中国地质大学（北京）王瑞课题组探究了阿尔泰稀有元素伟晶岩的形成过程。2024年12月3日出版的《地质学》发表了这项成果。

据介绍，随着变质-混染带中稀有元素伟晶岩的发现，变质原岩的部分熔融作用在伟晶岩形成中的作用引起了人们的广泛关注。尽管缺少系统的地质实例，但先前提出的变质沉积岩和随后的花岗质岩石的两阶段熔融模型，仍可以解释锂矿化伟晶岩岩浆的形成。

研究团队提供了中国阿尔泰造山带锂-铯-钽（LCT）伟晶岩的系统地球化学(年龄为400-150Ma)，S型花岗岩(年龄为500-350Ma)和哈巴河群变质沉积岩(HGMRs, 年龄为600-450Ma)数据，为自然界中发生的两阶段熔融过程提供了证据。锆石Hf-O同位素分析和全岩地球化学表明，伟晶岩形成于二叠纪-侏罗纪(280-150Ma)，是S型花岗岩体的深熔作用的结果，该花岗岩类最初由HGMRs的部分熔体结晶而成。

研究结果显示，从HGMRs到S型花岗岩再到LCT伟晶岩，稀有元素含量逐渐增加，与模拟的熔融过程一致。HGMR原岩的两阶段熔融引起稀有元素的富集显著，Li、Be、Rb、Cs、Nb和Ta的最大富集因子分别达到20、31、31、120、45和44。这种明显的金属富集引发了锂辉石、铯榴石和铌铁矿族矿物的稀有元素矿物组合的形成。本研究证实了多阶段地壳熔融在稀有元素的富集和矿化中是有效的。

附：英文原文

Title: Formation of rare-element pegmatites in the Chinese Altai: Contribution of two-stage melting

Author: Siyu Liu, Rui Wang, Roman E. Botcharnikov, Hao Sha

Issue&Volume: 2024-12-03

Abstract: With increasing discoveries of rare-element pegmatites in metamorphic-migmatitic belts, the role of partial melting of metamorphic protoliths in the formation of pegmatites has attracted significant attention. A previously proposed two-stage melting model for metamorphic sedimentary rocks and subsequent granitic rocks can explain the formation of Li-mineralized pegmatitic magmas, although systematic geologic examples are still missing. Here, we present systematic geochemical data from lithium-cesium-tantalum (LCT) pegmatites (with ages of 400-150 Ma), S-type granitoids (500-350 Ma), and metasedimentary rocks of the Habahe group (HGMRs, 600-450 Ma) in the Chinese Altai orogenic belt, providing evidence of a two-stage melting process occurring in nature. Zircon Hf-O isotope analyses and whole-rock geochemistry suggest pegmatite formation in the PermianJurassic (280-150 Ma) as a result of the anatexis of S-type granitoids, which originally crystallized from partial melts of HGMRs. The content of rare elements increases progressively from HGMRs to S-type granitoids to LCT pegmatites, aligning with the modeled melting process. The two-stage melting of the source HGMR protolith resulted in significant extraction of rare elements, with the maximum enrichment factors for Li, Be, Rb, Cs, Nb, and Ta reaching 20, 31, 31, 120, 45, and 44, respectively. This pronounced metal enrichment led to the formation of rare-element mineral assemblages of spodumene, pollucite, and columbite group minerals. This study confirms that multistage crustal melting can be efficient in the enrichment and mineralization of rare elements.

DOI: 10.1130/G52880.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G52880.1/650446/Formation-of-rare-element-pegmatites-in-theredirectedFrom=fulltext