂岩的碎屑锆石，以确定其最大沉积年龄。 还将对位于昆西Houghs Neck更南部的火山流与砾岩Squantum序列互层进行测年。 这一结果将更直接地制约沉积年龄，从而制约该区的年龄冰川作用。 将通过碎屑锆石研究寻求更广泛的观点。 对于一个花了二十年时间教授本科生的首席研究员来说，这个项目提供的在麻省理工学院放射性同位素实验室学习U-Pb地质年代学方法的机会代表了一个重大的职业发展。 一旦高精度的年龄测定能够与现有的野外、岩相学和地球化学数据相结合，必将出现更广泛和更有启发性的研究问题。 这样的研究结果肯定会回到一个充满智力活力的教师回到韦尔斯利的教室。

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.