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Westerman lasi iv

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LASI 4 PowerPoint presentation, Moab, UT

LASI 4 PowerPoint presentation, Moab, UT
Fall 2010

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    Westerman lasi iv Westerman lasi iv Presentation Transcript

    • Waves-ropes-lobes, fluidizationand deformationat laccolith-host contacts(Elba Island, Italy)
      David S. Westerman – Norwich University, VT, USA
      Andrea Dini – IGG-CNR, Pisa
      Sergio Rocchi - Universitàdi Pisa, Pisa
      EmanueleRoni - Universitàdi Pisa, Pisa
      Ethan J. Thomas - Norwich University, VT, USA
    • low-anglegravitational-tectonicfaulting
      1 km
      1 km
      CEF
      complex V
      complex IV
    • 5
      SAN MARTINO LACCOLITH (2)
      (Dini et al., 2006)
      • Reconstructed laccolithic shape (diameter ~ 8.3 km)
      • 3 tabular layers (thickn. = 700 m)
      • 3 identified dikes
      • Inferred filling time: <100 years
      • Emplacement: depths 2-3.5 km
      • Filling and growth modalities (geometric study):
      2 stage filling: sill + inflation (Rocchi et al., 2002, Geology)
      Layer 3
      Layer 2
      Layer 1
    • San Martino Porphyry
      layers map out as sheets
      Portoferraio Porphyry
    • geometric forms
      Waves – simple crests and troughs ranging from strongly pointed crests with open troughs to rounded crests and V-shaped troughs
      Ropes – extreme example of rounded crests and V-shaped troughs with wave heights and lengths of similar dimensions
      Lobes – similar in form to load casts and pillows
    • large waves against fluidized serpentinite
      (“fluidized” is used to describe the complete loss of competency in water-rich host rock rock)
    • small waves against fluidized shale
      phenocrysts stretched perpendicular to rounded crests and troughs
    • multiple waves patterns
      Rounded crests and V-shaped troughs
    • small pointed crests against fluidized flysch
    • ropes – the extreme V-troughs
    • lobes – wave interference?
      (“load casts”; “pillows”)
      basal contact – roof of cave
      ramp contact against fluidized flysch
      basal “load casts”
    • deformation structures
      linear strain – stretched quartz and feldspars
      disruption structures
      porphyry breccia-mylonite
      host breccia
      breccia dikes in poprhyry
      breccia dikes in host
    • linear strain at contacts
      1.57
      1.41
      1.00
      - lineations very common when waves are present
      - characteristically oriented perpendicular to crests and troughs
      - both quartz and feldspar phenocrysts are stretched, often by a factor of 10x!
      - this exceeds realistic stretching from wave growth by inflation
      ex: a side of a square stretched to a 90° arc adds only 11%
    • linear strain parallel waves & decreases inward
      sense of strain consistent – inflation would produce opposite sense on opposing limbs of crests
    • myloniticfabricsmost brittle at contact, grading to plastic toward magma
    • disruption structures
      fluidized breccia invading porphyry
    • fluidized contact breccia at porphyry base
    • fluidized contact breccia
      Pp
      ss
    • fluidized host dike in porphyry
    • mixed porphyry-ophiolite-flysch-breccia dike invading flysch host
    • summary
      waves, set up by two fluids flowing past each other, are the rule where host material is fluidized
      extreme fluidization leads to breccia contacts and, ultimately, to breccia dikes both in porphyries and their host rocks
      strong linear fabrics develop parallel flow in chilled porphyry and adjacent host rock, with decreasing strain away from the contact