@article{b5b532144bf3490096438a3d507e234e,
title = "A New Correction for He Loss Applied to (U-Th)/He Dating of Grains with Complex Shapes and Polymineralic Aggregates",
abstract = "Applying the (U-Th)/He chronometer to small domains with complex shapes is challenging because of He recoil loss. The development of date correction factors proves challenging when considering either a single grain with complex geometry or polymineralic crystal aggregates composed of many small U-Th-bearing grains with additional impurities, such as iron-oxide aggregates. We introduce a new geometrical metric for the recoil loss correction factor—the two-point correlation distribution S2(r)—that is independent of dimensionality (i.e., two-dimensional [2-D] or three-dimensional [3-D] images), grain shape, and existence or absence of internal porosity. S2(r) measures the probability of finding two points within the target phase (U-Th-He host, such as Fe oxides here) separated by a distance r in the physical sample (single grain or aggregate). It provides a metric that is independent of grain or aggregate size. We use a combination of forward recoil loss simulations in 2-D and 3-D domains (both complex single grains and aggregates) to show a one-to-one correspondence between a recoil loss factor and S2(r = He stopping distance). We illustrate the workflow to retrieve the loss factors for different isotopes and correct date determination in a complex 3-D jasperoid sample imaged by X-ray computed microtomography. Our jasperoid sample contains appreciable amounts of iron oxide with quartz impurities and is representative of a sample for which completely monomineralic separates cannot be obtained. The computation of loss factors based on S2(r) is extremely efficient, and the codes, including a simple user interface, are made available at https://repository.library.brown.edu/studio/item/bdr:957056/.",
keywords = "aggregates, complex grains, geochronology, recoil loss",
author = "Christian Huber and William Guenthner and Hamid Karani",
note = "Funding Information: We thank Alexis Ault (Utah State University) for sharing some of her Fe‐oxide SEM imagery with us and Jenna Kaempfer (UIUC) for help with preparing the Fe‐oxide grain for micro‐CT analysis. We thank Leilei Yin and Cate Wallace at the Beckman Institute (UIUC) for their assistance with micro‐CT analysis and Mayandi Sivaguru at the Carl R. Woese Institute for Genomic Biology (UIUC) for assistance with micro‐CT image processing. The authors are grateful to Cecile Gautheron, Richard Ketcham, and Matthew Fox for helpful and constructive comments and to editor Janne Blichert‐Toft for handling the manuscript. W. G. acknowledges support from NSF‐EAR Grant 1641138 for micro‐CT and SEM work at UIUC. Codes are available and archived at the Brown Digital Repository, Brown University Library, https://repository.library.brown.edu/studio/item/bdr:957056/ , and a user manual is also available at the Brown Digital Repository, Brown University Library, https://repository.library.brown.edu/studio/item/bdr:957057/ . Funding Information: We thank Alexis Ault (Utah State University) for sharing some of her Fe-oxide SEM imagery with us and Jenna Kaempfer (UIUC) for help with preparing the Fe-oxide grain for micro-CT analysis. We thank Leilei Yin and Cate Wallace at the Beckman Institute (UIUC) for their assistance with micro-CT analysis and Mayandi Sivaguru at the Carl R. Woese Institute for Genomic Biology (UIUC) for assistance with micro-CT image processing. The authors are grateful to Cecile Gautheron, Richard Ketcham, and Matthew Fox for helpful and constructive comments and to editor Janne Blichert-Toft for handling the manuscript. W. G. acknowledges support from NSF-EAR Grant 1641138 for micro-CT and SEM work at UIUC. Codes are available and archived at the Brown Digital Repository, Brown University Library, https://repository.library.brown.edu/studio/item/bdr:957056/, and a user manual is also available at the Brown Digital Repository, Brown University Library, https://repository.library.brown.edu/studio/item/bdr:957057/. Publisher Copyright: {\textcopyright}2019. American Geophysical Union. All Rights Reserved.",
year = "2019",
month = dec,
day = "1",
doi = "10.1029/2019GC008475",
language = "English (US)",
volume = "20",
pages = "5744--5764",
journal = "Geochemistry, Geophysics, Geosystems",
issn = "1525-2027",
publisher = "American Geophysical Union",
number = "12",
}