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U-Pb Ages, Neodymium Isotope Ratios, and Trace Element Concentrations by Laser-Ablation Split Stream (LASS) Analysis of Igneous Titanite and Apatite from Interior and Southcentral Alaska

April 24, 2025
This dataset contains U-Pb isotopic data and ages plus trace element concentrations from titanite and apatite in igneous rocks collected for USGS projects in the Alaska Range, Yukon Tanana uplands of eastern Alaska, and a study of ophiolites in Alaska. A subset of analyses also includes simultaneous measurements of Sm-Nd isotope ratios. For this subset, split-stream configuration analyzed U-Pb isotope ratios and trace element concentrations by quadrupole inductively coupled plasma mass spectrometry (Q-ICPMS), and Sm-Nd isotope ratios by multi collector inductively coupled plasma mass spectrometry (MC-ICP-MS). For other samples, where grain sizes were small (<50um mean minimum grain dimension), split-stream analysis consisted of U-Pb isotope ratios by MC-ICP-MS and trace elements by Q-ICPMS. Analyzed titanite grains were hand-picked grains, separated by traditional mineral separation techniques, mounted in epoxy, as well as in-situ analyses of titanite and apatite from sample thin sections, where grains were small and unyielding to mineral separations, or where complimentary in-situ zircon analyses (Todd et al., 2023) merited complimentary in-situ titanite analyses. The sample suite was collected as part of multiple (3) distinct geological mapping and supporting geochemical and geochronological surveys, conducted between 2013 to 2021. We also analyzed portions of previously collected igneous bedrock samples from the USGS archive (collected from 1968 to 1985), allowing expansion of the dataset to include igneous bodies that were not sampled during recent field work or were outside the area of focused project field work. Titanite was obtained from these igneous rocks to determine the crystallization age for the bedrock samples. The data tables accompanying this data release report the composition of uranium (U) and thorium (Th) measured in each grain, ratios of three isotopes of lead (206Pb, 207Pb, 208Pb), two isotopes of uranium (235U and 238U), and one isotope of thorium (232Th), as well as the calculated age of each grain, plus trace element abundances from the same ablated aliquot, including P, V, Sr, high field strength elements (HFSE), and rare earth elements (REE). Reported Nd (and Sm) isotope data includes 143Nd/144Nd and 147Sm/144Nd, and calculated epsilon Nd values, and age-corrected isotope ratios and epsilon values. A summary table includes location and sample information, plus interpreted age and Nd isotopes and parameters (when interpretable).
Publication Year 2025
Title U-Pb Ages, Neodymium Isotope Ratios, and Trace Element Concentrations by Laser-Ablation Split Stream (LASS) Analysis of Igneous Titanite and Apatite from Interior and Southcentral Alaska
DOI 10.5066/P17CRYHT
Authors Erin Todd, Andrew R.C. Kylander-Clark
Product Type Data Release
Record Source USGS Asset Identifier Service (AIS)
USGS Organization Alaska Science Center
Rights This work is marked with CC0 1.0 Universal
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