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Fred Jourdan

Bio: Fred Jourdan is an academic researcher from Curtin University. The author has contributed to research in topics: Basalt & Zircon. The author has an hindex of 49, co-authored 248 publications receiving 7301 citations. Previous affiliations of Fred Jourdan include University of Nice Sophia Antipolis & Centre national de la recherche scientifique.


Papers
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Journal ArticleDOI
TL;DR: In this article, major and trace element abundances for 147 samples and Sr, Nd, Hf, and Pb isotope compositions for a 36 sample subset of basaltic lava flows, sills, and dykes from the Karoo continental flood basalt (CFB) province in Botswana, Zimbabwe, and northern South Africa are included.
Abstract: We report major and trace element abundances for 147 samples and Sr, Nd, Hf, and Pb isotope compositions for a 36 sample subset of basaltic lava flows, sills, and dykes from the Karoo continental flood basalt (CFB) province in Botswana, Zimbabwe, and northern South Africa. Both low- and high-Ti (TiO2 2 wt %) rocks are included. MELTS modeling shows that these magmas evolved at low pressure (1 kbar) through fractional crystallization of gabbroic assemblages. Whereas both groups display enrichment in light rare earth elements (LREE) relative to heavy REE (HREE) and high field strength elements, and systematic negative Nb anomalies, they differ in terms of contrasting middle REE (MREE) to HREE fractionation, which is greater for the high-Ti basalts. This reflects different depths of melting of slightly enriched mantle sources: calculations suggest that the low-Ti basalts were generated by melting of a shallow spinel-bearing (2 % spinel) lherzolite, whereas the high-Ti magmas originated from a deeper-seated garnet-bearing (2–7% garnet) lherzolite. In most isotope plots, the high-Ti lavas together with the picrites define a common trend from Bulk Silicate Earth (BSE) to compositions with strongly negative ɛNdi and ɛHfi akin to those of some nephelinites and lamproites. The low-Ti rocks are shifted from BSE-like to more radiogenic Sr isotope ratios, indicative of upper crustal contamination. Trace element and isotope characteristics of the Karoo magmas require a combination of enrichment processes (subduction induced?) and long-term isolation of the mantle sources. We propose two distinct scenarios to explain the origin of the Karoo province. The first calls for polybaric melting of spatially heterogeneous, partially veined, sub-continental lithospheric mantle (SCLM). Calculations show that mixing between SCLM (∼BSE) and a strongly Nd–Hf unradiogenic nephelinite-like component (sediment input?) could account for the compositional variations of most of the high-Ti group lavas, whereas the mantle composition responsible for the low-Ti magmas is more likely to be similar to a vein-free, metasomatically enriched SCLM component. The second scenario involves mixing between two end-members represented by the SCLM and its deep-seated alkalic veins and a sub-lithospheric (asthenospheric- or ocean island basalt-like?) mantle plume. In this case, the data are compatible with an increasing mantle plume contribution as the plume rises and expands through the lithosphere. Regardless of which of the two scenarios is invoked, the spatial distribution of the low- and high-Ti magmas matches the relative positioning of the cratons and the Limpopo belt in such a way that strong control of the lithosphere on magma composition and distribution is a mandatory requirement of any petrogenetic model applied to the Karoo CFB.

264 citations

Journal ArticleDOI
01 Sep 2005-Geology
TL;DR: The peak activities of continental flood basalts are currently considered as huge and brief (∼1 m.y.) events, with strong implications for geodynamics and biotic turnover as mentioned in this paper.
Abstract: The peak activities of continental flood basalts are currently considered as huge and brief (∼1 m.y.) magmatic events, with strong implications for geodynamics and biotic turnover. New 4 0 Ar/ 3 9 Ar dates on the Karoo flood basalts (southern Africa) show a longer duration of magmatism (∼8 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.

230 citations

Journal ArticleDOI
TL;DR: In this article, the authors present 40Ar/39Ar ages from basalts interbedded with fluvial sediments from the lower reaches of the Yangtze together with detrital zircon U-Pb ages from sand grains within these sediments.
Abstract: The development of fluvial systems in East Asia is closely linked to the evolving topography following India–Eurasia collision. Despite this, the age of the Yangtze River system has been strongly debated, with estimates ranging from 40 to 45 Ma, to a more recent initiation around 2 Ma. Here, we present 40Ar/39Ar ages from basalts interbedded with fluvial sediments from the lower reaches of the Yangtze together with detrital zircon U–Pb ages from sand grains within these sediments. We show that a river containing sediments indistinguishable from the modern river was established before ∼23 Ma. We argue that the connection through the Three Gorges must postdate 36.5 Ma because of evaporite and lacustrine sedimentation in the Jianghan Basin before that time. We propose that the present Yangtze River system formed in response to regional extension throughout eastern China, synchronous with the start of strike–slip tectonism and surface uplift in eastern Tibet and fed by strengthened rains caused by the newly intensified summer monsoon.

