Abstract

Based on a compilation of the vast literature, we typify the peculiar mantle-derived adakitic volcanic rocks in the Sea of Okhotsk, Kamchatka, and Bering Sea regions. The low-silica (LSA) and high-silica (HSA) types are distinguished in each region. The prevailing adakite type corresponds to the bimodal basalt–andesite series in the Kamchatka region and the basanite–dacite series in the Bering Sea region. In the Kamchatka region, the formation of LSA was related to the fractionation and melting of pyroxene, while the origin of HSA was related to the fractionation, melting, and breakdown of amphibole. Alkaline metasomatism plays a subordinate role in these processes. In the Bering Sea region, the formation of both types of adakites was mainly controlled by amphibole, with the assistance of alkaline metasomatism. The isotope–geochemical compositions of the adakites and within-plate volcanic rocks shows that both these rock types can be equally regarded as indicators of plume petrogenesis and geodynamics. Based on a comparison of the compositions of the adakites and glasses derived by xenolith melting, a two-stage genetic model is proposed: formation of black pyroxenites through melting of mantle lherzolites and generation of the entire rock complex owing to the repeated melting of the same lherzolites and newly formed pyroxenites. The formation of adakitic and within-plate signatures in the volcanic products beginning from the Eocene indicates the transition of the spacious territory of the NE continental margin from subduction-related compression to a setting of rift extension.

中文翻译：

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大陆边缘的Adakite火山活动及相关问题。第二部分 鄂霍次克海，堪察加半岛和白令海地区的Adakites：典型化和成因

摘要

在汇总大量文献的基础上，我们对鄂霍次克海，堪察加半岛和白令海地区特有的地幔衍生的埃达克火山岩进行了分类。低硅（LSA）和高硅（HSA）类型在每个区域中都不同。占主导地位的ad石类型对应于堪察加地区的双峰玄武岩-安山岩系列和白令海地区的玄武岩-石系列。在堪察加地区，LSA的形成与辉石的分馏和熔融有关，而HSA的起源与闪石的分离，熔融和分解有关。碱性交代作用在这些过程中起次要作用。在白令海地区，在碱性交代作用的辅助下，两种类型的黄连石的形成主要受角闪石控制。蓝云母和板内火山岩的同位素-地球化学组成表明，这两种岩石类型均可以视为羽状岩石成因和地球动力学的指标。在比较异岩体熔融产生的黄ak石和玻璃的成分的基础上，提出了一个两阶段的遗传模型：通过地幔锂铁矿的熔融形成黑色辉石岩，以及由于反复地融化而形成整个岩石复合体锂铁矿和新形成的辉石岩。始于始新世的火山产物中的Adakitic和板内特征形成，表明NE大陆边缘的宽阔区域已从俯冲相关的压缩转变为裂谷扩展。