A new perspective on Cenozoic calc-alkaline and shoshonitic volcanic rocks, eastern Saveh (central Iran)
A new perspective on Cenozoic calc-alkaline and shoshonitic volcanic rocks, eastern Saveh (central Iran)
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DOI：
10.1080/00206814.2020.1718005
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发表时间：
2020-01
影响因子：
2.6
通讯作者：
F. Nouri;H. Azizi;Y. Asahara;R. Stern
中科院分区：
文献类型：
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作者：
F. Nouri;H. Azizi;Y. Asahara;R. Stern
乌鲁木齐-多赫塔尔岩浆弧（UDMA）东部Saveh地区晚始新世-渐新世火山岩是伊朗古近纪岩浆活动的代表。从玄武岩-粗质玄武岩、绢云母-phonolite到粗云母-latite，硅质不饱和到硅质过饱和的成分范围很广。整个岩石的化学成分根据SiO2 （46.3 ~ 71.1 wt.%）、Al2O3 （12.5 ~ 19.2 wt.%）、K2O （2.06 ~ 12.23 wt.%）和TiO2 （0.41 ~ 1.75 wt.%）含量、Mg数（6.8 ~ 51）和K2O/Na2O比值（0.53 ~ 30.2）定义了基性和长英质岩石的连续组合。绢云母岩组稀土元素的丰度远高于粗面-黑土岩组和玄武岩-粗面玄武岩组。大离子亲石元素如Ba （191-7311 ppm）和Pb （6.49-118 ppm）的含量升高以及高场强元素如Nb （2.43-40.6 ppm）、Ta （0.15-2.24 ppm）、Zr （40.8-258 ppm）和TiO2 （0.40-1.77 wt.%）的消耗是这些岩石的特征。87Sr/86Sr初始比值在0.7046 ~ 0.7074之间，Nd(t)比值在+0.9 ~ +3.3之间，表明这些岩浆来源于交代地幔部分熔融提取的母岩浆，即含角闪孔和/或含辉云母的橄榄岩。长石、斜辉石、角闪石和云母的分选作用以及与上地壳的轻微污染是导致岩石类型变化较大的原因。我们解释了UDMA同时期晚始新世-渐新世钙碱性和高钾岩浆活动是由于热交代软流圈和次大陆岩石圈地幔在伸展构造制度下的部分熔融。这种伸展状态可能是由于俯冲的新特提斯洋板块的回滚而形成的。
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 ɛNd(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.