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1. Dating young MORB of the Central Indian Ridge (19°S): Unspiked K-Ar technique limitations versus 40Ar/39Ar incremental heating method

Author

Christophe Hémond, Brad S. Singer, Jérôme Dyment, Hervé Guillou, Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Paléocéanographie (PALEOCEAN), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Laboratoire Géosciences Océan (LGO), Institut Français de Recherche pour l'Exploitation de la Mer - Brest (IFREMER Centre de Bretagne), Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Bretagne Sud (UBS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), Department of Geology and Geophysics [Madison], University of Wisconsin-Madison, Institut de Physique du Globe de Paris (IPGP), Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS), Université de Bretagne Sud (UBS)-Université de Brest (UBO)-Institut Universitaire Européen de la Mer (IUEM), Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD), Centre National de la Recherche Scientifique (CNRS)-Université de La Réunion (UR)-Université Paris Diderot - Paris 7 (UPD7)-IPG PARIS-Institut national des sciences de l'Univers (INSU - CNRS), Université de Brest (UBO)-Université de Bretagne Sud (UBS)-Centre National de la Recherche Scientifique (CNRS)-Institut Français de Recherche pour l'Exploitation de la Mer - Brest (IFREMER Centre de Bretagne), Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Université de Bretagne Sud (UBS)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), and Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Systematic error, [SDU.STU.TE]Sciences of the Universe [physics]/Earth Sciences/Tectonics, geography, geography.geographical_feature_category, 010504 meteorology & atmospheric sciences, Stratigraphy, Mineralogy, Geology, 010502 geochemistry & geophysics, 01 natural sciences, Volcano, Geochronology, Earth and Planetary Sciences (miscellaneous), Ridge (meteorology), [SDU.STU.VO]Sciences of the Universe [physics]/Earth Sciences/Volcanology, [SDU.STU.PG]Sciences of the Universe [physics]/Earth Sciences/Paleontology, ComputingMilieux_MISCELLANEOUS, [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography, 0105 earth and related environmental sciences
Abstract

We have applied the unspiked K-Ar and the 40 Ar/ 39 Ar methods to samples precisely collected and localised, on both Central Indian Ridge flanks, to test their effectiveness and reliability when applied to the dating of recent (i.e. less than 1 Ma) MORBs. Twenty six samples) from the sixty five samples collected every ∼500 m up to the Brunhes-Matuyama boundary on both ridge flanks, were selected based on their distance from the ridge axis. Therefore, we can evaluate whether the isotopic ages are a good indicator of the crystallisation age by considering their geographic position with respect to the ridge axis (zero age) and the B/M magnetic boundary. Direct comparison of the isotopic and model ages shows that only 9 out of 26 samples were successfully dated. The GIMNAUT – MORB's test case amply demonstrates that the unspiked K-Ar technique, when applied to submerged volcanic samples, is subject to potentially defective assumptions of trapped atmospheric argon, excess/fractionated argon and extremely sensitive to alteration. Although the unspiked K-Ar technique is theoretically capable to produce high precision ages, the comparison with the 40 Ar/ 39 Ar techniques reveals that only 15% (i.e. 4 samples out of 26) of the ages obtained here are geologically meaningful. Five of the seven 40 Ar/ 39 Ar incremental heating experiments provide meaningful ages. Because potential sources of systematic errors such as excess 40 Ar*, recoil of 39 Ar K and 37 Ar Ca can be identified and because effects of alteration are significantly reduced by the pre-heating of the samples up to 500–600°c, the 40 Ar/ 39 Ar incremental heating method appears to be the method of choice to date MORBs.

