Herve Bertrand | Université Claude Bernard Lyon 1 (original) (raw)
Papers by Herve Bertrand
Social Science Research Network, 2021
Geophysical monograph, 2003
The Central Atlantic Magmatic Province (CAMP) is defined by tholeiitic basaltic flows and dikes a... more The Central Atlantic Magmatic Province (CAMP) is defined by tholeiitic basaltic flows and dikes associated with the initial break-up of Pangea at 200 Ma, preceding the opening of the Atlantic Ocean. These tholeiites occur in once-contiguous parts of North America, Africa, South ...
HAL (Le Centre pour la Communication Scientifique Directe), 2007
International audienc
HAL (Le Centre pour la Communication Scientifique Directe), 2006
Resume Le volcanisme du bassin triasique des monts des Ksour est constitue de trois unites basalt... more Resume Le volcanisme du bassin triasique des monts des Ksour est constitue de trois unites basaltiques, separees par des intervalles sedimentaires silicoclastiques a evaporitiques et surmontees par des calcaires du Rheto-Hettangien. Ces basaltes sont des tholeiites continentales pauvres en Ti, qui montrent, de la base au sommet, la meme evolution chimique que les basaltes des bassins triasiques du Haut Atlas marocain. Ce volcanisme represente le temoin le plus oriental de la province magmatique de l’Atlantique central (CAMP) associee au rifting de l’Atlantique central, a la limite Trias–Jurassique.
Journal of African Earth Sciences, 2001
EGU General Assembly Conference Abstracts, Apr 1, 2019
The African part of the Karoo Large Igneous Province (K-LIP) comprises a range of basaltic lava f... more The African part of the Karoo Large Igneous Province (K-LIP) comprises a range of basaltic lava flows, sills, dyke swarms and evolved volcanic rocks that were emplaced approximately in the time interval between 185 to 175 Ma [1]. Currently, rocks associated with K-LIP are found between the Karoo Basin that is located in South Africa and Swaziland [2] and further north, in Zimbabwe, Mozambique, Botswana, Zambia and Namibia [1]. Available Ar-Ar ages document an apparent south-to-north migration of the magmatic activity [1]. Furthermore, the density distribution of Ar-Ar ages from K-LIP rocks suggests 2 to 3 peaks in the magmatic activity at ∼183 Ma, ∼180 Ma and ∼176 Ma respectively (e.g., [3]). The onset of the magmatic activity in the Karoo Basin at ∼183 Ma is of global importance due to the probable connection with the climatic and biotic crisis during the Toarcian oceanic anoxic event (T-OAE). The second question of importance is verifying the duration of the K-LIP, or, in other words, corroborating the apparently protracted K-LIP activity until 176 Ma by accurate zircon and baddeleyite U-Pb ages. With the goal of reducing the uncertainty between both the correlation with the T-OAE and the total duration of the K-LIP, we dated zircon and baddeleyite from a series of samples across a S-toN transect of the K-LIP: three dykes from the Karoo Basin, one rhyolite north of Swaziland and a syenite from Zimbabwe. Only considering the small dataset we report here together with the ages published in Sell et al. [4] confirms (i) the south-to-north migration of the magmatic activity over around 6 My from 183.0 to 176.7 Ma, and (ii) that the dyke emplacement in the Karoo Basin occurred over a restricted time interval between 183.01 ± 0.06 Ma and 182.68 ± 0.14 Ma. This latter result is in perfect agreement with the range of dyke U-Pb ages from Svensen et al. [2] and Corfu et al. [5] ranging from 183.4 ± 0.5 to 182.7 ± 0.6 Ma, corroborating our excellent interlaboratory reproducibility. These data support the hypothesis that a ca. 300 ky long pulse of basalt dyke injection into the sediments of the Karoo Basin, and associated release of magmatic and thermogenic volatiles into the atmosphere caused the environmental and biotic changes known as Toarcian oceanic anoxic event. Our new U-Pb data set together with the Sell et al. [4] data are as well in line with the hypothetic peaks of younger magmatic activity at ∼180 and ∼176-177 Ma. Ongoing work will study the significance of these pulses as well as temporal change of melt sources over the lifetime of the K-LIP.
