Zusammenfassung
Die Gesteine im Nasafjällfenster in den nördlichen Skandinavischen Kaledoniden bestehen aus proterozoischen Granitoiden mit einer spätpräkambrischen bis ordovicischen Decke, der Mierkenis Gruppe. Im Fenster erhöht sich der Metamorphosengrad von der Grünschieferfazies im Osten zur Amphibolitfazies im Westen. Bezüglich der penetrativen Verschieferung, die während der Überschiebungen entstanden ist, ist das metamorphe Maximum synbis post-kinematisch. Zur Erklärung dieser Beobachtungen ist vorgeschlagen, daß zur Folge der spätsilurischen bis frühdevonischen Überschiebungen sich die Temperatur des Grundgebirges schnell erhöhte. Die kaledonische metamorphe Phase war von Druckentlastung geprägt. Diese Interpretationen schlagen auch vor, daß die späteren Stadien der Überschiebungen nicht mit einer Zunahme der Mächtigkeit von der Überschiebungsdecke verbunden waren.
Abstract
The rocks of the Nasafjäll Window comprise Proterozoic granitoids with a metasedimentary cover of Late Precambrian to Ordovician age, the Mierkenis Group. The metamorphic grade in the window varies from greenschist facies in the eastern part of the window to amphibolite facies in the western part. The metamorphic maximum is syn- to post-kinematic in relation to the formation of the thrust-related pervasive foliation. This suggests a rapid basement heating in response to the Late Silurian to Early Devonian nappe emplacement. The Caledonian metamorphism terminated in Middle Devonian times and the retrograde phase was characterized by decompression. This implies that the later stage of the thrusting was not associated with an increase in thickness of the nappe pile above the rocks of the Nasafjäll Window.
Résumé
Les roches de la fenêtre de Nasafjäll (Calédonides scandinaves) comprennent des granitoïdes protérozoïques et une couverture métasédimentaire d'âge précambrien supérieur à ordovicien. Ces métasédiments font partie du groupe Mierkenis. Le degré métamorphique varie du faciès des schistes verts dans l'est de la fenêtre au faciès des amphibolites dans l'ouest. Le métamorphisme maximal est syn- à post-cinématique; il est lié à la genèse de la schistosité pénétrative, en relation avec le charriage. Cette observation suggère un échauffement rapide du socle consécutif à la mise en place de la nappe au Silurien supérieur et au Dévonien inférieur. Le métamorphisme calédonien a pris fin au Dévonien moyen et sa phase rétrograde a été caractérisée par une baisse de la pression. En conséquence, la dernière phase du charriage n'a pas été associée à une augmentation de l'épaisseur de la nappe sur les roches de la fenêtre de Nasafjäll.
Краткое содержание
Породы окна Nasfjäll на севе рной части скандинав ских Каледонид состоят из протерозойских гран итоидов с метаседиментным по кровом возраста от позднего докембрия д о ордовика — группой Mierkenis. Степень метаморфизм а в окне колеблется от фация зеленого сланца на во стоке до фация амфибо литов на западе. Пронизываю щее сланцевание появ илось во время надвига, прич ем максимум метаморф изма совпадает с этими дви жениями, или же следуе т непосредственно за н ими. Это разрешает пре дполагать, что температура осно вных гор в результате надвига за период от п озднего силура до ран него девона резко повысил ась. Каледонская стад ия метаморфизма характеризуется пад ением давления. Такое объяснение вытекает из факта, что поздняя с тадия надвигов не привела к увеличению мощности надвинутого покрова.
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Lindqvist, JE. Metamorphism in basement rocks and the implications for the tectonic evolution, Nasafjäll Window, Scandinavian Caledonides. Geol Rundsch 76, 837–850 (1987). https://doi.org/10.1007/BF01821067
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DOI: https://doi.org/10.1007/BF01821067