Eric Humler - Academia.edu (original) (raw)

Papers by Eric Humler

Research paper thumbnail of Symptoms of stress in the post KT coastal ecosystem of Rajahmundry (SE India) in relationship with Deccan giant lava flows

Research paper thumbnail of Isotopic systematics of an ultra-slow spreading centre: The Southwest Indian Ridge

The eastern extremity of the Southwest Indian Ridge (SWIR) is one of the deepest (4000--5000 m) a... more The eastern extremity of the Southwest Indian Ridge (SWIR) is one of the deepest (4000--5000 m) and slowest spreading (full rate: 11--15 mm.y-1) parts of the global mid-ocean ridge system. Based on contrasts in seafloor morphology, the eastern extremity between 49^oE and the Rodriguez Triple Junction (RTJ) can be divided into three provinces separated by two major boundaries: the Melville Fracture Zone (MFZ, 60^o45'E) and the Gallieni Fracture Zone (GaFZ, 52^o20'E). Basaltic glasses located east of the MFZ differ from all other MORB in having higher Na8.0, Sr, Al_2O_3 and lower CaO/Al_2O_3, Ti8.0 and HREE. Basalts to the west generally overlap the compositional field defined by North-Atlantic lavas. Here, we present double spike high precision Pb-isotope and Sr-Nd-isotope data for these basaltic glasses, dredged during the EDUL cruise (R/V Marion Dufresne, summer 1997). The along-axis (Sr-Nd-Pb) isotopic patterns define five distinct isotopic domains in which adjacent domains are sharply bounded by transform faults. The longitudinal organization of the isotopic domains do not generally coincide with the boundaries of the geochemical provinces defined previously on the basis of major and trace geochemical compositions. The section located to the east of the MFZ is different chemically and isotopically from the RTJ. A rather abrupt eastern boundary to Southwest Indian Ridge type compositions occurs at, or very near, the RTJ. Samples from the section located between the Novara FZ and MFZ are characterised by some of the highest 143Nd/144Nd ratios (0.51309--0.51315) encountered to date along the SWIR. These lavas also display some of the most unradiogenic Pb-Sr isotopic compositions (206Pb/204Pb =17.363--17.450, 87Sr/86Sr= 0.70258--0.70289) among the Indian MORB population. However, these lavas are still characterised by elevated Delta7/4 (1.9--2.2) and Delta8/4 (41.1--45.1) typical of Indian MORB. These features are unlike the extreme DUPAL signature exhibited by the 39--41^oE section of the SWIR. The unradiogenic Pb-Sr and radiogenic Nd of these lavas appear difficult to reconcile with models suggesting recycling of pelagic sediment for the origin of the distinctive Pb isotopic signature of Indian MORB.

Research paper thumbnail of Isotopic variations along the Southwest Indian Ridge, 30-50°E

Research paper thumbnail of Constraints on the DUPAL anomaly from helium isotope systematics in the Southwest Indian mid-ocean ridge basalts

Research paper thumbnail of Fe3+/∑Fe vs. FeLα peak energy for minerals and glasses: Recent advances with the electron microprobe

American Mineralogist, Apr 1, 2001

Research paper thumbnail of Direct determination of ferrous-ferric concentrations with the electron microprobe

Research paper thumbnail of Influence of crustal thickness on partial melting in subduction zones : numerical modelling basis and first results

Research paper thumbnail of A > 26 Myrs record of melt supply variations and axial tectonics in a magma-poor region of the very slow spreading Southwest Indian Ridge

Geochimica et Cosmochimica Acta

Research paper thumbnail of Campagne SWIFT sur la dorsale Sud Ouest Indienne entre 30°E et 50°E (N.O. Marion Dufresne, du 14 février au 21 mars 2001). Caractérisation géophysique et géochimique

Research paper thumbnail of Fe3+/ΣFe vs. FeLα peak energy for minerals and glasses: Recent advances with the electron microprobe

American Mineralogist, 2001

Research paper thumbnail of Continental Flood Basalt Chemistry, Age and Volcanic Volumes

