Abstract—

The paper presents results of the first geochronologic study (LA-ICP-MS zircon method) of metasedimentary rocks that host the banded iron formation (BIF) and the metarhyolites (halleflinta) of the Gimoly Group in the Kostimuksha greenstone belt,Karelian Craton. Felsic magmatism that produced the rhyolite sills and dikes was dated at 2759 ± 19–2743 ± 15 Ma. The clearly predominant group of zircons in the schists (metagraywacke) has an isotope age of 2753 ±19 Ma, and scarce zircon grains of these rocks vary in age from 3.1 to 2.8 Ga. Geochemically, zircons from metarhyolites fall into three types (1) Eu-depleted and Ce-enriched, (2) Eu- and Ce-enriched, and (3) LREE- and MREE-enriched. The zircons of geochemical types (1) and (2) are also predominant in the sediments. The morphology and structure of zircon crystals in the rhyolites and sediments are also identical. The rhyolites were thus a major source of zircons for the metagraywacke, which alternates with BIF, while the Mesoarchean rocks played a subordinate role. The BIF of the Gimoly Group in the Kostomuksha Greenstone Belt was formed simultaneously with felsic volcanism at 2760–2740 Ma.

中文翻译：

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科斯图穆克沙绿岩带，卡雷利安·克拉顿，芬诺斯堪的亚盾构的带状铁形成的太古宙地层时代：锆石的地球化学和年代学约束

摘要-

本文介绍了首次沉积时代的研究成果（LA-ICP-MS锆石方法），该沉积物中的岩石为卡累利安克拉通Kostimuksha绿岩带中的吉莫利群带状铁形成（BIF）和变质岩（halleflinta）所带。产生流纹岩基岩和堤坝的长英质岩浆作用的年代为2759±19–2743±15 Ma。片岩中明显占优势的锆石（同位素）年龄为2753±19 Ma，稀少的锆石晶粒年龄从3.1到2.8 Ga不等。从地球化学上讲，变流石中的锆石分为三种类型（1）贫铀和富铈，（2）富富铈和铈，以及（3）富稀土和富稀土。地球化学类型为（1）和（2）的锆石也主要存在于沉积物中。流纹岩和沉积物中锆石晶体的形态和结构也相同。因此，流纹岩是变质灰ack的锆石的主要来源，变质灰alternate与BIF交替出现，而Mesoarchean岩石起着次要作用。科斯图穆克沙绿岩带吉莫利群的BIF与2760-2740 Ma的长英质火山活动同时形成。