TY - JOUR

T1 - Olivine Major and Trace Element Compositions in Southern Payenia Basalts, Argentina

T2 - Evidence for Pyroxenite–Peridotite Melt Mixing in a Back-arc Setting

AU - Søager, Nina

AU - Portnyagin, Maxim

AU - Hoernle, Kaj

AU - Holm, Paul Martin

AU - Hauff, Folkmar

AU - Garbe-Schönberg, Dieter

PY - 2015

Y1 - 2015

N2 - Olivine major and trace element compositions from 12 basalts from the southern Payenia volcanicprovince in Argentina have been analyzed by electron microprobe and laser ablation inductivelycoupled plasma mass spectrometry. The olivines have high Fe/Mn and low Ca/Fe and many fall atthe end of the global olivine array, indicating that they were formed from a pyroxene-rich sourcedistinct from typical mantle peridotite. The olivines with the highest Fe/Mn have higher Zn/Fe, Znand Co and lower Co/Fe than the olivines with lower Fe/Mn, also suggesting contributions from apyroxene-rich source. Together with whole-rock radiogenic isotopes and elemental concentrations,the samples indicate mixing between two mantle sources: (1) a pyroxene-rich source with EM-1ocean island basalt type trace element and isotope characteristics; (2) a peridotitic source withmore radiogenic Pb that was metasomatized by subduction-zone fluids and/or melts. The increasingcontributions from the pyroxene-rich source in the southern Payenia basalts are correlatedwith an increasing Fe-enrichment, which caused the olivines to have lower forsterite contents at agiven Ni content. Al-in-olivine crystallization temperatures measured on olivine–spinel pairs are between1155 and 1243C and indicate that the magmas formed at normal upper mantle (asthenospheric)temperatures of 1350C. The pyroxene-rich material is interpreted to have been broughtup from the deeper parts of the upper mantle by vigorous asthenospheric upwelling caused bybreak-off of the Nazca slab south of Payenia during the Pliocene and roll-back of the subductingslab beneath Payenia. The pyroxene-rich mantle mixed with peridotitic metasomatized SouthAtlantic mantle in the mantle wedge beneath Payenia.

AB - Olivine major and trace element compositions from 12 basalts from the southern Payenia volcanicprovince in Argentina have been analyzed by electron microprobe and laser ablation inductivelycoupled plasma mass spectrometry. The olivines have high Fe/Mn and low Ca/Fe and many fall atthe end of the global olivine array, indicating that they were formed from a pyroxene-rich sourcedistinct from typical mantle peridotite. The olivines with the highest Fe/Mn have higher Zn/Fe, Znand Co and lower Co/Fe than the olivines with lower Fe/Mn, also suggesting contributions from apyroxene-rich source. Together with whole-rock radiogenic isotopes and elemental concentrations,the samples indicate mixing between two mantle sources: (1) a pyroxene-rich source with EM-1ocean island basalt type trace element and isotope characteristics; (2) a peridotitic source withmore radiogenic Pb that was metasomatized by subduction-zone fluids and/or melts. The increasingcontributions from the pyroxene-rich source in the southern Payenia basalts are correlatedwith an increasing Fe-enrichment, which caused the olivines to have lower forsterite contents at agiven Ni content. Al-in-olivine crystallization temperatures measured on olivine–spinel pairs are between1155 and 1243C and indicate that the magmas formed at normal upper mantle (asthenospheric)temperatures of 1350C. The pyroxene-rich material is interpreted to have been broughtup from the deeper parts of the upper mantle by vigorous asthenospheric upwelling caused bybreak-off of the Nazca slab south of Payenia during the Pliocene and roll-back of the subductingslab beneath Payenia. The pyroxene-rich mantle mixed with peridotitic metasomatized SouthAtlantic mantle in the mantle wedge beneath Payenia.

U2 - 10.1093/petrology/egv043

DO - 10.1093/petrology/egv043

M3 - Journal article

VL - 56

SP - 1495-1518.

JO - Journal of Petrology

JF - Journal of Petrology

SN - 0022-3530

IS - 8

ER -