近日，印度棉花大学Bibhuti Gogoi团队研究了印度东北部阿萨姆邦-梅加拉亚邦片麻岩杂岩混合岩成因模型。该项研究成果发表在2025年9月9日出版的《地球化学学报》杂志上。

人们当前致力于研究位于印度东北部阿萨姆-梅加拉亚片麻岩杂岩北部边缘古瓦哈蒂的Chandrapur地区的杂岩中细粒至粗粒磁铁矿晶体的赋存情况。这一贡献的目的是提出一种新的方法来证明他们研究地区混杂岩中磁铁矿的起源。野外调查表明，研究区内的片麻岩中渗透着许多大小不等的伟晶岩脉。晚期泛非构造热事件被认为是研究区伟晶岩侵入的主要原因。混合岩的压力-温度（P-T）条件表明，在构造热事件期间，热升高的片麻岩的部分熔融是由富含挥发物的伟晶岩熔体的侵入所驱动的。

随后，部分熔融的岩石与富含钾的伟晶岩岩浆混合，形成了一种混合岩石，现在被保存为新岩。岩石学检查表明，新体显示出不同程度的杂化，从角闪石-黑云母转化的程度可以看出。较高的杂交程度导致角闪洞更广泛地被黑云母取代。新岩还具有细粒至粗粒的磁铁矿晶体。根据研究结果，研究组推测K₂O从伟晶岩岩浆转移到部分熔融的岩石或新近岩中，有助于角闪孔向黑云母的分解。角闪孔与黑云母的置换反应导致FeO析出，并在主要氧化条件下转化为磁铁矿（Fe₃O₄）。新体中磁铁矿的存在反映了岩浆相互作用和演化过程中以氧化环境为主。

附：英文原文

Title: A petrogenetic model for the origin of migmatites in the Assam-Meghalaya Gneissic Complex, Northeast India: Constraints from mineralogy with special reference to magnetite

Author: Gogoi, Bibhuti, Basumatary, Pallabi

Issue&Volume: 2025-09-09

Abstract: The current work is dedicated to studying the occurrence of fine- to coarse-grained magnetite crystals in migmatites of Chandrapur area located in Guwahati, along the northern fringe of the Assam-Meghalaya Gneissic Complex, Northeast India. The objective of this contribution is to present a novel approach demonstrating the origin of magnetite in the migmatites of our study area. Field investigations reveal that the gneissic rocks within the study area are penetrated by numerous pegmatitic veins of varying sizes. The late Pan-African tectonothermal event is deemed responsible for the pegmatitic intrusions in the study area. The pressure-temperature (P-T) conditions estimated from the migmatites revealed that fluid-present partial melting of the thermally elevated gneissic rocks during the tectonothermal episode was driven by the intrusion of volatile-laden pegmatitic melts. Subsequently, the partially molten rocks mingled with the K-rich pegmatitic magma, resulting in a mixed rock now preserved as neosome. Petrographic examinations reveal that the neosome displayed different degrees of hybridization, as indicated by the extent of amphibole-biotite transformation. Higher degrees of hybridization led to more extensive replacement of amphibole by biotite. The neosomes are also characterized by fine- to coarse-grained magnetite crystals. Based on the findings of this work, we infer that the transfer of K2O from the pegmatite magma to the partially molten rocks or neosome assisted in the breakdown of amphibole to biotite. The replacement reaction of amphibole to biotite led to the liberation of FeO, which was subsequently converted into magnetite (Fe3O4) in the prevailing oxidizing conditions. The presence of magnetite in the neosome reflects the dominance of an oxidizing environment during magma interaction and evolution.

DOI: 10.1007/s11631-025-00820-8

Source: https://link.springer.com/article/10.1007/s11631-025-00820-8