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The 40Ar/39Ar apparent ages found by Qiu and Wijbrans [Qiu, H.N. and Wijbrans, J.R., 2008. The Paleozoic metamorphic history of the Central Orogenic Belt of China from 40Ar/39Ar geochronology of eclogite garnet fluid inclusions. Earth... more
The 40Ar/39Ar apparent ages found by Qiu and Wijbrans [Qiu, H.N. and Wijbrans, J.R., 2008. The Paleozoic metamorphic history of the Central Orogenic Belt of China from 40Ar/39Ar geochronology of eclogite garnet fluid inclusions. Earth Planet. Sci. Lett., 268, 501-514. doi: 10.1016/j.epsl.2008.01.042; Qiu, H.N. and Wijbrans, J.R., 2006. Paleozoic ages and excess 40Ar in garnets from the Bixiling eclogite in
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Research Interests: Earth Sciences, Geology, Paleontology, Morphology, Geochronology, and 15 morePlate Tectonics, Movement, Volcano, Physical sciences, Seamounts, South Pacific, Pb isotopes, Earth and Planetary Science, Hot Spot, Volcanism, Seamount, Mantle plume, Earth and Planetary Sciences, Plate tectonic, and Hot Spots
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Research Interests: Geology and Geochronology
On the Earth, noble gases are present as rare elements and in most of the cases their concentration within samples is extremely low. Therefore their analysis requires a high detection efficiency which implies ultra high vacuum systems,... more
On the Earth, noble gases are present as rare elements and in most of the cases their concentration within samples is extremely low. Therefore their analysis requires a high detection efficiency which implies ultra high vacuum systems, mass spectrometers able to operate in static mode, and detectors capable of reading small signals. Here we present a comparison between the latest amplifiers equipped with 1013 Ω resistors and the established state-of-art Thermo Scientific detector technology, represented by: 1012 amplifiers and the latest electron multiplier: Compact Discrete DynodeTM (CDD).
The Himalayan syntaxes, characterized by extreme rates of rock exhumation co-located with major trans-orogenic rivers, figure prominently in the debate on tectonic versus erosional forcing of exhumation. Both the mechanism and timing of... more
The Himalayan syntaxes, characterized by extreme rates of rock exhumation co-located with major trans-orogenic rivers, figure prominently in the debate on tectonic versus erosional forcing of exhumation. Both the mechanism and timing of rapid exhumation of the Namche Barwa massif in the eastern syntaxis remain controversial. It has been argued that coupling between crustal rock advection and surface erosion initiated in the late Miocene (8–10 Ma). Recent studies, in contrast, suggest a Quaternary onset of rapid exhumation linked to a purely tectonic mechanism. We report new multisystem detrital thermochronology data from the most proximal Neogene clastic sediments downstream of Namche Barwa and use a thermo-kinematic model constrained by new and published data to explore its exhumation history. Modeling results show that exhumation accelerated to ∼4 km/m.y. at ca. 8 Ma and to ∼9 km/m.y. after ca. 2 Ma. This three-stage history reconciles apparently contradictory evidence for early a...
Research Interests: Earth Sciences, Geology, Tectonics, Evolution, Thermochronology, and 7 moreQuaternary, River, Late Miocene, Neogene, Constraints, DDC, and Rock Uplift
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Detrital zircon U-Pb and muscovite 40Ar/39Ar dating are useful tools for investigating sediment provenance and regional tectonic histories. However, the two types of data from same sample do not necessarily give consistent results. Here,... more
Detrital zircon U-Pb and muscovite 40Ar/39Ar dating are useful tools for investigating sediment provenance and regional tectonic histories. However, the two types of data from same sample do not necessarily give consistent results. Here, we compare published detrital muscovite 40Ar/39Ar and zircon U-Pb ages of modern sands from the Yangtze River to reveal potential factors controlling differences in their provenance age signals. Detrital muscovite 40Ar/39Ar ages of the major tributaries and main trunk suggest that the Dadu River is a dominant sediment contributor to the lower Yangtze. However, detrital zircon data suggest that the Yalong, Dadu, and Min rivers are the most important sediment suppliers. This difference could be caused by combined effects of lower reaches dilution, laser spot location on zircons and difference in closure temperature and durability between muscovite and zircon. The bias caused by sediment laser spot targeting a core or rim of zircon and zircon reworking...
