General relations in the trace-element composition of zircons from eclogites with implications for the age of eclogites in the belomorian mobile belt

Скублов, С. Г.; Березин, А. В.; Berezhnaya, N. G.

doi:10.1134/s0869591112050062

Cited by 59 publications

(72 citation statements)

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“…The trace element compositions of zircon in garnet have low Th/U, minimal Eu/Eu * , low total REE concentrations, and flat to negative heavy rare earth element (HREE) profiles that are consistent with having formed at eclogite conditions (Rubatto, ; Skublov et al, ). In contrast, the trace element chemistry of matrix zircon has elevated and variable Th/U, Eu/Eu * , and REE concentrations that may reflect trace element enrichment with progressive hydration of the early eclogite assemblage.…”

Section: Discussionmentioning

confidence: 99%

Early Onset of Franciscan Subduction

et al. 2018

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The Franciscan subduction complex of California is considered a type example of a subduction-accretion system, yet the age of subduction initiation and relationship to the tectonic history of western North America remain controversial. Estimates for the timing of Franciscan subduction initiation are largely based either indirectly on regional tectonic arguments or from the ages of high-grade blocks within mélange. Many of the high-grade blocks record counterclockwise pressure-temperature paths with early amphibolite overprinted by later eclogite and blueschist; however, their origin and significance with respect to subduction initiation have been debated. In contrast, some high-grade blocks show evidence for clockwise pressure-temperature paths and an early eclogite assemblage overprinted by later amphibolite. Zircon U-Pb ages from inclusions in garnet and Lu-Hf estimates of initial garnet growth ages from these samples record early eclogite metamorphism at~176 Ma. Matrix zircon U-Pb ages and Lu-Hf estimates of final garnet growth ages record a barroisite-amphibolite assemblage overprint of eclogite at~160 Ma. Combined with petrologic data and existing geochronology, the data suggest that (1) Franciscan subduction was underway by no later than 180 Ma, (2) continuous subduction metamorphism occurred for at least 100 Ma, and (3) Franciscan subduction initiation predated the formation of the overlying Coast Range Ophiolite, supporting models that form the ophiolite above an east dipping Franciscan subduction zone.

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Section: Discussionmentioning

confidence: 99%

Early Onset of Franciscan Subduction

et al. 2018

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“…However, Type I zircon has mineral inclusions of metamorphic mineral phases including epidote and clinozoisite, indicating that they must be metamorphic zircon grains. Trace element geochemical signatures of zircon are strongly influenced by garnet, because garnet preferentially incorporates the bulk of the rock's HREE budget into its crystal structure, leaving zircon and all other syn-and post-genetic phases relatively depleted in HREE (Rubatto 2002;Rubatto and Hermann 2003;Gilotti et al 2004, Skublov et al 2012). In contrast, metamorphic zircon growing in the presence of garnet is greatly enriched in Hf relative to garnet with published Hf D Zrn/Grt values in the range 24,085-170,739 (Rubatto 2002).…”

Section: U-pb Age and Trace Element Geochemistrymentioning

confidence: 99%

Taconic Metamorphism Preserved in the Baie Verte Peninsula, Newfoundland Appalachians: Geochronological Evidence for Ophiolite Obduction and Subduction and Exhumation of the Leading Edge of the Laurentian (Humber) Margin During Closure of the Taconic Seaway

Castonguay

Staal

Joyce

et al. 2014

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The Baie Verte Peninsula, western Newfoundland Appalachians, preserves evidence for Early to Mid Ordovician closure of the Taconic seaway, which led to obduction of the Baie Verte oceanic tract (BVOT) ophiolites onto the Laurentian (Humber) margin and Taconic orogenesis. The scarcity of Taconic radiometric ages (and predominance of Silurian (Salinic) data) from the Humber margin rocks (down-going plate) has been problematic, calling into question the intensity and existence of Taconic collisional orogenesis. 40Ar/39Ar and in situ U–Pb geochronology was undertaken on metamorphosed units from the Laurentian basement (Mesoproterozoic East Pond Metamorphic Suite), from the ca. 560 Ma Birchy Complex forming the leading edge of the Humber margin, and from the ca. 490 Ma ophiolitic rocks of the BVOT (Advocate Complex) in order to address this question. Our results confirm evidence of Taconic metamorphism along the Humber margin and at the base of the ophiolites. Ages obtained from the structural base of the Advocate Complex (481–465 Ma) are interpreted to reflect the timing of accretion and internal thickening of the ophiolite, whereas data from the underlying Birchy Complex (467–461 Ma) record the underthrusting and exhumation of the leading edge of the Humber margin along a subduction channel, penecontemporaneously with final obduction of the BVOT. A concordant ca. 465 Ma zircon age and REE data obtained from retrogressed eclogite of the East Pond Metamorphic Suite suggest that the parautochthonous Humber margin was locally subducted to eclogite-facies conditions during the Taconic collision and partly exhumed to amphibolite-facies conditions prior to a strong Silurian (Salinic) tectonometamorphic overprint.SOMMAIRELa péninsule de Baie Verte dans les Appalaches de l’ouest de Terre-Neuve a conservé des indices de la fermeture du bras de mer taconique, qui a mené à l’obduction des ophiolites de la bande océanique de Baie Verte (BOBV) sur la marge laurentienne (Humber) et à l’orogénèse taconique. La rareté des âges radiométriques taconiques (et la prédominance des données siluriennes (saliniques)) provenant des roches de la marge de Humber (i.e. la plaque subductée) a été problématique, mettant en question l’intensité et l’existence de la collision orogénique taconique. De la géochronologie 40Ar/39Ar et U–Pb in situ a été réalisée sur des unités métamorphisés provenant du socle laurentien (la Suite Métamorphique d’East Pond d’âge Mésoprotérozoïque), du Complexe de Birchy daté à ca. 560 Ma formant la partie frontale de la marge de Humber, and des roches ophiolitiques de la BOBV (Complexe d’Advocate) datée à ca. 490 Ma afin de confronter ce questionnement. Nos résultats confirment les indices de métamorphisme taconique le long de la marge de Humber et à la base des ophiolites. Les âges obtenus à la base structurale du Complexe d’Advocate (481–465 Ma) sont interprétés comme reflétant la période d’accrétion et d’épaississement interne de l’ophiolite, tandis que les données du Complexe de Birchy sous-jacent (467–461 Ma) enregistrent le sous-charriage et l’exhumation de la partie frontale de la marge de Humber au sein d’un chenal de subduction, de façon pénécontemporaine à l’obduction finale de la BOBV. Un âge concordant de ca. 465 Ma d’un zircon et les données de terres rares provenant d’une éclogite rétromorphosée de la suite métamorphique d’East Pond suggèrent que la marge de Humber parautochtone a été localement subductée à des conditions du faciès éclogitique durant la collision taconique et partiellement exhumée à des conditions du faciès des amphibolites précédant la forte surimposition tectonométamorphique silurienne (salinique).

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“…Zircon Hf contents reach ~10 200 ppm, and the Y contents do not exceed ~45 ppm (Table 2). These REE and trace element data on zircons from the Fe rich gabbro dyke, which are typical of zircons from many other of the world's eclogite-facies massifs, were also reported on the Svecofennian eclogitic zircons from massive metabasic rocks in the Salma and Gridino areas [9]. Since our study provided no geochemical evidence of earlier magmatic zircon components, even in the oscillatory zoned euhedral grain (spot 5.1, Fig.…”

Section: Geochemistrymentioning

confidence: 58%