Torellian (c. 640 Ma) metamorphic overprint of Tonian (c. 950 Ma) basement in the Caledonides of southwestern Svalbard

Abstract

Ion microprobe dating in Wedel Jarlsberg Land, southwestern Spitsbergen, provides new evidence of early Neoproterozoic (c. 950 Ma) meta-igneous rocks, the Berzeliuseggene Igneous Suite, and late Neoproterozoic (c. 640 Ma) amphibolite-facies metamorphism. The older ages are similar to those obtained previously in northwestern Spitsbergen and Nordaustlandet where they are related to the Tonian age Nordaustlandet Orogeny. The younger ages complement those obtained recently from elsewhere in Wedel Jarlsberg Land of Torellian deformation and metamorphism at 640 Ma. The Berzeliuseggene Igneous Suite occurs in gently N-dipping, top-to-the-S-directed thrust sheets on the eastern and western sides of Antoniabreen where it is tectonically intercalated with younger Neoproterozoic sedimentary formations, suggesting that it provided a lower Tonian basement on which upper Tonian to Cryogenian sediments (Deilegga Group) were deposited. They were deformed together during the Torellian Orogeny, prior to deposition of Ediacaran successions (Sofiebogen Group) and overlying Cambro-Ordovician shelf carbonates, and subsequent Caledonian and Cenozoic deformation. The regional importance of the late Neoproterozoic Torellian Orogeny in Svalbard's Southwestern Province and its correlation in time with the Timanian Orogeny in the northern Urals as well as tectonostratigraphic similarities between the Timanides and Pearya (northwestern Ellesmere Island) favour connection of these terranes prior to the opening of the Iapetus Ocean and Caledonian Orogeny.

Magmatic and metamorphic events recorded within the Southwestern Basement Province of Svalbard

“…A suite of pervasively tectonized augen gneiss occurs around the Antoniabreen on Martinfjella, Berzeliuseggene and Aldegondaberget ridges. These rocks were initially called the Berzeliuseggene Igneous Suite [32], while Dallmann et al [10] preferred the informal name 'Berzeliuseggene unit'. Ion microprobe zircon U-Pb dating yielded a 950 ± 5 Ma protolith crystallization age of the augen gneisses [32].…”

“…These rocks were initially called the Berzeliuseggene Igneous Suite [32], while Dallmann et al [10] preferred the informal name 'Berzeliuseggene unit'. Ion microprobe zircon U-Pb dating yielded a 950 ± 5 Ma protolith crystallization age of the augen gneisses [32]. The Berzeliuseggene unit displays a tectonic contact with the Neoproterozoic Deilegga and Sofiebogen groups and other sediments of unknown, but probable Early Paleozoic age [9,32,33].…”

“…Ion microprobe zircon U-Pb dating yielded a 950 ± 5 Ma protolith crystallization age of the augen gneisses [32]. The Berzeliuseggene unit displays a tectonic contact with the Neoproterozoic Deilegga and Sofiebogen groups and other sediments of unknown, but probable Early Paleozoic age [9,32,33]. This contact has been interpreted as a rotated, large-scale sinistral shear zone, similar to the aforementioned Vimsodden-Kosibapasset zone [33].…”

“…The oldest magmatism recorded within the SBP is of Stenian-Ectasian age [3,4,28] and comprises a continental rifting-related suite of rocks [8] that only occur locally in the southern part of the SBP. Similarly, occurrences of Tonian igneous rocks are very limited as, to date, they are only known from two localities in Wedel Jarlsberg Land and Oscar II Land [12,32]. Both Stenian-Ectasian and Tonian igneous rocks (at least in the southern part of the SBP), as well as associated amphibolite facies metasedimentary successions, were affected by Late Neoproterozoic Torellian metamorphism (e.g.…”

“…Both Stenian-Ectasian and Tonian igneous rocks (at least in the southern part of the SBP), as well as associated amphibolite facies metasedimentary successions, were affected by Late Neoproterozoic Torellian metamorphism (e.g. [29,32]). The Torellian Orogeny is also manifested in the form of a regional-scale angular unconformity [6,7], which divides substantially folded, but weakly metamorphosed, Early Neoproterozoic metasediments from overlying Late Neoproterozoic and less deformed metasediments.…”