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Four-stage building of the Cambrian Carion pluton (Madagascar)

By
M. O. M. Razanatseheno
M. O. M. Razanatseheno
1
Department of Earth Sciences, BP 906, Antananarivo University, Madagascar
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A. Nédélec
A. Nédélec
2
LMTG – OMP, Toulouse University – CNRS-IRD, 14 avenue Edouard Belin, 31400 Toulouse, France, Email: nedelec@lmtg.obs-mip.fr
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M. Rakotondrazafy
M. Rakotondrazafy
1
Department of Earth Sciences, BP 906, Antananarivo University, Madagascar
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J. G. Meert
J. G. Meert
3
Department of Geological Sciences, 241 Williamson Hall, Gainesville University, Florida 32611, USA
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B. Ralison
B. Ralison
1
Department of Earth Sciences, BP 906, Antananarivo University, Madagascar
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Published:
October 01, 2010

The 532 ± 5 Ma old Carion pluton is a dark, porphyritic ferro-potassic granitoid emplaced near the late Pan-African Angavo mega-shear zone. A rough normal zoning from tonalitic to granitic compositions can be recognised in the field. Steep magmatic foliations are evidenced by K-feldspar megacryst preferred orientations. Microstructures are either magmatic or typical of incipient solid-state deformation in near solidus conditions. Magnetic susceptibility magnitudes (K) range from 11 to 111 × 10−3 SI in the pluton and can be correlated to the petrography (highest K values in the tonalites; lowest K in the granites; granodiorites in between). The susceptibility magnitudes display a complex zoning pattern. Combined with the arrangement of magnetic foliation trajectories, it is possible to delineate four nested sub-units, regarded as four magmatic pulses successively emplaced from the west to the east of the pluton. The four pulses are characterised by very similar magma geochemistry, but variable magmatic differentiation. The highest degrees of magnetic susceptibility anisotropies (up to 1·6) are observed along internal contacts between sub-units and along the borders of the pluton. The magnetic lineations are also steeply plunging in some places in each sub-unit, possibly imaging the different feeder zones. Magma emplacement occurred at the end of the activity of the Angavo shear zone, hence avoiding re-orientation of the magmatic structures by the late Pan-African transcurrent tectonics. The diachronicity of the four magmatic pulses is consistent with previously determined palaeomagnetic data, because only the two older sub-units display a magnetic reversal sequence, whereas the two youngest sub-units lack any reversion. Emplacement of these four magmatic batches was responsible for a strain aureole and suggests a diapiric mode of ascent.

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GSA Special Papers

Sixth Hutton Symposium on The Origin of Granites and Related Rocks: Proceedings of a Symposium held in Stellenbosch, South Africa, 2- 6 July 2007

John D. Clemens
John D. Clemens
Department of Earth Sciences, University of Stellenbosch, South Africa
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Colin Donaldson
Colin Donaldson
EESTRSE Editor:
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Carol D. Frost
Carol D. Frost
Guest Editors:
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Alexander F.M. Kisters
Alexander F.M. Kisters
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Jean-François Moyen
Jean-François Moyen
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Tracy Rushmer
Tracy Rushmer
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Gary Stevens
Gary Stevens
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Geological Society of America
Volume
472
ISBN print:
9780813724720
Publication date:
October 01, 2010

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