We have compiled a large collection of published chemical analyses of the 11 known continental fl... more We have compiled a large collection of published chemical analyses of the 11 known continental flood basalts of the last 250 millions years. Only basaltic lavas and some related basic intrusive rocks are considered to be representative of the major episodes. Differentiation trends exhibit varying amounts of scatter, the trends for SiO2, FeO, and TiO2 are quite well defined, have slopes of the same sign, and can be represented adaquately by straigth lines. In contrast, the trends of CaO, Al2O3 and Na2O are often poorly defined. There are clear differences in major element abundances between volcanic suites, particularly for elements with well defined slopes. The results of our regressions are generally consistent with those of Turner and Hawkesworth (1995), Peng et al (1994) and Lassister and DePaolo (1997), although some differences exist. Examination of the global data base shows that there are systematic global variations in continental flood basalt chemistry that correlate with a...

Research paper thumbnail of The Upper Mantle Flow Field around South-Africa as Reflected by Isotopic Provinciality

Isotopic studies of MORB have established the existence of broad isotopic provinces within the un... more Isotopic studies of MORB have established the existence of broad isotopic provinces within the underlying asthenosphere, such as in the Indian Ocean (DUPAL). How these features relate to mantle circulation is, however, still unknown. The steepness of the transition between such isotopic provinces will define the geometry of the velocity field in the upper mantle. In this respect, the transition between the Indian and South Atlantic provinces, two domains that are isotopically contrasted, should be readily identifiable over this long ridge segment. Here, we present Hf isotope data for 60 samples dredged along the SWIR between 35° and 69°E. The new Hf isotope data show that the Indian asthenosphere does not spill directly into the South Atlantic upper mantle: the general decreasing southward gradient observed for ^{176}Hf/^{177}Hf down the mid- Atlantic Ridge, and also for Sr isotopes and model Th/U ratios (derived from Pb isotopes), is overprinted by material with radiogenic Sr, unra...

Research paper thumbnail of Helium and trace element geochemical signals in the southwest Indian Ocean

Geochmica et Cosmochimica Acta

Research paper thumbnail of CO2/N2 in MORB vesicles using Raman spectroscopy: Implications for global volatile fluxes

Geochmica et Cosmochimica Acta

Research paper thumbnail of Periodicity in the accretion process on the Southeast Indian Ridge at 27°40′S

Research paper thumbnail of The chemical composition of the Earth

Research paper thumbnail of Global correlations of mid-ocean-ridge basalt chemistry with seismic tomographic images

Research paper thumbnail of Colorimetric Fe2+ measurements and the Fe3+/ΣFe ratio of glassy lavas from the Lau and East Scotia back-arc basins

It has been clearly shown that subduction fluids are related to greater oxidation state in arc an... more It has been clearly shown that subduction fluids are related to greater oxidation state in arc and backarc magmas compared to mid oceanic ridge basalts. However, little is known on the nature of the processes that may cause this shift in oxidation, and there is furthermore no real evidence that the source itself gets oxidized. In order to assess the role of subduction fluids on the oxidation states of back-arc magmas and of their source, we have applied a colorimetric method to analyze FeO contents in glassy samples using 7 to 10 mg of samples (Wilson, 1960; Kilinc et al., 1983). Our FeO measurements on 6 geo-referenced materials and 2 internal standards agree within 0.71% (relative) with the recommended values and within 0.10 % (relative) with the study of Bézos & Humler (2005). Replicate analyses on standards (3 different dissolutions) give a precision of 0.05 % on FeO measurements. We have applied this analytical protocol on glassy samples from the Lau and East Scotia backarc bas...

