Early Jurassic and Late Cretaceous plagiogranites in Nain-Baft ophiolitic mélange zone in Iran: remnants of rift–drift and SSZ evolution of a Neotethyan seaway

IF 2.6 3区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY Journal of the Geological Society Pub Date : 2024-01-05 DOI:10.1144/jgs2023-181
N. Shirdashtzadeh, Y. Dilek, H. Furnes, E. Dantas
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Abstract

We have investigated the geology, geochemistry, and geochronology of various plagiogranite intrusions that are spatially associated with ophiolitic subunits in a mélange terrain exposed within the Nain–Baft fault zone along the western boundary of the Central–East Iranian Microcontinent (CEIM). One group of plagiogranites is intrusive into foliated amphibolites, whereas the plagiogranites of the other group are intrusive into gabbros, dike swarms, and pillow lavas that are tectonically juxtaposed. U–Pb zircon dating of the first group of plagiogranites has revealed near concordant crystallization ages of 176.94±0.71, 179.84±0.92, and 190.40±2.1 Ma, indicating the early Jurassic timing of their emplacement. U–Pb zircon dating of the second group of plagiogranites has revealed a weighted average age of 92.34±0.38 Ma, indicating that they were emplaced in the early Late Cretaceous. The Early Jurassic plagiogranites are low–K, sub–alkaline rocks with negative Eu anomalies, low Ti and high La and Ce contents. They display elevated LILE/HFSE ratios. They were part of a magmatic system which facilitated the earliest rift–drift stages of a Neotethyan seaway development, and their magmas were produced by fractional crystallization of a mafic melt associated with asthenospheric upwelling beneath a rift system. The Late Cretaceous plagiogranites are low–K, sub–alkaline rocks with negative Eu anomalies, high Y and low Ta contents. They show LREE depletion relative to flat HREE patterns, and high Ba/Th ratios. Magmas of these plagiogranites were the products of partial melting of amphibolites in the subducting oceanic lithosphere in the same Neotethyan seaway. Thus, we posit that plagiogranite rocks in suture zones can be excellent trackers of geochemical, geochronological, and magmatic evolution of various types of oceanic crust through rift–drift, seafloor spreading, and subduction initiation stages within the same ocean basins in the past. Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists
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伊朗纳因-巴夫特蛇绿岩混杂带的早侏罗世和晚白垩世长花岗岩:新特提安海道的裂谷-漂移和SSZ演化遗迹
我们对伊朗中部-东部微大陆(CEIM)西部边界纳因-巴夫特断裂带内出露的在空间上与蛇绿岩亚单位相关的各种长花岗岩侵入体的地质、地球化学和地质年代进行了研究。其中一组斜长花岗岩侵入到叶状闪长岩中,而另一组斜长花岗岩则侵入到构造并列的辉长岩、梭状岩群和枕状熔岩中。第一组斜长花岗岩的铀-铅锆石年代测定显示了近乎一致的结晶年龄,分别为 176.94±0.71、179.84±0.92 和 190.40±2.1Ma,表明它们的成岩时间为侏罗纪早期。第二组长花岗岩的U-Pb锆石年代测定显示其加权平均年龄为(92.34±0.38)Ma,表明其成岩时间为晚白垩世早期。早侏罗世长花岗岩是低 K、亚碱性岩石,具有负 Eu 异常、低 Ti 以及高 La 和 Ce 含量。它们显示出较高的 LILE/HFSE 比率。它们是岩浆系统的一部分,该岩浆系统促进了新近纪海道发展的最早裂谷-漂移阶段,其岩浆是由裂谷系统下与星体层上升流有关的黑云母熔体分块结晶产生的。晚白垩世长花岗岩是低K、亚碱性岩石,具有负Eu异常、高Y和低Ta含量。相对于平坦的 HREE 模式,它们显示出 LREE 贫化以及高 Ba/Th 比率。这些斜长花岗岩的岩浆是同一新特提安海道中俯冲洋岩石圈中的闪长岩部分熔融的产物。因此,我们认为缝合带中的长花岗岩可以很好地追踪过去同一大洋盆地内各类大洋地壳在经历裂谷-漂移、海底扩张和俯冲起始阶段的地球化学、地质年代和岩浆演化过程。 专题集:本文是蛇绿岩、熔岩和蓝晶岩文集的一部分,可在以下网址查阅:https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists。
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来源期刊
Journal of the Geological Society
Journal of the Geological Society 地学-地球科学综合
CiteScore
6.00
自引率
3.70%
发文量
68
审稿时长
6-12 weeks
期刊介绍: Journal of the Geological Society (JGS) is owned and published by the Geological Society of London. JGS publishes topical, high-quality recent research across the full range of Earth Sciences. Papers are interdisciplinary in nature and emphasize the development of an understanding of fundamental geological processes. Broad interest articles that refer to regional studies, but which extend beyond their geographical context are also welcomed. Each year JGS presents the ‘JGS Early Career Award'' for papers published in the journal, which rewards the writing of well-written, exciting papers from early career geologists. The journal publishes research and invited review articles, discussion papers and thematic sets.
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