Paleomagnetism, geochronology and tectonic implications of the Cambrian-age Carion granite, Central Madagascar

J.G. Meert, A. Nedelec, C. Hall, Michael Wingate, M. Rakotondrazafy

    Research output: Contribution to journalArticle

    44 Citations (Scopus)

    Abstract

    The Carion granitic pluton in central Madagascar was intruded into warm. continental crust following orogenic events related to the final amalgamation of Gondwana. U-Pb SHRIMP dating of the pluton yields an emplacement age of 532.1 +/- 5.2 Ma followed by relatively slow cooling as constrained by Ar-40/Ar-39 ages on hornblende and biotite. Four hornblende samples yielded a mean Ar-40/Ar-39 age of 512.7 +/- 1.3 Ma. A biotite sample yielded an age of 478.9 +/- 1.0 Ma. Paleomagnetic samples from the pluton and surrounding country rocks exhibit either SE-upwardly directed magnetizations (mean Dec = 113 degrees, Inc = -56 degrees, k = 106, alpha (95) = 12 degrees) or NW-downwardly directed magnetizations (mean Dec = 270 degrees, Inc = +64 degrees, k = 30, alpha (95) = 11 degrees) that pass a reversal test with a classification of 'C' and an angular difference of 14.4 degrees. The 'normal' (negative inclinations) and 'reverse' (positive inclinations) directions also show a spatial bias within the pluton, suggesting a field transition from reverse to normal during cooling. The paleomagnetic pole calculated from the mean direction falls at 6.8 degreesS, 001 degreesE (dp = 13 degrees, dm = 17 degrees). Estimates Of the blocking temperature for the magnetization are compared to the cooling history of the pluton and an age of 508.5 +/- 11.5 Ma is assigned to the pole. The Carion pole falls near similar-age poles from elsewhere in Gondwana, supporting the idea that the major orogenic events during Gondwana assembly were complete. A slight revision of the Gondwana apparent polar wander path (APWP) is proposed with rapid APW from 540 to 520 Ma; however, the proposed mechanisms to explain this rapid APW (including intertial-interchange true polar wander (TPW) or enhanced mantle driving forces) cannot fully explain all the data. (C) 2001 Elsevier Science B.V. All rights reserved.
    Original languageEnglish
    Pages (from-to)1-21
    JournalTectonophysics
    Volume340
    DOIs
    Publication statusPublished - 2001

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    Madagascar
    paleomagnetism
    geochronology
    granite
    tectonics
    poles
    pluton
    Gondwana
    biotite
    cooling
    magnetization
    inclination
    hornblende
    dating
    SHRIMP dating
    apparent polar wander path
    crusts
    Earth mantle
    assembly
    histories

    Cite this

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    title = "Paleomagnetism, geochronology and tectonic implications of the Cambrian-age Carion granite, Central Madagascar",
    abstract = "The Carion granitic pluton in central Madagascar was intruded into warm. continental crust following orogenic events related to the final amalgamation of Gondwana. U-Pb SHRIMP dating of the pluton yields an emplacement age of 532.1 +/- 5.2 Ma followed by relatively slow cooling as constrained by Ar-40/Ar-39 ages on hornblende and biotite. Four hornblende samples yielded a mean Ar-40/Ar-39 age of 512.7 +/- 1.3 Ma. A biotite sample yielded an age of 478.9 +/- 1.0 Ma. Paleomagnetic samples from the pluton and surrounding country rocks exhibit either SE-upwardly directed magnetizations (mean Dec = 113 degrees, Inc = -56 degrees, k = 106, alpha (95) = 12 degrees) or NW-downwardly directed magnetizations (mean Dec = 270 degrees, Inc = +64 degrees, k = 30, alpha (95) = 11 degrees) that pass a reversal test with a classification of 'C' and an angular difference of 14.4 degrees. The 'normal' (negative inclinations) and 'reverse' (positive inclinations) directions also show a spatial bias within the pluton, suggesting a field transition from reverse to normal during cooling. The paleomagnetic pole calculated from the mean direction falls at 6.8 degreesS, 001 degreesE (dp = 13 degrees, dm = 17 degrees). Estimates Of the blocking temperature for the magnetization are compared to the cooling history of the pluton and an age of 508.5 +/- 11.5 Ma is assigned to the pole. The Carion pole falls near similar-age poles from elsewhere in Gondwana, supporting the idea that the major orogenic events during Gondwana assembly were complete. A slight revision of the Gondwana apparent polar wander path (APWP) is proposed with rapid APW from 540 to 520 Ma; however, the proposed mechanisms to explain this rapid APW (including intertial-interchange true polar wander (TPW) or enhanced mantle driving forces) cannot fully explain all the data. (C) 2001 Elsevier Science B.V. All rights reserved.",
    author = "J.G. Meert and A. Nedelec and C. Hall and Michael Wingate and M. Rakotondrazafy",
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    Paleomagnetism, geochronology and tectonic implications of the Cambrian-age Carion granite, Central Madagascar. / Meert, J.G.; Nedelec, A.; Hall, C.; Wingate, Michael; Rakotondrazafy, M.