Journal of Geophysical Research, Feb 10, 1993
Large-scale magmatic activity, ranging from late Oligocene to Quatemary, is associated with the R... more Large-scale magmatic activity, ranging from late Oligocene to Quatemary, is associated with the Red Sea-Gulf of Aden titling throughout the Arabian passive margin. The Southem Yemen area represents the southernmost extremity of this magmatic range, facing the Afar area, and provides a means of studying the magmatic records of early stages of rifting (30-16 Ma) in a plume-related context. We investigate major and trace elements, and Nd, Sr and Pb isotopes of a bimodal series of transitional affinity consisting of (1) thick elivine-basalt traps overlain by ignimbrific rhyolites, (2) basaltic, rhyolific, trachytic and peralkaline dykes with a prevailing N120-140 ø E orientation, and (3) gabbroic, syenitic and granitic plutons. Major and some trace element variations from basalts to felsic rocks are consistent with low-pressure fractional crystallization. Mass balance calculations using major elements suggest the fractionation of clinopyroxene (6-9%), elivine (-6%), plagioclase (42-43%), magnetite (-12%), apatite (1-2%) + alkali feldspar (16%). However, LILE (large ion lithophile element) enrichment and high initial 87Sr/86Sr ratios (up to 0.7074 and 0.710 in rhyolites and pantellerites, respectively) require the felsic rocks to be generated through significant crustal assimilation. Nd and Sr isotopic ratios of the rhyolitic traps can be reproduced by bulk mixing between magmas similar to the underlying basaltic unit and the Arabian Proterozoic basement. On the other hand, an assimilation-fractional crystallization process is required to account for the isotopic diversity of the rhyolitic and peralkaline dykes. Rhyolites can be derived from a basaltic liquid by a moderate fractionation rate (F = 0.47) and a high crustal assimilation rate (R = 0.45), whereas the pantellerites require more significant fractionation rate (F = 0.07) and a very low assimilation rate (R = 0.05). Elemental and isotopic signatures of the basalts do not support a significant crustal contribution in their formation and their isototfic diversity (87Sr/86Sr from 0.7034 to 0.7051, 143 144 206 204-Nd/ Nd from 0.512676 to 0.513045 and Pb/ Pb from 17.96 to 18.66) mainly reflects mantle source heterogeneifies. Sr-Nd-Pb isotopic data are consistent with a binary mixing between depleted and enriched source regions. The depleted end-member corresponds to an asthenospheric reservoir approaching that producing mid-ocean ridge basalts at Gulf of Aden/Red Sea spreading centers. The enriched reservoir, intermediate between enriched mantle I and II end-members, is supposed to be located within old subcontinental lithosphere related to the Pan-African orogenic events. Unlike the modem volcanics from Afar, no HIMU (high U/Pb ratio) signature has been recognized in our sampling. This rules out any significant chemical influence of the Afar plume upon early rift-related volcanism in Southern Yemen and suggests a continental rift initiation of passive type. [towever, one can suspect that the Afar plume may have supplied the excess heat required to produce so voluminous traps and to trigger melting in the lithospheric mantle, making the distinction between passive and active rifling more ambiguous.
Geology, 2005
The peak activities of continental flood basalts are currently considered as huge and brief (ϳ1 m... more The peak activities of continental flood basalts are currently considered as huge and brief (ϳ1 m.y.) magmatic events, with strong implications for geodynamics and biotic turnover. New 40 Ar/ 39 Ar dates on the Karoo flood basalts (southern Africa) show a longer duration of magmatism (ϳ8 m.y., with 6 m.y. for the main volume) with an apparent south-to-north migration, along with briefer distinctive pulses inside the province. This suggests that the Karoo province does not fit the general plume model invoked for most continental flood basalts (including the Karoo) and may explain the absence of a major contemporaneous mass extinction.
Comptes Rendus Geoscience, 2007
Resume Le volcanisme du bassin triasique des monts des Ksour est constitue de trois unites basalt... more Resume Le volcanisme du bassin triasique des monts des Ksour est constitue de trois unites basaltiques, separees par des intervalles sedimentaires silicoclastiques a evaporitiques et surmontees par des calcaires du Rheto-Hettangien. Ces basaltes sont des tholeiites continentales pauvres en Ti, qui montrent, de la base au sommet, la meme evolution chimique que les basaltes des bassins triasiques du Haut Atlas marocain. Ce volcanisme represente le temoin le plus oriental de la province magmatique de l’Atlantique central (CAMP) associee au rifting de l’Atlantique central, a la limite Trias–Jurassique.
