Zusammenfassung
Wir folgern, daß die Formationsgruppe der Halbinsel Trinity in der antarktischen Halbinsel in ein Vorderbecken des Kompositentyps abgelagert wurde, das sich zwischen dem aus plutonischen und älteren gneißosen Urgesteinen bestehenden Bogengebirgsmassiv von Gondwana und einem Unterziehungskomplex befindet, der jetzt durch „Grünschiefer“ und „Blauschiefer“ und Albit-Epidot-Hornblende tragenden Gesteine von dem vorjurassischen metamorphen Komplex vertreten wird.
Die Formationsgruppe der Halbinsel Trinity ist hinsichtlich des Typs nochmals geprüft geworden und kann in Hope Bay-, View Point- und Legoupil-Formationen eingeteilt werden. Sedimentgesteine von allen Formationen sind von Turbiditfazies: Metalagerlaven werden zum ersten Mal durch diese Gesteine beschrieben.
Mehrphasige Schichtenfaltung ist in allen Formationen bemerkt geworden, und Regionalmetamorphose erreichte Prehnit- und Pumpellytfazies.
Analysen mit Mikrosonden der Relectpyroxenen in den Lagerlaven weisen darauf hin, daß das Stammagma wahrscheinlich Innenplattealkalibasalt war. Analysen der Schuttgranaten zeigen, daß sie sich von den metamorphen Granaten im Unterziehungskomplex auf Grund von Komposition unterscheiden, was darauf hinweist, daß diese dem Vorderbogenbecken keine bedeutende Belieferung von Material beschaffte.
Eine nahe Ähnlichkeit mit dem Terrane von Toriesse in Neuseeland wird bemerkt und wir schließen daraus, daß eine spätpalaeozoische - frühmesozoische Vorderbogenbeckenumgebung um den Rand des Pazifiks von Südamerika bis Neuseeland fast ununterbrochen erkannt werden kann.
Abstract
We infer that the Trinity Peninsula Group of the Antarctic Peninsula was deposited in a fore-arc basin(s) of composite type located between the Gondwanian arc massif (consisting of plutonic and older gneissose basement rocks) and a subduction complex, now represented by “greenschists”, “blueschists” and albite-epidote-hornblende-bearing rocks of the pre-Jurassic metamorphic complex.
The Trinity Peninsula Group has been re-examined in the type area and can be divided into the Hope Bay, View Point and Legoupil Formations. Sedimentary rocks of all formations are of turbidite facies; meta-pillow lavas are described for the first time from these rocks.
Multiphase folding has been observed in all formations and regional metamorphism reached prehnite-pumpellyite facies.
Microprobe analyses of relict pyroxenes in the pillow lavas indicate the parent magma was probably within-plate alkali basalt. Analyses of detrital garnets show that they are different in composition from metamorphic garnets in the subduction complex, indicating that the latter did not supply a significant amount of material to the fore-arc basin(s).
A close similarity with the Torlesse terrane in New Zealand is noted and we conclude that a late Palaeozoic-early Mesozoic fore-arc basin environment can be traced almost continuously around the Pacific margin from South America to New Zealand.
Résumé
Nous pensons que le Groupe de la Péninsule Trinity de la Péninsule Antarctique a été déposé dans un bassin de Farce externe de type composite situé entre le massif de l'arc Gondwanien (composé de roches plutoniques et de gneiss d'un socle plus ancien) et d'un complexe de subduction, représenté actuellement par des « schistesverts », «schistes-bleus» et des roches ă hornblende, albite et épidote du complexe métamorphique pré-Jurassique. Le Groupe de la Péninsule Trinity a été réexaminé dans la région-type; il peut être subdivisé en formations de Hope Bay, de View Point et de Legoupil. Les roches sédimentaires de toutes les formations sont du faciés turbiditique; pour la premiére fois des laves en coussins mêtamorphisées y sont décrites.
Un plissement multiphasé est observé dans toutes les formations, et le faciés préhnite pumpellyte marque le métamorphisme régional. Des analyses par microsonde de restes de pyroxene dans les laves en coussins démontrent que le magma parental etait probablement un basalte alcalin. Des analyses de grenats détritiques démontrent que les grenats sont d'une composition différente des grenats métamorphiques dans le complexe de subduction, indiquant que ces derniers n'ont fourni que peu de matériaux au bassin de l'arc externe.
La ressemblance est proche avec le terrain Torlessse de la Nouvelle Zélande et nous concluons qu'un environement de bassin d'arc externe (fin du Paléozoique à début du Mésozoique) peut être tracé presque sans interruption auteur de la marge Pacifique, entre l'Amérique du Sud et la Nouvelle-Zélande.
Краткое содержание
Авторы пришли к вывод у, что свиты полуостро ва Тринити антарктического полуострова отложен ы в бассейне передней дуги сложного типа, находи вшимся между дуговым массив ом Гондваны, составле нными плутонитами и древними гнейсовыми породами фундамента, и субдуцированным ком плексом, представлаенным сег одня „зеленым сланце м“, „голубыми сланцами“ и породами, вмещающим и альбит, эпидот и рого вую обманку из доюрского метаморфоного компл екса. Исследовали сви ты полуострова Тринити по их типам и подразде лили на формации: Hope Bay, View Point и Legoupil. Осадочные породы вс ех этих формаций проя вляют фаций мути; среднеподушечные да вы описаны здесь впер вые.
Многофазная складча точть слоев отмечена но всех отложениях, а региона льный метаморфизм достига ет фация Prehnit'a и Pumleppyit'a.
Данные анализа с помо щью микрозондов оста точных пироксенов в подушеч ных лавах указывают на то, что исходная магма, ве роятно, являлась внутриплитоным щело чным базальтом. Анали з обломков граната показал, что эти резко отличаю тся по своему составу от метаморфизированны х гранатов в субдуцированном ар еале; это говорит о том, что в бассейн передних дуг не поставлялось з начительных количес тв материала.
Отмечается сходство с областью Torlesse в Новой Зе дандии, и авторам кажется, что здесь в по зднем палеозое-ранне м мезозое простиралась непрер ывная дуга от Южной Америки до Новой Зеландии, кот орая обрамляла Тихий океан.
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Hyden, G., Tanner, P.W.G. Late Palaeozoic-early Mesozoic fore-arc basin Sedimentary rocks at the Pacific margin in Western Antarctica. Geol Rundsch 70, 529–541 (1981). https://doi.org/10.1007/BF01822133
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DOI: https://doi.org/10.1007/BF01822133