The Structure Update

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The Structure Update

• Large Scale Geophysical Structure
• Structure of Kitlope Range

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Hollister and Andronicos in Preparation
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Summary

• Western Belt is Thin and Fast (Vp)- basalt/gabbro
• Coast Belt is thicker, but still thin, and slower
  (Vp) diorite and granulite/restite
• Intermontane Belt is thickest, and slowest,
  granodiorite with amphibolite at base
• Boundary between Western Belt and Coast Belt is
  vertical-CSZ
• Boundary between Coast Belt and Intermontane belt
  is gradational

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Central Gneiss Complex in the Kitlope Range

• Composed of amphibolite facies migmatite and
  amphibolite
• Intruded by two distinct plutonic bodies, an
  older diorite and a younger granodiorite

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Map pattern dominated by second generation folds
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S1 Fabric
L1 Lineation
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S2 Fabric
L2 Lineation
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Left Lateral shears
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Right Lateral shears
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Mean Shears
Mean ShearsS2 Foliation
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Timing of shearing and folding
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Granodiorite intrudes diorite, during shearing
and folding
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Gneissic fabric in Granodiorite
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Weakly Deformed Enclaves in Granodiorite with
magmatic fabric
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Low angle extensional shears
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Summary

• Amphibolite and feldspathic gneiss isoclinally
  folded into recumbent (?) folds
• Intruded by diorite deformation field unknown
• Granodiorite intruded, sheared and folded into
  steeply plunging isoclinal folds
• F2 folds and associated shears record
  northeast-southwest horizontal shortening and
  northwest-southeast extension (strike slip
  strain)
• Low angle shear zones cut all structures

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Wright Sound
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Low Strain
High Strain
Low Strain
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Sheath Fold
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Cross section
Folds tighten towards the shear
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Shear directed increasing strain
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NW
SE
S
C
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Shear directed increasing strain
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Foliations rotate into parallelism With Shear
Zone
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Data Region
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Ecstall Pluton
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Grenville Channel Shear Zone

• The shear zone was active during emplacement of
  the Ecstall Pluton at 90 Ma
• It is a left lateral transpressive shear zone
• Shear zone will likely be seismically transparent
  (steep fabrics over great distance)

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