Sr-Nd Isotopic Composition of Pyroxenes as a Provenance Indicator of a Double-Volcanic Source in Sands of the Ofanto River (Southern Italy)

Paola Donato,Federica Totaro,Raffaella Silvia Iovine,Mariano Tenuta,Massimo D’Antonio,Rosanna De Rosa

doi:10.3390/min12020232

Abstract

The sands of the Ofanto River (Southern Italy) include a volcaniclastic component represented by clinopyroxene, melanite garnet, amphibole and subordinate volcanic lithics. In order to infer the provenance of this component, we have conducted a microanalytical and isotopic study on the volcanic minerals of the sands collected in three different sites along the Ofanto River: (1) upstream sector, where only sedimentary rocks are drained; (2) middle course, along a tributary draining only the Monte Vulture volcanic rocks, (3) the mouth of the Ofanto. Moreover, minerals of the beach sands of the Tyrrhenian Cilento coast were analyzed for comparison. The microanalytical study and the Sr-Nd isotopic composition reveal the existence of two populations of pyroxenes characterized by distinct isotopic signatures and indicating a provenance from two different volcanic sources. One is confidently identifiable with Monte Vulture, and is evident in the minerals of the middle course and mouth sands. The pyroxenes of the upstream sector, isotopically similar to those of the Cilento coast, have a Campanian signature. The simultaneous occurrence of amphibole and garnet point to the explosive eruptions of Mount Vesuvius as the most probable sources of these minerals. The absence of Campanian pyroxenes at the mouth of the Ofanto River could be related to the occurrence of dams limiting the transport of solids along the river.

Highlights

The Cenozoic magmatic rocks of Italy show extremely variable radiogenic and stable isotopic signatures (e.g., [1] and references therein)
The results of combined mineral chemistry and Sr-Nd isotopic characterization point to the identification of a double volcanic source that contributed to the heavy mineral fraction of the sands of the Ofanto River (Southern Italy)
Monte Vulture for sands of the central and final sectors of the river, and from the Campanian volcanoes for sands of the upstream area. For this river sector, located at less than 100 km from the Campanian volcanoes, the occurrence along with the clinopyroxene of amphibole and garnet suggested that Vesuvius was the most likely volcanic source

Summary

Introduction

The Cenozoic magmatic rocks of Italy show extremely variable radiogenic and stable isotopic signatures (e.g., [1] and references therein). A decrease in 87 Sr/86 Sr, δ18 O, δ13 C and 3 He/4 He ratios and an increase in 143 Nd/144 Nd and 206 Pb/204 Pb from northwest to southeast is observed (e.g., [2,3] and references therein) Despite this wide heterogeneity at the scale of the whole peninsula, each Italian magmatic province exhibits rather restricted and distinct isotopic signatures [1,3]. This allows the use of isotopic compositions as a tool to infer the provenance of volcanic material (glass, whole rock or minerals) in the Italian Peninsula and Mediterranean area, in tephrostratigraphic (e.g., [4,5,6]) and archaeometric studies of pottery made from volcanic rocks as raw material (e.g., [7]). In the central part of its course, the river and its tributaries drain through the volcanic rocks of

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