Journal of Volcanology and Geothermal Research, Aug 1, 2013
Highlights ► New geochemical study with Hf-Pb isotopes of Lopevi, including recent and old lavas ... more Highlights ► New geochemical study with Hf-Pb isotopes of Lopevi, including recent and old lavas ► Evidences for interactions between ascending magmas and sub-arc crust ► Evidence for short time scale mantle source variations (~ 20 years) ► Involvement of a different metasomatic agent in the pre-and post-1960 lavas
Journal of Volcanology and Geothermal Research, Aug 1, 2016
Gaua Island (also called Santa Maria), from the central part of the Vanuatu arc, consists of a la... more Gaua Island (also called Santa Maria), from the central part of the Vanuatu arc, consists of a large volcano marked by a caldera that hosts the active Mount Garet summit cone. In this paper, a geochemical study including Sr, Nd, Pb and Hf isotopic compositions of 25 lavas emitted since 1.8 Ma is presented, with a focus on the volcanic products that preceded (old volcanics, main cone and pyroclastic series) and followed (Mount Garet) the caldera forming event. All lavas show an island arc signature with enrichment in LILE and depletion in HFSE. Post-caldera lavas define a medium-K calc-alkaline trend, whereas lavas from the former main cone have high-K calc-alkaline compositions. Compared to the pre-caldera volcanic suite, the Mount Garet lavas have similar Th/Nb (~ 1.5), 143Nd/144Nd (~ 0.51295) and 176Hf/177Hf (~ 0.28316) ratios, but higher Ba/La (~ 42 vs. ~ 27) and 87Sr/86Sr (0.70417 vs. 0.70405) ratios and lower Ce/Pb (~ 2.7 vs. ~ 4.6), La/Sm (~ 2.5 vs. ~ 4.0) and 206Pb/204Pb (18.105 vs. 18.176) ratios. High Th/Nb and low Nd and Hf isotopic ratios compared to N-MORB suggest the contribution of ~ 2% of subducted sediment melt to the mantle source of Gaua magmas. Most of the observed differences between pre-and post-caldera lavas can be accounted for by the involvement of at least two portions of the mantle wedge, metasomatized by different slab-derived aqueous fluids. In addition, the lower La/Sm (at a given 143Nd/144Nd) ratios of Mount Garet lavas suggest a higher degree of partial melting (~ 10-15%) compared to the pre-caldera lavas (~ 5%). The Santa Maria Pyroclastic Series (SMPS) eruption probably triggered the caldera collapse, in response to emptying of the magmatic chamber. This event may have allowed new access to the surface for a geochemically distinct batch of magma issued from a separate magma chamber, resulting in the birth and construction of Mount Garet within the caldera. As both magmatic suites were emitted over a very short time, the storage of their parental magmas beneath the volcano is still possible. Highlights ► New Hf-Pb isotopes and geochemical study of Gaua, on pre-and post-caldera lavas ► Post-caldera lavas are geochemically distinct from older lavas. ► Evidences of short-term changes in the mantle source ► Involvement of different metasomatic agents and variable degrees of partial melting ► Pyroclastic Series eruption triggered caldera collapse and gave access to new magma.
Bulletin De La Societe Geologique De France, 1977
Proceedings of the Ocean Drilling Program, Feb 1, 1990
During ODP Leg 107, two holes were drilled in the basement of Vavilov Basin, a central oceanic ar... more During ODP Leg 107, two holes were drilled in the basement of Vavilov Basin, a central oceanic area of the Tyrrhe nian sea. Hole 655B is located near the Gortani ridge in off-axis position at the western rim of the basin; Hole 651A is located on a basement swell at the axis of the basin. This paper deals with mineral chemistry, major and trace element geochemistry, and petrogenesis of the basalts recovered in the two holes. The mineralogy of the basalts is broadly homogeneous, but all of them have suffered important seawater alteration. Their major-element compositions are similar to both normal-mid-ocean-ridge-basalts (N-MORB) and back-arc-basalts (BAB) except for Na 2 0 contents (BAB-like), and K 2 0 which is somewhat enriched in upper unit of Hole 651 A. Their affinity with N-MORB and BAB is confirmed by using immobile trace elements such as Zr, Y, and Nb. However, basalts from the two sites present contrasting geochemical characteristics on spidergrams using incompatible elements. Hole 655B basalts are homogeneous enriched tholeiites, similar to those from DSDP Hole 373 (located on the opposite side of the basin near the eastern rim), and show affinities with enriched MORB (E-MORB). At Hole 651 A, the two basalt units are chemically distinct. One sample recovered in lower unit is rather similar to those from Hole 655B, but basalts from upper unit display calc-alkaline characteristic evidenced by the increase of light-ion-lithophile-element (LILE)/ high-field-strength-element (HFSE) ratio, and appearance of a negative Nb-anomaly, making them comparable with orogenic lavas from the adjacent Eolian arc. The observed chemical compositions of the basalts are consistent with a derivation of the magmas from a N-MORB type source progressively contaminated by LILE-enriched fluids released from dehydration of the bordering subducted plate. Implications for evolution of the Tyrrhenian basin are tentatively proposed taking into consideration geochemical and chronological relationships between basalts from Leg 107 Holes 655B and 651 A, together with data from Leg 42 Site 373 and Vavilov Seamount. These data illustrate back-arc spreading in ensialic basin closely associated with the maturation of the adjacent subduction, followed by the growth of late off-axis central volcano, whereas the active sub duction retreats southeastward.