Published
2017
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2. Geochronologic and stratigraphic constraints on canyon incision and Miocene uplift of the Central Andes in Peru

Author

Jean-Claude Thouret, Brad S. Singer, Xifan Zhang, Gerhard Wörner, T. Souriot, Yanni Gunnell, Laboratoire Magmas et Volcans (LMV), Institut national des sciences de l'Univers (INSU - CNRS)-Université Jean Monnet [Saint-Étienne] (UJM)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de géographie physique : Environnements Quaternaires et Actuels (LGP), Université Paris 1 Panthéon-Sorbonne (UP1)-Université Paris-Est Créteil Val-de-Marne - Paris 12 (UPEC UP12)-Centre National de la Recherche Scientifique (CNRS), Department of Geology and Geophysics [Madison], University of Wisconsin-Madison, Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Jean Monnet - Saint-Étienne (UJM)-Centre National de la Recherche Scientifique (CNRS), and Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)

Subjects
010504 meteorology & atmospheric sciences, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, Pyroclastic rock, Andes, Late Miocene, 010502 geochemistry & geophysics, Clastic wedge, 01 natural sciences, Paleontology, tectonic uplift, Tectonic uplift, argon dating, Geochemistry and Petrology, Peru, [SDU.STU.VO]Sciences of the Universe [physics]/Earth Sciences/Volcanology, Earth and Planetary Sciences (miscellaneous), Geomorphology, 0105 earth and related environmental sciences, Canyon, geography, Plateau, geography.geographical_feature_category, Landform, 15. Life on land, valley incision, Geophysics, Denudation, Space and Planetary Science, ignimbrites, Geology
Abstract

International audience; The deepest valleys of the Andes have been cut in southern Peru by the Ríos Cotahuasi Ocoña and Colca–Majes. These canyons are Late Miocene landforms based on a new ignimbrite stratigraphy supported by 42 new 40Ar/39Ar age determinations obtained on plateau-forming and valley-filling ignimbrites. Between 19 and 13 Ma, a gently sloping surface bevelling the clastic wedge southeast of the developing mountain front was mantled by widespread ignimbrites. After 13 Ma, this paleosurface was tilted up from 2.2 km a.s.l. at the mountain front to 4.3 km a.s.l. at the base of the Pliocene and Pleistocene volcanoes that crown the southwestern edge of the Altiplano. The canyons incised this topography after 9 Ma, while the dated base of younger ignimbrite valley fills suggests that these canyons had been cut down to near their present depths as early as 3.8 Ma. By 1.4 Ma, however, the canyons had been almost completely refilled by 1.3 km-thick unwelded pyroclastic deposits, which were subsequently eroded. Valley incision since 9 Ma at an average rate of 0.2 mm yr−1 is the response to topographic uplift after 13 Ma combined with increasing runoff due to a wetter climate recorded after 7 Ma. Although long-term aridity generated an imbalance between high long-term uplift rates and low plateau denudation rates, the combination of aridity and volcanism still promoted canyon incision because episodic volcanic fills maintained a cycle of catastrophic debris avalanches and subsequent dam breakouts.

Published
2007
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3. The Kamikatsura event and the Matuyama-Brunhes reversal recorded in lavas from Tjörnes Peninsula, northern Iceland

Author

Brad S. Singer, G. Fanjat, Avto Goguitchaichvili, Claire Carvallo, Pierre Camps, B. Allen, Manteau et Interfaces, Géosciences Montpellier, Université des Antilles et de la Guyane (UAG)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Université des Antilles et de la Guyane (UAG)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Department of Geology and Geophysics [Madison], University of Wisconsin-Madison, Institut de minéralogie et de physique des milieux condensés (IMPMC), Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Paris Diderot - Paris 7 (UPD7)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS), Laboratorio Interinstitucional de Magnetismo Natural[Mexico], Instituto de Geofisica [Mexico], Universidad Nacional Autónoma de México = National Autonomous University of Mexico (UNAM)-Universidad Nacional Autónoma de México = National Autonomous University of Mexico (UNAM), Université Pierre et Marie Curie - Paris 6 (UPMC)-IPG PARIS-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), and Universidad Nacional Autónoma de México (UNAM)-Universidad Nacional Autónoma de México (UNAM)

