Hydrothermal spinel, corundum and diaspore in lower oceanic crustal troctolites from the Hess Deep Rift

Toshio Nozaka, Romain Meyer, Robert P. Wintsch, Bryan Wathen

Research output: Contribution to journalArticle

7 Citations (Scopus)

Abstract

Aluminous spinel, corundum and diaspore are reported from intensely altered parts of primitive troctolites recovered from IODP Site U1415 at the Hess Deep Rift. The spinel is green-colored, has an irregular shape, has low Cr concentrations, and is so distinct from primary igneous chromite. Corundum and diaspore occur mainly at the rims of green spinel grains with a texture suggesting a sequential replacement of spinel by corundum, and then corundum by diaspore. The green spinel is associated with anorthite and pargasite, which is overgrown by tremolite that forms coronitic aggregates with chlorite around olivine. These petrographic observations are supported by pressure–temperature pseudosections, which predict spinel + pargasite stability field, and tremolite/hornblende + chlorite field at lower temperature conditions. From these pseudosections and simplified system phase diagrams, estimated formation temperature conditions calculated at 2 kbar are 650–750 °C for spinel + pargasite, 410–690 °C for tremolite/hornblende + chlorite, 400–710 °C for corundum, and 2O3/CaO and Al2O3/SiO2 ratios, it is likely that the stabilization of spinel was caused by the loss of Ca2+ and SiO2(aq) in high-temperature hydrothermal fluids. The results of this study suggest that (1) the concentrations of aluminous phases in the lower oceanic crust are presently underestimated, and (2) chemical modification of the lower oceanic crust due to high-temperature hydrothermal metasomatic reactions could be common near spreading axes.

Original languageEnglish
Article number53
JournalContributions to Mineralogy and Petrology
Volume171
Issue number6
DOIs
Publication statusPublished - Jun 1 2016

Fingerprint

diaspore
corundum
Aluminum Oxide
spinel
aluminum oxides
pargasite
tremolite
chlorite
hornblende
oceanic crust
lower crust
crusts
Chromite
Temperature
chromites
anorthite
spinell
Chemical modification
chromite
rims

Keywords

  • Corundum
  • Diaspore
  • Hydrothermal alteration
  • Oceanic crust
  • Spinel
  • Troctolite

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics

Cite this

Hydrothermal spinel, corundum and diaspore in lower oceanic crustal troctolites from the Hess Deep Rift. / Nozaka, Toshio; Meyer, Romain; Wintsch, Robert P.; Wathen, Bryan.

In: Contributions to Mineralogy and Petrology, Vol. 171, No. 6, 53, 01.06.2016.

Research output: Contribution to journalArticle

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