Contributions to Mineralogy and Petrology, 1977
Results in geochemistry, Sep 1, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Geophysical Research Letters, Feb 1, 1991
ABSTRACT The early opening of the Red Sea rift is accompanied by tholeiitic magmatism stretching ... more ABSTRACT The early opening of the Red Sea rift is accompanied by tholeiitic magmatism stretching at least 1700 km along the western coast of Saudi Arabia, and consisting of thick gabbroic dykes, dense dyke swarms, plutons and discrete lava flows. Whereas the conventional K-Ar measurements have furnished a wide variety of ages, the 40Ar/39Ar analyses presented here (giving 17 plateau-ages) display a pronounced cluster of ages from 24 to 21 Ma. Such a short-lived magmatic event has been suggested for other continental rifts.
Geochemistry Geophysics Geosystems, Jun 1, 2008
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Copyright 40Ar/39Ar ages of the sill complex of the Karoo large igneous province: implications for the Pliensbachian-Toarcian climate change.
HAL (Le Centre pour la Communication Scientifique Directe), 2007
International audienc
Social Science Research Network, 2021
Geophysical monograph, 2003
The Central Atlantic Magmatic Province (CAMP) is defined by tholeiitic basaltic flows and dikes a... more The Central Atlantic Magmatic Province (CAMP) is defined by tholeiitic basaltic flows and dikes associated with the initial break-up of Pangea at 200 Ma, preceding the opening of the Atlantic Ocean. These tholeiites occur in once-contiguous parts of North America, Africa, South ...
HAL (Le Centre pour la Communication Scientifique Directe), 2007
International audienc
HAL (Le Centre pour la Communication Scientifique Directe), 2006
Resume Le volcanisme du bassin triasique des monts des Ksour est constitue de trois unites basalt... more Resume Le volcanisme du bassin triasique des monts des Ksour est constitue de trois unites basaltiques, separees par des intervalles sedimentaires silicoclastiques a evaporitiques et surmontees par des calcaires du Rheto-Hettangien. Ces basaltes sont des tholeiites continentales pauvres en Ti, qui montrent, de la base au sommet, la meme evolution chimique que les basaltes des bassins triasiques du Haut Atlas marocain. Ce volcanisme represente le temoin le plus oriental de la province magmatique de l’Atlantique central (CAMP) associee au rifting de l’Atlantique central, a la limite Trias–Jurassique.
