Abstract We discuss the geology, petrology, and major and trace element geochemistry of Late Cenozoic volcanic rocks in the Almaludag region in the Western Azerbaijan province, northwest Iran. Geology of this region evolved through the northward subduction of the Neotethyan oceanic lithosphere and subsequent collision of the Arabian and Eurasian plates during the Alpine-Himalayan orogeny. Two different Late Cenozoic periods of volcanic activity are recognized: Episode I produced pyroclastic deposits and trachydacitic lava (1.47 Ma, U-Pb dating) and Episode II generated mafic lava and scoria cones (including spatter/cinder). Geochemical data indicate that Episode I lavas have high-silica adakitic compositions, similar to the post-collisional and continental adakites, that formed from the partial melting of the thickened lower crust. Episode II lavas vary in composition and fall into two distinct geochemical groups. The first group includes picrobasalt-basanite and tephrite compared to the more evolved trachybasalt and basaltic trachyandesite of the second group. Both of these groups show alkaline to shoshonitic affinities. The binary geochemical plots of the Episode II samples display compositional trends that indicate magmatic processes such as fractional olivine ± clinopyroxene crystallization. The major and minor elemental variations of these samples reflect a mantle source heterogeneity and minor crustal contamination. The REE (rare earth elements) patterns and spider diagrams indicate enrichment of the large ion lithophile elements (LILE) and depletion of the high field strength elements (HFSE) relative to the heavy rare earth elements (HREE), and reveal an enriched lithospheric mantle source which was previously metasomatized by subduction components. The mantle source of the Episode II lavas was enriched by fluids and melts which were released from a subducted slab between Late Mesozoic and Early Cenozoic in northwest Iran. The Si-undersaturated lavas of the first group of Episode II probably originated in the garnet stability field in the lithospheric mantle with carbonate residue or veins, suggesting that the mantle source probably underwent carbonate metasomatism. Geochemistry of the SiO2 rich lavas of the second group of Episode II is consistent with a melt extracted from a peridotitic mantle source. The compositional variation from the rocks of the first group to those in the second group suggests a diminishing degree of metasomatic veins-wallrock interactions. The Late Cenozoic mafic rocks in the Almaludag region probably formed through extension in a post-collision, post-orogenic setting. The extension was likely the result of the delamination of the thickened subcontinental lithospheric mantle (SCLM) and ensuing asthenospheric upwelling after the collision of the Arabian and Eurasian plates.

中文翻译：

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伊朗西北部阿塞拜疆省 Almaludag 地区晚新生代火山活动：碰撞后延伸的证据

摘要 我们讨论了伊朗西北部阿塞拜疆西部省 Almaludag 地区晚新生代火山岩的地质、岩石学以及主要和微量元素地球化学。该地区的地质是通过新特提斯大洋岩石圈向北俯冲以及随后在高山-喜马拉雅造山运动期间阿拉伯和欧亚板块的碰撞而演变的。确认了两个不同的晚新生代火山活动时期：第一集产生了火山碎屑沉积物和粗晶质熔岩（1.47 Ma，U-Pb 测年），第二集产生了镁铁质熔岩和火山渣锥（包括飞溅物/煤渣）。地球化学数据表明，第一集熔岩具有高硅埃达克岩成分，类似于碰撞后和大陆埃达克岩，由增厚的下地壳部分熔化形成。第二集熔岩的成分不同，分为两个不同的地球化学组。与第二组更进化的粗面玄武岩和玄武质粗面岩相比，第一组包括微玄武岩-玄武岩和软玉。这两个基团都显示出碱性对钾离子的亲和力。第二集样本的二元地球化学图显示了表明岩浆过程的成分趋势，例如分馏橄榄石 ± 单斜辉石结晶。这些样品的主要和次要元素变化反映了地幔源的异质性和轻微的地壳污染。REE（稀土元素）图案和蜘蛛图表明大离子亲石元素（LILE）的富集和高场强元素（HFSE）相对于重稀土元素（HREE）的耗尽，并揭示了一个丰富的岩石圈地幔源，该地幔源以前被俯冲成分交代过。第二集熔岩的地幔源富含流体和熔体，这些流体和熔体从伊朗西北部中生代晚期和新生代早期之间的俯冲板片中释放出来。第二集第一组硅不饱和熔岩可能起源于具有碳酸盐残留或脉的岩石圈地幔中的石榴石稳定场，表明地幔源可能经历了碳酸盐交代作用。第二组第二组富含 SiO2 的熔岩的地球化学与从橄榄岩地幔源提取的熔体一致。从第一组岩石到第二组岩石的成分变化表明交代脉-围岩相互作用的程度在减弱。Almaludag 地区的晚新生代基性岩可能是在碰撞后、造山后环境中通过伸展形成的。这种延伸很可能是加厚的次大陆岩石圈地幔 (SCLM) 分层以及随后阿拉伯和欧亚板块碰撞后软流圈上升流的结果。