Subjects
Paleomagnetism, 010504 meteorology & atmospheric sciences, Lava, Polarity (physics), [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], [SDE.MCG]Environmental Sciences/Global Changes, Iceland, [PHYS.PHYS.PHYS-GEO-PH]Physics [physics]/Physics [physics]/Geophysics [physics.geo-ph], 010502 geochemistry & geophysics, 01 natural sciences, Geomagnetic reversal, paleointensity, Paleontology, Geochemistry and Petrology, Earth and Planetary Sciences (miscellaneous), Tjörnes, 0105 earth and related environmental sciences, Isochron, Geomagnetic pole, Ar-Ar dating, Matuyama Brunhes reversal, Geophysics, Earth's magnetic field, 13. Climate action, Space and Planetary Science, Geomagnetic excursion, Seismology, Geology
Abstract

International audience; We report paleomagnetic results from four overlapping stratigraphic sections (55 flows) through the lava pile in Tjörnes peninsula (North Iceland). The initial aim of our study was to check the existence of intermediate directions previously interpreted as belonging to the Matuyama-Brunhes geomagnetic reversal (MBR), and complete this record with Thellier-Thellier paleointensity determinations and 40Ar/39Ar radioisotopic dating. The directional results corroborate the findings by Kristjánsson et al. (1988): a sequence of reversed, transitional, normal, and transitional polarity (R-T-N-T) is found in each section. The polarity change is characterized by a jump from reversed virtual geomagnetic poles (VGPs) to a quasi-cluster of transitional VGPs located over China, followed by a second jump to a cluster of normal polarity before moving again towards intermediate polarities. Reversely magnetized flows exhibit a magnetic mineralogy well suited for paleointensity determination. Of these 25 flows, 20 yielded paleointensity estimates of good quality. Unfortunately, the systematic presence of coarse multidomain (MD) titanomagnetite in the transitional and normal polarity flows hampered paleointensity estimates for these flows. The Virtual Dipole Moments (VDM) calculated for the reversed polarity flows vary from 4.9 to 7.0 × 1022 Am2 with an arithmetic mean value of 5.5 ± 0.8 × 1022 Am2. This value is identical to the mean VDM obtained for the 0.3-5 Ma time window and thus strengthens the conclusion that the recent geomagnetic field strength is anomalously high compared to that older than 0.3 Ma. 40Ar/39Ar isochron ages were obtained with the incremental heating technique on groundmass separates or phenocryst-poor whole rock samples. Six of the transitionally magnetized lavas yielded isochron ages that are indistinguishable from one another at the 95% confidence level. The weighted average age is 862 ± 51 ka. In the upper part of this volcanic sequence, the normally magnetized flows yielded a weighted average age of 787 ± 40 ka. This finding supports the conclusion that a geomagnetic excursion within the Matuyama chron is recorded in the lower part of the Tjörnes volcanic sequence, whereas only the latest portion of the MBR is recorded by flows in the upper part of the lava pile. This conclusion is supported via comparison of the VGPs obtained from the lavas with those predicted by a geomagnetic field model.

Published
2011
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4. Fiabilidad de la interpretación de las referencias de erupciones subhistóricas de Tenerife: la erupcion pre-Holocena de Montaña Taoro

Author

Juan Carlos Carracedo, Francisco José Pérez Torrado, Eduardo Rodríguez Badiola, Raphael Paris, Brad Singer, Estacion Volcanologica de Canarias IPNA-CSIC, Consejo Superior de Investigaciones Científicas [Madrid] (CSIC), University of Las Palmas de Gran Canaria (ULPGC), Museo Nacional de Ciencias Naturales, Laboratoire de Géographie Physique et Environnementale (GEOLAB), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Université Clermont Auvergne (UCA)-Institut Sciences de l'Homme et de la Société (IR SHS UNILIM), Université de Limoges (UNILIM)-Université de Limoges (UNILIM)-Centre National de la Recherche Scientifique (CNRS), Department of Geology and Geophysics [Madison], University of Wisconsin-Madison, Museo Nacional de Ciencias Naturales [Madrid] (MNCN), Université Blaise Pascal - Clermont-Ferrand 2 (UBP)-Institut Sciences de l'Homme et de la Société (IR SHS UNILIM), and Université de Limoges (UNILIM)-Université de Limoges (UNILIM)-Université Clermont Auvergne [2017-2020] (UCA [2017-2020])-Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne (UCA)

Subjects
[SDU.STU.GM]Sciences of the Universe [physics]/Earth Sciences/Geomorphology, ComputingMilieux_MISCELLANEOUS
Abstract

