ABSTRACT

Late Eocene – Oligocene volcanic rocks in the eastern Saveh region of the Urumieh-Dokhtar magmatic arc (UDMA) are representative of Paleogene magmatic activity in Iran. They show a wide range of silica-undersaturated to silica-oversaturated compositions, from basalt-trachy basalt and tephri-phonolite to trachyte-latite. Whole rock chemical compositions define a continuous assemblage of mafic and felsic rocks in terms of SiO₂ (46.3 to 71.1 wt.%), Al₂O₃ (12.5–19.2 wt.%), K₂O (2.06–12.23 wt.%) and TiO₂ (0.41–1.75 wt.%) contents, Mg number (6.8–51) and K₂O/Na₂O ratios (0.53–30.2). Abundances of rare earth elements in the tephri-phonolite group are much higher than in the trachyte-latite and basalt-trachy basalt groups. Elevated contents of large ion lithophile elements such as Ba (191–7311 ppm) and Pb (6.49–118 ppm) as well as depletions in high field strength elements such as Nb (2.43–40.6 ppm), Ta (0.15–2.24 ppm), Zr (40.8–258 ppm) and TiO₂ (0.40–1.77 wt.%) characterize these rocks. Initial ratios of ⁸⁷Sr/⁸⁶Sr from 0.7046 to 0.7074 and ɛ_Nd(t) from +0.9 to +3.3 show that these were derived from parental magma extracted from partial melting of metasomatized mantle, namely amphibole- and/or phlogopite-bearing peridotite. Fractionation of feldspar, clinopyroxene, amphibole and phlogopite, and minor contamination with upper crust was responsible for the large variation of the rock types observed. We explain contemporaneous late Eocene – Oligocene calc-alkaline and high-K magmatic activity in the UDMA as due to the partial melting of both hot metasomatized asthenospheric and subcontinental lithospheric mantle in an extensional tectonic regime. This extensional regime probably developed due to the rollback of the subducted Neo-Tethys oceanic plate.

抽象的

晚始新世– Urumieh-Dokhtar岩浆弧（UDMA）东部Saveh地区的渐新世火山岩是伊朗古近纪岩浆活动的代表。它们显示了从饱和玄武岩玄武岩玄武岩和三方辉石-方沸石到纤长晶岩的各种不饱和二氧化硅到过饱和二氧化硅的组合物。整个岩石化学成分以SiO ₂（46.3至71.1 wt。％），Al ₂ O ₃（12.5-19.2 wt。％），K ₂ O（2.06-12.23 wt。％）的形式定义了镁铁质和长英质岩石的连续组合。 ）和TiO ₂（0.41-1.75 wt。％）含量，Mg数（6.8-51）和K ₂ O / Na ₂O比率（0.53–30.2）。球铁-方铅矿组中的稀土元素含量远高于曲奇-latite组和玄武岩-曲奇玄武岩组中的稀土元素含量。诸如Ba（191–7311 ppm）和Pb（6.49–118 ppm）之类的大型离子亲石元素的含量升高，以及诸如Nb（2.43–40.6 ppm），Ta（0.15–2.24 ppm）之类的高场强元素的耗竭Zr（40.8–258 ppm）和TiO ₂（0.40–1.77 wt。％）表征了这些岩石。的初始比率⁸⁷ SR / ⁸⁶的Sr从0.7046到0.7074和ɛ_钕（t）从+0.9到+3.3，表明这些岩浆来自母岩浆，该母岩浆是从交代地幔的部分融化中提取的，这些地幔即闪石和/或金云母的橄榄岩。长石，斜辉石，角闪石和金云母的分级分离以及上地壳的少量污染是导致观察到的岩石类型差异很大的原因。我们解释了由于在扩展的构造体制中热交代的软流变软流圈和次大陆岩石圈地幔的部分融化，UDMA中同时出现了晚始新世–渐新世的钙碱性和高K岩浆活动。这种扩展机制可能是由于俯冲的新特提斯洋板块的回滚所致。