Mount Bambouto, characterized by an elliptic collapse caldera (8 x 13 km), constitutes the third ... more Mount Bambouto, characterized by an elliptic collapse caldera (8 x 13 km), constitutes the third largest volcano (in volume) of the Cameroon Volcanic Line (CVL) after Mounts Cameroon and Manengouba. This volcano is considered to be still active since the recent discovery of quaternary basalt (0.5 Ma) at Totap near the Bambouto caldera. The Bambouto volcano covers an area of about 500 km2 with Mount Mélétan (2740 m) as its highest point. It is made up of volcanic products dated from 21.12 Ma to 0.5 Ma comprising basalts, trachytes, phonolites, rhyolite and ignimbrites locally covered with sedimentary and surface residual formations. Ignimbritic flow deposits which derived from pyroclastic density current are scarce and mainly observed in the central part of the CVL, especially in Mounts Bambouto (and in Mount Bamenda, its NE extension) covering approximately 20% (≈100 km2) of the massif surface with thickness ranging from 30 to 120 m representing a total volume estimated at 10 km3. T...
The basement of central Madagascar registered a polyphase history during Panafrican times. The la... more The basement of central Madagascar registered a polyphase history during Panafrican times. The latest events (560--530 Ma) are responsible for a major N-S shear zone, the Angavo shear zone, characterized by steep foliation planes and N-S subhorizontal lineations (Nédélec et al., 2000). This shear zone has been active in low-pressure granulitic conditions and favoured the emplacement of shoshonitic magmas (e.g.
... ANNE NEDELEC1*, W. EDRYD STEPHENS2 AND ANTHONY E. FALLIGK3 'URA 67 CNRS, PET... more ... ANNE NEDELEC1*, W. EDRYD STEPHENS2 AND ANTHONY E. FALLIGK3 'URA 67 CNRS, PETROPHYSIQUE ET TECTONIQUE, UNIVERSITE PAUL-SABATIER, 38 RUE DES ... and Research Centre (SURRC) in East Kilbride, using the method described in detail by Recio et al ...
ABSTRACT The Tertiary trachytic dome of Foréké–Dschang is located on the southwestern slope of Mo... more ABSTRACT The Tertiary trachytic dome of Foréké–Dschang is located on the southwestern slope of Mount Bambouto. This dome, made of porphyritic and microlitic lavas which enclose sanidine, pyroxene and oxides, is dated at 16 – 8.8 Ma and was emplaced in gneisses belonging to the Pan-African basement. The mean magnetic susceptibility magnitude Km values of the trachytic dome show a ferromagnetic behaviour in 79% of the stations, likely due to the presence of more or less maghemitized titanomagnetite based on thermomagnetic and hysteresis data. The Foréké-Dschang dome is elliptical and strikes NE–SW, parallel to a border fracture. The Pan-African host gneisses display N70° striking and steeply dipping foliations crosscut by the dome. Some Tertiary sinistral reworking of these foliations may have induced the opening of a local tension gash in agreement with the regional model suggesting that the N30° Cameroon Volcanic Line opened as a mega- tension gash with respect to the N70° Adamawa fault zone. Two petrographic types are recognized in the trachytic dome, aphyric (domain I) or porphyritic (domain II). The magnetic foliations show an outward-dipping concentric pattern in domain I. A flat lying zone with the highest magnetic anisotropy (18%) is regarded as overlying the vent. The organization of magnetic fabrics suggests that domain II was emplaced before domain I. As a whole, the Foréké-Dschang trachytes represent a multilobate dome emplaced in a pulsatory manner.
ABSTRACT This book - translated, edited, and updated from the original French edition Pétrologie ... more ABSTRACT This book - translated, edited, and updated from the original French edition Pétrologie des Granites published by Vuibert in 2011 - gives a modern presentation of granitic rocks, or granites, from magma genesis to their emplacement into the crust and their crystallization. Mineralogical, petrological, physical, and economical aspects are developed in a succession of 14 chapters. Special 'info boxes' discuss topics for those wishing to deepen their knowledge of the subject. Also included is a glossary, a comprehensive bibliography, as well as descriptions of modern techniques. Granites are considered in their geological spatial and temporal frame, in relation with Plate Tectonics and Earth History, and assisted by a large number of high quality illustrations.
