Heterogeneous Metamorphism in Metabasites of the Kem-Ludy Islands, Belomorian Mobile Belt

The Kem-Ludy Islands represent a poorly studied locality of the Early Precambrian Belomorian Eclogite Province. This study presents a detailed petrological investigation of four mafic rock types: eclogite, quartz-clinopyroxene-plagioclase-amphibole-garnet granofels, garnet amphibolite, and quartz-bearing gabbronorite. These rocks, hosted in a common gneissic substrate, exhibit varying degrees of metamorphic transformation, distinct mineral assemblages, and differences in mineral chemistry. The cores of garnets in the eclogite, granofels, and garnet amphibolite contain epidote inclusions, indicating an early metamorphic stage. Peak metamorphic conditions for the eclogite facies, reconstructed using mineral geothermobarometry, are estimated at T ~ 670°C and P_min ~ 1.3 GPa. While the granofels retains indirect evidence of the eclogite-facies stage, the garnet amphibolite and quartz-bearing gabbronorite are completely devoid of such features. Amphibolite-facies metamorphism is recorded in all rock types but varies due to differences in fluid activity. The P–T conditions of the amphibolite stage have been reconstructed for each metamorphic rock using mineral geothermobarometry, phase equilibrium modeling (PerpleX), and multi-equilibrium thermobarometry (TWQ), yielding estimates of T = 610–730°C and P = 0.4–0.8 GPa. The P–T evolution of the eclogite suggests a near-isothermal decompression path from ~1.3 to 0.6 GPa, similar to trends observed in some eclogites and meta-ultramafic rocks from the Gridino tectonic mélange. However, this trend is different from those proposed for eclogites from the Salma and Kuru-Vaara localities.