New palaeomagnetic data from metamorphosed carbonates of Western Oscar II Land, Western Spitsbergen

Abstract

Palaeomagnetic−petrographic−structural analyses of Proterozoic-Lower Palaeozoic metamorphosed carbonates from 12 locations within Oscar II Land (Western Spitsbergen) have been carried out to determine their usefulness in palaeogeographic reconstructions for Caledonian time. Structural analyses confirm that metacarbonates record several stages of deformation: D1, D2 ductile phases related to Caledonian metamorphism and a D3 brittle phase related to Late Cretaceous-Paleogene evolution of the West Spitsbergen Fold Belt. The latter is represented by thrust faults, localized folds with strain slip cleavages and late extensional collapse. Petrographic investigations reveal that Caledonian greenschist facies metamorphism was characterized by the high activity of H 2 O−CO 2 −rich fluids which pro− moted extensive recrystallization and within−rock spatial reorganization of sampled meta− carbonates. Microscopic, SEM and microprobe analyses exclude the existence of any pri− mary pre−metamorphic ferromagnetic minerals (primary−related to sedimentation and or early diagenesis) and point to metamorphic 4C superstructure (Fe 7 S 8 ) pyrrhotite as the main ferromagnetic carrier in investigated rocks. This is confirmed by the three−component iso− thermal remanent magnetization (IRM) procedures and the results of thermal demagnetiza− tions. In 12 sites a total number of 72 independently oriented palaeomagnetic samples were collected from which 181 specimens were drilled and thermally demagnetized. Sampled metacarbonates are weakly magnetized (NRM <0.2mA/m). The statistically significant palaeomagnetic results were achieved only from 1 of 12 investigated sites. In one site situ− ated in the Western overturned limb of the Holmesletfjellet Syncline intermediate unblock− ing temperatures -"pyrrhotite related" component WTSJ5M superimposed on the S1 Cal− edonian schistosity was recognized (D = 100.7°, I = −21.4°a95% = 5.5°, k = 58.23). Coinci− dence of WTSJ5M with Silurian-Devonian sector of the Baltica reference path after unfold− ing of the syncline by the angle of 130°suggests synfolding origin of this direction. Further, this suggests that Holmesletfjellet Syncline originated as an open fold and has been trans− formed into an overturned syncline during the Late Caledonian shortening or in the Late Cretaceous-Palaeogene time.

Mineralogical, Rock-Magnetic and Palaeomagnetic Properties of Metadolerites from Central Western Svalbard

“…The presence of magnetite within the examined samples has also been confirmed by rock-magnetic experiments. The presence of the above ferromagnetic Fe-oxides has proven to be common in the metamorphic basement of western Spitsbergen [13][14][15]49,50]. In many thin sections, small amounts of anataze were also found ( Figure 4C).…”

“…Michalski et al [12] have questioned, from palaeomagnetic and isotopic data, the timing of the amalgamation of Svalbard [1] suggesting that the Eastern and Central Caledonian Svalbard Terranes sensu Harland and Wright [1] had already docked by Late Silurian time. Although several palaeomagnetic attempts have been undertaken to establish the pre-Caledonian palaeogeographic position of the pre-Late Devonian location of Western Svalbard [13,14], it remains unresolved.…”

Early Devonian sinistral shearing recorded by retrograde monazite-(Ce) in Oscar II Land, Svalbard

“…F1 and F2 show E vergences in OIIL, and their age was inferred to be pre-mid-Carboniferous (Morris 1988). D2 has affected the northward thrusted Vestgötabreen Complex and Bullbreen Group, which are characterized by different tectonometamorphic history prior to D2 (Labrousse et al 2008;Michalski et al 2014;Morris 1988). 40 Ar/ 39 Ar cooling age for Ordovician HP metamorphism yields ca.…”

Seeking the Sources of Dust: Geochemical and Magnetic Studies on “Cryodust” in Glacial Cores from Southern Spitsbergen (Svalbard, Norway)

“…We propose that magnetite in the cryodust originated from Svalbard itself. Indeed, there are many sedimentary and/or igneous rocks exposed around Southern Spitsbergen that could be sources of magnetite [54][55][56][57][58][59]. Magnetite has also been found in the exposed Triassic rocks of Eastern Edgeøya [60].…”