Structural state of smectite and mixed layer

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Crater mechanics and structural characteristics
NIRworkshop Gardnos/Gol, Norway, June 8 11
Structural state of smectite and mixed layer
smectite-illite minerals as temperature
indicator in impact induced hydrothermal
systems example of Ries crater Peeter Somelar,
Nele Muttik and Kalle Kirsimäe
University of Tartu, Department of Geology,
Estonia
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Clays and clay minerals
hydrated (alumo)silicates with sheet-like
structure form by alteration of primary
silicates (but not only) the composition,
structure and morphology of clay minerals
depends on temperature fluid
composition pH, Eh etc clays can be used
for reconstruction of environmental
variables/conditions
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Formation of clay minerals
H
temperatuere / time
K
Mg2
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Results XRD
17.0 -17.21Å
Surficial suevites Montmorillonite type smectite
fully expandable in ethylene glycol (EG)
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Results XRD
16.48 -16.95 Å
Crater fill suevites Mixed-layer
illite-smectite Random ordering (R0) 90of
smectite layers 10 of illite layers
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Results XRD
d values in surficial smectites ranges from
17.0 to 17.21 Å The crater fill
matherial Illite-smectites 16.48 to 16.95 Å
(Å)
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Results XRD Modeling
Surficial suevites
measured modelled
MLM2C code (Plancon and Drits 2000)
R-04 lt2µm, EG Depth 385.8m
S 95 I 5
Crater fill matherial
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Summary
mixed-layer smectite-illite mineral with random
ordering (R0) The surficial suevites are
without any exception the fully expandable Al-Fe
montmorillonite (smectite) minerals The
crater fill material shows up to 5-10 of illitic
layers There is no clear observable tendency
of the expandablity changing with the depth of
the samples analysed however, the mixed
layering indicates the initial phase of the
illitization, probably at elevated temperatures
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Conclusions
the heating (lifetime of the hydrothermal
activity) must have been relatively short
Illitization of smectite in bentonites
(originally volcanic glass) occurs at 70 C
and the mixed-layer I/S structural ordering
transition from R0 to R1 at 35S at temperatures
150 C The temperatures did not exceeded
150 C The estimated temperatures of 70-150
C according to illitization are, however, in
good accordance with the fluid temperatures
(range from 60 to 120 C) according to stable
isotope composition
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Thanks for listening!