The Appalachian Fold and Thrust Belt of Southern New England: Tectonic Petrology of Massachusetts

Massachusetts includes numerous units of volcanic, igneous intrusive, metamorphic, and sedimentary rock formed within the last 1.2 billion years ago (bya). The oldest formations are gneiss rocks in the Berkshires metamorphosed from older rocks during the Proterozoic Grenville orogeny as Laurentia collided against proto South America. Through the Paleozoic, a series of six island arcs collided with Laurentian continental margin. These sections of continental rock typically formed offshore or onshore of Gondwana which in many cases experienced volcanic events and faulting before joining the Laurentian continent. These sequential collisions metamorphosed new rocks from sediments creating uplands and faults resulting in widespread volcanic activity. Simultaneously, these collisions raised the Appalachian Mountains to the current height of the Himalayans.

Warped and faulted basins formed in eastern Massachusetts preserving coal from massive Paleozoic swamps while preserving fossil plants and insects. The final phases of mountain building occurred when Laurentia collided with Gondwana and Europe to form the supercontinent called Pangea. Beginning around 200 million years ago (mya), rifting broke apart Pangea. Erupting basalt lavas formed new oceanic crust of the Atlantic Ocean wedging apart Africa, Europe, and North America along the approximate lines where the continents orginally collided. The Connecticut River Valley and the Middleton Basin formed as failed rifts filling with sediments that preserved dinosaur footprints. Following Jurassic time, Massachusetts experienced long running and continuous erosion with the absence of volcanic activity and low level seismicity. The Appalachians shed sediments eastward, accumulating as the Atlantic Coastal Plain of Massachusetts.

Rapid cooling of the planet in the last 2.5 million years of the Quaternary resulted in one mile thick ice sheets advancing south accelerating erosion. Pleistocene glaciation rechanneled rivers and created large sedimentary deposits including the terminal moraines on Cape Cod, Martha's Vineyard, and Nantucket. Hundreds of smaller drumlins, eskers, and kame deposits were formed.

Chapter 1 presents the general geology of Massachusetts, paleo-tectonic, and structural history. Chapter 2 begins the regional geology discussion with the Berkshire Massif. Chapter 3 discusses the Rowe-Hawley zone and the Connecticut River Valley belt. Chapter 4 continues with eastern Massachusetts geology discussion of the Milford-Dedham zone and its paleo-tectonics. Chapter 5 presents the Nashoba zone and its enigmatic terrane including the Massabesic Gneiss Complex. Chapter 6 presents the Merrimack belt stratigraphy. Chapter 7 ends with a summary and conclusion on the structural and metamorphic history of Eastern Massachusetts.