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Igneous Rocks and Plate Tectonics

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Igneous Rocks and Tectonics. Igneous rock formation largely tied to tectonic activity ... Mafic to intermediate batholiths (Gabbro, diorite) 8 ... – PowerPoint PPT presentation

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Title: Igneous Rocks and Plate Tectonics


1
Igneous Rocks and Plate Tectonics
  • Igneous Petrotectonic Assemblages

2
Igneous Rocks and Tectonics
  • Igneous rock formation largely tied to tectonic
    activity
  • 3 main tectonic settings for making igneous rocks

3
Igneous Rocks at Divergent Margins Mid-Ocean
Ridges
  • Magma origin
  • Partial melting of ultramafic, fertile mantle
    rock (lherzolite)
  • Decompression melting due to mantle convection
  • Magmatic processes
  • Mantle melting produces dominantly primitive,
    mafic magma (basalt) magma may be modified
    slightly by fractional crystallization
  • Rocks structures
  • Ophiolite suite
  • Cool and crystallize in magma chamber
  • Erupted onto sea floor as effusive lava flows or
    pillows

4
Igneous Rocks at Divergent Margins Mid-Ocean
Ridges
5
Igneous Rocks at Divergent Margins Continental
Rifts
  • Magma origin
  • Partial melting of ultramafic mantle rocks
  • Decompression melting due to rise of material in
    a hot spot (?)
  • Magmatic processes
  • Initial mantle melting produces primitive,
    mafic magma (basalt)
  • Magma accumulates in chambers
  • Fractional crystallization, contamination produce
    intermediate (andesite) and feslic (rhyolite)
    magmas
  • Rocks structures
  • Highly varied
  • Dominated by bimodal volcanic activity
  • Early basalt lava flows, shield volcanoes,
    cinder cones
  • Later rhyolite flows and calderas (ignimbrites)
  • Also mafic through felsic plutons

6
Igneous Rocks at Convergent Margins
  • Ocean-Continent Plate convergence
  • Continental arcs
  • Ocean-Ocean Plate convergence
  • Ocean Island arcs

Recycled magmas!
  • Continent-Continent Plate convergence

7
Igneous Rocks at Convergent Margins Ocean Island
Arcs
  • Magma origin
  • Water released from subducting slab due to T-P
    increase
  • Flux melting (partial) of overlying ultramafic
    mantle rocks
  • Magmatic processes
  • Initial melting produces mafic magma (basalt)
  • Basalt magma rises into crust fractional
    crystallization, melting and assimilation of
    crust modifies composition (intermediate
    andesite)
  • Rocks structures
  • Dominantly andesite stratovolcanoes (Ring of
    Fire)
  • Mafic to intermediate batholiths (Gabbro, diorite)

8
Igneous Rocks at Convergent Margins Continental
Arcs
  • Magma origin
  • Water released from subducting slab due to T-P
    increase
  • Flux melting (partial) of overlying ultramafic
    mantle rocks
  • Magmatic processes
  • Initial melting produces mafic magma (basalt)
  • Basalt magma rises into crust fractional
    crystallization, melting and assimilation of
    crust modifies composition (intermediate to
    felsic)
  • Rocks structures
  • Dominantly andesite to rhyolite stratovolcanoes
  • Rhyolite calderas and ignimbrites (tuffs)
  • Vast intermediate to felsic batholiths
    (granodiorite, granite)

9
Igneous Rocks at Convergent Margins Continental
Collisions
  • Magma origin
  • Crustal thickening due to thrust faulting during
    collision
  • Causes partial meting of crustal rocks (anatexis)
  • Magmatic processes
  • Magma composition depends largely on the source
    rocks that were melted
  • Dominantly felsic composition
  • Rocks structures
  • Extensive batholiths and plutons of mostly felsic
    composition (granite)
  • Compression and thick crust prevent eruption
    volcanoes rare

10
Igneous Rocks at Hot Spots
  • Magma origin
  • Partial melting of ultramafic mantle rocks
  • Decompression melting due to rise of hot material
  • Magmatic processes
  • Initial mantle melting produces primitive,
    mafic magma (basalt)
  • Heat from mafic magma can melt overlying crustal
    rocks, producing felsic magmas
  • Rocks structures
  • Initial flood basalts erupted from fissures
    (associated dikes)
  • Oceanic basalt lava flows, shield volcanoes,
    cinder cones
  • Continental bimodal (basalt-rhyolite) volcanic
    activity rhyolite calderas and ignimbrites
  • Also mafic through felsic plutons
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