Upper Neoproterozoic series in the Central Iberian, Cantabrian and West Asturian Leonese Zones (Spain): Geochemical data and statistical results as evidence for a shared homogenised source area

Abstract

Analyses (100) of six groups of Upper Neoproterozoic shales from different areas in Central and Northern Spain covering an extension of over 60,000 km 2 reveal relatively uniform major and trace element abundances and values of relevant ratios such as Al 2O 3/TiO 2, K 2O/Al 2O 3 (mol), Ti/Zr, Ti/Nb, Rb/Zr, Rb/Th, Sm/Nd, Eu/Eu*, (La/Yb) n, La/Nb, Zr/Y, Zr/Nb, Th/Nb, Th/Yb, Th/U, and Cr/Zr. The six groups of shales define indistinguishable chondrite-normalised and upper continental crust-normalised patterns for rare earth and trace elements, respectively, and show relatively low fractionated geochemical features compared with those of the continental upper crust. Statistical calculations demonstrate a normal distribution of the abundances of major and trace elements and element ratios , they suggest a remarkable geochemical homogeneity for the Upper Neoproterozoic series studied and they separate this series from the Lower Cambrian one in the Central Iberian Zone on the basis of 15 element ratios. The extension of the Upper Neoproterozoic detrital series and the similar geochemical features of shales in all the studied areas suggest an extensive and homogenised source region. Thus, the mean of the 100 analyses (Neoproterozoic Iberian Average Shale: NIBAS) is proposed as a standard of comparison to identify the specific recycled and homogenised source for detrital Upper Neoproterozoic sediments in Central and Northern Iberia and probably also in other European peri-Gondwanan areas. The ranges of statistically distinctive geochemical parameters separating the Upper Neoproterozoic from the Lower Cambrian series are given as possible criteria to help in the studies of areas where no other data provide conclusive information about the series’ ages.