Abstract

The results of the isotope dating of the crystalline basement of the Greater Caucasus (the Elbrus subzone of the Main Caucasus Range) within of the high-temperature gneiss–migmatite area of the Gondaray metamorphic complex is discussed. The relationships between regional metamorphism, migmatization, and heat flows in the lithosphere are considered. The measurements of the zircon isotope compositions were performed on a SHRIMP-II ion microprobe at the CIR VSEGEI (St. Petersburg). All zircon crystals from gneiss sample 526 have a zonal structure with ancient detrital cores. Almost all U–Pb isotope dating points lie on the concordant line and show a wide age range from 320–1000 Ма, partially inherited from detrital zircon grains from primary pelitic sediments. The youngest ages (320 Ма) were measured in the regeneration zones of zircon grains recrystallized during stage of the anatexis and migmatization. The other points of detrital zircons form an age cluster of 540–1000 Ма, which indicates their origin from different magmatic sources that existed during the formation of the protometamorphic protolith. Several detrital zircon grains yielded a Cambrian age; this is evidence for an Early Paleozoic age of the metamorphic protolith, which was traditionally suggested to be Precambrian or even Archean. The ages of the rims of recrystallized zircons (320 Ма) have a direct correlation with the postmetamorphic granitoid ages of the Greater Caucasus. The thermochronological modeling of the transformation of the Gondaray metamorphic complex during the retrogressive stage of metamorphism demonstrates that its cooling from the temperature of migmatite crystallization (650°С) to the closure of the temperature of the K–Ar biotite isotope system (350°С) was relatively rapid (the rate of cooling was 8–10°С/Ma) under subisobaric conditions and during a time range approximately 30–40 Ма.

中文翻译：

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冈达雷变质带（大高加索地区）的片麻片麻岩的锆石学和热年代学

摘要

讨论了冈多雷变质复合体的高温片麻岩-辉锰矿区域内高加索地区（主要高加索山脉的布鲁斯子带）的结晶基底的同位素测年结果。考虑岩石圈中区域变质作用，迁移作用和热流之间的关系。锆石同位素组成的测量是在CIR VSEGEI（圣彼得堡）的SHRIMP-II离子微探针上进行的。来自片麻岩样品526的所有锆石晶体具有带古老碎屑核的带状结构。几乎所有的U–Pb同位素测年点都位于一致的直线上，并显示出320–1000Ма的较宽年龄范围，部分年龄是从原始胶质沉积物中的碎屑锆石中遗传的。在麻醉和迁移过程中重结晶的锆石晶粒的再生区中测量了最小年龄（320Ма）。碎屑锆石的其他点形成了一个540-1000Ма年龄群，这表明它们的起源是在原形原岩形成过程中存在的不同岩浆源。几种碎屑锆石颗粒产生了寒武纪。这是变质原生石早期古生代的证据，传统上认为这是前寒武纪甚至太古代。重结晶锆石的轮缘年龄（320Ма）与大高加索地区的后变质花岗岩年龄直接相关。