Martin, A.P.; Turnbull, R.E.; Roudier, P.; Cavanagh, J.; Rattenbury, M.S.; Rogers, K.M.; Vandergoes, M.J.; Reyes, L.; Gard, H.J.L.; Richardson, S.J.; Clarkson, B.R.; Kah, M. 2023 Geochemical atlas of Aotearoa New Zealand. Lower Hutt, N.Z.: GNS Science. GNS Science report 2023/23. 247 p.; doi: 10.21420/P9BK-7016
Abstract
A geochemical atlas for Aotearoa New Zealand is presented that highlights the variation in trace element concentrations in near-surface soil materials across Te Ika-a-Maui North Island, Te Waipounamu South Island and Rakiura Stewart Island. Samples were sourced from previous studies, collated from 833 sites from the top 30 cm (maximum) of soil by hand auger from across Aotearoa New Zealand. All samples were dried and sieved to <2 mm, and 15 g aliquots were analysed for a suite of 65 elements (Ag, Al, As, Au, B, Ba, Be, Bi, Ca, Cd, Ce, Co, Cr, Cs, Cu, Dy, Er, Eu, Fe, Ga, Gd, Ge, Hf, Hg, Ho, In, K, La, Li, Lu, Mg, Mn, Mo, Na, Nb, Nd, Ni, P, Pb, Pd, Pr, Pt, Rb, Re, S, Sb, Sc, Se, Sm, Sn, Sr, Ta, Tb, Te, Th, Ti, Tl, Tm, U, V, W, Y, Yb, Zn and Zr) using inductively coupled plasma mass spectrometry (ICP-MS)on aqua regia. The analytical results have undergone comprehensive quality assurance and quality control and are internally consistent and in line with typical worldwide element concentration ranges for soils. Most elements have all or most measured values above their lower method detection limit, and these elements show variation across the survey area consistent with both an anthropogenic (in particular for As, Cd, Pb, S, P) and geogenic influence. A reference split of each <2 mm sieved sample has been retained for future use, where possible. The results are presented as a series of interpolated plots using inverse distance weighted and Kriging methods, as well as plots of soil element concentration by geological subdivision and a plot of cumulative distribution function, which shows the data distribution. There are five unique plots per element and 325 unique plots in total, providing a wealth of new information regarding near-surface chemical variation across Aotearoa New Zealand. The new plots reveal a first-order geological control on Aotearoa New Zealand soil element chemistry. Of particular importance to soil element concentrations are basement terrane type, metamorphic grade and the presence of volcanic rocks such as in the Taupo Volcanic Zone. Chemical differences are marked where there is a juxtaposition of lithologies, for example, around the Alpine Fault in the northern Te Waipounamu South Island. These rocks have also contributed through their erosion to the soil element concentration of many downstream alluvial sediment sites (auths)
