K-Ar dating of magmatic rocks from the Urup Island, Kuril Island Chain

An isotope-geochronological study of Neogene-Quaternary igneous rocks from the Urup Island (Greater Kuril Ridge) was carried out. It was established that magmatic activity in the island developed during the last 10 my and it was not interrupted by long inactive periods. K-Ar data obtained along with results of diatomic analysis are in good agreement with the regional stratigraphic scheme of Paleogene and Neogene deposits and the intraregional correlation scheme of magmatic rocks in the Kuril Islands, which are developed for the State Geologic Map, scale 1:200 000 (Second edition). In the present-day territory of the Urup Island, the earliest Late Miocene - Early Pliocene (10.5-4.5 Ma) magmatic stage was associated with formation of the Rybakovsky andesite volcanic complex, which is represented by an effusive series (Rybakovskaya Suite) and subvolcanic rocks. Actually at the same time (6.6-4.7 Ma), but at a great depth, intrusive bodies of the Prasolovsky plagiogranite-diorite plutonic complex were intruded. The Pliocene stage of magmatism in the Urup Island is characterized by formation of rocks of the Kamuysky dacitic volcanic complex (4.0-2.1 Ma). This complex is locally represented only by subvolcanic acidic bodies, and its occurrence in the island is limited. During the Pliocene - Early Neopleistocene stage of magmatism (3.0-0.8 Ma) the Fregatsky andesibasalt volcanic complex was formed in the Urup Island. This complex includes effusive series (Fregatskaya unit) and subvolcanic bodies. Quaternary time in the Urup Island is characterized by eruptive activity in subaerial conditions with formation of effusive-pyroclastic intermediate-basic rocks of the Bogatyrsky Middle Neopleistocene - Holocene complex (<0.5 Ma). Rocks of this complex formed stratovolcano cones. Pyroclastic rocks of the Rokovsky dacitic volcanic complex were erupted simultaneously. The mentioned magmatic complexes of the Urup Island well correlate with the distinguished magmatic complexes within the bounds of contiguous insular blocks of the Greater Kuril Arc and confirm uniform geologic history of magmatic development of the region.

本次研究针对大千岛脊（Greater Kuril Ridge）乌鲁普岛的新近纪-第四纪火成岩开展了同位素地质年代学研究。研究证实，该岛的岩浆活动始于距今约10 Ma，期间未出现长期的静止间歇。本次获得的钾氩（K-Ar）测年数据与双原子分析结果，与千岛群岛古近纪、新近纪沉积的区域地层格架，以及为1:20万第二版国家地质图编制的千岛群岛岩浆岩区域对比方案高度吻合。在乌鲁普岛现今分布范围内，最早的晚中新世-早上新世（10.5~4.5 Ma）岩浆期对应雷巴科夫斯基安山岩火山杂岩的形成，该杂岩以溢流岩系（雷巴科夫斯卡亚组，Rybakovskaya Suite）及次火山岩为主要产出形式。几乎同期（6.6~4.7 Ma），在深部就位了普拉索洛夫斜长花岗岩-闪长岩深成杂岩的侵入体。乌鲁普岛的上新世岩浆活动以卡穆伊斯基英安岩火山杂岩（4.0~2.1 Ma）的形成为典型特征，该杂岩在岛内仅局部分布，以次火山酸性岩体为主要产出形式且分布范围有限。在上新世-早新更新世（3.0~0.8 Ma）岩浆活动期内，乌鲁普岛形成了弗雷加特安山玄武岩火山杂岩，该杂岩包含溢流岩系（弗雷加茨基站，Fregatskaya unit）与次火山岩体。乌鲁普岛的第四纪时期以陆上喷发活动为特征，形成了博加特尔斯基中更新世-全新世杂岩（<0.5 Ma）的溢流-火山碎屑型中基性岩石，该杂岩的岩石构成了层状火山锥。同期还喷发了罗科夫斯基英安岩火山杂岩的火山碎屑岩。上述乌鲁普岛的各类岩浆杂岩，与大千岛弧（Greater Kuril Arc）相邻岛块内识别出的岩浆杂岩具有良好的可对比性，证实了该区域岩浆演化的统一地质历史。