Helium-strontium isotope constraints on mantle evolution beneath the Roman Comagmatic Province, Italy

Martelli, M., Nuccio, P.M., Stuart, F.M. , Burgess, R., Ellam, R.M. and Italiano, F. (2004) Helium-strontium isotope constraints on mantle evolution beneath the Roman Comagmatic Province, Italy. Earth and Planetary Science Letters, 224(3-4), pp. 295-308. (doi: 10.1016/j.epsl.2004.05.025)

Abstract

A study of the He isotopic ratios of fluid inclusions in olivine and pyroxene from the Roman Comagmatic Province (RCP), Italy, is presented together with ⁸⁷Sr/⁸⁶Sr isotope compositions of the whole rock or pyroxene phenocrysts. A clear covariation in He and Sr isotopes is apparent, with a strong northward increase in radiogenic He and Sr being evident. He and Sr isotopes ratios range from ³He/⁴He=5.2 <i>R</i>_a and ⁸⁷Sr/⁸⁶Sr=0.7056 in south Campania, to ³He/⁴He=0.44 <i>R</i>_a and ⁸⁷Sr/⁸⁶Sr=0.715905 in the northernmost Latium. Helium isotope ratios are significantly lower than MORB values and are among the lowest yet measured in subduction zone volcanism. The ³He/⁴He of olivine and pyroxene phenocryst-hosted volatiles appear to be little influenced by posteruptive processes and magma-crust interaction. The ³He/⁴He–⁸⁷Sr/⁸⁶Sr covariation is consistent with binary mixing between an asthenospheric mantle similar to HIMU ocean island basalts, and an enriched (radiogenic) mantle end member generated from subduction of the Ionian/Adriatic plate. The contribution of radiogenic He from metasomatic fluids and postmetasomatism radiogenic ingrowth in the wedge is strongly dependent on the initial He concentration of the mantle. Only when asthenosphere He concentrations are substantially lower than the MORB source mantle, and metasomatism, occurred at the beginning of the subduction (~30 Ma), can ingrowth in the mantle wedge account for the ³He/⁴He of most radiogenic basalts.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Ellam, Professor Rob and Stuart, Professor Fin
• Authors: Martelli, M., Nuccio, P.M., Stuart, F.M., Burgess, R., Ellam, R.M., and Italiano, F.
• Subjects: Q Science > QE Geology
• College/School: College of Science and Engineering > Scottish Universities Environmental Research Centre
• Journal Name: Earth and Planetary Science Letters
• ISSN: 0012-821X
• Published Online: 08 July 2004