TEXTURAL AND MICROANALYSIS OF IGNEOUS ROCKS: TOOLS ...

crystals using a New Wave UP-213 UV laser ablation system interfaced with a
ThermoFinnigan Element 2 ICP-MS operated in fast magnet scanning mode at
the University of Notre Dame. I used a laser frequency of 4 Hz, pulse energy of
0.02-0.03 mJ pulse −1 , 12 µm or 20 µm diameter pits depending on crystal size,
and helium as the carrier gas (∼ 0.7 l min −1 ) mixed with argon (∼ 1.0 l min −1 )
before introduction to the plasma. Analyses were conducted in peak jumping
mode with one point quantified per mass. The LA-ICP-MS spots were coincident
with previous EPMA analyses, and Ca measured by EPMA was used as an inter-
nal standard for each spot analysis. The trace element glass NIST 612 was used
as a calibration standard in all laser ablation analyses. Although heterogeneity
for certain elements has been documented in the widely used NIST 612 glass i.e.,
[44], Eggins et al. [44] considered it a reliable calibration standard for Sr, Ba, Y,
and the REE. The methods of Longerich et al. [88] and Norman et al. [112] were
used to reduce LA-ICP-MS data and calculate analytical uncertainty for each spot
analysis (Table 2.1).
2.4.2 Data Quality
The quality of EPMA data were monitored by major element and cation totals.
Data points where major element totals were greater than 101.5% or less than
98.5% are not used in further discussion nor are points with cation totals greater
or less than 20 ± 0.1 cations (based on 32 O). All laser ablation analyses were
collected in time-resolved mode so that signal from inclusions and alteration filled
fractures could be easily excluded. Results from laser ablation spots close to
fractures or that penetrated into underlying fractures were discarded. The rate of
laser ablation was tested using a 100 µm thick plagioclase wafer prior to sampling,
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