Earth Sciences - Petrology Brunch - Dr Dan Smith - University of Leicester - The Petrogenesis of Savo volcano, Solomon Islands
Dr Dan Smith - University of Leicester
G8, School of Earth Sciences, Wills Memorial Building
We are pleased to welcome Dr Dan Smith from University of Leicester who will be delivering the Petrology Brunch:-
Title: The Petrogenesis of Sava volcano, Soloman Islands
The Solomon Islands are one of a series of volcanic arcs that mark the convergence of the Indo-Australian and Pacific Plates. The partial subduction of the Ontong Java oceanic Plateau 25–20 Ma “choked” the northern subduction zone, and led to the initiation of a southern trench with reversed polarity. The recently active Woodlark spreading ridge is being subducted at the southern trench. The history of subduction, extension, polarity reversal and ridge subduction have given rise to a number of exotic features for an arc – volcanism on the downgoing slab, forearc volcanism, and arc picrites.
Savo volcano is in the central portion of the arc, and is the easternmost of historically active volcanoes. Previous studies have described it as adakitic, derived by partial melting of the edges of the subducted Woodlark ridge, based particularly on anomalously high whole rock Sr/Y and Na. However, abundant and diverse cumulates allow for a detailed reconstruction of the petrogenesis of Savo shows that the adakitic signatures develop through fractionation from a hydrous arc basalt.
Magmatic differentiation at Savo is dominated by clinopyroxene then amphibole. Little to no plagioclase is fractionated – it is absent from the cumulates, and whole rock chemistry lacks feldspar fractionation signatures. The erupted products of Savo (lava domes and block-and-ash-flow deposits) are feldspar-phyric, pointing to closed system crystallisation of plagioclase at a late stage, potentially related to decompression and degassing at shallow crustal levels.Present-day Savo is hydrothermally active, with hot springs and ~100°C fumaroles fed by a meteoric water-dominated reservoir in the shallow subsurface. The chemistry of the fluids – in particular the stable isotopes of sulfur – indicate a magmatic component driving the ~260°C reservoir at depth. The active hydrothermal system perhaps points to a deeper, degassing package of magma at Savo.
All staff and students welcome.
For further information, please contact Dr Lena Melekhova