Northeastern and northwestern margins of Baltica in Neoproterozoic time: evidence from the Timanian and Caledonian Orogens

Abstract

The Neoproterozoic depositional histories of the Timanian and Baltoscandian, orthogonal margins of Baltica show several important differences but also some similarities. The Timanian margin comprises mainly low-grade, terrigenous sedimentary successions with a distinctive, margin-parallel fault zone separating pericratonic and basinal domains. Magmatic rocks are comparatively rare on land, but are common in deep drillcores recovered from beneath the Pechora Basin. Conversion to an active margin occurred in latest Riphean time, ultimately leading to the accretionary and transpressional regime of the Vendian-age, Timanian Orogeny. Along the Baltoscandian margin, successions of low to high metamorphic grade are preserved in diverse Caledonian nappe complexes. Three main types of palaeobasin are distinguished, based largely on sedimentary facies and basin geometry. Magmatic rocks are more common than in the Timanides, ranging from mafic dyke swarms to the voluminous Seiland Igneous Province. This margin remained passive throughout the Neoproterozoic era. The Vendian-dated dyke swarms signify the onset of Iapetus/,zEgir ocean opening at precisely the time when the orthogonal Timan margin was being deformed and telescoped during the Timanian Orogeny.

Middle to Late Devonian–Carboniferous collapse basins on the Finnmark Platform and in the southwesternmost Nordkapp basin, SW Barents Sea

“…In map view, the TKFZ is irregular, with different structural segments and branching subsidiary faults both across and along strike, locally showing duplex structures (Siedlecka and Siedlecki, 1967;Siedlecka, 1975). The TKFZ formed along the southwestern boundary of the Timanian Orogeny in the late CryogenianEdiacaran (Roberts and Siedlecka, 2002;Siedlecka et al, 2004) and was later reactivated as a strike-slip fault during the Caledonian Orogeny when it accommodated significant lateral displacement constrained to 200-250 km of dextral strike-slip movement (Bylund, 1994;Rice, 2013).…”

“…Recent geophysical studies by Pastore et al (2016) show that the base of the Seiland Igneous Province defines two deep-reaching roots located below the islands of Seiland and Sørøya constraining the thickness of the Kalak Nappe Complex in this area to a maximum of 10 km. On the Porsanger and Varanger peninsulas, ENE-WSW-to NNE-SSW-trending Ediacaran metadolerite dyke swarms are particularly common, and they are associated with the rifting of the Iapetus Ocean as well (see Roberts, 1972;Siedlecka et al, 2004;Nasuti et al, 2015).…”

Laurentia-Baltica-Amazonia relations during Rodinia assembly

“…Rb-Sr and K-Ar dates on the intrusions suggest a pre-1.1 Ga age of the lower part of succession (Puchkov, 2010) and acritarchs from the mid to upper parts of the succession extend the age of sedimentation to the midNeoproterozoic (late Riphean, Siedlecka et al, 2004, and references therein). This succession is interpreted to record an initial history of Mesoproterozoic intracratonic extension and riftrelated sedimentation and magmatism (Mezen' Rift and lower Timanide succession) followed by, in the latest Mesoproterozoic to early Neoproterozoic, development of a passive-margin succession containing cratonic-derived siliciclastic sedimentary rocks (Maslov, 2004;Maslov et al, 1997;Maslov and Isherskaya, 2002;Nikishin et al, 1996;Siedlecka et al, 2004). The rifting could be related to the 1385-1380 Ma Mashak igneous event in southern Urals (Puchkov et al, 2013).…”

Mid/Late Devonian-Carboniferous collapse basins on the Finnmark Platform and in the southwesternmost Nordkapp basin, SW Barents Sea

“…On the Porsanger and Varanger Peninsula, ENE-WSW to NNE-SSW trending, Ediacaran metadolerite dyke swarms are particularly common, and they are as well associated to the rifting of the Iapetus Ocean (cf. Roberts, 1972;Siedlecka et al, 2004;Nasuti et al, 2015).…”

“…In map view, the TKFZ is irregular, with different structural segments and branching 160 subsidiary faults both across-and along-strike, locally showing duplex structures (Siedlecka & Siedlecki, 1967;Siedlecka, 1975). The TKFZ formed along the southwestern boundary of the Timanian Orogeny in the late Cryogenian-Ediacaran (Roberts & Siedlecka, 2002;Siedlecka et al, 2004), and was later reactivated as a strike-slip fault during the Caledonian Orogeny when it accommodated significant lateral displacement constrained to 200-250 km of dextral strike-slip 165 movement (Bylund, 1994;Rice, 2013).…”