Автор(ы):Aubourg C., Callot J.-P., Geoffroy L., Mege D., Pozzi J.P.
Издание:Journal Tectonophysics, 2001 г., 17 стр.
Magma flow directions of shallow dykes from the East Greenland volcanic margin inferred from magnetic fabric studies

The role played by plume-generated crustal magmatic complexes in the segmentation of volcanic margins is highlighted by a preliminary study of magma flow directions in shallow intrusives from the East Greenland volcanic margin. We investigate the magmatic texture using anisotropy of magnetic susceptibility for eight dykes of tholeitic affinity belonging to a dyke swarm associated with the Tertiary opening of the North Atlantic Ocean. The thickness of the sampled dykes ranges from 3 to 37 m. The dykes are of doleritic texture and contain up to 12% of opaque minerals and 35% of plagioclase laths. Dykes showing a magnetic foliation plane within the dyke plane, i.e. a magnetic fabric usually attributed to magmatic processes, represent 40% of the samples from the studied swarm. These dykes have a low degree of anisotropy and their ellipsoid of magnetic susceptibility is strongly oblate. Inverse magnetic fabrics, where the maximum principal susceptibility axis lies near the pole to the dyke account for 60% of the data. We interpret these inverse fabrics either as alteration minerals with highly prolate ellipsoids of magnetic susceptibility or primary titanomagnetites with oblate ellipsoid of low anisotropy. The flow direction is inferred for normal fabric dykes using the mirror imbrication of magnetic lineation. Analysis of thin sections shows a good agreement between magnetic fabric directions and phenocryst preferred orientations. The inferred flow directions are predominantly horizontal, throwing a new light on volcanic margin development. 

ТематикаПетрография, Региональная геология
МеткиAMS, Basalt, Dyke, Greenland, Magma flow, Magnetic fabric, Volcanic margin, Базальты, Вулканическая деятельность, Гренландия, Дайки, Течение магмы
Выпуск 4
Автор(ы):Коваленко Д.В., Колосков В.А., Флеров Г.Б.
Издание:Russian journal of Pacific geology, 2009 г., 19 стр.
Late cretaceous–paleocene magmatic complexes of Central Kamchatka: geological settings and compositional features

A comparative analysis of the Late Cretaceous–Paleocene volcanism was conducted for four areas of Kamchatka: the Pravyi Tolbachik–Levaya Shchapina–Adrianovka interlfuve (the northern part of the Tum-rok Range), the area south of the Ipuin River and Mt. Khrebtovaya (the northern Valaginsky Range), the area of Mt. Savul’ch (the upper reaches of the Kitil’gina River, northern Valaginsky Range), and the Kirganik– Levaya Kolpakova interfluve (the Sredinny Range). New petrochemical, geochemical, and isotopic data on the volcanic rocks from these areas are reported. The examination of this material, together with already published data on volcanic and plutonic rocks of similar composition and age, made it possible to establish the following: (1) the considered basaltoids are ascribed to the subalkali basalt–trachyandesite series with transition toward a meymechite–picrite rock association; (2) the alkali content in the rocks of the Valaginsky–Tumrok–Sredinny ranges increases simultaneously with the increase of the Rb content, while the contents of HFSE and radioactive elements decrease and then again increase. Two trends are identified in the Ybn–Cen diagram: a positive trend spanning most of the volcanic and plutonic rocks and a negative trend defined by the data points of the meyme-chite–picrite association. The first trend reflects the rock evolution during crystallization differentiation, while the second trend was produced by different degrees of melting of initial protolith. The possible geodynamic reconstructions of this volcanism are discussed as well

ТематикаПетрология, Региональная геология
МеткиBasalt, Geochemistry, Isotopy, Kamchatka Peninsula, Meymechite, Petrochemistry, Picrite, Volcanics, Камчатка
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