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Research Interests: Geology and Geochronology
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DOI = 10.3126/hjs.v5i7.1288 Himalayan Journal of Sciences Vol.5(7) (Special Issue) 2008 p.94
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The peak of high-temperature, low-pressure anti-clockwise granulite facies metamorphism in the northernmost part of the Northern Marginal Zone of the Limpopo Belt has been dated at 2591+/-4 Ma using conventional U-Pb zircon geochronology... more
The peak of high-temperature, low-pressure anti-clockwise granulite facies metamorphism in the northernmost part of the Northern Marginal Zone of the Limpopo Belt has been dated at 2591+/-4 Ma using conventional U-Pb zircon geochronology on a syntectonic charnockite intrusion. The thermal peak of 800°C at 0.5 GPa reflects a strong perturbation of the geotherm and was reached during compressional deformation and coincides with vast granite intrusion into the overlying craton. The coincidence of the temperature (T) maximum and compression is thought to be a response to lithospheric mantle thinning that resulted in granite emplacement and a consequent change in upper crustal rheology. After initial exhumation and cooling, these high-temperature, low-pressure rocks resided at a comparatively shallow depth (~10 km) for 620 Ma. Field, microstructural, and geochronological investigation of a low-temperature overprint establishes that reworking and final exhumation occurred at 1.97 Ga along discrete greenschist facies thrusts. The 40Ar/39Ar laser ablation of hornblende and biotite and Pb-Pb step leaching of sphene are shown to be useful geochronometers in dating the low-grade assemblages. Our results indicate that early Proterozoic deformation lasted 10 to 20 Ma. However, a number of ages intermediate between the events at 2.6 and 2.0 Ga have been reported for the Northern Marginal Zone. These include Pb-Pb garnet, Ar-Ar step heating amphibole, and U-Pb zircon ages. Such ages suggest that these minerals were partially rejuvenated below their commonly believed closure temperature. Reinterpreting these intermediate ages as partial overprint or inheritance was possible in the Northern Marginal Zone due both to the large time gap between the two tectonometamorphic events and the use of a multimethod multichronometer approach. These observations call for great caution when extrapolating mineral ages into cooling histories, especially so when the resulting cooling is slower than thermally and/or mechanically possible and suggests that the geochronometry in other regions that underwent multiple tectono-metamorphic events may need to be reassessed.
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An integrated magneto-biostratigraphic framework is presented for Middle Miocene sediments of DSDP Site 372 located in the Western Mediterranean. Detailed biostratigraphic analysis shows a nearly complete sequence of early Middle Miocene... more
An integrated magneto-biostratigraphic framework is presented for Middle Miocene sediments of DSDP Site 372 located in the Western Mediterranean. Detailed biostratigraphic analysis shows a nearly complete sequence of early Middle Miocene calcareous plankton bioevents in the Mediterranean, including the LCO (Last Common Occurrence) of the nannofossil Sphenolithus heteromorphus which has been astronomically dated in the Ras il Pellegrin (RIP) section
Research Interests: Evolutionary Biology, Palaeogeography, Geology, Paleontology, Stratigraphy, and 15 morePaleomagnetism, Ecology, Mediterranean, Biostratigraphy, Magnetostratigraphy, Chronology, Late Miocene, Neogene, Cenozoic, Late Cretaceous, Volcanic ash, Mediterranean region, Low Temperature, Sedimentation Rate, and Middle Miocene
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A detailed integrated stratigraphic study (lithostratigraphy, biostratigraphy, magnetostratigraphy, 40Ar/39Ar dating) was carried out on twelve sections from the eastern part of the Upper Freshwater Molasse of the North Alpine Foreland... more
A detailed integrated stratigraphic study (lithostratigraphy, biostratigraphy, magnetostratigraphy, 40Ar/39Ar dating) was carried out on twelve sections from the eastern part of the Upper Freshwater Molasse of the North Alpine Foreland Basin (NAFB), improving greatly the chronostratigraphy and the temporal resolution (up to 100 kyr) of these sediments. The sections contain 19 new small-mammal bearing levels. Based on this material and 24 already published localities we propose a new taxon-range-zonation for ...
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Calibration of the geological time scale is achieved by independent radioisotopic and astronomical dating, but these techniques yield discrepancies of ∼1.0% or more, limiting our ability to reconstruct Earth history. To overcome this... more
Calibration of the geological time scale is achieved by independent radioisotopic and astronomical dating, but these techniques yield discrepancies of ∼1.0% or more, limiting our ability to reconstruct Earth history. To overcome this fundamental setback, we compared astronomical and 40 Ar/ 39 Ar ages of tephras in marine deposits in Morocco to calibrate the age of Fish Canyon sanidine, the most widely used standard in 40 Ar/ 39 Ar geochronology. This calibration results in a more precise older age of 28.201 ± 0.046 million years ago (Ma) and reduces the 40 Ar/ 39 Ar method's absolute uncertainty from ∼2.5 to 0.25%. In addition, this calibration provides tight constraints for the astronomical tuning of pre-Neogene successions, resulting in a mutually consistent age of ∼65.95 Ma for the Cretaceous/Tertiary boundary.
