Abstract—

The Lower Oligocene Kal-e-kafi (East of Anarak, Central Iran) lamprophyres occur as stocks and dikes, which cross-cut the Eocene volcanic and Cretaceous sedimentary rocks. The predominant minerals of these lamprophyres are hornblende (magnesiohastingsite) and clinopyroxene (diopside) phenocrysts set in a fine- to medium-grained matrix of the same minerals plus plagioclase (labradorite to bytownite), sanidine, apatite, and magnetite. Secondary minerals are chlorite, magnetite, calcite, and epidote. Petrography, mineral chemistry, and whole rock compositions classify these rocks as calc-alkaline lamprophyre, in general, and spessartite in particular. These samples have intermediate compositions (SiO₂ ~ 58 wt %). The chondrite-normalized REE patterns and primitive mantle-normalized multi-element spider diagram of Kal-e-kafi lamprophyres are remarkably parallel and suggest that these dikes and stocks were derived from the same parental magma and underwent similar melt extraction. These rocks are enriched in alkalies, large-ion lithophile elements (e.g., Rb, Ba, K), and light rare-earth elements (e.g., La, Ce), and exhibit moderate to high fractionation in LREE patterns, with an average La/Lu ratio of 112. The large amount of hydrous fluids coming from the subducted slab rather than sediments caused to the enrichment and metasomatism of subcontinental lithospheric mantle source. Crustal contamination and assimilation of host rocks also played role in the genesis of these lamprophyres. Geochemical characteristics of the studied rocks suggest that parental magma have been derived from partial melting of a metasomatized amphibole-bearing spinel lherzolite of lithospheric mantle, which was previously modified by dehydration of a subducting slab. Subduction of oceanic crust around the Central-East Iranian Microcontinent (CEIM) is the most reasonable mechanism to explain enrichment in volatiles of the mantle, and the lamprophyric magmatism of the Kal-e-kafi area in Lower Oligocene times. Several tectonomagmatic discrimination diagrams indicate that the Kal-e-kafi lamprophyres occurred during postcollisional period of lithospheric extension.

中文翻译：

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来自伊朗中部（阿纳拉克地区东部）的下渐新世钙碱性杂类灯藻；来自新特提斯俯冲作用有关的地幔富集东部分支的证据

摘要—

下渐新世Kal-e-kafi（伊朗中部的阿纳拉克东部）的煌斑岩以种群和堤坝的形式出现，横切了始新世的火山岩和白垩纪的沉积岩。这些煌斑岩的主要矿物质是角闪石（镁锰矿）和斜辉石（透辉石）类隐晶石，分布在相同矿物质加斜长石（拉长石到亚钙钛矿），山梨，磷灰石和磁铁矿的中细粒度基质中。次生矿物是绿泥石，磁铁矿，方解石和附子。岩石学，矿物化学和整个岩石成分通常将这些岩石归类为钙碱性煌斑岩，尤其是碳酸锂。这些样品具有中间成分（SiO ₂〜58wt％）。Kal-e-kafi煌斑岩的球粒陨石归一化REE模式和原始地幔归一化多元素蜘蛛图显着平行，表明这些堤防和储量来自相同的母岩浆，并经历了相似的熔体提取。这些岩石富含碱金属，大离子亲石元素（例如，Rb，Ba，K）和轻稀土元素（例如，La，Ce），并且在LREE模式中表现出中等至高分馏，平均La / Lu比为112。大量的含水流体来自俯冲板块，而不是沉积物，导致了陆下岩石圈地幔源的富集和交代作用。地壳污染和主岩的同化作用在这些煌斑岩的成因中也起着作用。所研究岩石的地球化学特征表明，母岩浆来自岩石圈地幔中交代化的含闪石尖晶石锂铁矿的部分熔融，该熔融先前通过俯冲板的脱水而被改性。伊朗中东部微洲（CEIM）周围洋壳的俯冲是解释下渐新世时期地幔挥发物富集以及Kal-e-kafi地区日光岩浆作用最合理的机制。几个构造学上的判别图表明，Kal-e-kafi煌斑岩发生在岩石圈伸展后碰撞期。之前已通过俯冲板的脱水进行了修改。伊朗中东部微大陆（CEIM）周围洋壳的俯冲是解释下渐新世时期地幔挥发物富集以及Kal-e-kafi地区的煌斑岩浆作用的最合理机制。几个构造学上的判别图表明，Kal-e-kafi煌斑岩发生在岩石圈伸展后碰撞期。之前已通过俯冲板的脱水进行了修改。伊朗中东部微洲（CEIM）周围洋壳的俯冲是解释下渐新世时期地幔挥发物富集以及Kal-e-kafi地区日光岩浆作用最合理的机制。几个构造学上的判别图表明，Kal-e-kafi煌斑岩发生在岩石圈伸展后碰撞期。