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Did Modern Subduction Zones Appear in the Late Archean?

Did Modern Subduction Zones Appear in the Late Archean?. Kent C. Condie Department of Earth and Environmental Science New Mexico Tech Socorro, NM 87801 USA. POSSIBLE PLATE TECTONIC RETURNS. 2. Symmetric Subduction. 1. Asymmetric Subduction. 3. Plate Sinking. OCEANIC PLATEAUS.

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Did Modern Subduction Zones Appear in the Late Archean?

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  1. Did Modern Subduction Zones Appear in the Late Archean? Kent C. Condie Department of Earth and Environmental Science New Mexico Tech Socorro, NM 87801 USA

  2. POSSIBLE PLATE TECTONIC RETURNS 2. Symmetric Subduction 1. Asymmetric Subduction 3. Plate Sinking

  3. OCEANIC PLATEAUS ISLAND ARCS Pillow basalts Mafic intrusions Andesites Breccia-tuff Felsic volcs Graywackes Boninites Pillow basalts Mafic-ultramafic intrusions Picrites Komatiites Minor felsic volcs OPHIOLITES Pillow basalts Sheeted dykes Mafic intrusions Harzburgite-dunite Serpentinite Plagiogranite Podiform chromite

  4. LATE ARCHEAN GREENSTONES Mafic Plain (Plume) Types Arc Types Modern Arcs

  5. LATE ARCHEAN GREENSTONES Mafic Plain (Plume) Types Arc Types

  6. ARC CALDERA VOLCANSIM & LATE PLUME ACTIVITY ABITIBI GREENSTONE BELT 2700 Ma Courtesy of Wulf Mueller

  7. EVOLVING TECTONIC REGIMES Arc n = 1 n = 28 n = 35 Plume n = 9 n = 25 n = 18 > 3 Ga 2.5 - 3 Ga 1.0 - 2.5 Ga

  8. OCEANIC PLATEAUS

  9. LATE ARCHEAN GREENSTONES Arc-Type Plume-Type

  10. Zr/Nb-Nb/Th in Greenstone Basalts Arc n = 1 (n = 2) n = 16 n = 19 Plume n = 9 n = 11 n = 6 > 3 Ga 2.5 - 3 Ga 1.0 - 2.5 Ga

  11. SIGNIFICANCE OF CONVERGENT PLATE ASSEMBLAGES A Few occurrences does NOT necessarily mean modern subduction was global A high frequency of occurrence reflects widespread distribution (BUT this assumes a representative sample)

  12. 3.0 2.5 2.0 1.5 1.0 0.5 0 AGE (Ga) Ophiolites 2.5 Ga ? 2.0 Ga Island Arcs 3.0 Ga Oceanic Plateaus 3.5 Ga TECTONIC SETTINGS IN TIME

  13. FLAT TO STEEP SUBDUCTION Abbott et al. 1994 Geology 22: 937-940

  14. Steep Subduction 3.0 - 2.5 Ga Flat Subduction 4.5 - 3.0 Ga Symmetric Subduction > 4.5 Ga ?

  15. Depth (km) Pressure (Gpa) Temperature (ºC)

  16. SUMMARY • Plate tectonics, in some form, probably existed on planet Earth from the magma ocean stage onwards. • Modern type subduction became important beginning in the Late Archean. • Ancient tectonic regimes should be constrained only by a convergence of multidisciplinary evidence. • It is easier to criticize someone else’s tectonic model than to create your own.

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