East Coast of North America: Classic Passive Margin

Definition

A passive margin is the transition between oceanic and continental crust that is not an active plate boundary. It forms when continents rift apart, creating a new ocean basin.

Formation of the Atlantic Margin

• ~200 Ma (Early Jurassic): Pangaea breaks up; North America separates from Africa.
• Rifting thins continental crust, creates basin that becomes Atlantic Ocean.
• Thermal subsidence forms broad coastal plain and continental shelf.
• No subduction, volcanism, or major earthquakes along the margin itself.

Key Features

• Wide continental shelf (e.g., Georges Bank, Blake Plateau).
• Thick sedimentary sequences (potential hydrocarbon reservoirs).
• Barrier islands, estuaries, drowned river valleys (Chesapeake, Delaware Bay).
• Low seismicity compared to active margins (e.g., West Coast).

Contrast: Active Margin

West Coast of North America = convergent/transform boundary (subduction, volcanoes, frequent quakes).