Sr-Nd-Mg isotopic compositions of the AD 1718 lavas from Pico volcano

Pyroxenes and olivines are significant phases that crystallise from magma and form cumulates and crystal mushes. They often exhibit thermal and chemical disequilibrium with the host rock, as evidenced by multi-analytical studies, including the textural and chemical characterisation of zoning patterns. Isotopic studies (e.g. Sr and Nd) can be crucial in revealing the history of changing conditions during their growth and ascent in different portions of a magma system. Sr-Nd and Mg isotopic ratios will be analysed in mafic minerals extracted from the magma batches erupted during the 1718 eruption at Pico Island, Azores. The aim is to identify possible mixing between the batches and to determine the role of pyroxene mushes at depth. Together with the conventional technique, microsampling using MicroMill, coupled with isotopic ratio determination by TIMS, will be carried out to measure isotopic ratios with increasing precision and at smaller length scales on zoned crystals.
In 1718, a transtensive fault opened from north to south across Pico volcano and erupted three different magmas from different sections of the fault. The goal of this study is to define the pre-eruptive petrogenetic processes that occurred in different storage areas of the volcano by the analysis of the Sr-Nd-Mg isotopic ratios of juvenile material and the crystal cargo.
This publication results from work conducted under the transnational access/national open access action supported by WP3 ILGE - MEET project, PNRR - EU Next Generation Europe program, MUR grant number D53C22001400005.

Sr-Nd isotope ratios were determined using a Thermo Finnigan Triton TI Plus multi-collector mass spectrometer in static mode on rock nad crystal powdres after chromatographic separation. Mg isotopes were measured on rock powders by the INGV-OV team. Powders from olivine and clinopyroxene crystals were obtained by microdrilling.