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Plate Tectonics Origins & Orogenic Processes: Evidence from Isua, Greenland

This article explores the beginnings of plate tectonics and orogenic processes based on evidence from the Isua region in Greenland, including the presence of accretionary complexes, water depth, and the composition of basalt. It discusses the rigidity of oceanic plates, orogenic processes at plate boundaries, dissimilarities in temperature and viscosity, and the formation of orogenic belts and continents. The article also examines the change in plate tectonics style over time and provides modern analogs and processes observed in orogenic belts worldwide.

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Plate Tectonics Origins & Orogenic Processes: Evidence from Isua, Greenland

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  1. When did plate tectonics start? Ans. Since 4.0 Ga Maruyama, S. (Tokyo Inst. Tech., Japan) Content Geology of Isua (3.8Ga), Greenland, (1) presence of accretionary complex (horizontal stress field same as today), (2) presence of water >1000m, and (3) AMORB is FeO-rich basalt, source T, 200K higher than today, and 2 wt% more FeO-rich than today. 2. Calculation of how rigid was the oceanic plate; thinner plate (40km vs 50km at 50Ma) with thicker crust (15-20km vs 6-7km) 3. Orogenic process at plate boundary, same as today (TTG formation & accretionary complex) 4. Dissimilarity, higher-T (200K higher, lower viscosity, double-layered mantle convection) 5. Orogenic belts over the world, i.e., island arcs, size of orogenic belt, collision-amalgamation to form continents

  2. Dissimilarity • Dissimilarity, higher-T (200K higher, lower viscosity, double-layered mantle convection) • 5. Orogenic belts over the world, i.e., island arcs, size of orogenic belt, collision-amalgamation to form continents

  3. Change of style of plate tectonics • Archean style; young-hot buoyant subduction due to double-layered convection • Mantle overturn (2.8-2.7Ga) • Paleoproterozoic (2.3-0.7Ga); superplume, supercontinent-pPV cycle • Phanerozoic (0.7Ga-present);Cold subduction zone

  4. ■ Orogenic belts of the world

  5. Modern analog • Western Pacific underlain by wet mantle with Archean viscosity • Numbers of microplates (700km across, double-layered convection) • Numbers of intra-oceanic arcs (70% of all arcs) • Arc collisions to form a primitive continent

  6. ■ Orogenic belts of the world

  7. Consuming plate boundary process • (1)Pacific-type accretionary complex • (2)Presence of ocean>1000m (pillowed basalt) • (3)Followed by TTG plutonism • (4)OPS tells origin of magma, MORB, OIB, or ARC, then source mantle T ＆ X

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