Abstract—The paper reports new geochronological, petrological, and isotope-geochemical data on the syenites and alkali syenites of the Artyushki massif, and the monzonites of the Gusikha massif. These massifs are located along the southwestern and northeastern margins of the Pachelma aulacogen, in the southeastern part of the East European Platform (EEP). They have Early Cambrian ages of 524 ± 3 (Artyushki) and 514 ± 2 Ma (Gusikha) obtained by the U-Pb zircon method and similar ages of amphibole and K-feldspar by the ⁴⁰Ar/³⁹Ar method. This time period has previously been regarded as amagmatic in the EEP evolution. The Artyushki massif is made up of Amp–Cpx syenite porphyries and Grt–Cpx alkali syenite porphyries and their fenitized varieties. As compared to the Amp–Cpx varieties the Grt–Cpx rocks are more peralkaline (A/NK > 0.9) and have higher LREE and HFSE, and fractionated HREE patterns. The metasomatized (fenitized) varieties are more potassic and bear geochemical evidence of fluid reworking (high Y/Ho ratios, significant Zn variations, and etc.). Bulk samples have weakly radiogenic Sr isotopic compositions: (⁸⁷Sr/⁸⁶Sr)₅₂₀ are within 0.703066–0.703615. The values of ε_Nd(520) vary from –0.69 to +1.64. The Grt–Cpx syenite porphyries have the positive ε_Nd(520), while the Amp–Cpx and fenitized syenite porphyries feature negative ε_Nd. The Gusikha massif consists of biotite–amphibole and biotite monzonites. Similar to the Artyushki syenites in SiO₂ contents, the Gusikha monzonites have higher Mg# (0.22–0.54 and 0.34–0.71 for the Artyushki and Gusikha massifs, respectively). They are also characterized by a negative Nb–Ta anomaly (Nb/Nb* = 0.5), high Ва/Sr ratio, and highly radiogenic (⁸⁷Sr/⁸⁶Sr)₅₂₀ = 0.705204 and 0.705320. Their Nd-isotopic compositions correspond to ε_Nd(520) = –6.7 and ‒7.0. Two melts contributed to the formation of the Artyushki massif. One was a strongly contaminated melt (Amp–Cpx syenite porphyries, the other was weakly contaminated (Grt–Cpx syenite porphyries). The main contribution was phonolitic melt derived from the melting of a moderately metasomatized (carbonate- and amphibole-bearing) shallow lithospheric mantle. The earliest and deepest melt portions were carbonate–silicate in composition. The geochemical, as well as the Sr and Nd isotopic compositions of the Gusikha monzonites indicate a predominant crustal contribution and pervasive reworking of the lithospheric mantle beneath southeastern Volgo–Uralia of the EEP in the Mesoproterozoic. Both massifs feature the geochemistry of within-plate and supra-subduction derivatives, which suggests a postorogenic tectonic setting of the magmatism. The presence of the Early Cambrian postorogenic magmatism within the East European Platform/Baltica is direct evidence for the involvement of Baltica in the collisional and/or accretionary events during the terminal Neoproterozoic–the beginning of the Paleozoic. This suggests reworking of the lithospheric mantle of Baltica during its collision with Timanian and East Avalonian/Cadomian terranes, including Scythia.

中文翻译：

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东欧平台东南部的早寒武纪正长岩和辉长岩岩浆作用：成岩作用和构造环境

摘要—本文报道了Artyushki地块的正长岩，正长岩和古西哈地块的辉长岩的新的年代学，岩石学和同位素地球化学数据。这些地块位于东欧平台（EEP）东南部的Pachelma aulacogen的西南边缘和东北边缘。通过U-Pb锆石方法获得的早寒武纪年龄为524±3（Artyushki）和514±2 Ma（Gusikha），通过⁴⁰ Ar / ³⁹ Ar方法获得的闪石和钾长石的年龄相似。在EEP演变过程中，这个时间段以前被认为是奇幻的。Artyushki地块由Amp – Cpx硒斑岩和Grt – Cpx组成碱性正长岩斑岩及其特征化变种。与Amp – Cpx品种相比，Grt – Cpx岩石的碱性更高（A / NK> 0.9），具有更高的LREE和HFSE，以及分馏的HREE模式。交代化的（芬尼特化的）品种钾质更高，并具有流体返工的地球化学证据（高的Y / Ho比，显着的Zn变异等）。大量样品的放射同位素Sr同位素组成很弱：（⁸⁷ Sr / ⁸⁶ Sr）₅₂₀在0.703066-0.703615之间。ε的值_的Nd（520）改变从-0.69至1.64。该石榴石-单斜辉石正长岩斑岩具有积极的ε_钕（520），而放大器-单斜辉石和fenitized正长斑岩具有负ε_钕。古西卡地块由黑云母-闪石和黑云母蒙脱石组成。与SiO ₂含量中的Artyushki榴辉岩相似，Gusikha锰锌矿的Mg＃较高（Artyushki和Gusikha岩块的Mg＃分别为0.22-0.54和0.34-0.71）。它们的特征还在于负Nb-Ta异常（Nb / Nb * = 0.5），高Ва/ Sr比和高放射源性（⁸⁷ Sr / ⁸⁶ Sr）₅₂₀ = 0.705204和0.705320。它们的Nd-同位素组成对应于ε_钕（520）= -6.7 -7.0和。两次融化促进了Artyushki断层的形成。一个是被严重污染的熔体（Amp – Cpx堇青石斑岩，另一个被轻度污染（Grt – Cpx硒矿斑岩。主要是由中等交代化（含碳酸盐和含闪石的）浅岩石圈地幔的熔融而产生的火山岩熔体。熔体中最早和最深的部分是碳酸盐-硅酸盐。古西卡蒙脱石的地球化学以及Sr和Nd同位素组成表明，中元古生代中EEP东南伏尔加-乌拉里东南部的岩石圈地幔起着重要的地壳作用和普遍的改造作用。两种地块都具有板内和超俯冲导数的地球化学特征，这表明岩浆作用的后造山构造背景。东欧平台/波罗的海内部早寒武世的成岩浆作用存在，直接证明了波罗的海参与了新元古代末期（古生代的开始）的碰撞和/或增生事件。这表明波罗的海岩石圈地幔在与Timanian和东Avalonian / Cadomian地貌（包括Scythia）碰撞时进行了改造。