Data Revues 16310713 03390003 05003627, Feb 13, 2008
A coupled climate–geochemical model of new generation (GEOCLIM) is used to investigate the possib... more A coupled climate–geochemical model of new generation (GEOCLIM) is used to investigate the possible causes of the initiation of snowball glaciations during Neoproterozoic times. This model allows the calculation of the partial pressure of atmospheric CO2 simultaneously with the climate at the continental surface with a rough 2D spatial resolution (10° lat.× 50° long.). We calculate that the breakup of the Rodinia supercontinent, starting 800Myr ago, results in a global climatic cooling of about 8° C triggered by enhanced consumption of ...
ABSTRACT The end of the Neoproterozoic is characterized by ubiquitous glacial deposition being fo... more ABSTRACT The end of the Neoproterozoic is characterized by ubiquitous glacial deposition being followed by the onset of extensive carbonate platforms, marking important changes in climate. The duration of these climatic oscillations is still poorly constrained with estimates varying from hundreds to hundreds of thousand years. Here we report a high-resolution magnetostratigraphic study of Neoproterozoic cap carbonates from the Amazon Craton. These rocks represent the first transgressive carbonate sequence after glacial deposits and present the isotopic signatures and sedimentary structures that typify cap carbonates elsewhere in the world, such as negative delta13C values, tubes, aragonite-pseudomorph crystal fans, pseudo-tepees (megaripples). Age constraints are given by shifts in 87Sr/86Sr ratios towards values greater than 0.7081 and by a Pb-Pb age of 627 ± 32 Ma. Two sections five kilometers apart were sampled with a 20 cm spacing (=101 sites) and revealed five coherent reversals. Magnetization is carried by detrital hematite. These data were used to constrain both the paleogeographic position of the Amazon Craton by the end of Neoproterozoic glaciations, and the time of cap carbonate deposition (in the order of hundreds of thousand years) with implications for geochemical models. Comparison with results from correlative successions in Africa, Oman and Australia will also be presented.
Mount Bambouto, characterized by an elliptic collapse caldera (8 x 13 km), constitutes the third ... more Mount Bambouto, characterized by an elliptic collapse caldera (8 x 13 km), constitutes the third largest volcano (in volume) of the Cameroon Volcanic Line (CVL) after Mounts Cameroon and Manengouba. This volcano is considered to be still active since the recent discovery of quaternary basalt (0.5 Ma) at Totap near the Bambouto caldera. The Bambouto volcano covers an area of about 500 km2 with Mount Mélétan (2740 m) as its highest point. It is made up of volcanic products dated from 21.12 Ma to 0.5 Ma comprising basalts, trachytes, phonolites, rhyolite and ignimbrites locally covered with sedimentary and surface residual formations. Ignimbritic flow deposits which derived from pyroclastic density current are scarce and mainly observed in the central part of the CVL, especially in Mounts Bambouto (and in Mount Bamenda, its NE extension) covering approximately 20% (≈100 km2) of the massif surface with thickness ranging from 30 to 120 m representing a total volume estimated at 10 km3. T...
The basement of central Madagascar registered a polyphase history during Panafrican times. The la... more The basement of central Madagascar registered a polyphase history during Panafrican times. The latest events (560--530 Ma) are responsible for a major N-S shear zone, the Angavo shear zone, characterized by steep foliation planes and N-S subhorizontal lineations (Nédélec et al., 2000). This shear zone has been active in low-pressure granulitic conditions and favoured the emplacement of shoshonitic magmas (e.g.
... ANNE NEDELEC1*, W. EDRYD STEPHENS2 AND ANTHONY E. FALLIGK3 'URA 67 CNRS, PET... more ... ANNE NEDELEC1*, W. EDRYD STEPHENS2 AND ANTHONY E. FALLIGK3 'URA 67 CNRS, PETROPHYSIQUE ET TECTONIQUE, UNIVERSITE PAUL-SABATIER, 38 RUE DES ... and Research Centre (SURRC) in East Kilbride, using the method described in detail by Recio et al ...