224 citations

01 Dec 2006
TL;DR: In this article, Steiger and Jager proposed a calibration of the Fish Canyon sanidine (FCs) standard based on four primary K/Ar standards (GA-1550, Hb3gr, NL-25, and GHC-305) on which K and Ar concentrations have been determined in different labs with independently calibrated tracers.
Abstract: The 40 Ar/ 39 Ar dating technique requires the use of neutron fluence monitors (standards). Precise calibrations of these standards are crucial to decrease the uncertainties associated with 40 Ar/ 39 Ar dates. Optimal calibration of 40 Ar/ 39 Ar standards should be based on K/Ar standards having independent isotope dilution measurements of 40 K and 40 Ar*, based on independent isotope tracers (spikes) because this offers the possibility to eliminate random interlaboratory errors. In this study, we calibrate the widely used Fish Canyon sanidine (FCs) standard based on four primary K/Ar standards (GA-1550, Hb3gr, NL-25, and GHC-305) on which K and Ar* concentrations have been determined in different labs with independently calibrated tracers. We obtained a mean age of 28.03 ± 0.08 Ma (1 σ ; neglecting uncertainties of the 40 K decay constants) for FCs, based on the decay constant recommended by Steiger and Jager [Steiger R.H., Jager. E. 1977. Subcommission on geochronology: convention of the use of decay constants in geo- and cosmochronology. Earth Planet. Sci. Lett. 36 , 359–362.]. This age corresponds to a mean 40 Ar*/ 40 K value of (1.6407 ± 0.0047) × 10 −3 . We also discuss several criteria that prevent the use of previous calibrations of FCs based on other primary standards (LP-6, SB-3 and MMhb-1). The age of FCs obtained in this study is based on the 40 K decay constants of Steiger and Jager (1977) but we anticipate the imminent need for revision of the value and precision of the 40 K decay constants (representing the main source of uncertainties in 40 Ar/ 39 Ar dating). The 40 Ar*/ 40 K result of FCs obtained in this study allows therefore a rapid calibration of the age of FCs with uncertainties at the 0.29% level but perhaps more importantly this value is independent of any particular value of the 40 K decay constants and may be used in the future in conjunction with revised decay constants.

207 citations

Journal ArticleDOI
TL;DR: In this article, Steiger and Jager proposed a calibration of the Fish Canyon sanidine (FCs) standard based on four primary K/Ar standards (GA-1550, Hb3gr, NL-25, and GHC-305) on which K and Ar concentrations have been determined in different labs with independently calibrated tracers.

198 citations


Cited by
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Journal ArticleDOI
TL;DR: In this paper, a new type of global plate motion model consisting of a set of continuously-closing topological plate polygons with associated plate boundaries and plate velocities since the break-up of the supercontinent Pangea is presented.

1,519 citations

Journal ArticleDOI
TL;DR: A significant number of new palaeomagnetic poles have become available since the last time a compilation was made (assembled in 2005, published in 2008) to indicate to us that a new and significantly expanded set of tables with palaeOMagnetic results would be valuable, with results coming from the Gondwana cratonic elements, Laurentia, Baltica/Europe, and Siberia as mentioned in this paper.

1,094 citations

Journal ArticleDOI
TL;DR: In this article, a statistical optimization approach was proposed for estimating the 40Ar/39Ar decay constants from 40K activity data, K-Ar isotopic data, and pairs of 238U-206Pb and 40Ar-39Ar data for rigorously selected rocks to estimate the partial decay constants (λe and λβ).

836 citations

Journal ArticleDOI
TL;DR: The Sundaland region was assembled by closure of Tethyan oceans and addition of continental fragments in the Cretaceous and Cenozoic as discussed by the authors, and a marked change in deep mantle structure at about 110°E reflects different subduction histories north of India and Australia since 90-Ma.

777 citations

Journal Article
TL;DR: In this article, a digital age grid of the ocean floor with a grid node interval of 6 arc min using a self-consistent set of global isochrons and associated plate reconstruction poles was created.
Abstract: We have created a digital age grid of the ocean floor with a grid node interval of 6 arc min using a self-consistent set of global isochrons and associated plate reconstruction poles. The age at each grid node was determined by linear interpolation between adjacent isochrons in the direction of spreading. Ages for ocean floor between the oldest identified magnetic anomalies and continental crust were interpolated by estimating the ages of passive continental margin segments from geological data and published plate models. We have constructed an age grid with error estimates for each grid cell as a function of (1) the error of ocean floor ages identified from magnetic anomalies along ship tracks and the age of the corresponding grid cells in our age grid, (2) the distance of a given grid cell to the nearest magnetic anomaly identification, and (3) the gradient of the age grid: i.e., larger errors are associated with high age gradients at fracture zones or other age discontinuities. Future applications of this digital grid include studies of the thermal and elastic structure of the lithosphere, the heat loss of the Earth, ridge-push forces through time, asymmetry of spreading, and providing constraints for seismic tomography and mantle convection models.

752 citations