Uranium-lead zircon and titanite ages from the northern portion of the Western Gneiss Region, south-central Norway

Tucker, Robert D.; Råheim, A.; Krogh, T. E.; Corfú, Fernando

doi:10.1016/0012-821x(87)90156-7

Cited by 139 publications

(61 citation statements)

References 16 publications

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“…Similar cases of growth or resetting of U-bearing minerals in fluid-rich high-strain environment are reported in many areas (e.g. Tucker et al 1987;Gromet 1991;Ketchum et al 1998). This would also be consistent with the formation of CL structureless rim domains in some zircons that yield SHRIMP U Pb ages at ca.…”

Section: The Early Ordovician Eventsupporting

confidence: 78%

U-Pb evidence for a polyorogenic evolution of the HP-HT units of the NW Iberian Massif

Fernández‐Suárez

Corfú²,

Arenas

et al. 2002

Contributions to Mineralogy and Petrology

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A isotope dilution thermal ionisation mass spectrometry U Pb geochronological study was carried out on the high-pressure and high-temperature units (HP HT units) overlying the oceanic suture in the Allo chthonous Complexes of the NW Iberian Variscan Belt. The rocks investigated are seven granulite-to eclogite facies paragneisses and one leucosome within mafi c high pressure granulites in the Ordenes and Cabo Ortegal Complexes of NW Spain. U Pb dating of zircon, monazite, titanite and rutile reveal the presence of a pervasive Early Ordovician metamorphic event at ca. 500 480 Ma and a later Early Devonian event at ca. 400 380 Ma. The U Pb ages, in conjunction with petrological and structural data, indicate that the high-pressure event recorded by these rocks is Early Ordovician in age. Monazite ages in the paragneisses suggest that peak metamorphic conditions were reached at ca. 500 485 Ma. Subsequently, the rock ensemble underwent exhumation accompanied by partial melting and zircon growth at ca. 485 470 Ma. Melting of mafi c granulites was coeval with this latter episode as indicated by zircon crystallisation age in the leucosomes dated at ca. 486 Ma. Based on these data and on the general features of magmatism and metamorphic evolution, it is proposed that this process took place at a convergent plate boundary within a peri Gondwanan oceanic domain. Monazite, titanite and rutile data in some of the samples studied show evidence of a second metamorphic episode that took place between ca. 400 and 380 Ma (with a peak at ca. 390 385 Ma). This Early Devonian event, at variance with the previous one, was not pervasive, but, rather, was localised in areas of intense Variscan tectonothennal reworking. It is claimed that this later metamorphic event was recorded by the U Pb system in areas where monazite and titanite growth was enhanced by fluid circulation in highly strained rocks (Variscan shear zones). According to previous structural studies and Ar Ar dating of fabrics, this Early Devonian episode took place as the HP HT units were deformed and thrusted upon the ophiolitic units in the early stages of the Variscan collision.

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Section: The Early Ordovician Eventsupporting

confidence: 78%

U-Pb evidence for a polyorogenic evolution of the HP-HT units of the NW Iberian Massif

Fernández‐Suárez

Corfú²,

Arenas

et al. 2002

Contributions to Mineralogy and Petrology

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“…In a study of the titanite occurring in the 1.6 Ga protoliths of the Norwegian Caledonides, Tucker et al (1987) showed that a younger generation of titanite was present, in addition to older crystals, with core-rim zoning being observed. The U-Pb systematics of titanite from various samples preserved a striking linear array on the concordia diagram connecting the original titanite age (1.66 Ga) with the 395 Ma age of the Caledonian metamorphic event.…”

Section: Prograde Reworking: Eclogite and Granulite Developmentmentioning

confidence: 99%

“…Although recrystallisation of these accessory minerals does occur and is sometimes visible as core/rim overgrowth relationships (Tucker et al 1987), titanite and allanite appear to have greater internal strength than most rock forming minerals. They often resist recrystallisation during penetrative fabric development, although a common feature is a partial resorption of sharp edges and surfaces of euhedral phenocyrsts to produce a rounded subhedral appearance, as illustrated by zircon in figures 5d and 5e .…”

Section: Reworking Of Rocks Under Amphibolite Facies Conditionsmentioning

confidence: 99%

The response of mineral chronometers to metamorphism and deformation in orogenic belts

Parrish

2001

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Mineral chronometers, especially accessory minerals using the U-Pb decay system, can reveal important information regarding the environmental conditions and duration of metamorphic-deformation events during the re-working of older rocks. Minerals such as zircon can newly grow during amphibolite facies or granulite facies events, providing direct ages of metamorphism. Pre-existing minerals like monazite, allanite, and titanite can preserve a component of their original age in spite of upper amphibolite facies re-working and very thorough recrystallisation of the rock fabric during mylonite development. The degree of incomplete Pb loss can be used to deduce, at least semi-quantitatively, the temperature and duration of the subsequent event. In well-studied examples, the relative retentivity of Pb is highly predictable, and this helps place strong constraints on relative closure temperatures, even when laboratory experimental data are lacking or inconclusive. A number of examples are presented from a wide variety of geological environments to illustrate the response of U-Pb isotope systematics within accessory minerals superimposed deformation, metamorphism and/or mineral growth.2

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“…Ar mica geochronology reveal at least two periods of metamorphism in most of the WGR: one Proterozoic and one Caledonian [Tucker et al, 1987;1990;Walsh et al, 2007;Kylander-Clark et al, 2008;Corfu et al, 2013]. In the eastern part of the WGC, metamorphic titanite and garnet are Proterozoic, whereas in the western part titanite and garnet at most locations are Caledonian [Johnston et al, 2007b;Peterman et al, 2009;Spencer et al, 2013] (Fig.…”

mentioning

confidence: 99%

Monazite response to ultrahigh-pressure subduction from U–Pb dating by laser ablation split stream

et al. 2015

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To assess the response of monazite during subduction of continental crust to mantle depths, U-Pb isotopic ratios and elemental abundances were measured simultaneously by laser-ablation split-stream inductively-coupled plasma mass spectrometry (LASS) in rocks from the ultrahigh-pressure Western Gneiss Region of the Scandinavian Caledonides. Nearly seventy different samples of quartzofeldspathic basement and overlying metasedimentary rocks were studied. Pre-subduction monazite (chiefly 1.6 Ga and 1.0 Ga) is preserved locally in the structurally lowest, basement rocks because earlier, Precambrian tectonism produced coarse-grained, high-grade rocks that were resistant to further recrystallization in spite of syn-subduction temperatures and pressures of 650-800°C and 2-3.5 GPa. A few of the monazite in the metasedimentary rocks atop the basement preserve syn-subduction U-Pb dates, but the majority continued to recrystallize during post-subduction exhumation and record a general westward decrease in age related to westward-progressing exhumation. The absence of Precambrian monazite in the metasedimentary rock atop the basement suggests that sedimentation postdated the 1.0-0.9 Ga high-grade metamorphism and was late Proterozoic to early Paleozoic.

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Uranium-lead zircon and titanite ages from the northern portion of the Western Gneiss Region, south-central Norway

Cited by 139 publications

References 16 publications

U-Pb evidence for a polyorogenic evolution of the HP-HT units of the NW Iberian Massif

U-Pb evidence for a polyorogenic evolution of the HP-HT units of the NW Iberian Massif

The response of mineral chronometers to metamorphism and deformation in orogenic belts

Monazite response to ultrahigh-pressure subduction from U–Pb dating by laser ablation split stream

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