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We present results from a natural deformed shear zone in the Turon de Técouère massif of the French Pyrenees that directly addresses the processes involved in strain localization, a topic that has been investigated for the last 40 years... more
We present results from a natural deformed shear zone in the Turon de Técouère massif of the French Pyrenees that directly addresses the processes involved in strain localization, a topic that has been investigated for the last 40 years by structural geologists. Paleopiezometry indicates that differential stresses are variable both spatially across the zone, and temporally during exhumation. We have, however, also calculated strain rate, which remains constant despite changes in stress. This result appears to be at odds with recent experimental deformation on monophase (olivine) rocks, which indicate that strain localization occurs dominantly as a result of constant stress. We hypothesize that in the Turon de Técouère massif—and many natural shear zones—strain localization occurs as a result of reactions, which decrease the grain size and promote the activation of grain size sensitive deformation mechanisms. From a tectonics perspective, this study indicates that the deformation rat...
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We present the first apatite and zircon fission-track results coupled with new muscovite and biotite 40Ar/39Ar analysis on samples from the pre-Mesozoic granitic basement and the Upper Cretaceous to Danian volcano-sedimentary cover, which... more
We present the first apatite and zircon fission-track results coupled with new muscovite and biotite 40Ar/39Ar analysis on samples from the pre-Mesozoic granitic basement and the Upper Cretaceous to Danian volcano-sedimentary cover, which allowed us to reveal the Alpine thermal and tectonic evolution of the central parts of Sredna Gora Zone. Our new results disclosed the existence of several heating and cooling episodes related to distinct tectonic and magmatic events in the studied area.
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ABSTRACT SynonymsMetamorphic basement; Metamorphic beltsDefinitionMetamorphism in its widest sense refers to processes of alteration of rocks within the Earth crust and mantle that cause recrystallization of an original mineralogy to form... more
ABSTRACT SynonymsMetamorphic basement; Metamorphic beltsDefinitionMetamorphism in its widest sense refers to processes of alteration of rocks within the Earth crust and mantle that cause recrystallization of an original mineralogy to form new minerals that are thermodynamically stable at depth and thus reflect in their chemistry and mineralogy the changed physical conditions of pressure, temperature, stress regime, and partial pressures of volatile phases such as H2O, CO2, CH4, and others during the time of recrystallization.Metamorphism covers a spectrum from partial recrystallization to complete recrystallization. Partial recrystallization may reflect processes within a single cycle (pluri-facial metamorphism) or multiple cycles of metamorphism spaced out in time (poly-metamorphism). Retrograde metamorphism reflects often partial recrystallization after peak metamorphism.Terranes are units of rocks at the crustal scale that share common geological features and a common geological history. ...
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Research Interests: Geology, Geochemistry, Sedimentology, Volcanology, Igneous petrology, and 5 moreVolcano, Paleosol, Basalt, Lava, and Tapping
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ABSTRACT The drivers behind the inception of, and the variable, pulsatory eruption rates at distributed intraplate volcanic fields are not well understood. Such broad areas of monogenetic volcanism cover vast areas of the world and are... more
ABSTRACT The drivers behind the inception of, and the variable, pulsatory eruption rates at distributed intraplate volcanic fields are not well understood. Such broad areas of monogenetic volcanism cover vast areas of the world and are often heavily populated. Reliable models to unravel their behaviour require robust spatio-temporal frameworks within the fields, but an analysis of the potential proximal and distal regional volcano-tectonic processes is also needed. Jeju Island (Republic of Korea) is a volcanic field that has been extensively drilled and dated. It is also located near one of the world’s best-studied tectonic plate boundaries: the subduction zone in southwestern Japan, which generates the Ryukyu and SW Japan arcs. A new set of 40Ar/39Ar ages collected from cores penetrating the entire Jeju eruptive pile, along with geochemical information, is used to construct a temporal and volumetric model for the volcano’s growth. The overall pattern indicates inception of volcanism at ~1.7 Ma, with an initial 1.2 Myr of low-rate activity, followed by over an order of magnitude rise over the last 0.5 Myr. The magma flux at Jeju correlates well with increased extension rates in the arc/backarc region. In particular, we infer that the increased trenchward mantle flow, caused by the greater rollback of the Philippine Sea Plate, activated pre-existing shear weaknesses in the mantle beneath Jeju, resulting in mantle upwelling and decompression melting that caused a change in compositions and an increase in eruption rates at Jeju. Thus, the volcanic activity of an intraplate field system can be modulated by regional subduction processes occurring more than 650 km away. This model may explain the frequent observation of pulsatory behaviour seen in many monogenetic volcanic fields worldwide that lie within 1,000 km of subduction zones.
Research Interests: Geology and Subduction
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Abstract Structural analyses along selected transects across the Menderes Massif and incorporation of exist- ing data have resulted in a synthetic cross section across southwestern Turkey. The tectonic interpreta- tion has been combined... more
Abstract Structural analyses along selected transects across the Menderes Massif and incorporation of exist- ing data have resulted in a synthetic cross section across southwestern Turkey. The tectonic interpreta- tion has been combined with 40 Ar/ 39 Ar laser-probe experiments on ...