Journal ArticleDOI
Chronology of the pressure-temperature history recorded by a granulite terrain
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In this paper, the authors considered that Coronites formed near T = 900°C and P = 10 Kb by two stages of subsolidus reaction from an anorthositic gabbro parent.Abstract:
Coronite-bearing anorthositic granulites consisting of olivine, orthopyroxene, clinopyroxene, garnet and plagioclase assemblages are particularly well preserved at Gaupas and Holsnoy in the Bergen Arc of West Norway. The coronites are considered to have formed near T= 900° C and P=10 Kb by two stages of subsolidus reaction from an anorthositic gabbro parent. The first reaction involved ol+plag→cpxI+opxI+sp and the second cpxI+opxI+sp+pl→cpxII+opxII+gn. The incomplete reaction products are preserved to varying extents in different corona structures. Sm-Nd isotopic data for each of four coronas yield precise isochrons, and demonstrate isochronism both between the constituent phases of the corona assemblages and dispersed ground mass phases. Three individual coronas not associated with shear zones yield ages of 907±9 my, 912±18 my and 905±37 my. Eclogite facies mineralogy is developed locally in shear zones, which are shown by Sm-Nd and Rb-Sr analyses to be Caledonian in age. Where relict corona structures survive unsheared within these zones, Nd exchange between the constituent phases cannot be resolved. This observation together with sympathetic Ca/Mg and Sm/Nd zoning preserved at T∼900° C in the garnet mantles of coronites places a limit on the diffusivity of Nd in pyropic garnets which is no higher than published experimental values for Mg in pyrope-almandine garnets. Consequently even in slowly-cooled granulite terrains, garnet grains are expected to yield Sm-Nd chronologies very close to the time of mineral growth.read more
Citations
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Journal ArticleDOI
Concomitant separation of strontium and samarium-neodymium for isotopic analysis in silicate samples, based on specific extraction chromatography
TL;DR: In this paper, a separation scheme for strontium and light rare earth elements and its application to the isotopic analysis of strons and neodymium in silicate rocks are presented.
Journal ArticleDOI
Subduction and eduction of continental crust: major mechanisms during continent‐continent collision and orogenic extensional collapse, a model based on the south Norwegian Caledonides
TL;DR: In this paper, the authors show that during continental collision in the middle Silurian, the thickness of the lithosphere under the Caledonides of S. Norway was doubled by subduction of the western margin of Baltica including the Western Gneiss Region under Laurentia.
Journal ArticleDOI
Strong and deep Atlantic meridional overturning circulation during the last glacial cycle
Evelyn Böhm,Jörg Lippold,Marcus Gutjahr,Martin Frank,Patrick Blaser,Benny Antz,Jens Fohlmeister,Norbert Frank,Morten B. Andersen,Michael Deininger +9 more
TL;DR: It is shown that a deep and vigorous overturning circulation mode has persisted for most of the last glacial cycle, dominating ocean circulation in the Atlantic, whereas a shallower glacial mode with southern-sourced waters filling the deep western North Atlantic prevailed during glacial maxima.
Journal ArticleDOI
Lu–hf garnet geochronology: closure temperature relative to the Sm–Nd system and the effects of trace mineral inclusions
TL;DR: In this article, the authors used thermal ionization mass spectrometry (TIMS) and MC-ICP-MS techniques to determine the Lu-Hf and Sm-Nd ages of garnet-bearing rocks for which the general thermochronology had been previously established.
Journal ArticleDOI
The significance of monazite U–Th–Pb age data in metamorphic assemblages; a combined study of monazite and garnet chronometry
TL;DR: In this article, a coupled U-Th-Pb isotopic and EMP chemical study was carried out in situ on monazite (micro-inclusions within garnet as well as matrix grains) from rocks recovered from two chronologically well-constrained areas of the Himalayan orogen.
References
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Journal ArticleDOI
Closure temperature in cooling geochronological and petrological systems
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Journal ArticleDOI
An experimental study of the effect of Ca upon garnet-clinopyroxene Fe-Mg exchange equilibria
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TL;DR: In this paper, a series of basaltic compositions and compositions within the simple system CaO-MgO-FeO-Al2O3-SiO2 have been crystallized to garnet-clinopyroxene bearing mineral assemblages in the range 24-30 kb pressure, 750°-1,300° C temperature.
Journal ArticleDOI
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Journal ArticleDOI
Eclogitization of lower crustal granulites by fluid migration through shear zones
TL;DR: In this paper, a detailed mapping of three localities of the Caledonian mountain chain was carried out and it was shown that eclogites account for up to 30-45% of the volume of the rock volume.
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