Paleomagnetism of the Franz Josef Land Archipelago: Application to the Mesozoic Tectonics of the Barents Sea Continental Margin

—We report new paleomagnetic and geochronological data for rocks of the Franz Josef Land archipelago and generalize available information about the paleomagnetism of the Barents Sea continental margin as applied to the issues of the Mesozoic Arctic tectonics. Specifically, the obtained age estimates are indicative of a brief episode of mantle plume magmatism at the Barremian–Aptian boundary (Early Cretaceous). The paleomagnetic data shows that intraplate magmatism formations in the High Arctic, including the Franz Josef Land traps, are nothing else than a trace of the Iceland plume on the migrating tectonic plates of the region. Thus, the Iceland plume was geographically stationary for at least the last 125 Myr. Our paleotectonic reconstructions suggest a direct connection of the intraplate strike-slip systems of the Eurasian continent with the configuration and subsequent evolution mode of Mesozoic marginal basins and spreading axes during the initial opening stage of the Arctic Ocean.

Petrology of lamprophyric in northern Jirandeh, Iran

This study was performed on the outcrops of lamprophyric lavas found in the north of Jirandeh and east of Lushan in the mountain of Alborz (north of Iran). These lavas has been placed discordantly on the middle Eocene lime..Petrographic observation indicates olivine phenocrysts, green-core alkaline clinopyroxenes, nepheline, abundant biotite, and apatites with flakes. and in the matrix it also contains biotite, olivine, clinopyroxene and plagioclase.The presence of carbonates, plagioclase and xenocrystals with rounded margins asserts the contamination with continental crust Petrologically, these rocks classify as alkaline lamprophyres of comptonite variety.These rocks can be subsumed under alkaline sodic categories at K2O/Na2O<1 ratio. The rare elements patterns in the rocks, normalized with the primitive mantle, causing partial negative Nb anomalies and showing no blades at the surface. It, therefore, can be indicative of the evidence for an intraplate magmatism with the different degree in the crustal contamination. Geochemistry states the first cause of asthenospheric flow can be occurred at La/Nb<1 and La/Ta 13 ratios, and the presence of garnet can be assumed at 1/8< (Tb/Yb) N ratio in the rocks origin area. In tectonic discrimination diagrams, these rocks fall in the range of intra-continental rift zones. Geochemical analyses indicate that these lamprophyres originate from partial (1%) melting of an OIB-like asthenospheric mantle source of lherzolite garnet nature.

Geochemical Characterization of Intraplate Magmatism from Quaternary Alkaline Volcanic Rocks on Jeju Island, South Korea

The major and trace elements of Quaternary alkaline volcanic rocks on Jeju Island were analyzed to determine their origin and formation mechanism. The samples included tephrite, trachybasalts, basaltic trachyandesites, tephriphonolites, trachytes, and mantle xenoliths in the host basalt. Although the samples exhibited diversity in SiO2 contents, the relations of Zr vs. Nb and La vs. Nb indicated that the rocks were formed from the fractional crystallization of a single parent magma with slight continental crustal contamination (r: 0–0.3 by AFC modeling), rather than by the mixing of different magma sources. The volcanic rocks had an enriched-mantle-2-like ocean island basalt signature and the basalt was formed by partial melting of the upper mantle, represented by the xenolith samples of our study. The upper mantle of Jeju was affected by arc magmatism, associated with the subduction of the Pacific Plate beneath the Eurasian Plate. Therefore, we inferred that two separate magmatic events occurred on Jeju Island: one associated with the subduction of the Pacific Plate beneath the Eurasian Plate (represented by xenoliths), and another associated with a divergent setting when intraplate magmatism occurred (represented by the host rocks). With AFC modeling, it can be proposed that the Jeju volcanic rocks were formed by the fractional crystallization of the upper mantle combined with assimilation of the continental crust. The xenoliths in this study had different geochemical patterns from previously reported xenoliths, warranting further investigations.

The role of island-arc oceanic, collisional and intraplate magmatism in the formation of continental crust in the Mongolia-Trasnbaikalia region: geostructural, geochronological and Sm-Nd isotope data

The formation of continental crust in the Mongolia-Transbaikalia region is researched to identify the mechanisms of interactions between the crust and the mantle in the development of the Neoarchean, Proterozoic and Paleozoic magmatic and sedimentary complexes in the study area. Using the results of his own studies conducted for many years and other published data on this vast region of Central Asia, the author have analysed compositions, ages and conditions for the formation of Karelian, Baikalian, Caledonian and Hercynian structure-formational complexes in a variety of geodynamic settings. Based on the geostructural, petrological, geochemical, geochronological and Sm-Nd isotope data, he determines the crustal and mantle sources of magmatism, conducts the identification and mapping of isotopic provinces, and reveals the role of island-arc oceanic, accretion-collision and intraplate magmatism in the formation of continental crust. Considering the formation of the bulk continental crust, three main stages are distinguished: (1) Neoarchean and Paleoproterozoic (Karelian) (almost 30% of the crust volume), (2) Meso-Neoproterozoic (Baikalian) (50%), and (3) Paleozoic (Caledonian and Hercynian) (over 20%). This sequence of the evolution stages shows the predominance of the ancient crustal material in igneous rocks sources at the early stage. During the subsequent stages, tectonic structures created earlier were repeatedly reworked, and mixed crustal-mantle and juvenile sources were widely involved in the formation of the bulk continental crust in the study area.

Chapter 1.3 Antarctic volcanism: petrology and tectonomagmatic overview

Petrological investigations over the past 30 years have significantly advanced our knowledge of the origin and evolution of magmas emplaced within and erupted on top of the Antarctic Plate. Over the last 200 myr Antarctica has experienced: (1) several episodes of rifting, leading to the fragmentation of Gondwana and the formation by c. 83 Ma of the current Antarctica Plate; (2) long-lived subduction that shut down progressively eastwards along the Gondwana margin in the Late Cretaceous and is still active at the northernmost tip of the Antarctic Peninsula; and (3) broad extension across West Antarctica that produced one of the Earth's major continental rift systems. The dynamic tectonic history of Antarctica since the Triassic has led to a diversity of volcano types and igneous rock compositions with correspondingly diverse origins. Many intriguing questions remain about the petrology of mantle sources and the mechanisms for melting during each tectonomagmatic phase. For intraplate magmatism, the upwelling of deep mantle plumes is often evoked. Alternatively, subduction-related metasomatized mantle sources and melting by more passive means (e.g. edge-driven flow, translithospheric faulting, slab windows) are proposed. A brief review of these often competing models is provided in this chapter along with recommendations for ongoing petrological research in Antarctica.