The daughter-parent plot: A tool for analyzing thermochronological data

Abstract

Data plots of daughter against parent concentration (D-P plots) are a potential tool for analyzing low-Temperature thermochronology, similar to isochron plots in radioisotopic geochronology. Their purposes are to visualize the main term of the radiometric age equation-the daughter-parent ratio-and to inspect the daughter-parent relationship for anomalies indicating influences of geological processes or analytical bias. The main advantages of the D-P plot over other data analysis tools are (1) its ability to detect systematic offsets in D and P concentrations, (2) its unambiguous representation of radiation-damage-dependent daughter retention, and (3) the possibility to analyze potential age outliers. Despite these benefits, the D-P plot is currently not used for analyzing low-Temperature thermochronology data, e.g., from fission-Track, (U-Th) / He, or zircon Raman dating. We present a simple, decision-Tree-based classification for daughter-parent relationships based on the D-P plot that places a dataset into one of seven classes: linear relationship with zero intercept, cluster, linear relationship with systematic offset, nonlinear relationship, several age populations, scattered data, and inverse relationship. Assigning a class to a dataset enables choosing further data analysis steps and how to report a sample age, e.g., as a pooled, central, or isochron age or a range of ages. This classification scheme aims at facilitating thermochronological data analysis and making decisions more transparent. We demonstrate the proposed procedure by analyzing published datasets from a variety of geological settings and thermochronometers and introduce Incaplot, which is graphical user interface software that we developed to facilitate D-P plotting of thermochronology data.