伊朗沙赫鲁德理工大学Mohsen Mobasheri团队在研究伊朗东北部马什哈德附近上古生代的科马提岩中取得新成果。相关论文发表在2024年7月12日出版的《地质学》杂志上。

据介绍，本研究在伊朗东北部马什哈德附近发现了上古生代的科马提岩。与太古代的科马提岩一样，它们以不同熔岩流的形式喷发，上部为橄榄石多刺结构，下部为橄榄石堆积体。

研究人员解释说，它们与科马提质玄武岩和未分化的超基性单元伴生，并与碎屑岩和碳酸盐沉积岩互层。根据随机定向多刺样品的组成和橄榄石中镁橄榄石的含量，研究人员估计母岩浆中含有＞20wt%的MgO。因此，它们只代表了第二个已知的后太古代后科马提岩。

地球化学组成显示，Al/Ti较低，重稀土元素亏损，属于贫铝型。这是唯一报道过的后太古代这种类型的科马提岩的例子。母岩浆可能是由约180千米深度的含水橄榄岩中度熔融(约20%)形成的，并喷发到古特提斯洋边缘的俯冲带。

附：英文原文

Title: Upper Paleozoic komatiites near Mashhad, NE Iran

Author: Mohsen Mobasheri, Nicholas Arndt, Carole Cordier, Alexander Sobolev, Habibollah Ghasemi, Carlos J. Garrido

Issue&Volume: 2024-07-12

Abstract: We report the discovery of upper Paleozoic komatiites from a location near Mashhad in NE Iran. Like Archean komatiites, they erupted as differentiated lava flows with olivine spinifextextured upper portions and olivine cumulate lower portions. They are associated with komatiitic basalts and undifferentiated ultramafic units and are intercalated with clastic and carbonate sedimentary rocks. Using the compositions of samples with randomly oriented spinifex and the forsterite contents of olivine, we estimate that the parental magmas contained >20 wt% MgO. As such, they represent only the second known occurrence of post-Archean komatiite. Their geochemical compositions show relatively low Al/Ti and depleted heavy rare earth elements, indicating that they belong to the Al-depleted variety. This is the only reported post-Archean example of this type of komatiite. The parental magmas probably formed by moderate degrees of melting (～20%) of a hydrous peridotite source at a depth of ～180 km and erupted into a subduction zone at the margin of the Paleo-Tethys Ocean.

DOI: 10.1130/G52289.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G52289.1/645503/Upper-Paleozoic-komatiites-near-Mashhad-NE-Iran