Terranes in the Circum-Atlantic Paleozoic Orogens

Theiss, Sarah

doi:10.1130/spe230

Cited by 5 publications

(2 citation statements)

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“…They are traditionally interpreted as the result of the subduction beneath and collision with the Virisen Island Arc, an event called the Finnmarkian orogeny (e.g. Andr easson & Albrecht, 1995;Stephens & Gee, 1989 Figure 8a). The Finnmarkian subduction was initially of intraoceanic character and rather low temperature type, which was followed by involvement of the Baltica outermost margin, which in turn resulted in a change in the temperature regime.…”

Section: Tectonic Implicationsmentioning

confidence: 99%

UHP metamorphism recorded by phengite eclogite from the Caledonides of northern Sweden: P–T path and tectonic implications

Bukała

Klonowska

Barnes

et al. 2018

Journal Metamorphic Geology

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The Seve Nappe Complex (SNC) of the Scandinavian Caledonides records a well‐documented history of high pressure (HP) and ultra‐high pressure (UHP) metamorphism. Eclogites of the SNC occur in two areas in Sweden, namely Jämtland and Norrbotten. The Jämtland eclogites and associated rocks are well‐studied and provide evidence for late Ordovician UHP metamorphism, whereas the Norrbotten eclogites, formed during the late Cambrian (Furongian)/Early Ordovician, have not been studied in such detail, especially in terms of the P–T conditions of their formation. Within the studied eclogite, clinopyroxene contains a high‐Na core and two rims: inner, medium‐Na and outer, low‐Na. Garnet consists of a high‐Ca euhedral core, low‐Ca inner rim and medium‐Ca outer rim. A similar pattern occurs within phengite, where high‐Si cores are enveloped by medium and low‐Si rims. The compositions of the mineral cores, inner rims and outer rims reflect three stages in the metamorphic evolution of the eclogite. Applied Quartz‐in‐Garnet geobarometry, coupled with Zr‐in‐rutile geothermometry reveal that garnet nucleation (E0 stage) took place at 1.5–1.6 GPa and 620–660°C. The eclogite peak‐pressure assemblage developed during the E1 stage, it consists of garnet+omphacite+phengite+rutile+coesite? and yields P–T conditions of 2.8–3.1 GPa and 660–780°C as constrained by conventional geothermobarometry and thermodynamic modelling in the NCKFMMnASHT system. Later, lower‐pressure stages E2 and E3 record conditions of 2.2–2.8 GPa, 680–780°C and 2.1 GPa, 735°C, respectively. The prograde metamorphic evolution of the eclogite is inferred from inclusions of epidote, amphibole and clinopyroxene within garnet. The presence of amphibole–quartz–plagioclase symplectites, secondary epidote/zoisite and titanite replacing rutile record the later retrograde changes taking place at <1.5 GPa (referred as E4 stage). The obtained P–T conditions indicate that the Norrbotten eclogites underwent a metamorphic evolution characterized by a clockwise P–T path with peak metamorphism reaching up to coesite stability field within a relatively cold subduction regime (7.8°C/km). The obtained results provide the first evidence for UHP metamorphism in the SNC above the Arctic Circle and document cold subduction regime and multistage exhumation of the deeply subducted Baltican margin at early stage of the Caledonian Orogeny.

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Section: Tectonic Implicationsmentioning

confidence: 99%

UHP metamorphism recorded by phengite eclogite from the Caledonides of northern Sweden: P–T path and tectonic implications

Bukała

Klonowska

Barnes

et al. 2018

Journal Metamorphic Geology

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“…1), although the task has become more difficult with the reinterpretation of the lithotectonic zones as suspect terranes Hatcher 1982, 1983;Williams 1984;Keppie 1985), since the pattern and nomenclature of terrane assembly has become increasingly complex with time (e.g. Lefort 1989;Dallmeyer 1989;Keppie and Dallmeyer 1989;Hibbard et al 1995;van Staal et al 1998;Martínez Catalán et al 2002, and references therein).…”

Section: Introductionmentioning

confidence: 99%