Accounting for long alpha-particle stopping distances in (U-Th-Sm)/He geochronology:

I- Refinement of the baseline case

II- 3D diffusion and zoning

Cécile Gautheron and Laurent Tassan-Got

cecile.gautheron@u-psud.fr; tassango@ipno.in2p3.fr

The self-extracting and installing Windows program can be downloaded from http://hebergement.u-psud.fr/flojt/Flojt_windows.exe. The program computes the FT - ejection factor for the sphere, cylinder, ellipsoid, tetragonal, hexagonal, monoclinic and triclinic geometries (with or without pyramids, taking into account possible broken faces during sample preparation). In addition, the sphere equivalent radius for isotropic and anisotropic diffusion simulator is also associated. These interfaces are associated with the publication Gautheron and Tassan-Got, 2010; Ketcham et al., 2011 and Gautheron et al., 2011, submitted to GCA.

Ejection factors can be computed for any kind of stopping distances, homogeneous and heterogeneous U-Th distribution (i.e. zonation), and for multi-grains. The code can now be run under Windows systems using the graphical user interface, and the C++ source code is also delivered. Here is how the interface looks like:

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To be run, you need to launch the self-extracting executable Flojt_windows.exe and two interfaces calculating the equivalent radius for isotropic and anisotropic diffusion (Qt_SV), and the FT ejection calculator (Qt_FT) will be installed automatically. As the QT libraries and utilities are embedded in the distribution, no QT installation is needed and you can run directly our calculation.

For apatite and zircon (U-Th)/He, you can directly have the FT factor, if you choose apatite or zircon medium and alpha list = ThU with a Th/U ratio (you can add a mean value of 1 for example).

In case of apatite and hexagonal geometry, to be run, the L value should always be smaller than the W times the square root of 3.

If you have access to the zonation information, you can enter the number of zonation areas, the size and the ratio eUrime/core, from the surface to the core. The eU information is from 0 to 1.

For example:

- Depleted rim of 20 micron, 2 time depleted, you should enter number 1 ratio=0.5 and size=20micron, number 2 ratio=1 size=20micron (at least).

- Enriched rim of 20 micron, 2 time enriched, you should enter number 1 ratio=1 and size=20micron, number 2 ratio=0.5 size=20micron (at least).

More informations can be found in the help menu. However, if you have any problem to download or use the program, do not hesitate to contact us.

Acknowledgments:

These interfaces are part of the ANR-06-JCJC-0079 project granted to C. Gautheron. We would like to warmly thank Damien Barbosa for the QT interface creation.

References :

Ketcham et al., 2011; Accounting for long alpha-particle stopping distances in (U–Th–Sm)/He geochronology: Refinement of the baseline case. GCA, doi:10.1016/j.gca.2011.10.011

Gautheron et al., 2011; Accounting for long alpha-particle stopping distances in (U–Th–Sm)/He geochronology: 3D diffusion, zoning, implantation, and abrasion, submitted to GCA.

Gautheron and Tassan-Got, 2010; A Monte Carlo approach of diffusion applied to noble gas/helium thermochronology, Chem. Geology, doi:10.1016/j.chemgeo.2010.02.023