Timescales of quartz crystallization estimated from glass inclusion faceting using 3D propagation phase-contrast x-ray tomography: examples from the
Bishop (California, USA) and Oruanui (Taupo Volcanic Zone, New Zealand) Tuffs
V31C-2801
Ayla Pamukcu (ayla.s.pamukcu@vanderbilt.edu)1, Guilherme A. R. Gualda (g.gualda@vanderbilt.edu)1, Alfred T. Anderson, Jr. (canderso@uchicago.edu)2
1Department of Earth and Environmental Sciences, Vanderbilt University; 2Department of Geophysical Sciences, The University of Chicago
BACKGROUND
Glass Inclusion Faceting & Timescales
RESULTS
Geology/Samples
Faceting & Residence Times
1.55
(b)
•
•
Oruanui Tuff
The extent to which a glass inclusion is faceted can be used as a proxy for residence time of a crystal. Quartz is
ideal for studies of glass inclusion faceting because Si is the only diffusing element.
Taupo Volcanic Zone, New Zealand
•
Eastern California, USA
•
Erupted ~26.5 ka, 10 phases
•
Erupted ~760 ka, many phases classified
broadly into early- and late-erupted
deposits (Wilson & Hildreth, 1997)
500
~530 km3 of ash fall, pyroclastic density currents,
and intracaldera material
•
•
Large inclusions facet more slowly than smaller inclusions - greater volume of material to diffuse
Inclusions near center of crystal will be more faceted than those at edge - included for a longer time
Samples:
• P1577 (ash fall)
• ORN-016 (ash fall)
• ORN-067 (ash fall)
Propagation Phase-Contrast X-ray Tomography
Propagation phase-contrast tomography provides a new way to study glass inclusions in situ and in 3D. Edgeenhancement permits quantification of glass inclusion geometry, with a slight decrease in image resolution.
Images obtained here have 2.77 μm/voxel resolution, such that inclusions >10 voxels (~30 µm) in one
direction can be quantitatively resolved, though smaller inclusions can be qualitatively resolved.
a.
b.
Glass Inclusion Shapes
50
45
40
Abundance
35
d.
•
Samples (all early-erupted):
• BB08-21b (ash fall)
• BC17-Ia15 (ignimbrite)
• F8-15 (ash fall)
25
P1577 n = 35
ORN-016 n = 1
ORN-067 n = 72
BB08-21b n = 69
BC17-Ia15 n = 71
F8-15 n = 109
P1577 n = 35
ORN-016 n = 1
ORN-067 n = 75
BB08-21b n = 70
BC17-Ia15 n = 72
F8-15 n = 110
20
30
25
20
15
10
0
1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0+
Blue: volume representing the
intersection of inclusion and
ellipsoid; Red: excess volume of
inclusion; Green: excess volume of
ellipsoid
0
17
Aspect Ratio (Max/Min Axis)
•
500 μm
f.
5
5
Edge-detected absorptioncontrast tomographic image
e. 3D rendering of inclusion circled in
b & d. Inclusion (solid) is overlain
with a fitted ellipsoid (dotted).
1.05
SNSVR = 1
104
105
106
•
•
Increasing aspect ratio indicates more
elongation of inclusions.
ORN-067 inclusions are more elongated
than those in Bishop and other Oruanui
samples.
20
25
30
35
40
45
50+
Equivalent Radius (μm)
•
•
F8-15 inclusions are dominantly more
spherical (peak between 1.0-1.2) and are
generally more spherical than inclusions in •
other Bishop and Oruanui samples.
1.15
1.05
ENSVR = 1
0.95
103
107
P1577
ORN-016
ORN-067
BB08-21b
BC17-Ia15
F8-15
104
105
106
107
Inclusion Volume (μm3)
Partially Faceted
•
Large SNSVR values indicate faceted or elongate inclusions.
Large ENSVR values indicate faceted inclusions.
•
Generally, smaller inclusions have larger SNSVR/ENSVR values smaller inclusions are more faceted than larger inclusions.
