Appendix I - ANALYTICAL TECHNIQUES (for Online Supplement)
Sample Locality for CPP-02-01
The study area is on the border of Maine and Quebec within the Boundary Mountains. It
focuses on the CPP, a subdivision of the Seven Ponds pluton mapped by Harwood (1973) and
shown in Fig. S1. The CPP is a Devonian biotite-hornblende granodiorite that intrudes the Chain
Lakes massif, an Early Ordovician metasedimentary sequence (Gerbi et al. 2006). The CPP is
one of three Devonian plutonic bodies: the Big Island Pond pluton, a quartz monzonite, south of
the CPP, also part of Harwood’s (1973) Seven Ponds pluton; and the Spider Lake Granite, west
of the CPP. The CPP is concentrically zoned with a center that is fine- to medium-grained
granodiorite and a rim of coarsening hornblende, and Na-feldspar phenocrysts. Contact
metamorphism is observed overprinting the regional metamorphism, as an aureole around the
CPP, which was mapped by Harwood (1973) as having mineral assemblages grading from
sillimanite to andalusite to biotite. Post Devonian units in the area (Harwood 1973) are
lamprophyre dykes that intrude the Ordovician metasediments of the Chain Lakes massif and the
Devonian plutons.
Fieldwork for the project was completed by one of us (JMH) with the assistance of Dr.
Dan R. Lux, from the University of Maine, who located the collection site of CPP-02-01 at the
exact site of sample MH-10 from Heizler et al. (1988), the “domain” archetype of Lovera et al.
(1991), Fitz Gerald and Harrison (1993) and Lovera et al. (1993).
Mineral Separation
The rock was crushed in a disk mill. Grain size separates were obtained by sieving
between 300 and 250 µm, 180 and 150 µm, and 125 and 90 µm sieve openings. In the following
they will be referred to by their median grain radii, viz. 137, 82, and 54 µm, respectively.
The sieved material was separated into portions weighing ca. 50 g by dividing each
sample using an analytical splitter. Initial mineral separation was carried out on each grain size
separate using bromoform that has a specific gravity of 2.85 g/mL in order to float quartz,
plagioclase and Kfs away from biotite, amphibole, titanite and other dense accessory minerals.
K-feldspar was further separated using a solution of bromoform and acetone having a specific
gravity of 2.60 g/mL (monitored using a hydrometer accurate to 0.001 g/mL) so that quartz and
plagioclase sank while Kfs floated. Mounting random grains on a glass slide under a CLmicroscope, where Kfs luminesces blue, tested separation purity; plagioclase luminesces green
and quartz does not luminesce.
CL imaging of grains (Fig. S2) revealed that a separate containing 100% Kfs was
impossible to obtain by mechanical means (magnetic and gravimetric), even after
experimentation with various heavy liquid densities. As it is well known that mineral purity has a
decisive influence on the shape of age spectra (Turner et al. 1971), we resorted to handpicking,
aided by staining. Each of the three grain size separates was split into two aliquots. One half of
each sample was submerged in BaCl2 for 15 seconds, rinsed with deionized water and bathed in
rhodizonic acid for 5 minutes. This procedure stained plagioclase light red, allowing an easy
assessment of Kfs purity for handpicking. Handpicking was performed on the basis of very
inclusive a priori criteria: only grains whose shape or color were obviously devious were
discarded, while uncertain-looking grains were tolerated. The other aliquot was left unpicked
after the mechanical separation. In total, six fractions were produced: the handpicked and
unpicked aliquots of fractions with a = 54, 82, and 137 µm.
Cathodoluminescence Imaging
In addition to imaging of grain mounts, the thin section of CPP-02-01 was also imaged by
cathodoluminescence (CL). Cathodoluminescence microscopy was performed using a PATCO
ELM-3 Cathodoluminoscope at Memorial University. Operating conditions were 12 kV and
0.7mA, a vacuum of 50–70 mTorr, and an unfocused beam. Images were acquired using a
KAPPA DX-30C Peltier cooled charge-coupled device (CCD) camera and KAPPA Image
software. All CL images were acquired using consistent red-green-blue (RGB) settings so that
CL colors could be directly compared between samples.
