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Inverse modelling to unravel the radiogenic isotope signature of mantle sources from evolved magmas; the case study of Ischia Volcano

Martina Casalini, Arnd Heumann, Sara Marchionni, Sandro Conticelli, Riccardo Avanzinelli and Simone Tommasini
Inverse modelling to unravel the radiogenic isotope signature of mantle sources from evolved magmas; the case study of Ischia Volcano
Italian Journal of Geosciences (October 2018) 137 (3): 420-432

Abstract

The active volcano of Ischia, the well-known island off-shore the city of Naples, has had a discontinuous volcanic activity characterised by caldera-forming paroxysmal eruptions, lava flows, and lava domes for >150 kyr. The overall geochemical composition of erupted magmas includes shoshonite, latite, and trachyte/trachyphonolite. In a complementary study, we demonstrated that the evolution of Ischia trachytes with Sr <100 ppm occurred in a closed system environment, and depicted a scenario contemplating a complex magma chamber reservoir made up of multiple melt lenses isolated by largely crystalline mush portions. Here, we focus on the origin of the radiogenic isotope (Sr, Nd, Hf, Pb) signature of Ischia latites and trachytes with 100< Sr <800 ppm, in the context of the recent Neapolitan District volcanic activity, and bearing in mind that no parental mantle-derived magma outcrops at Ischia. Parental mantle-derived basalts with MgO > 10 wt.% outcrop a few kilometers apart at Procida island, and suggest that the evolved latites and trachytes at Ischia might have originated by crustal assimilation processes affecting Procida basalts. However, Energy Constrained Assimilation and Fractional Crystallisation modelling sets robust constraints against this hypothesis and provide geochemical arguments for a pristine mantle-derived radiogenic isotope signature for trachytes and latites, implying that they also evolved from parental basaltic magmas in a closed-system environment akin to trachytes with Sr <100 ppm. This result corroborates the model presented in the complementary study, suggesting a complex magma chamber reservoir formed by isolated magma batches with distinct radiogenic isotope compositions that evolved along similar liquid lines of descent and are separated by crystal mush zones. The Sr, Nd, Pb, and Hf isotope composition of Ischia latites and trachytes suggests metasomatic enrichment of a MORB-type asthenospheric mantle source by composite supercritical liquids originating from the altered oceanic basalt and pelagic sediment of the subducting Adriatic-Ionian slab. The results obtained on Ischia latites and trachytes, can be tentatively extended to the entire Neapolitan District volcanic system with important consequences for the isotopic signature of the mantle source and volcanic hazard assessment.


ISSN: 2038-1719
EISSN: 2038-1727
Coden: BOGIAT
Serial Title: Italian Journal of Geosciences
Serial Volume: 137
Serial Issue: 3
Title: Inverse modelling to unravel the radiogenic isotope signature of mantle sources from evolved magmas; the case study of Ischia Volcano
Affiliation: Universita degli Studi di Firenze, Dipartimento di Scienze della Terra, Florence, Italy
Pages: 420-432
Published: 201810
Text Language: English
Publisher: Societa Geologica Italiana, Rome, Italy
References: 95
Accession Number: 2019-004692
Categories: Isotope geochemistryIgneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables
N40°42'00" - N40°46'60", E13°50'60" - E13°58'00"
Secondary Affiliation: German Research Centre for Geosciences, DEU, GermanyCNR, Istituto di Geoscienze e Georisorse, ITA, Italy
Country of Publication: Italy
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Abstract, Copyright, Societa Geologica Italiana. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 2019
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