It goes without saying that these productions were never done alone and the people involved are systematically named, starting with C. Gautheron who opened up this world to me and guided me during my thesis.

Broad definition:

Geo-thermo-chrono-logy is a broad method/discipline/technique which, taken in a simple definition, corresponds to all temperature-sensitive geo-chronometers. This definition implies the existence of a very large number of geo-thermo-chronometers because there are very few physical phenomena, the basis of geo-chronometers, that are not affected by temperature.

In the geosciences, “low” or “high” temperature thermometers are often used to define their range of sensitivity. Note that this terminology implies a relativistic view (high and low in relation to something).

In my case, I mainly used low-temperature thermochronometers (below 200°C), a historical and methodological introduction can be found in chapter 2 of my thesis. The introductory figure shows a non-exhaustive list of some of the most common thermochronometers, and is linked to an interactive Excel chart download here.

Data processing (U-Th)/He :

The (U-Th)/He method is based on the alpha radioactive decay of uranium, thorium and samarium, which produces 4-helium nuclei.

Le fichier Excel Reduction (U-Th) l He permet de traiter les données brutes multiples et nécessaires à la méthode (U-Th(-Sm)) / He et de calculer les âges associés. Il a fait partie d’une publication en 2021 (Gautheron et al. 2021) et continue d’être mis à jour pour inclure d’autre aspect de cette méthode.

The current version includes the following options:

• U, Th and Sm: isotopic dilution, standard range, LA-ICPMS
• 4He: isotopic dilution (4He/3He), absolute
• unit: ccSTP, mol, ampere, cps

Furthermore, to calculate the ages, the Reduction (U-Th) l He file performs a linear approximation of 4He production over time. This approximation is acceptable for ages below ~250 Ma. The calculation for older ages can be carried out with the Age file (helium production with 2sd degree polynome) which recalculates the polynomial evolution of production for each sample and deduces the age.

Thermochronological data inversion :

In low-temperature thermochronology, it is common practice to invert data in order to reconstruct their thermal history, known as ‘time-temperature’. There are several software packages (HeFty, PeCube, etc.) for performing these inversions, including one that I have used in particular: QTQt.

QTQt is a software package written in C and C++ by Kerry Gallagher and published in Gallagher (2012). During my thesis and a post-doctoral fellowship under Kerry’s supervision I built several tools adjoining QTQt and facilitating its use:

• Helium files.xlsm (Excel) : help sheets for creating QTQt files
• Process QTQt.xlsm (Excel) : QTQt results extraction file
• QTQt displayer (.exe – python) :QTQt results representation software