Marzo 2023

We present the results of the tephrochronology study of a 14.49 m long marine sediment core (TR 17–08) collected in the Edisto Inlet, Ross Sea (Antarctica). The core contains four cryptotephra layers at 55–56, 512–513, 517–518, and 524–525 cm of depth, which have been characterised by a detailed description of the texture, mineral assemblage, and single glass shards major and trace element geochemistry. The age model of the investigated sedimentary sequence, based on radiocarbon dating, indicates that the topmost cryptotephra correlates with the widespread 1254 CE tephra erupted by a historical eruption (696 ± 2 cal yrs BP) of Mount Rittmann, in northern Victoria Land. Deeper cryptotephra layers were derived from previously unknown explosive eruptions of Mount Melbourne volcano and were emplaced between 1615 cal yrs BP and 1677 cal yrs BP, e.g. between the 3rd and 4th centuries CE. This discovery demonstrates that the Mount Melbourne volcanic complex has been highly active in historical times allowing significant progress in the current understanding of regional eruptive history. Moreover, from a tephrochronological point of view, the detected cryptotephra provide new regional isochron markers to facilitate high-precision correlations and help stratigraphically constrain changes in environmental and climatic conditions that are identified by multidisciplinary studies.

The Quantitative X-Ray Map Analyzer software, a new tool for image processing, has been tested on intertwined pumices and scoriae emitted during the two paroxysmal eruptions of Stromboli of 2019, whose textural and compositional heterogeneities reflect the coexistence of low porphyritic shoshonitic-basalts and high porphyritic shoshonites. The procedure applied was designed to quantitatively document the complex variations in texture and composition of these products, allowing substantial time reduction of analytical and data processing. The procedure utilizes Principal Components Analysis and supervised Maximum Likelihood Classification for multivariate statistical data handling of an array of X-ray elemental maps acquired at the millimeter scale in thin-sections. This technique permits the production of high-contrast colored images, which allow the classification of rock constituents, extrapolating the associated modal abundances and imaging chemical variations within the glass. Results highlight the close interconnection at the microscale of two types of magma in the erupted products, manifested in each processed image by the presence of contiguous areas preserving textural bulk properties typical of the pumice or scoria. The proportion of the two magmas feeding the eruptions is not simply represented by the proportions of scoria and pumice in individual clasts, as both scoria and pumice contain glass with the composition of shoshonitic-basalts and shoshonites. This method also allows the recognition of important discordances between the textural and chemical features of the two fractions involved, as well as discernment of the compositions of the two interacting magmas at the microscopic scale, even in those micro-domains showing evidence of intense interaction processes.