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Passive margins and their terminal collisions through Earth history

Passive margins and their terminal collisions through Earth history. Dwight Bradley U.S. Geological Survey. Conclusions about passive margins Passive margins are not known before the Neoarchean

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Passive margins and their terminal collisions through Earth history

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  1. Passive margins and their terminal collisions through Earth history Dwight Bradley U.S. Geological Survey

  2. Conclusions about passive margins • Passive margins are not known before the Neoarchean • As far back as the Neoarchean, most passive margins have ended their tenure by colliding with an arc • Peaks in the passive margin population at 1900 Ma, 550 Ma, and today correspond to times of continental dispersal • Lulls at 1750-1000 Ma and 300 Ma correspond to known (Pangea) or inferred supercontinents • Unexpectedly, the seven longest-lived margins are Precambrian. No evidence for short lifespans in Precambrian • Age distribution of blueschists and foredeep magmatism attests to real secular change in style of arc-passive margin collision, but does not require a fundamentally different tectonic regime

  3. Mechanisms for greater heat loss Longer ridge system ( = more plates) Faster spreading with modern-size plates (after Pollack, 1997)

  4. Modern passive margins • 94,000 km aggregate length • oldest one is ~175 m.y.

  5. Ancient passive margins • 55 margins so far, Neoarchean to Neogene • compilation still in progress

  6. Wopmay Orogen— Paleoproterozoic arc-passive margin collision Hoffman & Bowring, 1981

  7. SELECTED PASSIVE MARGINS

  8. Karlstrom, 2005 Laurentian NE-trending Proterozoic accretionary provinces– one of the most voluminous accretionary orogens in Earth history

  9. Conclusions about passive margins • Passive margins are not known before the Neoarchean • As far back as the Neoarchean, most passive margins have ended their tenure by colliding with an arc • Peaks in the passive margin population at 1900 Ma, 550 Ma, and today correspond to times of continental dispersal • Lulls at 1750-1000 Ma and 300 Ma correspond to known (Pangea) or inferred (Columbia) supercontinents • Unexpectedly, the seven longest-lived margins are Precambrian. No evidence for short lifespans in Precambrian • Age distribution of blueschists and foredeep magmatism attests to real secular change in style of arc-passive margin collision, but does not require a fundamentally different tectonic regime

  10. The End Taconic orogeny, forebulge unconformity, Newfoundland

  11. The Mesoproterozoic gap in passive margin that collided with an arc is either: An artifact a. compilation incomplete b. recognition problems 2. Real a. no plate tectonics b. plate tectonics but somehow different

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