    In: Tectonophysics, Vol. 340, 2001, p. 1-21.

    Research output: Contribution to journalArticle

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    AU - Meert, J.G.

    AU - Nedelec, A.

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    AU - Wingate, Michael

    AU - Rakotondrazafy, M.

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    N2 - The Carion granitic pluton in central Madagascar was intruded into warm. continental crust following orogenic events related to the final amalgamation of Gondwana. U-Pb SHRIMP dating of the pluton yields an emplacement age of 532.1 +/- 5.2 Ma followed by relatively slow cooling as constrained by Ar-40/Ar-39 ages on hornblende and biotite. Four hornblende samples yielded a mean Ar-40/Ar-39 age of 512.7 +/- 1.3 Ma. A biotite sample yielded an age of 478.9 +/- 1.0 Ma. Paleomagnetic samples from the pluton and surrounding country rocks exhibit either SE-upwardly directed magnetizations (mean Dec = 113 degrees, Inc = -56 degrees, k = 106, alpha (95) = 12 degrees) or NW-downwardly directed magnetizations (mean Dec = 270 degrees, Inc = +64 degrees, k = 30, alpha (95) = 11 degrees) that pass a reversal test with a classification of 'C' and an angular difference of 14.4 degrees. The 'normal' (negative inclinations) and 'reverse' (positive inclinations) directions also show a spatial bias within the pluton, suggesting a field transition from reverse to normal during cooling. The paleomagnetic pole calculated from the mean direction falls at 6.8 degreesS, 001 degreesE (dp = 13 degrees, dm = 17 degrees). Estimates Of the blocking temperature for the magnetization are compared to the cooling history of the pluton and an age of 508.5 +/- 11.5 Ma is assigned to the pole. The Carion pole falls near similar-age poles from elsewhere in Gondwana, supporting the idea that the major orogenic events during Gondwana assembly were complete. A slight revision of the Gondwana apparent polar wander path (APWP) is proposed with rapid APW from 540 to 520 Ma; however, the proposed mechanisms to explain this rapid APW (including intertial-interchange true polar wander (TPW) or enhanced mantle driving forces) cannot fully explain all the data. (C) 2001 Elsevier Science B.V. All rights reserved.

    AB - The Carion granitic pluton in central Madagascar was intruded into warm. continental crust following orogenic events related to the final amalgamation of Gondwana. U-Pb SHRIMP dating of the pluton yields an emplacement age of 532.1 +/- 5.2 Ma followed by relatively slow cooling as constrained by Ar-40/Ar-39 ages on hornblende and biotite. Four hornblende samples yielded a mean Ar-40/Ar-39 age of 512.7 +/- 1.3 Ma. A biotite sample yielded an age of 478.9 +/- 1.0 Ma. Paleomagnetic samples from the pluton and surrounding country rocks exhibit either SE-upwardly directed magnetizations (mean Dec = 113 degrees, Inc = -56 degrees, k = 106, alpha (95) = 12 degrees) or NW-downwardly directed magnetizations (mean Dec = 270 degrees, Inc = +64 degrees, k = 30, alpha (95) = 11 degrees) that pass a reversal test with a classification of 'C' and an angular difference of 14.4 degrees. The 'normal' (negative inclinations) and 'reverse' (positive inclinations) directions also show a spatial bias within the pluton, suggesting a field transition from reverse to normal during cooling. The paleomagnetic pole calculated from the mean direction falls at 6.8 degreesS, 001 degreesE (dp = 13 degrees, dm = 17 degrees). Estimates Of the blocking temperature for the magnetization are compared to the cooling history of the pluton and an age of 508.5 +/- 11.5 Ma is assigned to the pole. The Carion pole falls near similar-age poles from elsewhere in Gondwana, supporting the idea that the major orogenic events during Gondwana assembly were complete. A slight revision of the Gondwana apparent polar wander path (APWP) is proposed with rapid APW from 540 to 520 Ma; however, the proposed mechanisms to explain this rapid APW (including intertial-interchange true polar wander (TPW) or enhanced mantle driving forces) cannot fully explain all the data. (C) 2001 Elsevier Science B.V. All rights reserved.

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