Thermal modification of hematite-ilmenite intergrowths in the Ecstall pluton, British Columbia, Canada

S.J. Brownlee, J.M. Feinberg, R.J. Harrison, Takeshi Kasama, G.R. Scott, P.R. Renne

    Research output: Contribution to journalJournal articleResearchpeer-review

    Abstract

    In this study, we examine the effects of reheating on finely exsolved hematite-ilmenite intergrowths from the similar to 91 Ma Ecstall pluton using reflected light microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). As a result of the emplacement of the younger adjacent similar to 52 Ma Quottoon pluton, samples closer to a thermal boundary have experienced greater degrees of thermal alteration. Five main microstructural features characterize hematite-ilmenite intergrowths from the Ecstall: (I) exsolution lamellae of hematite and ilmenite; (II) oxidation of ilmenite to form hematite, rutile, and other Ti-rich phases; (III) 20-50 nm magnetite precipitates in hematite; (IV) rutile blitz texture; and (V) exsolution of hematite in rutile. Based on spatial relationships, textures I I through V appear to be related to reheating of the Ecstall by the Quottoon, and samples up to similar to 14 km from the thermal boundary intrusive contact have been affected. We propose a mechanism, similar to that of Kontny and Died (2001), in which reheating has driven T-f(O2) conditions across the hematite-magnetite buffer to lower f(O2) resulting in the reduction of hematite. Higher temperatures also enhanced oxidation in ilmenite. The formation of magnetite altered the bulk magnetic properties of these samples, increasing NRM intensity. This study underscores the need to consider a pluton's post-emplacement thermal history before making tectonic interpretations based on paleomagnetic data.
    Original languageEnglish
    JournalAmerican Mineralogist
    Volume95
    Issue number1
    Pages (from-to)153-160
    ISSN0003-004X
    DOIs
    Publication statusPublished - 2010

    Keywords

    • mineral intergrowths
    • hematite-ilmenite
    • Ecstall pluton
    • Electron microscopy
    • magnetite

    Cite this

    Brownlee, S. J., Feinberg, J. M., Harrison, R. J., Kasama, T., Scott, G. R., & Renne, P. R. (2010). Thermal modification of hematite-ilmenite intergrowths in the Ecstall pluton, British Columbia, Canada. American Mineralogist, 95(1), 153-160. https://doi.org/10.2138/am.2010.3191
    Brownlee, S.J. ; Feinberg, J.M. ; Harrison, R.J. ; Kasama, Takeshi ; Scott, G.R. ; Renne, P.R. / Thermal modification of hematite-ilmenite intergrowths in the Ecstall pluton, British Columbia, Canada. In: American Mineralogist. 2010 ; Vol. 95, No. 1. pp. 153-160.
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    abstract = "In this study, we examine the effects of reheating on finely exsolved hematite-ilmenite intergrowths from the similar to 91 Ma Ecstall pluton using reflected light microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). As a result of the emplacement of the younger adjacent similar to 52 Ma Quottoon pluton, samples closer to a thermal boundary have experienced greater degrees of thermal alteration. Five main microstructural features characterize hematite-ilmenite intergrowths from the Ecstall: (I) exsolution lamellae of hematite and ilmenite; (II) oxidation of ilmenite to form hematite, rutile, and other Ti-rich phases; (III) 20-50 nm magnetite precipitates in hematite; (IV) rutile blitz texture; and (V) exsolution of hematite in rutile. Based on spatial relationships, textures I I through V appear to be related to reheating of the Ecstall by the Quottoon, and samples up to similar to 14 km from the thermal boundary intrusive contact have been affected. We propose a mechanism, similar to that of Kontny and Died (2001), in which reheating has driven T-f(O2) conditions across the hematite-magnetite buffer to lower f(O2) resulting in the reduction of hematite. Higher temperatures also enhanced oxidation in ilmenite. The formation of magnetite altered the bulk magnetic properties of these samples, increasing NRM intensity. This study underscores the need to consider a pluton's post-emplacement thermal history before making tectonic interpretations based on paleomagnetic data.",
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    Brownlee, SJ, Feinberg, JM, Harrison, RJ, Kasama, T, Scott, GR & Renne, PR 2010, 'Thermal modification of hematite-ilmenite intergrowths in the Ecstall pluton, British Columbia, Canada', American Mineralogist, vol. 95, no. 1, pp. 153-160. https://doi.org/10.2138/am.2010.3191

    Thermal modification of hematite-ilmenite intergrowths in the Ecstall pluton, British Columbia, Canada. / Brownlee, S.J.; Feinberg, J.M.; Harrison, R.J.; Kasama, Takeshi; Scott, G.R.; Renne, P.R.