Research paper thumbnail of An experimental protocol for determining ferrous to ferric ratios in glasses with the electron microprobe

ABSTRACT The presence of an unfilled 3d electron shell in the transition metals of the first seri... more ABSTRACT The presence of an unfilled 3d electron shell in the transition metals of the first series is manifested in x-ray self-absorption effects that cause distortions in the L emission spectra. In particular, one observes peak shape changes and peak position shifts towards lower energies which are attributed to x-ray photon self-absorption in the specimen. Self-absorption corresponds to partial overlap of both L-emission and absorption transitions in the region of the Fermi level. Such an overlap is related to relaxation effects consecutive to the creation of the core hole in the studied ions. For iron, the overlap between the Fe La emission peak and the corresponding Fe LIII absorption band is clearly higher for Fe2+ than for Fe3+, leading to enhanced self-aborption induced shift of the Fe La peak for Fe2+. The shift of the La peak between Fe2+ and Fe3+ can be measured with the electron microprobe and hence exploited to determine the Fe3+/SFe ratios in silicates and glasses. For that purpose, an empirical method has been established based on working curves constructed from reference materials. A complete set of working curves is presented for glasses as well as an original experimental protocol. Most glasses are electron beam sensitive and suffer especially from beam-induced oxido-reduction mechanisms that are related to the implanted charge. The flux of Na+ ions from surface to the depth of the glass (drived by the electric field induced by the electrostatic charge) tends to oxidize the surface whereas, concurrently, the counterflux of electron produced by excitonic mechanisms and trapped at Fe3+ sites tends to reduce the surface. Therefore operating conditions should be set to minimise these phenomena that are source of large discrepancies in Fe3+/SFe. The application of the current protocol gives uncertainties of about ±5% absolute for specimens with nominal total Fe concentrations ranging from 6 to 9 wt% (accuracy and precision on Fe3+/SFe dramatically depend on the total Fe wt% concentration). Results obtained from a suite of basaltic glasses exhibit errors higher than ±5% absolute. Improved performances are expected for the method after the method can be used with promising new high resolution and high sensibility x-ray optics.

Research paper thumbnail of New constrains on ridge-hotspot interactions from the PLURIEL Cruise, Saint Paul-Amsterdam Plateau, Indian Ocean

10th International Congress of the Brazilian Geophysical Society & EXPOGEF 2007, Rio de Janeiro, Brazil, 19-23 November 2007, 2007

Research paper thumbnail of Symptoms of stress in the post KT coastal ecosystem of Rajahmundry (SE India) in relationship with Deccan giant lava flows

Research paper thumbnail of Isotopic systematics of an ultra-slow spreading centre: The Southwest Indian Ridge

The eastern extremity of the Southwest Indian Ridge (SWIR) is one of the deepest (4000--5000 m) a... more The eastern extremity of the Southwest Indian Ridge (SWIR) is one of the deepest (4000--5000 m) and slowest spreading (full rate: 11--15 mm.y-1) parts of the global mid-ocean ridge system. Based on contrasts in seafloor morphology, the eastern extremity between 49^oE and the Rodriguez Triple Junction (RTJ) can be divided into three provinces separated by two major boundaries: the Melville Fracture Zone (MFZ, 60^o45'E) and the Gallieni Fracture Zone (GaFZ, 52^o20'E). Basaltic glasses located east of the MFZ differ from all other MORB in having higher Na8.0, Sr, Al_2O_3 and lower CaO/Al_2O_3, Ti8.0 and HREE. Basalts to the west generally overlap the compositional field defined by North-Atlantic lavas. Here, we present double spike high precision Pb-isotope and Sr-Nd-isotope data for these basaltic glasses, dredged during the EDUL cruise (R/V Marion Dufresne, summer 1997). The along-axis (Sr-Nd-Pb) isotopic patterns define five distinct isotopic domains in which adjacent domains are sharply bounded by transform faults. The longitudinal organization of the isotopic domains do not generally coincide with the boundaries of the geochemical provinces defined previously on the basis of major and trace geochemical compositions. The section located to the east of the MFZ is different chemically and isotopically from the RTJ. A rather abrupt eastern boundary to Southwest Indian Ridge type compositions occurs at, or very near, the RTJ. Samples from the section located between the Novara FZ and MFZ are characterised by some of the highest 143Nd/144Nd ratios (0.51309--0.51315) encountered to date along the SWIR. These lavas also display some of the most unradiogenic Pb-Sr isotopic compositions (206Pb/204Pb =17.363--17.450, 87Sr/86Sr= 0.70258--0.70289) among the Indian MORB population. However, these lavas are still characterised by elevated Delta7/4 (1.9--2.2) and Delta8/4 (41.1--45.1) typical of Indian MORB. These features are unlike the extreme DUPAL signature exhibited by the 39--41^oE section of the SWIR. The unradiogenic Pb-Sr and radiogenic Nd of these lavas appear difficult to reconcile with models suggesting recycling of pelagic sediment for the origin of the distinctive Pb isotopic signature of Indian MORB.

