The Mineralogical Composition, Metamorphic Parameters, and Protoliths of Granulites from the Larba Block of the Dzhugdzhur–Stanovoy Fold Area

IF 0.9 4区地球科学 Q4 GEOSCIENCES, MULTIDISCIPLINARY

Russian Journal of Pacific Geology Pub Date : 2024-05-02 DOI:10.1134/s181971402402009x

A. V. Yurchenko, Sh. K. Baltybaev, Yu. R. Volkova, E. S. Malchushkin

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Abstract

This article focuses on the issues related to the primary nature and metamorphism of gneisses from the Larba block of the Dzhugdzhur–Stanovoy fold area, which are based on the study of the mineralogical composition of supracrustal rocks. The PT-parameters for the highest temperature and pressure metamorphic transformations of rocks of the Larba block are estimated as P = 6.5–8.5 kbar and T > 800°C. Relatively low-temperature garnet–biotite and garnet–biotite–chlorite mineral parageneses were formed at the regressive stage of metamorphism at ~4–6 kbar and temperatures up to 500–600°C. Wide variations in paragneiss compositions indicate that the studied gneisses were derived from protoliths of different composition. Overall, Larba metasedimentary rocks had weakly and moderately weathered source areas. Most of the compositions of paragneisses are located in the field of chlorite–montmorillonite, montmorillonite–kaolinite–hydromica, and chlorite clays formed from the mafic protolith. The low alkalinity in combination with a high MgO content indicates the presence of rock erosion products with a significant admixture of basic volcanic material in the detrital material. Migmatization of the rocks is the most significant factor that distorts the reconstruction of the original rock composition.

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朱格德朱尔-斯坦诺沃伊褶皱区拉巴地块花岗岩的矿物成分、变质参数和原岩

摘要本文根据对超岩壳岩石矿物成分的研究，重点讨论了与朱格特朱尔-斯坦诺沃伊褶皱区拉尔巴地块片麻岩的原生性质和变质作用有关的问题。拉尔巴地块岩石最高温度和压力变质转化的 PT 参数估计为 P = 6.5-8.5 千巴和 T > 800°C。相对低温的石榴石-生物沸石和石榴石-生物沸石-绿泥石矿物副岩是在约 4-6 千巴和高达 500-600°C 的变质回归阶段形成的。副片麻岩成分的巨大差异表明，所研究的片麻岩来自不同成分的原岩。总体而言，拉尔巴变质岩具有弱风化和中风化源区。大部分片麻岩的成分属于绿泥石-蒙脱石、蒙脱石-高岭石-水云母以及由黑云母原岩形成的绿泥石粘土。低碱度与高氧化镁含量相结合，表明岩石侵蚀产物的存在，并在碎屑物质中掺入了大量碱性火山物质。岩石的岩化是扭曲原始岩石成分重建的最重要因素。

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来源期刊

Russian Journal of Pacific Geology 地学-地球科学综合

CiteScore

1.30

自引率

37.50%

发文量

审稿时长

>12 weeks

期刊介绍： Russian Journal of Pacific Geology publishes the results of research on the Earth crust and mantle composition and provides articles on the geological structure and patterns of distribution of mineral deposits in the Pacific Ocean, marginal seas and continental margins. It discusses the topics of stratigraphy, sedimentology, magmatic activity, and seismicity. The journal deals with the problems of lithosphere plates tectonics, and offers the results of neotectonic, geomorphological, geodesic, environmental and mining studies in the Pacific region. The journal accepts theoretical, methodical and philosophical articles covering general issues of geology, geophysics, geochemistry, geoecology and mining. The journal also publishes critical notes and comments, and reviews.