In this paper, we provide insight into the evolution of syenite magmas based on geological data and petrographic, geochemical, and O-Nd isotope parameters of rocks of the Saibar intrusion located within the Minusinsk Trough, Altay-Sayan area. The intrusive suite includes predominant syenites, few bodies of melanocratic and leucocratic nepheline syenites (foyaites), and granites. In addition, dykes of granites and mafic rocks are present. The U-Pb zircon age from the melanocratic foyaites was determined to be 457 ± 27 Ma. Examined rocks show fractionated light rare earth element patterns, normalized to chondrite, with (La/Sm)_n varying from 4 to 9, and a weakly fractionated distribution of medium and heavy rare elements, with (Dy/Yb)_n from 0.35 to 1.23 and (Sm/Yb)_n from 0.63 to 2.62. The spidergram normalized to the primitive mantle shows negative Ba, Sr, Nb, Ta, Ti, and Eu anomalies (Eu* = 0.48–0.60) and positive Rb, Th, and U anomalies. The δ¹⁸O values vary within 6.3 to 10.2‰, and εNd(t) from +4.1 to +5.0. We observe gradual transitions from syenites to foyaites. Assimilation by syenite magma of the host carbonate rocks was followed to transition from silica-saturated to silica-undersaturated conditions and removal of anorthite from the melt, which then led to nepheline. Granites of the main phase show depleted lithophile incompatible elements in comparison with syenites and foyaites. They originate via interaction of magmas at the marginal part (endocontact zone) of the intrusion, corresponding to north contact of the granites with the host felsic rocks. In comparison, the rock composition of granite dykes is enriched in lithophile incompatible elements, except for Zr, Hf, and Ti. These rocks are formed due to the differentiation of syenite magma without a significant effect of host rock assimilation. Mantle magmas must be used as parent magmas for syenites based on analysis of the formation model of other alkaline intrusions, which are similar in age to the Saibar intrusion. In the line of syenite intrusions of the Altai-Sayan province, the Saibar intrusion is no exception, and its origin is related to the evolution of mafic magmas that arose during the melting of the mantle under the influence of a mantle plume.

中文翻译：

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堇青石岩浆的演化：俄罗斯阿尔泰－萨彦地区奥陶纪塞巴人入侵的地质，地球化学和O-Nd同位素特征的见解

在本文中，我们基于地质数据以及位于Altay-Sayan地区Minusinsk槽内的Saibar侵入体的岩石的岩石学，地球化学和O-Nd同位素参数，洞悉了正岩岩浆的演化。侵入性套件包括主要的正长岩，少量的黑克拉通和白垩纪霞石正长岩（泡沫岩）和花岗岩。此外，还存在花岗岩和镁铁质岩的堤坝。从黑阶方质岩中获得的U-Pb锆石年龄为457±27 Ma。被检查的岩石显示出轻质稀土元素的形态，按球粒陨石归一化，（La / Sm）_n在4到9之间变化，中，重稀土元素的分布较弱，（Dy / Yb）_n在0.35到1.23之间。和（Sm / Yb）_n从0.63到2.62。标准化为原始地幔的蜘蛛图显示负的Ba，Sr，Nb，Ta，Ti和Eu异常（Eu * = 0.48–0.60）和正的Rb，Th和U异常。该δ ¹⁸O值在6.3到10.2‰之间变化，而εNd（t）在+4.1到+5.0之间变化。我们观察到从正长岩到多叶岩的逐渐过渡。接着，由碳酸盐岩的正长岩浆同化，从饱和的二氧化硅过渡到饱和的二氧化硅，然后从熔体中除去钙长石，然后形成霞石。与正长岩和水辉石相比，主相花岗岩显示出贫化的不亲石的元素。它们是通过岩浆在侵入体边缘部分（内接触带）的相互作用而产生的，这对应于花岗岩与主体长英质岩石的北接触。相比之下，除了Zr，Hf和Ti以外，花岗岩堤坝的岩石成分中富含不易石溶的元素。这些岩石是由于正长岩浆的分化而形成的，没有明显的基质岩同化作用。根据对其他碱性侵入岩形成模型的分析，必须将地幔岩浆用作正长岩的母浆。在阿尔泰-萨彦省（Altai-Sayan）的正长岩侵入线中，塞巴尔（Saibar）侵入岩也不例外，其起源与地幔羽化作用下地幔融化过程中产生的镁铁质岩浆的演化有关。