Stable isotopic and petrological constraints on scapolitization of the Whitestone meta‐anorthosite, Grenville Province, Ontario


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The Whitestone Anorthosite (WSA), located in the Central Gneiss Belt of the south‐western Grenville Province, Ontario, exhibits a nearly concentric metamorphic envelope characterized by an increase in modal scapolite, hornblende, epidote and garnet, developed around a core of granulite facies clinopyroxene ± orthopyroxene ± garnet meta‐anorthosite. Scapolite‐ and hornblende‐bearing assemblages develop mainly at the expense of plagioclase and pyroxene within the envelope. Stable isotopic and petrological data for scapolite‐bearing mineral assemblages within meta‐anorthosite constrain the source of carbon responsible for CO3‐scapolite formation and the extent of fluid/rock interaction between the anorthosite and adjacent lithologies. Stable isotopic data indicate increasing δ18O and δ13C from core to margin of the meta‐anorthosite and for samples from the southern extension of the WSA, where it is ductilely deformed within the Parry Sound Shear Zone (PSSZ). The average δ18OSMOW value (whole rock) for the WSA core is 6.9‰, increasing to 11.5‰ where the WSA is in tectonic contact with marble breccia. The average δ13CPBD value of scapolite in meta‐anorthosite from the centre of the WSA is ‐3.4‰, increasing to ‐0.5‰ at the eastern (marble) contact. Average values of δ13C for scapolite and whole‐rock δ18O for samples from the shear zone are ‐1.0 and 8.0‰, respectively. Marbles have average δ18O and δ13C values of 19.2 and ‐0.4‰, respectively. The sulphate content of texturally primary scapolite decreases from the core of the WSA (XSO4= 0.48) to the eastern contact (≤0.05). Texturally late scapolite after plagioclase and garnet tends to be CO3‐rich relative to texturally primary scapolite, and some scapolite grains show zoning in the anion site with CO3‐enriched rims. Scapolite composition may vary at any scale from a single grain to outcrop. The pattern of isotopic enrichment in 13C and 18O preserved in the eastern margin of the WSA is consistent with marble as the major source of fluid contributing to the formation of the metamorphic envelope. The decrease in XSO4 and increase in XCO3 in scapolite toward the margin of the WSA indicate that the volatile content was reset by, or developed from, a CO2‐bearing fluid. Assuming derivation of fluid from marble, minimum fluid/rock values at the margin of the WSA range from 0.03 for the least enriched, to 0.30 for the most isotopically enriched samples. Although marble is not found in immediate contact with samples of sheared meta‐anorthosite from the PSSZ, a marble source is also consistent with the C and O isotope composition and anion chemistry of scapolite within these samples.

Original languageEnglish
Pages (from-to)745-762
Number of pages18
JournalJournal of Metamorphic Geology
Issue number6
StatePublished - Nov 1992


  • Grenville Province, Canada
  • fluid infiltration
  • meta‐anorthosite
  • scapolite
  • stable isotopes

ASJC Scopus subject areas

  • Geology
  • Geochemistry and Petrology


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