印度科学与工业研究委员会-国家地球物理研究所 Manikyamba, C.团队，在研究印度达尔瓦克拉通西部Sargur群中铬云母石英岩的地球化学及沉积环境中取得新进展。相关论文发表在2023年12月13日出版的《地球化学学报》杂志上。

研究人员探讨了Ghattihosahalli带中铬云母石英岩的岩相学和地球化学特征，并探讨了其成因、沉积环境和古沉积史之谜。它们的主要矿物组合包括石英、铬云母和长石以及附属的蓝晶石和金红石。与上部大陆地壳(UCC)相比，地球化学成分的特征为高SiO₂、Al₂O₃，低MgO、CaO，高度富集Cr(1326-6899 ppm)、Ba(1165-3653 ppm)、Sr(46-210 ppm)、V(107-868 ppm)和Zn(11-158 ppm)。

上部大陆地壳标准化化稀土元素(REE)模式的特征表现为与相对重稀土元素[(Gd/Yb)_UCC=0.42-1.65)]相比，贫化贫轻稀土元素[(La/Sm)_UCC=0.33-0.95]具有明显的正Eu-异常(Eu/Eu*=1.35-18.27)，通过层间重晶石的证据证明了热液的特征。

总的主微量元素系统反映了镁铁质—长英质复合物源，表明其沉积于被动大陆边缘环境。综合野外、岩相学和地球化学研究表明，这些石英岩被伴生超镁铁质岩高变质过程中释放的富铬流体所渗透。Sargur和随后的达尔瓦尔造山运动融合了来自不同构造背景下的不同岩石单元，可能导致造山运动期间或之后富铬流体的释放和铬云母石英岩的形成。这些发现表明，在Sargur群形成之前就存在稳定的地壳，造山活动与达尔瓦克拉通中各种矿床之间存在联系。

据介绍，中—新太古代铬云母石英岩发育于达尔瓦尔克拉通的不同层位，包括达尔瓦尔克拉通西部最古老(约3.3Ga)的Sargur群。

附：英文原文

Title: Geochemistry and depositional environment of fuchsite quartzites from Sargur Group, western Dharwar Craton, India

Author: Sindhuja, C. S., Harshitha, G., Manikyamba, C., Subramanyam, K. S. V.

Issue&Volume: 2023-12-13

Abstract: Meso-Neoarchean fuchsite quartzites are present in different stratigraphic positions of Dharwar Craton including the oldest (~3.3 Ga) Sargur Group of western Dharwar Craton. The present study deals with the petrographic and geochemical characteristics of the fuchsite quartzites from the Ghattihosahalli belt to evaluate their genesis, depositional setting and the enigma involved in the ancient sedimentation history. Their major mineral assemblages include quartz, fuchsite, and feldspars along with accessory kyanite and rutile. The geochemical compositions are characterized by high SiO₂, Al₂O₃, low MgO, CaO, strongly enriched Cr (1326–6899 ppm), Ba (1165–3653 ppm), Sr (46–210 ppm), V (107–868 ppm) and Zn (11–158 ppm) contents compared to the upper continental crust (UCC). The UCC normalized rare earth element (REE) patterns are characterized by depleted light REE [(La/Sm)_UCC=0.33–0.95] compared to heavy REE [(Gd/Yb)_UCC=0.42– 1.65)] with conspicuous positive Eu-anomalies (Eu/Eu*=1.35–18.27) characteristic of hydrothermal solutions evidenced through the interlayered barites. The overall major and trace element systematics reflect a combined mafic-felsic provenance and suggest their deposition at a passive continental margin environment. The comprehensive field, petrographic, and geochemical studies indicate that these quartzites are infiltrated by Cr-rich fluids released during high-grade metamorphism of associated ultramafic rocks. The Sargur and the subsequent Dharwar orogeny amalgamated diverse lithounits from different tectonic settings, possibly leading to the release of Cr-rich fluids and the formation of fuchsite quartzite during or after the orogeny. These findings suggest a pre-existing stable crust prior to the Sargur Group and the link between orogenic events and various mineral deposits in the Dharwar Craton.

DOI: 10.1007/s11631-023-00661-3

Source: https://link.springer.com/article/10.1007/s11631-023-00661-3