National audience

Published
2008

5. Stability of mantle control over dynamo flux since the mid-Cenozoic

Author

Brad S. Singer, Kris A. Johnson, Lars N. Hansen, Pierre Camps, C. Carvallo, Kenneth A. Hoffman, S. Clipperton, Department of Geology and Geophysics [Madison], University of Wisconsin-Madison, Géosciences Montpellier, Université des Antilles et de la Guyane (UAG)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS), Physics Department [San Luis Obispo], California Polytechnic State University [San Luis Obispo] (CAL POLY), Ocean and Earth Science [Southampton], and University of Southampton-National Oceanography Centre (NOC)

Subjects
records, Paleomagnetism, Physics and Astronomy (miscellaneous), reversals, [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], [SDE.MCG]Environmental Sciences/Global Changes, [PHYS.PHYS.PHYS-GEO-PH]Physics [physics]/Physics [physics]/Geophysics [physics.geo-ph], 010502 geochemistry & geophysics, 01 natural sciences, Mantle (geology), Geomagnetic reversal, 03 medical and health sciences, earths magnetic-field, volcanic islands, secular variation, geomagnetic reversal paths, 030304 developmental biology, 0105 earth and related environmental sciences, 0303 health sciences, f rench-Polynesia, paleomagnetism, core, Astronomy and Astrophysics, Geomagnetic pole, Geophysics, 15. Life on land, Secular variation, Earth's magnetic field, 13. Climate action, Space and Planetary Science, Geomagnetic excursion, Geology, mantle, Dynamo
Abstract

International audience; Studies of paleomagnetic fields during polarity transitions recorded over the past few million years frequently suggest a configurational persistence consistent with long-lived mantle control over the pattern of flux emanating from Earth's fluid core. Fundamental to an understanding of the core-mantle dynamics involved is the question of the spatial-temporal nature of the physical conditions at the base of the mantle that may be responsible. Our analysis of the field during a mid-Cenozoic, reverse-to-normal (R-N) polarity change, recorded in a continuous sequence of lava flows in southeastern Queensland, Australia, provides strong evidence that the time span over which local mantle features retain such an influence is far longer than had thus far been observed. Specifically. the reversal is dominated by two sequential groupings of transitional magnetic vector directions, each associated with a clustering of virtual geomagnetic poles (VGPs) at locations common to several more youthful reversal datasets from about the globe. Our Ar-40/Ar-39 age determinations indicate that these Australian lavas erupted 25.56 +/- 0.48 Ma, strongly suggesting that the characteristic time for invariant control by the mantle over flux emerging from the outer core is at least on order of a few tens of Myr. The availability of transitional paleomagnetic data from still earlier times within the Cenozoic may further delineate this duration and, perhaps, provide a means to track changes in the pattern of long-standing concentrations of magnetic flux at the core-mantle boundary. (C) 2008 Elsevier B.V. All rights reserved.

Published
2008
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6. Microsampling and Isotopic Analysis of Igneous Rocks: Implications for the Study of Magmatic Systems

Author

Jon P. Davidson, Bruce L. A. Charlier, Daniel J. Morgan, R. Harlou, John M. Hora, Department of Earth Sciences [Durham], Durham University, Laboratoire de Géodynamique des Chaines Alpines (LGCA), Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Institute of Geophysics and Tectonics, School of Earth and Environment, University of Leeds, School of Environment, Earth and Ecosystem Sciences [Milton Keynes], Faculty of Science, Technology, Engineering and Mathematics [Milton Keynes], The Open University [Milton Keynes] (OU)-The Open University [Milton Keynes] (OU), Danish Lithosphere Centre, Department of Geology and Geophysics [Madison], University of Wisconsin-Madison, Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Institut des Sciences de la Terre (ISTerre), Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-PRES Université de Grenoble-Institut de recherche pour le développement [IRD] : UR219-Institut national des sciences de l'Univers (INSU - CNRS)-Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR)-Université Joseph Fourier - Grenoble 1 (UJF)-Centre National de la Recherche Scientifique (CNRS)-PRES Université de Grenoble-Institut de recherche pour le développement [IRD] : UR219-Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux (IFSTTAR), Department of Earth Sciences [Milton Keynes], and The Open University [Milton Keynes] (OU)