Electron Probe Microanalysis and Back-scattered Electron Imaging
The electron microprobe analyses were completed and BSE images were acquired using a
JEOL JXA 8900 electron probe microanalyzer (EPMA) with five wavelength dispersive
spectrometers running JEOL software at the University of Maryland-College Park. The CITZAF
matrix correction algorithm of Armstrong (1995) was used for all analyzes. The operating
conditions used were an accelerating voltage of 15 kV, a Faraday cup current of 20 nA, and a
defocused beam diameter of 20 µm. The Kα X-ray lines were used for Na, Al, Si, K, Ca and Ti,
and the Lα X-ray line was used for Ba. The count time used for all elements on the unknowns
was 30 s on peak and 10 s on each background. The primary standards used were natural
orthoclase for Na, Al, Si, K, and Ba, and Kakanui, New Zealand, hornblende (USNM 143956)
for Ca and Ti, and were measured 10 s on peak and 5 s on each background. Natural orthoclase
and ilmenite were also analyzed as calibration materials.
40Ar/39Ar Analysis
The six sized Kfs aliquots from JH-02-01 were wrapped in aluminum foil and irradiated
at the McMaster nuclear reactor in Hamilton, Ontario, Canada, avoiding any Cd shielding. Fortynine days after irradiation, analysis commenced at the University of Bern, using a MAP™ 21550B noble gas mass spectrometer connected to a Heine resistance oven by an all-metal
purification line. The thermocouple providing temperature measurements was on the outside
bottom of the crucible; thermocouple readings were routinely calibrated by melting pure metal
foils. Step heating schedules are listed in Table S2 together with all Ar isotope concentrations.
Furnace temperature was kept within 1 °C of target temperature, and was not allowed to drop
between heating steps (Huneke et al. 1969). Active gases were removed by three SAES™ C-50
getters.
Transmission Electron Microscopy
Two TEM foils were cut using a focused ion beam (FIB) instrument from the sample
CPP-02-01 thin section, guided by previously acquired BSE and CL images at the HelmholtzZentrum Potsdam Deutsches GeoForschungsZentrum (GFZ). An “unaltered” sample, referred to
as TEM foil 1, was cut from the dark blue emission CL; and an “altered” sample, TEM foil 2,
was cut from the light blue CL emitting region along a grain boundary with plagioclase. Details
of FIB sample preparation can be found elsewhere (Wirth 2004, 2009).
The TEM imaging and EDAX were performed at the GFZ utilizing a FEI TECNAI F20XTwin transmission electron microscope operating at 200 keV with a Schottky field emitter as
electron source. The TEM is equipped with a Gatan energy Filter Tridiem™, a Fishione highangle annular dark field detector and an EDAX X-Ray analyzer with ultrathin window.
Analytical TEM was performed with an EDAX X-Ray analyzer in scanning transmission
mode (STEM) to minimize mass losses during spectra acquisition. Typical acquisition time was
60 seconds with the sample tilted 15° towards the detector. The X-ray detector is a Si-Li detector
with ultra thin window. Data evaluation occurred applying the TIA software package from FEI.
Semiquantitative analyses were calculated from the spectra using the k-AB factors from the TIA
software package.
REFERENCES
Armstrong JT (1995) CITZAF: A package of correction programs for the quantitative electron microbeam X-ray
analysis of thick polished materials, thin films, and particles. Microbeam Analysis 4: 177-200.
Gerbi C, Johnson S, Aleinikoff J (2006) Origin and orogenic role of the Chain Lakes massif, Maine and Quebec.
Can J Earth Sci 43: 339-366.
Harwood DS (1973) Bedrock geology of the Cupsuptic and Arnold Pond quadrangles, west-central Maine. US Geol
Surv Bull 1346: 1-90.