Yu. V. Karyakin

Jurassic-cretaceous Barents-Amerasian superplume and initial stage of geodynamic evolution of the Arctic Ocean

The distribution area of the Jurassic‐Cretaceous plume-derived basaltoid magmatism in the Barents Sea region and the entire Arctic was first outlined and reconstructed based on geological study of continental margins and interpretation of multidisciplinary marine geological‐geophysical data. It was shown that this magmatism occurred during the corresponding tectonomagmatic stage, which was caused by a plume event and led to the opening of the Canadian oceanic basin. This plume (called the Barents‐Amerasian plume [5]) is comparable in size with the Siberian (Triassic) and proto-Iceland (Cenozoic). The study of materials indicates that the Barents Sea area of the basaltoid magmatism has a much wider distribution than supposed previously, being only part of a “large igneous province,” which was formed prior to the opening of the Canadian basin. The reconstructions carried out showed that an extended Protoarctic oceanic basin existed at this time north of the Barents‐Kara Sea paleomargin. This basin was situated between the Siberia and North America margins and contained blocks of the New Siberian‐Chukchi region and Arctic Alaska. The Eastern Barents megatrough was the apical part of this oceanic basin at the paleomargin [3]. What was the geodynamic setting at the initial stage of the ocean formation in the Jurassic‐Cretaceous time? Which tectonic transformation of continental margins accompanied the formation of the Arctic’s largest Canadian oceanic basin?

The barents sea magmatic province: Geological-geophysical evidence and new 40 Ar/ 39 Ar dates

Resulting from study of the geological structure of the Franz Josef Land and Svalbard archipelagoes, this work presents new 17 40Ar/39Ar age datings for basalts taken during coastal expeditions in 2006–2010. Radiological age determination for intrusive units (sills) located in the western part of Nordensciold Land (Spitzbergen Island) has been made for the first time. In relation to use of the interpretation results of marine geological-geophysical data, the distribution peculiarities and time ranges for Jurassic-Cretaceous basic magmatism within the studied regions of the Barents Sea continental margin and within the Arctic as a whole are discussed.

New data on basaltoid magmatism of western Spitsbergen

New data on studies of the chemical composition of basaltoids of western Spitsbergen for the purposes of their comparison with the investigated magmatic rocks of the Franz Josef Land Archipelago (FJL) are presented in this study. The aim is to elucidate the features of their geochemical specialization, the distribution area of the Jurassic-Cretaceous magmatism in the Barents Sea region, and its geodynamic nature.

Geodynamics of the Barents–Kara margin in the Mesozoic inferred from paleomagnetic data on rocks from the Franz Josef Land Archipelago

New data on paleomagnetism and isotope geochronology of Jurassic and Early Cretaceous basic igneous rocks on Franz Josef Land Archipelago (FJL) represented by flows and dikes are discussed. The first paleomagnetic data obtained for these rocks offer the opportunity to suggest a model of spatial changes in the FJL block position during the Jurassic‒Cretaceous. In the Early Jurassic, the block occupied a different position relative to Europe from the modern one. It was displaced in the northeasterly direction by a distance of approximately 500 km and rotated clockwise by about 40° relative to its modern position. By the Early Cretaceous, the FJL block occupied a position close to the present-day one avoiding subsequent substantial relative displacements. The data obtained are of principal significance for reconstructing the geodynamic evolution of Arctic structures in the Mesozoic and contribute greatly to the base of paleomagnetic data for the Arctic region, development of which is now in progress.

Dikes of Hayes Island (Frantz Josef Land Archipelago): Tectonic position and geodynamic interpretation

The Frantz Josef Land Archipelago is surrounded by a shelf that crowns the block uplift of the basement located in the northern peripheral part of the Barents Sea continental margin. With respect to its morpho structural position, it is bordered by the Frantz Victo ria and Saint Anna troughs in the west and east, respectively. In the north, this uplift is truncated by the slope of the Nansen Basin of the Eurasian oceanic basin (Fig. 1a). By its relatively deep straits, canyons, and fiords directed mostly in the northwestern and northeastern directions, the archipelago is subdivided into individual islands and their groups. Such struc tural patterns provided grounds for a priori imaging a corresponding diagonal system of tectonic fractures and faults frequently of uncertain positions in various sketches and maps. At the same time, the bathymetric and geological maps [7] demonstrate the relatively dis tinct division of the archipelago by the Marcom Strait (with a series of subparallel narrow subordinate straits) and its northwestern continuation between Arthur and Harley islands in two main island groupings: south western and northeastern. The shelf segment of the archipelago located between the latter and Nansen Basin is similarly divided into two parts with a slight deviation of their separating conditional band in the northern direction. This conclusion is also derived from the analysis of the recent map of the anomalous magnetic field. The latter demonstrates that the dom inant linear magnetic anomalies in the archipelago and its surrounding shelf are characterized by a north western strike, while the above mentioned axial zone dividing these structures into two parts is marked by positive linear anomalies against the negative back ground (Fig. 1b). Moreover, the features that would indicate the presence of lineaments in the structure of the anomalous magnetic field determined by NE trend ing faults are poorly recognizable or obscure. Never theless, the available schematic maps of the Frantz Josef Land Archipelago show its three traditional NE oriented lithotectonic zones: Aleksandra, Vil’chek, and Sal’m. The conditional (?) lines that separate these zones are simultaneously considered as representing boundaries of both these lithotectonic zones and structural elements [3, 7]. These NE trend ing boundaries and faults are hypothetically viewed as being inherited from the Baikalian tectonic plan of the basement [3], although their strikes are more likely parallel to the front of the Norwegian Caledonides, as is assumed by some researchers. In our opinion, the tectonic situation under consideration is additionally complicated by the fact that the blocks of its basement are displaced along the listric faults toward the depo center of the North Barents basin, which follows from the distribution and stratigraphic range of deposits constituting the sedimentary cover of the archipelago. The presence of the relatively thick Triassic sedimen tary complex on the archipelago provides grounds for the assumption that this area represented at least the near slope zone of the East Barents megabasin with the corresponding sedimentation regimes and rates or even was its constituent. On the other hand, the absence of Jurassic strata in most of the northwestern archipelago may be explained to certain extent by the influence of fold–thrust processes in the Novaya Zem lya Archipelago at the Triassic–Jurassic transition. At the same time, trap magmatism of Jurassic–Creta ceous age was also registered by the geological–geo physical investigations in the East Barents megatrough [9–11], in addition to the Franz Josef Land Archipel ago [1–3, 5–7, 9–12, 14]. In the megatrough, it is largely reflected in development of sills. In the arch– Dikes of Hayes Island (Frantz Josef Land Archipelago): Tectonic Position and Geodynamic Interpretation

Igneous carbonates in dolerites of Franz Joseph land

Carbonates showing the signs of crystallization from a melt were found in dolerites and basalts of lava covers and dikes of Alexandra Land, Heiss, and Newcomb islands. These carbonates may fill interstitials between silicate minerals, as well as constitute wormlike or amebiform separations in dolerites. In other cases, the “bulbs” are formed within acidic glass in the centers of globules consisting of pyroxene and rimmed with ilmenite crystals in cryptocrystalline basalts. Most of the carbonate separations are constituted of siderite (80–95% of siderite minal); calcites (up to 20% of siderite minal) and carbonates of calcite–dolomite isomorphic series are found less frequently. In view of the plume nature of volcanic rocks at the archipelago, the capture of carbonatite melt by silicate magma seems to be the most likely. However, the possibility of the magma capture and melting of residual siderite fragments from the underlying terrigenous formation of Mesozoic age cannot be excluded.