Research paper thumbnail of Isotopic variations along the Southwest Indian Ridge, 30-50°E

Research paper thumbnail of Constraints on the DUPAL anomaly from helium isotope systematics in the Southwest Indian mid-ocean ridge basalts

Research paper thumbnail of Fe3+/∑Fe vs. FeLα peak energy for minerals and glasses: Recent advances with the electron microprobe

American Mineralogist, Apr 1, 2001

Research paper thumbnail of Direct determination of ferrous-ferric concentrations with the electron microprobe

Research paper thumbnail of Influence of crustal thickness on partial melting in subduction zones : numerical modelling basis and first results

Research paper thumbnail of A > 26 Myrs record of melt supply variations and axial tectonics in a magma-poor region of the very slow spreading Southwest Indian Ridge

Geochimica et Cosmochimica Acta

Research paper thumbnail of Campagne SWIFT sur la dorsale Sud Ouest Indienne entre 30°E et 50°E (N.O. Marion Dufresne, du 14 février au 21 mars 2001). Caractérisation géophysique et géochimique

Research paper thumbnail of Fe3+/ΣFe vs. FeLα peak energy for minerals and glasses: Recent advances with the electron microprobe

American Mineralogist, 2001

Research paper thumbnail of Continental Flood Basalt Chemistry, Age and Volcanic Volumes

We have compiled a large collection of published chemical analyses of the 11 known continental fl... more We have compiled a large collection of published chemical analyses of the 11 known continental flood basalts of the last 250 millions years. Only basaltic lavas and some related basic intrusive rocks are considered to be representative of the major episodes. Differentiation trends exhibit varying amounts of scatter, the trends for SiO2, FeO, and TiO2 are quite well defined, have slopes of the same sign, and can be represented adaquately by straigth lines. In contrast, the trends of CaO, Al2O3 and Na2O are often poorly defined. There are clear differences in major element abundances between volcanic suites, particularly for elements with well defined slopes. The results of our regressions are generally consistent with those of Turner and Hawkesworth (1995), Peng et al (1994) and Lassister and DePaolo (1997), although some differences exist. Examination of the global data base shows that there are systematic global variations in continental flood basalt chemistry that correlate with a...

Research paper thumbnail of The Upper Mantle Flow Field around South-Africa as Reflected by Isotopic Provinciality

Isotopic studies of MORB have established the existence of broad isotopic provinces within the un... more Isotopic studies of MORB have established the existence of broad isotopic provinces within the underlying asthenosphere, such as in the Indian Ocean (DUPAL). How these features relate to mantle circulation is, however, still unknown. The steepness of the transition between such isotopic provinces will define the geometry of the velocity field in the upper mantle. In this respect, the transition between the Indian and South Atlantic provinces, two domains that are isotopically contrasted, should be readily identifiable over this long ridge segment. Here, we present Hf isotope data for 60 samples dredged along the SWIR between 35° and 69°E. The new Hf isotope data show that the Indian asthenosphere does not spill directly into the South Atlantic upper mantle: the general decreasing southward gradient observed for ^{176}Hf/^{177}Hf down the mid- Atlantic Ridge, and also for Sr isotopes and model Th/U ratios (derived from Pb isotopes), is overprinted by material with radiogenic Sr, unra...