    In: American Mineralogist, Vol. 95, No. 1, 2010, p. 153-160.

    Research output: Contribution to journalJournal articleResearchpeer-review

    TY - JOUR

    T1 - Thermal modification of hematite-ilmenite intergrowths in the Ecstall pluton, British Columbia, Canada

    AU - Brownlee, S.J.

    AU - Feinberg, J.M.

    AU - Harrison, R.J.

    AU - Kasama, Takeshi

    AU - Scott, G.R.

    AU - Renne, P.R.

    PY - 2010

    Y1 - 2010

    N2 - In this study, we examine the effects of reheating on finely exsolved hematite-ilmenite intergrowths from the similar to 91 Ma Ecstall pluton using reflected light microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). As a result of the emplacement of the younger adjacent similar to 52 Ma Quottoon pluton, samples closer to a thermal boundary have experienced greater degrees of thermal alteration. Five main microstructural features characterize hematite-ilmenite intergrowths from the Ecstall: (I) exsolution lamellae of hematite and ilmenite; (II) oxidation of ilmenite to form hematite, rutile, and other Ti-rich phases; (III) 20-50 nm magnetite precipitates in hematite; (IV) rutile blitz texture; and (V) exsolution of hematite in rutile. Based on spatial relationships, textures I I through V appear to be related to reheating of the Ecstall by the Quottoon, and samples up to similar to 14 km from the thermal boundary intrusive contact have been affected. We propose a mechanism, similar to that of Kontny and Died (2001), in which reheating has driven T-f(O2) conditions across the hematite-magnetite buffer to lower f(O2) resulting in the reduction of hematite. Higher temperatures also enhanced oxidation in ilmenite. The formation of magnetite altered the bulk magnetic properties of these samples, increasing NRM intensity. This study underscores the need to consider a pluton's post-emplacement thermal history before making tectonic interpretations based on paleomagnetic data.

    AB - In this study, we examine the effects of reheating on finely exsolved hematite-ilmenite intergrowths from the similar to 91 Ma Ecstall pluton using reflected light microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). As a result of the emplacement of the younger adjacent similar to 52 Ma Quottoon pluton, samples closer to a thermal boundary have experienced greater degrees of thermal alteration. Five main microstructural features characterize hematite-ilmenite intergrowths from the Ecstall: (I) exsolution lamellae of hematite and ilmenite; (II) oxidation of ilmenite to form hematite, rutile, and other Ti-rich phases; (III) 20-50 nm magnetite precipitates in hematite; (IV) rutile blitz texture; and (V) exsolution of hematite in rutile. Based on spatial relationships, textures I I through V appear to be related to reheating of the Ecstall by the Quottoon, and samples up to similar to 14 km from the thermal boundary intrusive contact have been affected. We propose a mechanism, similar to that of Kontny and Died (2001), in which reheating has driven T-f(O2) conditions across the hematite-magnetite buffer to lower f(O2) resulting in the reduction of hematite. Higher temperatures also enhanced oxidation in ilmenite. The formation of magnetite altered the bulk magnetic properties of these samples, increasing NRM intensity. This study underscores the need to consider a pluton's post-emplacement thermal history before making tectonic interpretations based on paleomagnetic data.

    KW - mineral intergrowths

    KW - hematite-ilmenite

    KW - Ecstall pluton

    KW - Electron microscopy

    KW - magnetite

    U2 - 10.2138/am.2010.3191

    DO - 10.2138/am.2010.3191

    M3 - Journal article

    VL - 95

    SP - 153

    EP - 160

    JO - American Mineralogist

    JF - American Mineralogist

    SN - 0003-004X

    IS - 1

    ER -