Fe-Ti Oxide Assemblages from the Contact-Metamorphosed Mafic-Ultramafic Rocks of the Sedova Zaimka Intrusion (Western Siberia, Russia): The Tracking of Metamorphic Transformations

Abstract

Studies that track and compiled transformations of ilmenite and magnetite under conditions of different metamorphic grades are still very limited. The Sedova Zaimka intrusion in Western Siberia (Russia) is a good example to examine the effect of contact metamorphism from greenschist to low-amphibolite facies on magmatic Fe-Ti oxide minerals, as this small mafic-ultramafic body is located within contact metamorphic aureole of a large granite pluton. In the Sedova Zaimka, ilmenite with little to no magnetite is present as an accessory dissemination throughout metamorphosed rocks. Ilmenite is variably enriched in MnO (1 to 13.3 wt%) and depleted in MgO (less than 0.3 wt%), suggesting that its primary magmatic composition has been unevenly modified by diffusion re-equilibrium with coexisting metamorphic silicates. The elevated content of ZnO (up to 0.5 wt%) and NiO (up to 0.4 wt%) in ilmenite suggests that both ZnO and NiO, like MnO, must be strongly partitioned into ilmenite relatively to silicate minerals under the reducing contact metamorphic conditions, if chromite is absent. The textural observations of ilmenite–sulfide and ilmenite–titanite–sulfide relationships indicate that Ti-magnetite, in contrast to ilmenite, is an unstable phase in the presence of sulfur-rich reduced metamorphic fluids and is completely replaced by sulfides, with the development of specific “octahedral meshes” of ilmenite in sulfides.

Origin and evolution of vanadium‐rich oxide and titanite phases in lamprophyre and mafic dykes from the Nuapada diamondiferous Lamproite field, BastarCraton‐EasternGhats Mobile belt contact, India: Metallogenic and geodynamic implications

“…Alternatively, magmatic titanites can also break down to ilmenites in response to late‐stage fluid activity, associated with high fO 2 during the sub‐solidus cooling (Broska et al, 2007). Titanites from low‐grade meta‐igneous rocks are also discussed by many authors and the replacement of titanites by ilmenites and other associated secondary minerals like actinolite and chlorite are common (see Angiboust & Harlov, 2017; Svetlitskaya et al, 2020). Enrichment of V in low‐grade metamorphic rocks has also been noticed (Bernau & Franz, 1987).…”

Multistage Magmatism in Ophiolites and Associated Metavolcanites of the Ulan-Sar’dag Mélange (East Sayan, Russia)

“…Ilmenite in all rocks is replaced by titanite. A high content of MnO and low content of MgO in ilmenite indicate that it formed as a result of diffusion re-equilibrium with coexisting metamorphic silicates [71][72][73][74]. The metamorphosed igneous rocks of epidote-amphibolite facies have an indicative metamorphic mineral assemblage: Amphibole tremolite-actinolite, epidote, biotite, and albite.…”