Research paper thumbnail of Helium and trace element geochemical signals in the southwest Indian Ocean

Geochmica et Cosmochimica Acta

Research paper thumbnail of CO2/N2 in MORB vesicles using Raman spectroscopy: Implications for global volatile fluxes

Geochmica et Cosmochimica Acta

Research paper thumbnail of Periodicity in the accretion process on the Southeast Indian Ridge at 27°40′S

Research paper thumbnail of The chemical composition of the Earth

Research paper thumbnail of Global correlations of mid-ocean-ridge basalt chemistry with seismic tomographic images

Research paper thumbnail of Colorimetric Fe2+ measurements and the Fe3+/ΣFe ratio of glassy lavas from the Lau and East Scotia back-arc basins

It has been clearly shown that subduction fluids are related to greater oxidation state in arc an... more It has been clearly shown that subduction fluids are related to greater oxidation state in arc and backarc magmas compared to mid oceanic ridge basalts. However, little is known on the nature of the processes that may cause this shift in oxidation, and there is furthermore no real evidence that the source itself gets oxidized. In order to assess the role of subduction fluids on the oxidation states of back-arc magmas and of their source, we have applied a colorimetric method to analyze FeO contents in glassy samples using 7 to 10 mg of samples (Wilson, 1960; Kilinc et al., 1983). Our FeO measurements on 6 geo-referenced materials and 2 internal standards agree within 0.71% (relative) with the recommended values and within 0.10 % (relative) with the study of Bézos & Humler (2005). Replicate analyses on standards (3 different dissolutions) give a precision of 0.05 % on FeO measurements. We have applied this analytical protocol on glassy samples from the Lau and East Scotia backarc bas...

Research paper thumbnail of An experimental protocol for determining ferrous to ferric ratios in glasses with the electron microprobe

ABSTRACT The presence of an unfilled 3d electron shell in the transition metals of the first seri... more ABSTRACT The presence of an unfilled 3d electron shell in the transition metals of the first series is manifested in x-ray self-absorption effects that cause distortions in the L emission spectra. In particular, one observes peak shape changes and peak position shifts towards lower energies which are attributed to x-ray photon self-absorption in the specimen. Self-absorption corresponds to partial overlap of both L-emission and absorption transitions in the region of the Fermi level. Such an overlap is related to relaxation effects consecutive to the creation of the core hole in the studied ions. For iron, the overlap between the Fe La emission peak and the corresponding Fe LIII absorption band is clearly higher for Fe2+ than for Fe3+, leading to enhanced self-aborption induced shift of the Fe La peak for Fe2+. The shift of the La peak between Fe2+ and Fe3+ can be measured with the electron microprobe and hence exploited to determine the Fe3+/SFe ratios in silicates and glasses. For that purpose, an empirical method has been established based on working curves constructed from reference materials. A complete set of working curves is presented for glasses as well as an original experimental protocol. Most glasses are electron beam sensitive and suffer especially from beam-induced oxido-reduction mechanisms that are related to the implanted charge. The flux of Na+ ions from surface to the depth of the glass (drived by the electric field induced by the electrostatic charge) tends to oxidize the surface whereas, concurrently, the counterflux of electron produced by excitonic mechanisms and trapped at Fe3+ sites tends to reduce the surface. Therefore operating conditions should be set to minimise these phenomena that are source of large discrepancies in Fe3+/SFe. The application of the current protocol gives uncertainties of about ±5% absolute for specimens with nominal total Fe concentrations ranging from 6 to 9 wt% (accuracy and precision on Fe3+/SFe dramatically depend on the total Fe wt% concentration). Results obtained from a suite of basaltic glasses exhibit errors higher than ±5% absolute. Improved performances are expected for the method after the method can be used with promising new high resolution and high sensibility x-ray optics.

Research paper thumbnail of New constrains on ridge-hotspot interactions from the PLURIEL Cruise, Saint Paul-Amsterdam Plateau, Indian Ocean

10th International Congress of the Brazilian Geophysical Society & EXPOGEF 2007, Rio de Janeiro, Brazil, 19-23 November 2007, 2007