•
Scatter in SNSVR values reflects more elongated shape of some
inclusions (see Glass Inclusion Shapes).
•
All inclusions are faceted to some extent (ENSVR, SNSVR >1).
•
Most small inclusions are fully faceted (lie on 1:1 line), but
larger inclusions are not fully faceted (lie above 1:1 line).
•
Residence times must be greater than those recorded by fully
faceted inclusions but less than those recorded by partially
faceted inclusions.
400
300
200
P1577
ORN-016
ORN-067
BB08-21b
BC17-Ia15
F8-15
100
0
0
100
200
300
400
500
600
CONCLUSIONS
1. Propagation phase-contrast x-ray tomography can be used successfully to image glass inclusions in quartz crystals. Image
resolution of 2.77 μm/voxel allows inclusions with a volume greater than 1000 voxels (~21,000 μm3) to be quantitatively
resolved and measured. Inclusions smaller than this size can be qualitatively resolved.
2. Glass inclusions show a wide array of aspect ratio in both Oruanui and Bishop Tuff samples. Inclusions in Oruanui sample
ORN-067 are more elongate in shape than in other samples from both systems. Inclusions in F8-15 are dominantly more
spherical in shape and are more spherical than inclusions in other Oruanui and Bishop samples.
15
d. Edge-detected propagation phasecontrast tomographic image
f.
High-silica rhyolite
Glass Inclusion Sizes
10
e.
•
RESULTS
a. Standard absorption-contrast
tomographic image
c.
1.15
Time To Fully Facet (a)
b. Standard propagation phasecontrast tomographic image
c.
~1000 km3 of ash fall, ignimbrite, and
intracaldera material
99% high-silica rhyolite, 1% more mafic material
•
1.25
Bishop Tuff
•
Both size and position of a glass inclusion within a crystal influence the extent to which an inclusion will facet in
a given time interval:
1.35
Inclusion Volume (μm3)
600
•
1.45
0.95
103
Above: Long Valley Caldera and earlyand late-erupted Bishop Tuff outflow
deposits
(from Manville & Wilson, 2004)
Faceting of glass inclusions occurs over time at magmatic temperatures through dissolution and reprecipitation. This volume transported by this process is ΔV.
•
•
Right: Oruanui ash fall deposits
Time To Observed Shape (a)
•
Left: Oruanui ash flow deposits
Abundance
−𝑅𝑇
∆𝑡 =
∆𝑉
8𝜋𝐷𝐶𝑜 𝜎Ω
Ellipsoid-normalized surface area –tovolume ratio (ENSVR)
Sphere-normalized surface area –tovolume ratio (SNSVR)
(a)
1.25
Equivalent radius = radius of a sphere of the same
volume as a given inclusion. Minimum resolvable
inclusion has equivalent radius of ~17 μm.
BC17-Ia15 and F8-15 have a greater abundance of
inclusions than the BB08 and Oruanui samples.
Sample F815 has a noticeably greater abundance of
large inclusions than other samples.
Size distribution and abundances of ORN-067
inclusions are similar to that of BC17-Ia15 and F8-15
samples. P1577 and BB08-21b samples have
noticeably fewer inclusions.
3. Bishop Tuff samples have a greater abundance of inclusions, particularly sample F8-15, which has a strikingly large number
of large inclusions.
4. SNSVR and ENSVR values for both Oruanui and Bishop samples suggest smaller inclusions are more faceted than larger
inclusions and that all inclusions are faceted to some extent.
5. Many small inclusions in both the Oruanui and Bishop Tuffs are fully faceted, but larger inclusions are not yet entirely
faceted. The residence times calculated from the excess volumes of the inclusions and the best fit ellipsoid (volume
transported during faceting) suggest residence times of 101-103 a (including 2σ error) in both Oruanui and Bishop samples.
ACKNOWLEDGEMENTS This work was funded by an NSF EAPSI to A. Pamukcu and NSF EAR-1151337 to G. Gualda. Use of
the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of
Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357. Additional
thanks go to M. Rivers for assistance at APS.