GSA DATA REPOSITORY 2012117
O’Brien and van der Pluijm
Relative abundance procedure
To determine the proportion of clast in the matrix, at least two polished rock-chips were
cut perpendicular to veins for scanning electron microscopy (SEM) imaging. 500X SEM images
were collected from areas that contained minor amounts of clasts, which are preferred for Ar
analyses to best constrain the age of friction melting. Following the methodology of Warr et al.
(2007), the relative abundance of clasts was measured by determining the area of clasts by
tracing grains that lie within the 500X image using the imaging program SigmaScan Pro5. To
confirm the proportion of clasts in each sample, a second cut was made perpendicular to the
original rock-chip and the process is repeated. The difference between corresponding cuts was
always less than one percent, so the results were averaged for each of the samples analyzed.
Clast proportions between two perpendicular cuts vary by only a few tenths of a percent, and no
obvious trends of decreasing or increasing clast volume with depth into the vein.
Table DR1. CLAST PROPORTION AND AGES
% clast
(AVG) TGA (±2σ)
Sample #
exp(l.t) -1
TOQ50203(enp)
TOQ50203-1
20 663.9 ± 1.8
0.44484171
TOQ50203-2
13 648.2 ± 1.7
0.43232251
TOQ50203-3
10 641.82 ± 1.86 0.42726614
TOQ50203-4
10 641.49 ± 1.64 0.42700509
TOQ50203-5
9 634.98 ± 2.22 0.42186503
TOQ50203-6
9 634.7 ± 1.63
0.42164437
TOQ50204-1
16 655.6 ± 2.13
0.43820971
TOQ50204-2
18 659.53 ± 2.23 0.44134611
TOQ50204-3
10 640.4 ± 1.83
0.42614317
TOQ50204-4
13 644.45 ± 1.89 0.42934834
Note: All ages provided are total-gas ages except when indicated by an (R). Avg = average;
enp = encapsulation.
Figure DR1:
Figure DR2: