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University of Ottawa, Ottawa. Geological Survey of Canada, Québec.

Mantle evolution recorded in Cr-spinel from the Bay of Island Ophiolitic Complex, northern Appalachians. Fabio Stern 1 , Keiko Hattori 1 and Jean Bédard 2. University of Ottawa, Ottawa. Geological Survey of Canada, Québec. Introduction Location and Geological Settings Rock Types Results

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University of Ottawa, Ottawa. Geological Survey of Canada, Québec.

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  1. Mantle evolution recorded in Cr-spinel from the Bay of Island Ophiolitic Complex, northern Appalachians. Fabio Stern1, Keiko Hattori1 and Jean Bédard2 • University of Ottawa, Ottawa. • Geological Survey of Canada, Québec.

  2. Introduction Location and Geological Settings Rock Types Results Conclusions

  3. Introduction Cr-spinel (FeCr2O4) is a useful petrogenic indicator of mafic-ultramafic rocks since it is not easily altered. Therefore we examined Cr-spinels and olivines from the ultramafic complex to evaluate the mantle evolution of the BOIC.

  4. Location The area is located on the west coast of Newfoundland. It is part the western ultramafic belt of the northern Appalachians.V • The Bay of Islands Ophiolite Complex is exposed in four massifs: • Tablelands • North Arm • Blow Me Down • Lewis Hills

  5. Geological Settings

  6. Harzburgite harzburgite opxnite dunite 1 m 50cm

  7. Harzburgite 0.5mm Chr 0.5mm Ol Chr Opx Chr Ol 3mm

  8. Dunite Dunite contains lenses and veins of coarse grained wehrlites. wehrlite 50 cm

  9. Dunite Chr Ol Chr Ol Chr Ol 0.5mm

  10. Introduction Location and Geological Settings Rock Types Results Conclusions

  11. Results • Harzburgites have high Ir-type PGEs (Ir, Os, Ru) typical of residual mantle rocks; • Dunites have higher concentration of Pt and Pd, suggesting a cumulate origin.

  12. Results Harzburgite spinel Chr All harzburgite samples plot in the Ol-Sp mantle array (OSMA) defined by Shoji Arai (1994). 0.5mm Fosterite component of olivine vs Cr# of spinel. Olivine-spinel mantle array. After Arai (1994).

  13. Results Dunite spinel Dunites with Ol (Fo>90, ) plot in the OSMA; Dunites outside the OSMA were products from fractionated melt. Not considered for the evaluation of the mantle. 0.5mm Fosterite component of olivine vs Cr# of spinel. Olivine-spinel mantle array. After Arai (1994).

  14. Results HzandDun Large variation in the Cr#; Change in mantle conditions from fertile to more refractory (Abyssal field to Forearc peridotite). Chr Max Abyssal Per. 0.5mm Fosterite component of olivine vs Cr# of spinel. Olivine-spinel mantle array. After Arai (1994).

  15. Results Wide range from MORB to Boninitic fields Chr 0.5mm Modified from Kamenetsky et al. (2001). Modified from Dare et al. (2008). Boninites data from Barnes & Roeder (2001).

  16. Results • fO2 calc. based on Ballhaus (1991) Ol-Sp exchange thermometry. • Results: • Hz shows low fO2; • Dun shows higher fO2, suggesting the influence of subduction. Asthenospheric mantle Chr Modified from Wang et al. (2008).

  17. Subduction initiation

  18. Introduction Location and Geological Settings Rock Types Results Conclusions

  19. Conclusions • PGE abundance is effective in identifying its origin. • Dunite in BOIC is a cumulate based on low Ir-type PGEs • The mantle source had low S; • The mantle changed gradually from abyssal peridotite-like to more refractory conditions in subduction setting; 19

  20. References Arai, S., (1994). Characterization of spinel peridotites by olivine-spinel compositional relationships: review and interpretation. Chemical Geology 111: 191–204. Ballhaus, C., Berry, R.F., Green, D.H., 1991. High pressure experimental calibration of the olivine-orthopyroxene-spinel oxygen geobarometer: implications for the oxidation state of the upper mantle. Contributions to Mineralogy and Petrology 107: 27–40. Barnes, S.J., Roeder, P.L., (2001). The range of spinel compositions in terrestrial mafic and ultramafic rocks. Journal of Petrology 42: 2279–2302. Dare, S., Pearce, J., McDonald, I., Styles, M., (2008). Tectonic discrimination of peridotites using fO2–Cr# and Ga–Ti–FeIII systematics in chrome–spinel. Chemical Geology, 261: 199-216. Hattori, K., Wallis, S., Enami., Mizukami, T., (2009). Subduction of mantle wedge peridotites: Evidence from the Hgashi-akaiashi ultramafic body in the Sanbagawa metamorphic belt. Island Arc. 1-16. Kamenetsky, V.S., Crawford, A.J., Meffre, S., (2001). Factors controlling chemistry of magmatic spinel: an empirical study of associated olivine, Cr-spinel and melt inclusions from primitive rocks. Journal of Petrology 42: 655–671. McDonough, W.F., Sun, S.S. (1995): The composition of the earth. Chem. Geol.120: 223-253. Nikolaeva, K., Gerya, T.V., Marques, F.O. (2010). Subduction initiation at passive margins: Numerical modeling. Journal of Geophysical Research, 116: 1-19 Suhr, G. (1992): Upper mantle peridotites in the Bay of Islands Ophiolite, Newfoundland: formation during the final stages of a spreading centre? Tectonophysics, 206: 31-53. Wang, J., Hattori, K., Li, J., Stern., C. R., (2008). Oxidation state of Paleozoic subcontinental lithospheric mantle below the Pali Aike volcanic field in southernmost Patagonia. Lithos, 105: 98–110 20

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