Enhanced precision, accuracy, efficiency, and spatial resolution of U‐Pb ages by laser ablation–multicollector–inductively coupled plasma–mass spectrometry

Abstract

[1] U-Th-Pb geochronology by laser ablation -multicollector -inductively coupled plasma -mass spectrometry initiated during the mid to late 1990s as a reconnaissance tool, capable of generating ages of only moderate precision from relatively large volumes of zircon. New developments in instrumentation and experimental methodology, as described herein and by other researchers, now make it possible it to correct for common Pb accurately (using measured 204 Pb), to acquire geochronologic information rapidly (30-40 unknowns/h), to generate U-Pb ages with an accuracy of better than 1% for most zircon standards, and to conduct analyses on much smaller (e.g., 10 mm by 6 mm) volumes of material. These capabilities are driving important advances in many aspects of Earth science research.

Geochemistry of Permian to Triassic igneous rocks from northern Chile (28º-30º15’S): Implications on the dynamics of the proto-Andean margin.

“…Interelement fractionation of Pb/U is generally ~20%, whereas fractionation of Pb isotopes is generally <2%. In-run analysis of fragments of a large Sri Lanka zircon crystal (generally every fifth measurement) with known age of 564±4 Ma (2σ error) is used to correct for this fractionation (see Gehrels et al, 2008 …”

“…Analytical techniques, sample preparation procedures and standards were previously described in Chapman et al (2015) and Rossel et al (2013). U-Pb geochronology of zircons was conducted by LA-MC-ICP-MS at the Arizona LaserChron Center (Gehrels et al, 2008 Pb), and because very little Hg is present in the argon gas. Interelement fractionation of Pb/U is generally ~20%, whereas fractionation of Pb isotopes is generally <2%.…”

Geologic Setting of Eclogite-facies Assemblages in the St. Cyr Klippe, Yukon–Tanana Terrane, Yukon, Canada

“…The fourth metatonalite sample (11-98) was analyzed by laser ablation inductively coupled mass spectrometry (LA-ICP-MS) at the University of Arizona LaserChron Center using a spot size of 30 μm. Analytical procedures followed Gehrels et al (2006Gehrels et al ( , 2008. Common Pb corrections were made using 204 Pb measurements for each analysis, and initial Pb compositions of Stacey and Kramers (1975).…”

“…Common Pb corrections were made using 204 Pb measurements for each analysis, and initial Pb compositions of Stacey and Kramers (1975). U and Th concentrations and Pb/U fractionation were calibrated against the Arizona Laserchron Center Sri Lanka (SL) zircon standard (563.5 ± 3.2 Ma; ~518 ppm U and 68 ppm Th; Gehrels et al 2008). Standards were analyzed at the beginning, end, and after every 5 grains for the primary standard (SL) and after every 15 grains for the secondary standard (R33).…”

Lower Pliensbachian caldera volcanism in high-obliquity rift systems in the western North Patagonian Massif, Argentina

“…In order to obtain a precise age of the Garamilla volcanic unit in this area, one sample of the initial volcanic activity (sample DN4) was obtained from a dacitic lapilli-tuff located at 40°15'40"S and 69°5 7'35"W. From that, 33 zircon grains were recovered and analyzed for geochronology at the Arizona LaserChron Center, Department of Geosciences, University of Arizona, using the procedures described by Gehrels et al (2008). The data form a unimodal zircon distribution ( Fig.7A) comparable with the previously obtained age in the Quiñenao area (Benedini and Gregori, 2013), with a main population crystallizing between 186 and 197Ma (82.06%) and a main peak at 190Ma.…”