Journal of African Earth Sciences, 2001
EGU General Assembly Conference Abstracts, Apr 1, 2019
The African part of the Karoo Large Igneous Province (K-LIP) comprises a range of basaltic lava f... more The African part of the Karoo Large Igneous Province (K-LIP) comprises a range of basaltic lava flows, sills, dyke swarms and evolved volcanic rocks that were emplaced approximately in the time interval between 185 to 175 Ma [1]. Currently, rocks associated with K-LIP are found between the Karoo Basin that is located in South Africa and Swaziland [2] and further north, in Zimbabwe, Mozambique, Botswana, Zambia and Namibia [1]. Available Ar-Ar ages document an apparent south-to-north migration of the magmatic activity [1]. Furthermore, the density distribution of Ar-Ar ages from K-LIP rocks suggests 2 to 3 peaks in the magmatic activity at ∼183 Ma, ∼180 Ma and ∼176 Ma respectively (e.g., [3]). The onset of the magmatic activity in the Karoo Basin at ∼183 Ma is of global importance due to the probable connection with the climatic and biotic crisis during the Toarcian oceanic anoxic event (T-OAE). The second question of importance is verifying the duration of the K-LIP, or, in other words, corroborating the apparently protracted K-LIP activity until 176 Ma by accurate zircon and baddeleyite U-Pb ages. With the goal of reducing the uncertainty between both the correlation with the T-OAE and the total duration of the K-LIP, we dated zircon and baddeleyite from a series of samples across a S-toN transect of the K-LIP: three dykes from the Karoo Basin, one rhyolite north of Swaziland and a syenite from Zimbabwe. Only considering the small dataset we report here together with the ages published in Sell et al. [4] confirms (i) the south-to-north migration of the magmatic activity over around 6 My from 183.0 to 176.7 Ma, and (ii) that the dyke emplacement in the Karoo Basin occurred over a restricted time interval between 183.01 ± 0.06 Ma and 182.68 ± 0.14 Ma. This latter result is in perfect agreement with the range of dyke U-Pb ages from Svensen et al. [2] and Corfu et al. [5] ranging from 183.4 ± 0.5 to 182.7 ± 0.6 Ma, corroborating our excellent interlaboratory reproducibility. These data support the hypothesis that a ca. 300 ky long pulse of basalt dyke injection into the sediments of the Karoo Basin, and associated release of magmatic and thermogenic volatiles into the atmosphere caused the environmental and biotic changes known as Toarcian oceanic anoxic event. Our new U-Pb data set together with the Sell et al. [4] data are as well in line with the hypothetic peaks of younger magmatic activity at ∼180 and ∼176-177 Ma. Ongoing work will study the significance of these pulses as well as temporal change of melt sources over the lifetime of the K-LIP.
Journal of Geophysical Research, Feb 10, 1993
Large-scale magmatic activity, ranging from late Oligocene to Quatemary, is associated with the R... more Large-scale magmatic activity, ranging from late Oligocene to Quatemary, is associated with the Red Sea-Gulf of Aden titling throughout the Arabian passive margin. The Southem Yemen area represents the southernmost extremity of this magmatic range, facing the Afar area, and provides a means of studying the magmatic records of early stages of rifting (30-16 Ma) in a plume-related context. We investigate major and trace elements, and Nd, Sr and Pb isotopes of a bimodal series of transitional affinity consisting of (1) thick elivine-basalt traps overlain by ignimbrific rhyolites, (2) basaltic, rhyolific, trachytic and peralkaline dykes with a prevailing N120-140 ø E orientation, and (3) gabbroic, syenitic and granitic plutons. Major and some trace element variations from basalts to felsic rocks are consistent with low-pressure fractional crystallization. Mass balance calculations using major elements suggest the fractionation of clinopyroxene (6-9%), elivine (-6%), plagioclase (42-43%), magnetite (-12%), apatite (1-2%) + alkali feldspar (16%). However, LILE (large ion lithophile element) enrichment and high initial 87Sr/86Sr ratios (up to 0.7074 and 0.710 in rhyolites and pantellerites, respectively) require the felsic rocks to be generated through significant crustal assimilation. Nd and Sr isotopic ratios of the rhyolitic traps can be reproduced by bulk mixing between magmas similar to the underlying basaltic unit and the Arabian Proterozoic basement. On the other hand, an assimilation-fractional crystallization process is required to account for the isotopic diversity of the rhyolitic and peralkaline dykes. Rhyolites can be derived from a basaltic liquid by a moderate fractionation rate (F = 0.47) and a high crustal assimilation rate (R = 0.45), whereas the pantellerites require more significant fractionation rate (F = 0.07) and a very low assimilation rate (R = 0.05). Elemental and isotopic signatures of the basalts do not support a significant crustal contribution in their formation and their isototfic diversity (87Sr/86Sr from 0.7034 to 0.7051, 143 144 206 204-Nd/ Nd from 0.512676 to 0.513045 and Pb/ Pb from 17.96 to 18.66) mainly reflects mantle source heterogeneifies. Sr-Nd-Pb isotopic data are consistent with a binary mixing between depleted and enriched source regions. The depleted end-member corresponds to an asthenospheric reservoir approaching that producing mid-ocean ridge basalts at Gulf of Aden/Red Sea spreading centers. The enriched reservoir, intermediate between enriched mantle I and II end-members, is supposed to be located within old subcontinental lithosphere related to the Pan-African orogenic events. Unlike the modem volcanics from Afar, no HIMU (high U/Pb ratio) signature has been recognized in our sampling. This rules out any significant chemical influence of the Afar plume upon early rift-related volcanism in Southern Yemen and suggests a continental rift initiation of passive type. [towever, one can suspect that the Afar plume may have supplied the excess heat required to produce so voluminous traps and to trigger melting in the lithospheric mantle, making the distinction between passive and active rifling more ambiguous.
