Geology Reference
In-Depth Information
333
100
Area of grains
Area of subgrains
150
x
= 2.7 mm
2
x
= 6.05 mm
2
100
50
50
0
0
0.5
3
5.5
8
10.5
13
5
15
25
35
Area (mm
2
)
45
55
65
75
Area (mm
2
)
Major axis
Major axis of grains
150
150
x
= 4.5 mm
100
x
= 3.4 mm
100
50
50
0
0
5.5
8
10.5
135
7911
13
15
17
19
22
26
0.5
3
13
Major axis length (mm)
Major axis length (mm)
Minor axis
Minor axis of grains
100
80
60
40
20
0
150
100
x
= 1. 1mm
x
= 1. 6mm
50
0
0.5
2
3.5
5
6.5
8
9.5
0.1
0.7
1. 3 .9
2.5
3.1
3.7
Minor axis length (mm)
Minor axis length (mm)
Figure 4.45
Probability distribution of (
left
) macroscopic parameters
fo
r grains and (
right
) subgrains corresponding
to the objects that appear in Figure 4.44. Mean values are shown as
x
[adapted from
Johnston and Sinha,
1995].
(a)
(b)
Grains of thin section
Subgrains of thin section
25
16
14
12
10
8
6
4
2
0
y
= 2.6992×
0.9497
R
2
= 0.7419
y
= 2.7995×
0.9176
R
2
= 0.5424
20
15
10
5
0
0
2
4
6
8
10 2
0
2
4
6
Minor axis length (mm)
Minor axis length (mm)
Figure 4.46
Correlation of the major and minor axes lengths of (a) grains and (b) subgrains for the images in Figure 4.44
[
Johnston and Sinha
, 1995].
subgrains is rather poor. However, as a first approach,
the regressed plots of minor versus major axes lengths for
both grains and subgrains may be represented adequately
by a ratio of length to width approximating 2.5:1. These
results provide a statistically based support for the obser-
vations made by
Weeks and Hamilton
[1962] on grains in
young sea ice at Point Barrow in Alaska. The authors
reported a ratio of 2:1 for the sidewise to edgewise growth
of individual grains. As the brine drains out of the FY ice,
many demarcation lines in the intragranular spaces seem
to disappear. This applies particularly to the rows of brine
pockets along the subgrain boundaries with extremely
small lattice mismatch.
A systematic set of results on geometric characteristics
of FY columnar ice formed in Allen Bay (Canadian cen-
tral Arctic) is presented in
Johnston
[1998]. An example is
presented in Figure 4.47 from an ice core obtained from
site 3 shown in Figure 4.33. Ice was formed in a confined
area bordered by land on three sides under calm oceanic
conditions. This resulted in formation of fast ice with