Subjects
010504 meteorology & atmospheric sciences, Geochemistry, Astronomy and Astrophysics, Groundwater recharge, 010502 geochemistry & geophysics, melt inclusions, 01 natural sciences, Isotopic composition, Petrography, Igneous rock, Sr isotopes, contamination, recharge, Space and Planetary Science, Earth and Planetary Sciences (miscellaneous), Igneous differentiation, crystal isotope stratigraphy, Geology, 0105 earth and related environmental sciences, Isotope analysis, Melt inclusions
Abstract

International audience; Isotopic fingerprinting has long been used to trace magmatic processes and the components that contribute to magmas. Recent technological improvements have provided an opportunity to analyze isotopic compositions on the scale of individual crystals, and consequently to integrate isotopic and geochemical tracing with textural and petrographic observations. It has now become clear that mineral phases are commonly not in isotopic equilibrium with their host glass/groundmass. Isotopic ratios recorded from core to rim of a mineral grain reflect the progressive changes in the magma composition from which the mineral crystallized. The sense of these changes and the relationship between isotopic composition and petrographic features, such as dissolution surfaces, can be used to constrain magma evolution pathways involving open system processes such as magma mixing, contamination and recharge.

Published
2007
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7. Twenty-five years of geodetic measurements along the Tadjoura-Asal rift system, Djibouti, East Africa

Author

Khaled Kanbari, Laike M. Asfaw, Kurt L. Feigl, Jean-Bernard de Chabalier, Rodolphe Cattin, Philippe Huchon, Jean-Claude Ruegg, Christophe Vigny, Laboratoire de géologie de l'ENS (LGENS), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Département des Géosciences - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL), Institut de Physique du Globe de Paris (IPGP), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS), Institut des Sciences de la Terre de Paris (iSTeP), Université Pierre et Marie Curie - Paris 6 (UPMC)-Centre National de la Recherche Scientifique (CNRS), Department of Geology and Geophysics [Madison], University of Wisconsin-Madison, Geophysical Observatory, Space Science and Asreonomy [Addis Ababa] (IGSSA), Addis Ababa University (AAU), Department of Geosciences, University of Sana’a, Sana’a, École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL), and Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS)

Subjects
Atmospheric Science, 010504 meteorology & atmospheric sciences, Soil Science, Active fault, Aquatic Science, Induced seismicity, 010502 geochemistry & geophysics, Oceanography, 01 natural sciences, Paleontology, Geochemistry and Petrology, Earth and Planetary Sciences (miscellaneous), 0105 earth and related environmental sciences, Earth-Surface Processes, Water Science and Technology, Rift, Ecology, Triple junction, Geodetic datum, Forestry, Foyer, Block (meteorology), Plate tectonics, Geophysics, Space and Planetary Science, [SDU]Sciences of the Universe [physics], Seismology, Geology
Abstract

International audience; Since most of Tadjoura-Asal rift system sits on dry land in the Afar depression near the triple junction between the Arabia, Somalia, and Nubia plates, it is an ideal natural laboratory for studying rifting processes. We analyze these processes in light of a time series of geodetic measurements from 1978 through. A network of about 30 GPS sites covers the Republic of Djibouti. Additional points were also measured in Yemen and Ethiopia. Stations lying in the Danakil block have almost the same velocity as Arabian plate, indicating that opening near the southern tip of the Red Sea is almost totally accommodated in the Afar depression. Inside Djibouti, the Asal-Ghoubbet rift system accommodates 16 ± 1 mm/yr of opening perpendicular to the rift axis and exhibits a pronounced asymmetry with essentially null deformation on its southwestern side and significant deformation on its northeastern side. This rate, slightly higher than the large-scale Arabia-Somalia motion (13 ± 1 mm/yr), suggests transient variations associated with relaxation processes following the Asal-Ghoubbet seismovolcanic sequence of 1978. Inside the rift, the deformation pattern exhibits a clear two-dimensional pattern. Along the rift axis, the rate decreases to the northwest, suggesting propagation in the same direction. Perpendicular to the rift axis, the focus of the opening is clearly shifted to the northeast, relative to the topographic rift axis, in the ''Petit Rift,'' a rift-in-rift structure, containing most of the active faults and the seismicity. Vertical motions, measured by differential leveling, show the same asymmetric pattern with a bulge of the northeastern shoulder. Although the inner floor of the rift is subsiding with respect to the shoulders, all sites within the rift system show uplift at rates varying from 0 to 10 mm/yr with respect to a far-field reference outside the rift.