Geology, 2005
The peak activities of continental flood basalts are currently considered as huge and brief (ϳ1 m... more The peak activities of continental flood basalts are currently considered as huge and brief (ϳ1 m.y.) magmatic events, with strong implications for geodynamics and biotic turnover. New 40 Ar/ 39 Ar dates on the Karoo flood basalts (southern Africa) show a longer duration of magmatism (ϳ8 m.y., with 6 m.y. for the main volume) with an apparent south-to-north migration, along with briefer distinctive pulses inside the province. This suggests that the Karoo province does not fit the general plume model invoked for most continental flood basalts (including the Karoo) and may explain the absence of a major contemporaneous mass extinction.
Comptes Rendus Geoscience, 2007
Resume Le volcanisme du bassin triasique des monts des Ksour est constitue de trois unites basalt... more Resume Le volcanisme du bassin triasique des monts des Ksour est constitue de trois unites basaltiques, separees par des intervalles sedimentaires silicoclastiques a evaporitiques et surmontees par des calcaires du Rheto-Hettangien. Ces basaltes sont des tholeiites continentales pauvres en Ti, qui montrent, de la base au sommet, la meme evolution chimique que les basaltes des bassins triasiques du Haut Atlas marocain. Ce volcanisme represente le temoin le plus oriental de la province magmatique de l’Atlantique central (CAMP) associee au rifting de l’Atlantique central, a la limite Trias–Jurassique.
Journal of Volcanology and Geothermal Research, Aug 1, 2013
Highlights ► New geochemical study with Hf-Pb isotopes of Lopevi, including recent and old lavas ... more Highlights ► New geochemical study with Hf-Pb isotopes of Lopevi, including recent and old lavas ► Evidences for interactions between ascending magmas and sub-arc crust ► Evidence for short time scale mantle source variations (~ 20 years) ► Involvement of a different metasomatic agent in the pre-and post-1960 lavas
Journal of Volcanology and Geothermal Research, Aug 1, 2016
Gaua Island (also called Santa Maria), from the central part of the Vanuatu arc, consists of a la... more Gaua Island (also called Santa Maria), from the central part of the Vanuatu arc, consists of a large volcano marked by a caldera that hosts the active Mount Garet summit cone. In this paper, a geochemical study including Sr, Nd, Pb and Hf isotopic compositions of 25 lavas emitted since 1.8 Ma is presented, with a focus on the volcanic products that preceded (old volcanics, main cone and pyroclastic series) and followed (Mount Garet) the caldera forming event. All lavas show an island arc signature with enrichment in LILE and depletion in HFSE. Post-caldera lavas define a medium-K calc-alkaline trend, whereas lavas from the former main cone have high-K calc-alkaline compositions. Compared to the pre-caldera volcanic suite, the Mount Garet lavas have similar Th/Nb (~ 1.5), 143Nd/144Nd (~ 0.51295) and 176Hf/177Hf (~ 0.28316) ratios, but higher Ba/La (~ 42 vs. ~ 27) and 87Sr/86Sr (0.70417 vs. 0.70405) ratios and lower Ce/Pb (~ 2.7 vs. ~ 4.6), La/Sm (~ 2.5 vs. ~ 4.0) and 206Pb/204Pb (18.105 vs. 18.176) ratios. High Th/Nb and low Nd and Hf isotopic ratios compared to N-MORB suggest the contribution of ~ 2% of subducted sediment melt to the mantle source of Gaua magmas. Most of the observed differences between pre-and post-caldera lavas can be accounted for by the involvement of at least two portions of the mantle wedge, metasomatized by different slab-derived aqueous fluids. In addition, the lower La/Sm (at a given 143Nd/144Nd) ratios of Mount Garet lavas suggest a higher degree of partial melting (~ 10-15%) compared to the pre-caldera lavas (~ 5%). The Santa Maria Pyroclastic Series (SMPS) eruption probably triggered the caldera collapse, in response to emptying of the magmatic chamber. This event may have allowed new access to the surface for a geochemically distinct batch of magma issued from a separate magma chamber, resulting in the birth and construction of Mount Garet within the caldera. As both magmatic suites were emitted over a very short time, the storage of their parental magmas beneath the volcano is still possible. Highlights ► New Hf-Pb isotopes and geochemical study of Gaua, on pre-and post-caldera lavas ► Post-caldera lavas are geochemically distinct from older lavas. ► Evidences of short-term changes in the mantle source ► Involvement of different metasomatic agents and variable degrees of partial melting ► Pyroclastic Series eruption triggered caldera collapse and gave access to new magma.
