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How did island arcs and microcontinents add land to North America during the Jurassic Period?

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Jurassic paleogeography — Jurassic Period Distribution of landmasses, mountainous regions, shallow seas, and deep ocean basins during the late Jurassic Period. Included in the paleogeographic reconstruction are the locations of the interval's subduction zones.

During the Jurassic Period, the western margin of North America was defined by an active subduction zone where oceanic plates slid beneath the continental plate. Because island arcs and microcontinents carried on these oceanic plates were less dense than the subducting crust, they could not be pulled into the mantle.123

As these fragments reached the subduction zone, they were sutured onto the North American continent through a process known as accretionary tectonics. This collision of exotic terranes—geologic fragments that often originated in distant, tropical regions—contributed significantly to the growth of the continent and its mountain chains.3124

This tectonic activity culminated in events like the Nevadan orogeny, which involved the collision of volcanic island arcs with the continent from northern California to British Columbia. These collisions resulted in intense deformation, the emplacement of massive igneous batholiths, and the accretion of deep-sea sedimentary rocks, effectively stitching these displaced fragments into the western edge of North America.1254