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TITLE: Two Way Street at the Continent's Edge

[Photo: San Francisco's Golden Gate Bridge]
California grew when dinosaurs roamed the Earth. How? The forces that buried rocks in an ancient subduction zone returned them to the surface at the continent’s edge.

San Francisco’s Golden Gate Bridge is rooted in rock formed during subduction.


- What went down? A slab of oceanic lithosphere, topped with sea-floor and trench sediments.

- What came up? Some of these same rocks, now metamorphosed at high pressures and relatively low temperatures.

  [Photo: Blueschist, Metagraywacke, Eclogite, Lawsonite, Metaconglomerate, Glaucophane schist]

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