Mid-Cretaceous extensional magmatism in the Alborz Mountains, north Iran; geochemistry and geochronology of Gasht-Masuleh gabbros

IF 1.8 2区地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY

Swiss Journal of Geosciences Pub Date : 2023-09-22 DOI:10.1186/s00015-023-00443-2

Leila Rezaei, Martin J. Timmerman, Mohssen Moazzen, Uwe Altenberger, Jiří Sláma, Masafumi Sudo, Christina Günter, Franziska D. H. Wilke, Anja M. Schleicher

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Abstract

Abstract In the Gasht-Masuleh area in the Alborz Mountains, gabbroic magma intruded Palaeozoic metasediments and Mesozoic sediments and crystallised as isotropic and cumulate gabbros. LREE enrichment points to relatively low degrees of mantle melting and depletion of Ti, Nb and Ta relative to primitive mantle points to an arc related component in the magma. Clinopyroxene compositions indicate MORB to arc signatures. U–Pb zircon crystallisation ages of 99.5 ± 0.6 Ma and 99.4 ± 0.6 Ma and phlogopite 40 Ar/ 39 Ar ages of 97.1 ± 0.4 Ma, 97.5 ± 0.4 Ma, 97.1 ± 0.1 Ma, within 2σ error, indicate that gabbro intrusion occurred in the (Albian-)Cenomanian (mid-Cretaceous). As active subduction did not take place in the Cretaceous in North Iran, the small volume mafic magmatism in the Gasht-Masuleh area must be due to local, extension-related mantle melting. Melting was most likely caused by far field effects triggered by roll-back of the Neo-Tethys subducting slab. As subduction took place at a distance of ~ 400 km (present distance) from the Alborz Mountains, the observed arc geochemical signatures must be inherited from a previous subduction event and concomitant mantle metasomatism, possibly in combination with contamination of the magma by crustal material.

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伊朗北部Alborz山脉中白垩世伸展岩浆活动Gasht-Masuleh辉长岩的地球化学和年代学

在阿尔布尔士山脉Gasht-Masuleh地区，辉长岩岩浆侵入古生代变质沉积层和中生代沉积层，结晶为各向同性的堆积辉长岩。LREE富集表明地幔熔融程度相对较低，Ti、Nb和Ta相对原始地幔的亏缺表明岩浆中存在与弧相关的成分。斜辉石组成表明MORB弧特征。U-Pb锆石结晶年龄分别为99.5±0.6 Ma和99.4±0.6 Ma，辉云母40 Ar/ 39 Ar年龄分别为97.1±0.4 Ma、97.5±0.4 Ma和97.1±0.1 Ma，误差在2σ范围内，表明辉长岩侵入发生于中白垩世(阿尔比—)塞诺曼期。由于伊朗北部白垩纪没有发生活动俯冲，因此Gasht-Masuleh地区的小体积基性岩浆活动一定是由局部伸展相关的地幔熔融引起的。融化很可能是由新特提斯俯冲板块的回滚引发的远场效应引起的。由于俯冲发生在距Alborz山脉约400公里(目前距离)的地方，因此观测到的弧地球化学特征必须继承于先前的俯冲事件和伴随的地幔交代作用，可能与地壳物质对岩浆的污染有关。

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来源期刊

Swiss Journal of Geosciences 地学-地质学

CiteScore

4.50

自引率

12.90%

发文量

审稿时长

>12 weeks

期刊介绍： The Swiss Journal of Geosciences publishes original research and review articles, with a particular focus on the evolution of the Tethys realm and the Alpine/Himalayan orogen. By consolidating the former Eclogae Geologicae Helvetiae and Swiss Bulletin of Mineralogy and Petrology, this international journal covers all disciplines of the solid Earth Sciences, including their practical applications. The journal gives preference to articles that are of wide interest to the international research community, while at the same time recognising the importance of documenting high-quality geoscientific data in a regional context, including the occasional publication of maps.