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Petrography, mineralogy, and geochemistry of the Hemrin Basalt, Northern Iraq: Implications for petrogenesis and geotectonics
Lithos ( IF 2.9 ) Pub Date : 2021-03-15 , DOI: 10.1016/j.lithos.2021.106109
Yawooz A. Kettanah , Alan S. Abdulrahman , Sabah A. Ismail , Daniel J. MacDonald , Heider Al Humadi

The studied Hemrin Basalt (HB) was previously mis-identified and called burnt hills. The HB is studied petrographically and geochemically as constraints for its provenance and geotectonics. The immobile trace element plot of Zr/TiO2–Nb/Y as well as mineralogy, textures and hand specimen appearance indicate that the studied rocks are basalts. This basalt occurs as surficial thin layer capping few hills along a NW/SE oriented direction within the Injana Formation in the Low-Folded Tectonic Zone, which is not related and far from the ophiolites of northeastern Iraq. It consists dominantly of diopside, labradorite and volcanic glass, and many accessory and secondary vesicle-filling minerals (amygdules). The basalt is very fine-grained with a massive and vesicular/amygdaloidal structures, and sub-ophitic as well as very rare and unusual textures, called firework and feathery in this study which are very similar to those of lunar basalts. The large ion lithophile elements (LILE) are enriched 4.8 times relative to the high field strength elements (HFSE), indicated from the MORB-normalized diagram for major and trace elements. The average content of rare earth elements (REE) in HB is 140 ppm with 10.6 times enrichment of LREE relative to HREE which is reflected in their chondrite-normalized diagram having a negative slope of 7.6 and a small Eu-anomaly of 0.7. The (La/Yb)n–La plot showed that the source magma was fractionally crystallized; whereas, the immobile trace element ratios and elemental values such as Nb/U, Ce/Pb, Nb/La, LREE/HREE, LILE/HFSE, Zr, Hf, Nb, and Ta indicated that source magma for HB was contaminated while rising through the Arabian continental crust. Many major, immobile trace and REE element discriminating diagrams showed that the studied rocks are high-K calc-alkaline basalts formed as a continental volcanic arc under orogenic convergent tectonic conditions because of the continent-continent collision between the Arabian and Turkish/Iranian plates. The surficial HB and the surrounding calc-alkaline tuffs are probably related and formed by the same volcanic eruption during Quaternary period, <0.5 Ma ago. The source of HB is most probably a hot spot volcano erupted in the area close to the studied hills, ejecting large amounts of volcanic ash which deposited the tuff beds and the associated bentonites in the surroundings, and culminated by a basaltic flow which formed the HB.



中文翻译:

伊拉克北部Hemrin玄武岩的岩石学,矿物学和地球化学:对岩石成因和大地构造的意义

被研究的Hemrin玄武岩(HB)先前被错误地识别为烧山。对其进行了岩石学和地球化学研究,以此作为其起源和大地构造的限制条件。Zr / TiO 2的固定态痕量元素图–Nb / Y以及矿物学,质地和手标本外观表明所研究的岩石是玄武岩。该玄武岩发生在表层薄层上,在低折叠构造带的伊贾纳组内沿西北/东南向的几座山覆盖着,这些山与伊拉克东北的蛇绿岩没有关系,而且远非蛇绿岩。它主要由透辉石,拉长石和火山玻璃组成,并包含许多辅助和次级囊泡填充矿物质(杏仁)。玄武岩的颗粒非常细,具有块状和囊状/杏仁状的结构,并具有亚表观的,非常稀有和不寻常的质地,在本研究中被称为烟火和羽毛状,与月球玄武岩非常相似。相对于高场强元素(HFSE),大离子亲石元素(LILE)富集4.8倍,从MORB归一化图中指出的主要和痕量元素。HB中稀土元素(REE)的平均含量为140 ppm,相对于HREE,其LREE的富集度为10.6倍,这反映在它们的球粒陨石归一化图中,负斜率为7.6,Eu异常小,为0.7。(La / Yb)ñ-La图表明源岩浆已部分结晶;而痕量元素的固定比率和元素值(例如Nb / U,Ce / Pb,Nb / La,LREE / HREE,LILE / HFSE,Zr,Hf,Nb和Ta等元素)表明HB的源岩浆在上升时被污染穿越阿拉伯大陆壳。许多主要的,静止的痕迹和REE元素判别图表明,由于阿拉伯板块与土耳其/伊朗板块之间的大陆-大陆碰撞,在造山带汇聚的构造条件下,这些岩石是在大陆火山弧下形成的高K钙碱性玄武岩。地表HB与周围的钙碱性凝灰岩可能是相关的,并且是由第四纪<0.5 Ma年前的同一次火山喷发形成的。

更新日期:2021-03-19
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