Formation of clinohumite ± spinel in dolomitic marbles from the Makrohar Granulite Belt, Central India: Evidence for Ti mobility during regional metamorphism

Abstract

The mobility of Ti, a member of high field strength elements, in metamorphic fluids is crucial to understand the recycling of commonly perceived nominally soluble elements and for mass-flux calculations during crustal processes. In this study, we present evidence for large-scale Ti mobility from a suite of clinohumite±spinel-bearing dolomitic marbles from the Makrohar area in central India. The studied rocks mostly contain dolomite and calcite (in subequal proportions) and a subordinate amount of forsterite. It commonly develops 1–5 cm thick, laterally continuous, mostly parallel, sometimes anastomosing, brown-colored clinohumite rich bands with variable spinel. Clinohumite has moderate Ti and F (TiO2 = 0.55–2.88 wt%; F = 0.94–1.88 wt%; n = 32). Textural and phase equilibria modeling indicate that clinohumite grew at the expense of forsterite + dolomite under static conditions due to infiltration of F- and Ti-bearing extremely H2O-rich fluids (XCO2 < 0.03), at ~5–6 kbar pressure and ~650–700 °C temperature. The Ti and F were most likely supplied by highly channelized aqueous fluids restricted within the centimeter-thick bands. The negative volume change of the reactions further facilitated fluid ingress. The lateral continuity of the bands over several meters across multiple out-crops indicates that Ti was mobile at the meter to kilometer scale. The results are in accordance with experimental studies that solubility of Ti increases in the presence of halides and imply that Ti may be much more mobile in metamorphic fluids during regional metamorphism than previously anticipated.

Multiple growth of zirconolite in marble (Mogok metamorphic belt, Myanmar): evidence for episodes of fluid metasomatism and Zr–Ti–U mineralization in metacarbonate systems

“…Our results indicate an efficient mobilization and transfer of Zr (Hf), Ti (Nb and Ta), and U (Th) during the fluid-rock interactions, although high-field-strength elements (HFSEs) were typically regarded as sparingly soluble components in aqueous fluids (e.g., Wyllie, 1990, 1991;Audétat and Keppler, 2005;Tropper and Manning, 2005). Experimental and geological studies indicate that the enrichment of F and other halogens can significantly elevate the solubility of HFSEs by complexing with HFSEs in aqueous fluid Wyllie, 1990, 1991;Peiffer et al, 1996;Antignano and Manning, 2008;Cuney, 2009;Rapp et al, 2010;Bali et al, 2011;Migdisov et al, 2011;Tanis et al, 2016;Karmakar, 2021). The high F contents in phlogopite (1.6 wt %-1.9 wt %) from the reaction zones indicate that the reactive HFSE-bearing fluids also contain F. We thus suggest that F played an important role in transporting HFSEs in the fluids (Gieré, 1986;Salvi and WilliamsJones, 1996;Zhao et al, 2016;Guo et al, 2016;Duan and Li, 2017;Zeng and Liu, 2022), and the growth of phlogopite during the fluid-marble interaction decomposed F-HFSE complexes to deposit Zrl and other HFSE-rich minerals.…”