This study concentrates on the petrological and geochemical investigation of mafic rocks embedded within the voluminous Triassic June Complex of the central Sanandaj–Sirjan zone (Iran), which are crucial to reconstruct the geodynamics of the Neotethyan passive margin. The Triassic mafic rocks are alkaline to sub-alkaline basalts, containing 43.36–49.09 wt% SiO2, 5.19–20.61 wt% MgO and 0.66–4.59 wt% total alkalis. Based on MgO concentrations, the mafic rocks fall into two groups: cumulates (Mg# = 51.61–58.94) and isotropic basaltic liquids (Mg# = 24.54–42.66). In all samples, the chondrite-normalized REE patterns show enrichment of light REEs with variable (La/Yb)N ratios ranging from 2.48 to 9.00, which confirm their amalgamated OIB-like and E-MORB-like signatures. Enrichment in large-ion lithophile elements and depletion in high field strength elements (HFSE) relative to the primitive mantle further support this interpretation. No samples point to crustal contamination, all having undergone fractionation of olivine + clinopyroxene + plagioclase. Nevertheless, elemental data suggest that the substantial variations in (La/Sm)PM and Zr/Nb ratios can be explained by variable degrees of partial melting rather than fractional crystallization from a common parental magma. The high (Nb/Yb)PM ratio in the alkaline mafic rocks points to the mixing of magmas from enriched and depleted mantle sources. Abundant OIB alkaline basalts and rare E-MORB appear to be linked to the drifting stage on the northern passive margin of the Neotethys Ocean.

中文翻译：

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伊朗Sanandaj–Sirjan地区六月综合体的三叠纪镁铁质岩石的构造意义

这项研究的重点是埋藏在Sanandaj-Sirjan中部（伊朗）大量三叠纪六月复合体内的镁铁质岩石的岩石学和地球化学研究，这对于重建新特提斯洋被动缘的地球动力学至关重要。三叠纪的镁铁质岩为碱性至亚碱性玄武岩，包含43.36–49.09 wt％的SiO2、5.19–20.61 wt％的MgO和0.66–4.59 wt％的总碱。根据MgO的浓度，镁铁质岩石分为两类：堆积（Mg＃= 51.61–58.94）和各向同性玄武质液体（Mg＃= 24.54–42.66）。在所有样品中，球粒陨石标准化的REE图案均显示轻稀土元素的富集，其（La / Yb）N比率范围为2.48至9.00，这证实了它们的OIB样和E-MORB样特征的结合。相对于原始地幔，大离子亲石元素的富集和高场强元素（HFSE）的枯竭进一步支持了这种解释。没有样品指出地壳污染，所有样品都经历了橄榄石+斜py石+斜长石的分离。然而，元素数据表明，（La / Sm）PM和Zr / Nb比的显着变化可以通过部分熔融程度（而不是从普通母岩浆中进行分步结晶）来解释。碱性镁铁质岩石中较高的（Nb / Yb）PM比表明来自富地幔资源和贫地幔资源的岩浆混合。大量的OIB碱性玄武岩和稀有的E-MORB似乎与新特提斯洋北部被动边缘的漂移阶段有关。