Intraplate Basalt Alkalinity Modulated by a Lithospheric Mantle Filter at the Dunedin Volcano (New Zealand)

• Published in: Journal of Petrology
• Main Authors: Pontesilli, Alessio, Brenna, Marco, Ubide, Teresa, Mollo, Silvio, Masotta, Matteo, Caulfield, John, Le Roux, P, Nazzari, Manuela, Scott, J.M., Scarlato, Piergiorgio
• Other Authors: Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione Roma1, Roma, Italia, Department of Geology, University of Otago , PO Box 56 , Dunedin 9054, New Zealand, School of Earth and Environmental Sciences, The University of Queensland , Brisbane, QLD 4072, Australia, Dipartimento di Scienze Della Terra, Sapienza-università di Roma , P.le Aldo Moro 5 , Roma 00185, Italy, Dipartimento di Scienze Della Terra, Università Degli Studi di Pisa , Via S. Maria 53 , Pisa 56126, Italy, Central Analytical Research Facility, Institute for Future Environments, Queensland University of Technology , 2 George Street , Brisbane, QLD 4000, Australia, Department of Geological Sciences, University of Cape Town , Rondebosch 7701, South Africa
• Format: Article in Journal/Newspaper
• Language: English
• Published: Oxford University Press 2021
• Subjects: alkali basalts; Dunedin Volcano; thermobarometry; primary magma; lithospheric mantle filter; Igneous Petrology; Mantle melting and metasomatism; Magmatic plumbing systems; New Zealand; Antarctica Journal; Ocean Island
• Online Access: http://hdl.handle.net/2122/15164; https://academic.oup.com/petrology/advance-article-abstract/doi/10.1093/petrology/egab062/6321476?redirectedFrom=fulltext; https://doi.org/10.1093/petrology/egab062

Systematic variations in the crystal cargo and whole-rock isotopic compositions of mantle-derived basalts in the intraplate Dunedin Volcano (New Zealand) indicate the influence of a complex mantle-to-crust polybaric plumbing system. Basaltic rocks define a compositional spectrum from low-alkali basalts through mid-alkali basalts to high-alkali basalts. High-alkali basalts display clinopyroxene crystals with sector (hourglass) and oscillatory zoning (Mg#61–82) as well as Fe-rich green cores (Mg#43–69), whereas low-alkali basalts are characterized by clinopyroxenes with unzoned overgrowths (Mg#69–83) on resorbed mafic cores (Mg#78–88), coexisting with reversely zoned plagioclase crystals (An43–68 to An60–84 from core to rim). Complex magma dynamics are indicated by distinctive compositional variations in clinopyroxene phenocrysts, with Cr-rich zones (Mg#74–87) indicating continuous recharge by more mafic magmas. Crystallization of olivine, clinopyroxene and titanomagnetite occurred within a polybaric plumbing system extending from upper mantle to mid-crustal depths (485–1059 MPa and 1147–1286°C), whereas crystallization of plagioclase with subordinate clinopyroxene and titanomagnetite proceeded towards shallower crustal levels. The compositions of high-alkali basalts and mid-alkali basalts resemble those of ocean island basalts and are characterized by FOZO-HIMU isotopic signatures (87Sr/86Sri = 0.70277–0.70315, 143Nd/144Ndi = 0.51286–0.51294 and 206Pb/204Pb = 19.348–20.265), whereas low-alkali basalts have lower incompatible element abundances and isotopic compositions trending towards EMII (87Sr/86Sri = 0.70327–70397, 143Nd/144Ndi = 0.51282–0.51286 and 206Pb/204Pb = 19.278–19.793). High- and mid-alkali basalt magmas mostly crystallized in the lower crust, whereas low-alkali basalt magma recorded deeper upper mantle clinopyroxene crystallization before eruption. The variable alkaline character and isotope composition may result from interaction of low-alkaline melts derived from the asthenosphere with melts ...