Zr-Th-U MINERALS IN HIGH-MG DIORITE OF THE CHELYABINSK MASSIF (SOUTH URALS) – EVIDENCE FOR CRUST–MANTLE INTERACTION

IF 0.8 Q4 GEOCHEMISTRY & GEOPHYSICS

Geodynamics & Tectonophysics Pub Date : 2021-06-23 DOI:10.5800/gt-2021-12-2-0528

Т. А. Осипова, Г. А. Каллистов, Д. А. Замятин, В. А. Булатов

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Abstract

Zr-Th-U minerals, namely baddeleyite, zircon and U-Th-oxide, were found in high-Mg diorite from the Late Devonian – Early Carboniferous synplutonic dyke in granodiorites of the Chelyabinsk massif, South Urals. Micron-sized minerals were investigated by electron microscopy and cathodoluminescence spectroscopy. Their chemical compositions were determined by electron probe microanalysis that was optimized to ensure more precise measurements of the composition of minerals. Baddeleyite grains are found as inclusions in amphibole crystals and reside in intergranular areas. The former retain their composition and show no traces of corrosion or substitution. In the intergranular areas, baddeleyite grains were replaced by polycrystalline zircon due to the reaction with an acid melt, and the U-Th-oxide precipitated inside baddeleyite simultaneously, which suggests the restite origin of baddeleyite. The main features of the baddeleyite composition are extremely high concentrations of ThO2 and UO2 (to 0.03 wt. % and 1.0 wt. %, respectively), which may be due to the metasomatic interaction between the mantle peridotite and the crustal or carbonatite fluid or melt.

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车里雅宾斯克地块(南乌拉尔)高镁闪长岩中的Zr-Th-U矿物——壳幔相互作用的证据

南乌拉尔车里雅宾斯克地块花岗闪长岩中，在晚泥盆世—早石炭世同深岩脉的高镁闪长岩中发现了锆-钍-铀矿物，即坏闪长岩、锆石和氧化锆。采用电子显微镜和阴极发光光谱法对微米级矿物进行了研究。它们的化学成分是通过优化的电子探针微分析来确定的，以确保更精确地测量矿物的成分。坏辉石颗粒以包裹体的形式存在于角闪洞晶体中，存在于晶间区。前者保留了它们的成分，没有显示出腐蚀或取代的痕迹。在粒间区，由于酸熔体的作用，坏辉石颗粒被多晶锆石所取代，同时坏辉石内部也有氧化铀析出，说明坏辉石的成因为耐蚀岩。其主要特征是含极高的ThO2和UO2(分别为0.03 wt. %和1.0 wt. %)，这可能是由于地幔橄榄岩与地壳或碳酸岩流体或熔体之间的交代相互作用所致。

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来源期刊

Geodynamics & Tectonophysics GEOCHEMISTRY & GEOPHYSICS-

CiteScore

1.20

自引率

14.30%

发文量

审稿时长

24 weeks

期刊介绍： The purpose of the journal is facilitating awareness of the international scientific community of new data on geodynamics of continental lithosphere in a wide range of geolchronological data, as well as tectonophysics as an integral part of geodynamics, in which physico-mathematical and structural-geological concepts are applied to deal with topical problems of the evolution of structures and processes taking place simultaneously in the lithosphere. Complex geological and geophysical studies of the Earth tectonosphere have been significantly enhanced in the current decade across the world. As a result, a large number of publications are developed based on thorough analyses of paleo- and modern geodynamic processes with reference to results of properly substantiated physical experiments, field data and tectonophysical calculations. Comprehensive research of that type, followed by consolidation and generalization of research results and conclusions, conforms to the start-of-the-art of the Earth’s sciences.