Bulletin De La Societe Geologique De France, 1977
Proceedings of the Ocean Drilling Program, Feb 1, 1990
During ODP Leg 107, two holes were drilled in the basement of Vavilov Basin, a central oceanic ar... more During ODP Leg 107, two holes were drilled in the basement of Vavilov Basin, a central oceanic area of the Tyrrhe nian sea. Hole 655B is located near the Gortani ridge in off-axis position at the western rim of the basin; Hole 651A is located on a basement swell at the axis of the basin. This paper deals with mineral chemistry, major and trace element geochemistry, and petrogenesis of the basalts recovered in the two holes. The mineralogy of the basalts is broadly homogeneous, but all of them have suffered important seawater alteration. Their major-element compositions are similar to both normal-mid-ocean-ridge-basalts (N-MORB) and back-arc-basalts (BAB) except for Na 2 0 contents (BAB-like), and K 2 0 which is somewhat enriched in upper unit of Hole 651 A. Their affinity with N-MORB and BAB is confirmed by using immobile trace elements such as Zr, Y, and Nb. However, basalts from the two sites present contrasting geochemical characteristics on spidergrams using incompatible elements. Hole 655B basalts are homogeneous enriched tholeiites, similar to those from DSDP Hole 373 (located on the opposite side of the basin near the eastern rim), and show affinities with enriched MORB (E-MORB). At Hole 651 A, the two basalt units are chemically distinct. One sample recovered in lower unit is rather similar to those from Hole 655B, but basalts from upper unit display calc-alkaline characteristic evidenced by the increase of light-ion-lithophile-element (LILE)/ high-field-strength-element (HFSE) ratio, and appearance of a negative Nb-anomaly, making them comparable with orogenic lavas from the adjacent Eolian arc. The observed chemical compositions of the basalts are consistent with a derivation of the magmas from a N-MORB type source progressively contaminated by LILE-enriched fluids released from dehydration of the bordering subducted plate. Implications for evolution of the Tyrrhenian basin are tentatively proposed taking into consideration geochemical and chronological relationships between basalts from Leg 107 Holes 655B and 651 A, together with data from Leg 42 Site 373 and Vavilov Seamount. These data illustrate back-arc spreading in ensialic basin closely associated with the maturation of the adjacent subduction, followed by the growth of late off-axis central volcano, whereas the active sub duction retreats southeastward.
Contributions to Mineralogy and Petrology, 1977
Results in geochemistry, Sep 1, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Geophysical Research Letters, Feb 1, 1991
ABSTRACT The early opening of the Red Sea rift is accompanied by tholeiitic magmatism stretching ... more ABSTRACT The early opening of the Red Sea rift is accompanied by tholeiitic magmatism stretching at least 1700 km along the western coast of Saudi Arabia, and consisting of thick gabbroic dykes, dense dyke swarms, plutons and discrete lava flows. Whereas the conventional K-Ar measurements have furnished a wide variety of ages, the 40Ar/39Ar analyses presented here (giving 17 plateau-ages) display a pronounced cluster of ages from 24 to 21 Ma. Such a short-lived magmatic event has been suggested for other continental rifts.
Geochemistry Geophysics Geosystems, Jun 1, 2008
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Copyright 40Ar/39Ar ages of the sill complex of the Karoo large igneous province: implications for the Pliensbachian-Toarcian climate change.
HAL (Le Centre pour la Communication Scientifique Directe), 2007
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