Experimental evidence for decompression melting of metasomatized mantle beneath Colima Graben, Mexico

Eduardo Becerra Torres*, Elana Melekhova, Jon D Blundy, Richard A Brooker

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)

Abstract

Primitive subduction zone magmas provide information about the composition and thermal structure of the underlying mantle wedge. In the Colima Graben, Mexico, primitive lavas erupted from cinder cones range from high magnesium calc-alkaline basalts to high-K trachybasalts. This chemical diversity suggests that the sub-arc mantle wedge from which they derive is heterogeneous. To explore the conditions of magma generation in the wedge beneath Colima we used an inverse experimental approach to constrain multiple saturation points on the liquidus surface of a primitive high-K basanite (COM-1). Equilibrium piston-cylinder experiments were carried out between 1.0 and 2.4 GPa under hydrous (1.8 to 3.8 wt% H2O) and oxidizing (ƒO2 = -0.5 to 4.3 log units relative to NNO) conditions.

COM-1 + 3.8 wt% H2O is shown to be multiply-saturated with a phlogopite-bearing spinel pyroxenite assemblage (cpx+opx+phl+sp) close to its liquidus at 1.9 – 2.4 GPa and 1300°C. Experimental mapping of the liquidus surface reveals a multiple saturation point (MSP) where a lherzolitic phase assemblage of ol+cpx+opx+sp+phl coexist. The topology of the MSP indicates a peritectic of the form cpx+opx+phl+sp=liquid+ol. Four bracketing experiments define the MSP of COM-1 as 1300±10°C, 1.7±0.1 GPa, ∆NNO = 3.4±0.5 log units, for melt containing 3.6±0.4 wt% H2O. The MSP olivine is too forsterite-rich (Fo92-94) to be in equilibrium with mantle lherzolite, but matches phenocryst core compositions in the natural basanite. Thus, experimental results indicate that COM-1 was produced by incongruent melting of an olivine-free, phlogopite-pyroxenite source that itself is the result of metasomatism of mantle wedge by slab-derived fluids. These conditions provide a valuable constraint on the thermal structure and chemical composition of the mantle wedge beneath Colima.
Original languageEnglish
JournalContributions to Mineralogy and Petrology
Publication statusAccepted/In press - 18 Sep 2020

Keywords

  • Phlogopite peridotite
  • mantle heterogeneity
  • high-potassium basalt
  • Colima Graben
  • multiple saturation
  • incongruent melting

Fingerprint Dive into the research topics of 'Experimental evidence for decompression melting of metasomatized mantle beneath Colima Graben, Mexico'. Together they form a unique fingerprint.

Cite this