A NEW MATLAB©-BASED HELIUM MODELING PACKAGE (“HeMP”) FOR THERMAL HISTORY RECOVERY FROM SINGLE AND MULTI-THERMOCHRONOMETER (U-TH)/HE DATA AND DATA ARRAYS

With the proliferation of thermochronometric techniques, increasing effort has been invested into quantitative recovery of continuous thermal histories. Inverse modeling of thermochronometric ages is a well-established method and has been commonly used for apatite fission-track data to model t-T evolutions with a number of available software packages, based on the comparison of observed and modeled data derived from randomly generated t-T paths. While excellent software for inverse modeling of single sample (U-Th)/He ages is available (e.g., HeFTy), none can currently model multi-sample arrays (e.g., vertical transect, boreholes, etc.). We present a new comprehensive Matlab® (U-Th)/He modeling software package (HeMP) that allows inverse modeling of (U-Th)/He thermochronometric data from either single samples or vertical sample arrays to recover thermal histories. HeMP is a versatile (U-Th)/He modeling software developed to meet the modeling needs of the (U-Th)/He community, using standard He production and finite difference diffusion equations (Ketcham, 2005), that incorporates parent nuclide zoning through a He redistribution approach, grain size variation, and [eU] variation, implementing recently published models for radiation damage influence on He diffusion kinetics. In addition to single or multiple thermochronometer inverse modeling of single samples, the major components of HeMP include (1) a forward model for vertical arrays of (U-Th)/He ages and more importantly (2) a module for inverse modeling of single or multiple thermochronometer 1-D sample arrays (e.g., vertical transects and boreholes). The multi-sample inverse modeling is based on generation of random thermal histories combined with temperature offsets derived from vertical sample spacing and user-defined brackets of geothermal gradients to evaluate modeled (U-Th)/He ages with all observed ages. This approach yields improved thermal histories by leveraging the entire vertical age distribution and also sheds light on possible geothermal gradients consistent with the data. HeMP, however, does not incorporate 2-D or 3-D variations in the thermal field or transient geothermal gradients. The software is not intended solely as a research tool, but is also suited for teaching purposes in geo- and thermochronology classes.