Abstract—

The paper presents detailed geological, petrographic, geochemical, and isotope data on the dolerites from dykes of the Baikal dike subswarm in the central part of the Baikal basement inlier of the Siberian craton. The main geochemical and isotope criteria were identified for classifying the dolerites that are similar in geological–structural position and mineral composition into three geochemical groups. Provisional age estimates of the dolerites are presented. The dolerites of the first and, perhaps, second groups compose Neoproterozoic (715 Ma) dikes. The first group includes medium- to coarse-grained dolerites, which form thick (more than 5–10 m) dikes. The dolerites of this group are characterized by low concentrations of Th (0.6–2.1 ppm) and Nb (3.3–9.2 ppm) and by ɛNd(T) = ‒0.5 to ‒3.9. Considered together, the geochemical and isotope data show that these dolerites could be produced as a result of the melting of a mantle source produced by mixing mantle components close in composition to oceanic plateau basalts and subduction-related subcontinental lithospheric mantle. The second group includes fine-grained dolerites from thin (1–5 m) dikes, including dikes located in contact with the dikes of the first group. The dolerites of the second group are characterized by higher concentrations of Th (3.0–5.3 ppm) and Nb (9.8–21.1 ppm) and by ɛNd(T) = –5.3 to ‒6.0. Geochemical and isotopic data on the dolerites of the second group indicate that continental crustal material was added to the mantle source unified for the dolerites of first and second groups. The third group includes medium-grained dolerites, which make up individual dikes that are contrastingly different in geochemical and isotope characteristics from the Neoproterozoic dolerites of the first and second groups. Dolerites of this group show low concentrations of Th (0.6–1.6 ppm) and Nb (2.7–5.1 ppm) at low values of (Th/La)_pm (0.29–0.71) and ¹⁴³Nd/¹⁴⁴Nd (0.511223‒0.511544), which indicates that these dolerites may have been generated as a result of the melting of the subcontinental lithospheric mantle enriched in subduction components. Dolerites of the third group exhibit geochemical characteristics close to those of Paleoproterozoic (1.84 Ga) dikes of the South Siberian post-collisional magmatic belt.

中文翻译：

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西伯利亚克拉通贝加尔湖基底内层中部辉绿岩脉分类的地球化学标准

摘要-

本文提供了西伯利亚克拉通贝加尔湖基底内层中部贝加尔湖岩脉亚群岩脉中辉绿岩的详细地质、岩相、地球化学和同位素数据。确定了主要地球化学和同位素标准，将地质构造位置和矿物成分相似的辉绿岩分为三个地球化学组。给出了辉绿岩的临时年龄估计。第一组和第二组的辉绿岩组成了新元古代（715 Ma）岩墙。第一组包括中粒至粗粒辉绿岩，形成厚（超过 5-10 m）的岩脉。该组辉绿岩的特点是 Th (0.6–2.1 ppm) 和 Nb (3.3–9.2 ppm) 浓度较低，且 ɛNd(T) = –0.5 至 –3.9。综合考虑，地球化学和同位素数据表明，这些辉绿岩可能是由于地幔源熔化而产生的，该地幔源是通过混合与大洋高原玄武岩和与俯冲相关的次大陆岩石圈地幔成分接近的地幔成分而产生的。第二组包括来自薄（1-5 m）岩脉的细粒辉绿岩，包括与第一组岩脉接触的岩脉。第二组辉绿岩的特点是 Th (3.0–5.3 ppm) 和 Nb (9.8–21.1 ppm) 浓度较高，且 ɛNd(T) = –5.3 至 –6.0。第二组辉绿岩的地球化学和同位素数据表明，大陆壳物质被添加到第一组和第二组辉绿岩统一的地幔源中。第三组包括中粒辉绿岩，这些岩脉构成了与第一组和第二组新元古代辉绿岩在地球化学和同位素特征上截然不同的单独岩脉。该组辉绿岩在 (Th/La) 值较低时显示出较低浓度的 Th (0.6–1.6 ppm) 和 Nb (2.7–5.1 ppm)_pm (0.29~0.71) 和¹⁴³ Nd/ ¹⁴⁴ Nd (0.511223−0.511544)，这表明这些辉绿岩可能是由于富含俯冲成分的次大陆岩石圈地幔熔融而产生的。第三组辉绿岩表现出与南西伯利亚碰撞后岩浆带古元古代（1.84 Ga）岩脉相似的地球化学特征。