Published
2007
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8. Long-term cosmogenic 3 He production rates from 40 Ar/ 39 Ar and K–Ar dated Patagonian lava flows at 47°S

Author

Brad S. Singer, Hervé Guillou, Mark D. Kurz, Michael R. Kaplan, Robert P. Ackert, Woods Hole Oceanographic Institution (WHOI), Department of Geology and Geophysics [Madison], University of Wisconsin-Madison, Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Paléocéanographie (PALEOCEAN), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), and Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)

Subjects
Basalt, [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, 010504 meteorology & atmospheric sciences, Lava, Northern Hemisphere, Westerlies, Argon–argon dating, 15. Life on land, 010502 geochemistry & geophysics, 01 natural sciences, Geophysics, 13. Climate action, Space and Planetary Science, Geochemistry and Petrology, Earth and Planetary Sciences (miscellaneous), Glacial period, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, Geomorphology, Southern Hemisphere, Sea level, Geology, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences
Abstract

Exceptionally well-preserved basaltic lava flows on the cool, arid, eastern side of the southern Andes near Lago Buenos Aires (LBA) at Lat. 47°S provide ideal sites for calibration of in situ produced cosmogenic 3He. We report new 3He measurements and independent age determinations using unspiked K–Ar and 40Ar/39Ar incremental heating measurements from two basalt flows. Both age techniques give concordant ages, with analytical uncertainties of

Published
2003
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9. 40Ar/39Ar dating of latest Pleistocene (41 ka) marine tephra in the Mediterranean Sea: implications for global climate records

Author

Thao Ton-That, Brad S. Singer, Martine Paterne, Department of Geology and Geophysics [Madison], University of Wisconsin-Madison, Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Géochrononologie Traceurs Archéométrie (GEOTRAC), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), and Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)

Subjects
Isochron, [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Explosive eruption, 010504 meteorology & atmospheric sciences, Pleistocene, 010502 geochemistry & geophysics, 01 natural sciences, law.invention, Paleontology, Geophysics, Ice core, 13. Climate action, Space and Planetary Science, Geochemistry and Petrology, law, Earth and Planetary Sciences (miscellaneous), Geomagnetic excursion, Radiometric dating, 14. Life underwater, Radiocarbon dating, Tephra, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, Geology, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences
Abstract

Fifty-one 40 Ar/ 39 Ar laser heating analyses of sanidine crystals in the C-13 tephra layer, recovered out of a piston core raised from 3000 m depth in the Tyrrhenian Sea, yielded apparent ages between 25 and 112 ka. Twenty-four of these measurements define an age probability maximum and generate an isochron of 41.1±2.1 ka (2σ) with a 40 Ar/ 36 Ar intercept of 288±21 that is indistinguishable from the modern atmosphere. However, the entire population is skewed toward older apparent ages with smaller peaks at 48 ka, 55 ka, 67 ka, and 110 ka. The composition of glass shards in the C-13 tephra overlaps that of the SiO 2 -rich phase of the 150 km 3 Campanian Ignimbrite which erupted from the Campi Flegrei caldera 130 km northwest of the core site. Although the 41.1±2.1 ka isochron is ∼15% older than K–Ar and 14 C ages for the Campanian Ignimbrite, it is indistinguishable from recent 40 Ar/ 39 Ar age determinations. The Campanian Ignimbrite eruptions were also chemically similar to, and correlated with, the Y-5 ash layer – the most voluminous and widely dispersed late Pleistocene tephra in the Mediterranean region. The age of the Y-5 layer was constrained originally at 38.0±2.5 ka on the basis of astronomical dating of O-isotope stages. The 40 Ar/ 39 Ar ages, astronomical dating, plus chemical similarities permit correlation of the C-13 tephra layer with both the Campanian Ignimbrite and the Y-5 tephra layer. The older ages preserved in the C-13 tephra layer may reflect xenocrysts incorporated during the explosive eruption accompanying collapse of the Campi Flegrei caldera 41 ka. The C-13 tephra layer is correlated with a 10 Be peak in an adjacent marine core, O-isotope stage 3.12, and immediately preceded a cooling episode corresponding to Heinrich event 4, thus the age of these features is constrained by radioisotope dating. The 41 ka peak in 10 Be deposition is a global phenomenon whose age matches that of the Laschamp geomagnetic excursion. Thus, our results provide a new tie point among several polar ice core and marine proxy records of paleoclimate during the past 50 kyr. Precise age information, independent of radiocarbon dating, can be recovered from latest Pleistocene marine tephra using the 40 Ar/ 39 Ar laser heating method, despite the presence of multiple components that may have been incorporated during or after its deposition.

