Ice Fabrics

Fabrics in Ice Thin section

Clear ice vein crosscuts foliation

Faintly aligned fabric of ice crystals + bubbles

defined by bubble clustering

Clear Ice
Vein in t/s

cuts across foliation

irregular edges due to deformation

formed as even walled body metamorphically incorporated into ice

Firn as Sediment Analogue

Sediment on seafloor

Remains porous for some time

Retains connection with seawater

Has geochemical implications

Glacial Ice Evolution

  1. Snow deposited in layers - very porous
  1. Firn forms

Recrystallised into denser granular material

Partly compacted snow - open & porous

Open porous structure

communicates w/atmos &surface

pores trap air

  1. Glacial ice forms ~ 60-110m

Bubbles pinched off ∴ isolated from atmosphere

Gas pressure now = lithostatic pressure (~overburden)

Climate archive in gas etc.

Ice with isolated bubbles

Processes snow--> ice

Surface
ρ ~ 550 kg/m3

Firn grains rearranged to achieve more dense packing

Greater depth
~ 60-110 m

Plastic deformation
= most important transformation process
(not rearrangement)

ρ > 800 kg/m3

Pores become isolated

i.e. mechanisms primary foliation evolution

Mechanical Consequences
Ice Evolution

Fabric develops as snow column compacted

  1. Ice crystals assume very particular c-axis orientation
  1. Coarsening with increasing depth

influences mechanical response to strain

Fine
grained
rock

Has substantially larger surface area (vs coarse)

--> Influences all processes reliant on grain boundaries

i.e. favouring metamorphic processes
--> fluid migration occurs along grain boundaries

Shown by grain size profiles & lattice preferred orientations