Sm-Nd Model Age (T2DM) Grid (felsic igneous rocks) July 2024

This is an interpolated grid of Nd two-stage model ages, based on whole-rock Nd isotopic analyses from felsic magmatic rocks, particularly focusing on I- and A-type granites and volcanic rocks. The data provides an estimate of the timing of extraction from the mantle of the middle to lower crustal source regions from which the felsic melts were generated. The point data used for the interpolation is the “felsic igneous rock” subset of the Sm-Nd data held in the Isotopic Atlas as of July 2024. Point data added to the Isotopic Atlas after July 2024 is not represented in this grid. The grid is a Natural Neighbours interpolation with a cell size of 0.01 degrees, generated using the nn C code library published at https://github.com/sakov/nn-c. Two classifications are provided for this grid; a Jenks natural breaks classification with ten classes (classification 1) as per Champion (2013) http://pid.geoscience.gov.au/dataset/ga/77772, and; the same nine-class interval binning and colour scheme applied to the source point data in the Sm-Nd Isotope Data layer (classification 2).