ABSTRACT The Tertiary trachytic dome of Foréké–Dschang is located on the southwestern slope of Mo... more ABSTRACT The Tertiary trachytic dome of Foréké–Dschang is located on the southwestern slope of Mount Bambouto. This dome, made of porphyritic and microlitic lavas which enclose sanidine, pyroxene and oxides, is dated at 16 – 8.8 Ma and was emplaced in gneisses belonging to the Pan-African basement. The mean magnetic susceptibility magnitude Km values of the trachytic dome show a ferromagnetic behaviour in 79% of the stations, likely due to the presence of more or less maghemitized titanomagnetite based on thermomagnetic and hysteresis data. The Foréké-Dschang dome is elliptical and strikes NE–SW, parallel to a border fracture. The Pan-African host gneisses display N70° striking and steeply dipping foliations crosscut by the dome. Some Tertiary sinistral reworking of these foliations may have induced the opening of a local tension gash in agreement with the regional model suggesting that the N30° Cameroon Volcanic Line opened as a mega- tension gash with respect to the N70° Adamawa fault zone. Two petrographic types are recognized in the trachytic dome, aphyric (domain I) or porphyritic (domain II). The magnetic foliations show an outward-dipping concentric pattern in domain I. A flat lying zone with the highest magnetic anisotropy (18%) is regarded as overlying the vent. The organization of magnetic fabrics suggests that domain II was emplaced before domain I. As a whole, the Foréké-Dschang trachytes represent a multilobate dome emplaced in a pulsatory manner.
ABSTRACT This book - translated, edited, and updated from the original French edition Pétrologie ... more ABSTRACT This book - translated, edited, and updated from the original French edition Pétrologie des Granites published by Vuibert in 2011 - gives a modern presentation of granitic rocks, or granites, from magma genesis to their emplacement into the crust and their crystallization. Mineralogical, petrological, physical, and economical aspects are developed in a succession of 14 chapters. Special 'info boxes' discuss topics for those wishing to deepen their knowledge of the subject. Also included is a glossary, a comprehensive bibliography, as well as descriptions of modern techniques. Granites are considered in their geological spatial and temporal frame, in relation with Plate Tectonics and Earth History, and assisted by a large number of high quality illustrations.
Data Revues 16310713 03390003 05003627, Feb 13, 2008
A coupled climate–geochemical model of new generation (GEOCLIM) is used to investigate the possib... more A coupled climate–geochemical model of new generation (GEOCLIM) is used to investigate the possible causes of the initiation of snowball glaciations during Neoproterozoic times. This model allows the calculation of the partial pressure of atmospheric CO2 simultaneously with the climate at the continental surface with a rough 2D spatial resolution (10° lat.× 50° long.). We calculate that the breakup of the Rodinia supercontinent, starting 800Myr ago, results in a global climatic cooling of about 8° C triggered by enhanced consumption of ...
ABSTRACT The end of the Neoproterozoic is characterized by ubiquitous glacial deposition being fo... more ABSTRACT The end of the Neoproterozoic is characterized by ubiquitous glacial deposition being followed by the onset of extensive carbonate platforms, marking important changes in climate. The duration of these climatic oscillations is still poorly constrained with estimates varying from hundreds to hundreds of thousand years. Here we report a high-resolution magnetostratigraphic study of Neoproterozoic cap carbonates from the Amazon Craton. These rocks represent the first transgressive carbonate sequence after glacial deposits and present the isotopic signatures and sedimentary structures that typify cap carbonates elsewhere in the world, such as negative delta13C values, tubes, aragonite-pseudomorph crystal fans, pseudo-tepees (megaripples). Age constraints are given by shifts in 87Sr/86Sr ratios towards values greater than 0.7081 and by a Pb-Pb age of 627 ± 32 Ma. Two sections five kilometers apart were sampled with a 20 cm spacing (=101 sites) and revealed five coherent reversals. Magnetization is carried by detrital hematite. These data were used to constrain both the paleogeographic position of the Amazon Craton by the end of Neoproterozoic glaciations, and the time of cap carbonate deposition (in the order of hundreds of thousand years) with implications for geochemical models. Comparison with results from correlative successions in Africa, Oman and Australia will also be presented.
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