Published
2001
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10. Evolution of Holocene dacite and compositionally zoned magma, Volcán San Pedro, Southern Volcanic Zone, Chile

Author

Bradley S. Singer, Fidel Costa, Institut des Sciences de la Terre d'Orléans (ISTO), Institut national des sciences de l'Univers (INSU - CNRS)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Department of Geology and Geophysics [Madison], and University of Wisconsin-Madison

Subjects
geography, geography.geographical_feature_category, 010504 meteorology & atmospheric sciences, Gabbro, Holocene, Lava, Andesite, Geochemistry, Lava dome, Andes, 010502 geochemistry & geophysics, Dacite, 01 natural sciences, Geophysics, Volcano, Geochemistry and Petrology, Magma, strontium isotopes, [SDU.STU.VO]Sciences of the Universe [physics]/Earth Sciences/Volcanology, Xenolith, dacite, Geology, 0105 earth and related environmental sciences, gabbro
Abstract

International audience; Volcán San Pedro in the Andean Southern Volcanic Zone (SVZ) Chile, comprises Holocene basaltic to dacitic lavas with trace element and strontium isotope ratios more variable than those of most Pleistocene lavas of the underlying Tatara–San Pedro complex. Older Holocene activity built a composite cone of basaltic andesitic and silicic andesitic lavas with trace element ratios distinct from those of younger lavas. Collapse of the ancestral volcano triggered the Younger Holocene eruptive phase including a sequence of lava flows zoned from high-K calc-alkaline hornblende–biotite dacite to two-pyroxene andesite. Notably, hornblende–phlogopite gabbroic xenoliths in the dacitic lava have relatively low 87Sr/86Sr ratios identical to their host, whereas abundant quenched basaltic inclusions are more radiogenic than any silicic lava. The latest volcanism rebuilt the modern 3621 m high summit cone from basaltic andesite that is also more radiogenic than the dacitic lavas. We propose the following model for the zoned magma: (1) generation of hornblende–biotite dacite by dehydration partial melting of phlogopite-bearing rock similar to the gabbroic xenoliths; (2) forceful intrusion of basaltic magma into the dacite, producing quenched basaltic inclusions and dispersion of olivine and plagioclase xenocrysts throughout the dacite; (3) cooling and crystallization–differentiation of the basalt to basaltic andesite; (4) mixing of the basaltic andesite with dacite to form a small volume of two-pyroxene hybrid andesite. The modern volcano comprises basaltic andesite that developed independently from the zoned magma reservoir. Evolution of dacitic and andesitic magma during the Holocene and over the past 350 kyr reflects the intrusion of multiple mafic magmas that on occasion partially melted or assimilated hydrous gabbro within the shallow crust. The chemical and isotopic zoning of Holocene magma at Volcán San Pedro is paralleled by that of historically erupted magma at neighboring Volcán Quizapu. Consequently, the role of young, unradiogenic hydrous gabbro in generating dacite and contaminating basalt may be underappreciated in the SVZ.

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