The establishment of oceanic andesites tectonic environment discrimination diagrams with big data method.

Geochemical elements of magmatic rocks often indicate their tectonic environments. Previous geologists used tectonic environment discriminant diagrams to describe their correlation. However, it is too challenging to apply discriminant diagrams to identifying the tectonic environment of andesites because of their complexity of petrogenesis and the unicity of their tectonic environment. Based on the GEOROC and PetDB databases, the authors intergrated the global Cenozoic oceanic andesites with three categories:mid-oceanic ridge andesites (MORA), oceanic island andesites (OIA) and island arc andesites (IAA). With 924 element ratios consisting of any two of 43 elements, the authors built more than 420, 000 rectangular coordinate systems. 4 optimal discriminant diagrams were sifted by calculating overlap ratios among the three types of oceanic andesites:lg(Ba/Nb) versus lg(Ga/Cs), lg(Eu/Pb) versus lg(TFeO/Ga), lg(Ga/Cs) versus lg(K₂O/Nb) and lg(Cs/Nb) versus lg(MnO/Pb). The elements and element ratios were analyzed by comparing the kernel densities of the three types of andesites, with some conclusions reached:(1) The ratio of LILE and HFSE can effectively differentiate MORA and IAA; (2) the ratio of LILE and other elements is useful to identifying OIA from the other two types; (3) in a certain degree, LILE is more appropriate for determining tectonic environments of oceanic andesites than HFSE. This study presents that andesite is likely to be a widely used indicator of tectonic environments, which might be more appropiate than basalt discriminant diagram. It further indicates that even the andesite genesis is much more complicated than basalt, big data method is an effective approach to extract the correlation with tectonic discriminant significant.