A ring dike is an intrusive igneous body. Their chemistry, petrology and field appearance precisely match those of dikes or sill, but their concentric or radial geometric distribution around a centre of volcanic activity indicates their subvolcanic origins.
Well known examples
- One of the best exposed and studied ring dikes is the Loch Bà ring dike, Isle of Mull, Scotland
- The ring dikes in the Pawtuckaway State Park and the Ossipee Mountains of New Hampshire.
- The Pilanesberg Game Reserve in the North West Province of South Africa
- The Ring of Gullion in southern County Armagh, Northern Ireland
Ossipee Mountains ring dike complex
Alex MacPhail writes “…This is a recent geologic diagram of the Ossipee Ring (Dike) Complex from a paper written and presented by G. Nelson Eby, University of Massachusetts, Lowell, MA, and Ben Kennedy, McGill University, Montreal, QC, Canada. In their introduction they state that “Ossippee has played a central role in models dealing with the origin of ring dikes (Billings, 143, 1945; Chapman, 1976) and has long been considered a classic example of a ring-dike complex.” They also state that the ring dike is part of the Younger White Mountain igneous province and between 130-100 million years old. In this province, in addition to the Ossipee Ring Complex, they write that “the largest intrusive complex is the White Mountain batholith which consists of multiple ring dikes intruded into by composite plutons.””