A Quiet Maine Island With a Billion-Year-Old Secret

geologyprecambrianmainedeep-timegeochronology

Abstraction: 700 Acre Island in Penobscot Bay contains Maine's oldest rocks at 1.8 billion years

Key points:

700 Acre Island's rocks date to ~1.8 billion years old — Maine's and potentially New England's oldest — confirmed via uranium-lead zircon dating in 2014
Parent igneous material formed ~1.8 Ga; the ancient beach it eroded into is probably no younger than 1 billion years old
Similar-age quartzites appear along Morocco's coast, suggesting a once-shared landmass before Iapetus Ocean closure ~400 Ma
Rocks underwent deep burial (up to ~10 miles) and metamorphism, then uplift via erosion, resulting in today's metasedimentary outcrops
Most of Maine's bedrock is under 500 million years old; this formation is an anomalous outlier
University of Maine Farmington professor Doug Reusch and Maine Geological Survey senior geologist Henry Berry are leading ongoing detailed mapping

Connections: Geochronology · Plate Tectonics · Precambrian Geology