Ever since Tuzo Wilson asked whether the Atlantic Ocean closed and then reopened in a famous 1966 paper in the journal Nature, this idea has been generally accepted and explored. It is well established that ~180 million years ago the Atlantic Ocean opened along approximately the same line as where the continents around the pre-Atlantic Ocean had closed and formed supercontinent Pangea by ~250 million years ago. This supercontinent included the Americas to the west and Eurasia (Europe and Asia) and Africa to the east of the Pangean suture zone. It is possible, however, that some continental fragments were transferred from Eurasia/Africa to the Americas and/or vice versa, if the Atlantic Ocean opened anywhere along a line that did not follow the suture zone. To date, this has not been demonstrated. The eastern New England Appalachians consist of a collage of microcontinents that collided with and became part of North America between ~470 and ~360 million years ago, before the formation of Pangea. One of the last of these arriving microcontinents, the Avalon terrane, is interpreted to constitute southeastern Massachusetts, Rhode Island, and southeastern Connecticut. Recently, the principal investigator and coauthors of a 2017 paper published in the journal Geology discovered a fragment of West African (Moroccan) crust in offshore Massachusetts that was stranded during the breakup of Pangea. Careful review of existing data for what has been interpreted as the Avalon terrane of southeastern New England suggests that part of it may in fact be part of this West African fragment. The purpose of the proposed work is to test this hypothesis. If true, southeastern New England will be the first known location where the major Pangean suture zone is exposed on land. It may become the first location where geologists and geophysicists who work in the Appalachians, West Africa and beyond can come together and study the main suture zone that formed the most recent supercontinent. Bedrock geologic maps and our understanding of the geology of Massachusetts, Rhode Island, Connecticut and the northern Appalachians may change significantly.

The idea that part of what is generally accepted to be the southeastern New England Avalon terrane may actually be a west African fragment that remained after the breakup of Pangea has not previously been explored, because Avalonian and west African rocks have similar characteristics and ages. However, the ages of zircon in sedimentary and granitic rocks distinguishes them. For example, Avalonian rocks have a strong affinity with approximately one billion year old crust, and West African rocks with approximately two billion year old crust. Therefore, one billion year old zircon is common in Avalonian sedimentary rocks, where they were deposited as grains of sediment, and in Avalonian granitic rocks, where they were incorporated in the granitic melt as it penetrated the crust. The same is true for two billion year old zircon in West African rocks. At the latitude of Boston and to the north, existing data are indicative of the Avalon terrane. To the south, existing data are sparse and can be interpreted either way. The purpose of the proposed work is to analyze the ages of zircon grains in sedimentary and granitic rocks from the area south of the latitude of Boston to understand their origins and affinities. Where no bedrock is exposed, samples from existing drill core will be used.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

National Science Foundation (NSF)
Division of Earth Sciences (EAR)
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Dennis Geist
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Colorado School of Mines
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