Geothermometry of garnet-cordierite rocks in Kilsbergen and northern Tiveden, southern Sweden

Samples of garnet-cordierite rocks have been investigated in order to check if the estimated high-amphibolite facies conditions of the sampling areas (absence of orthopyroxene), also are reflected in different geothermometers (garnet-cordierite and garnet-biotite) when compared with a similar investigation of similar rocks in a nearby granulite facies area. The sampled garnet-cordierite rocks differ somewhat in geological character. At Svenshyttan they are similar to other high-grade Svecofennian veined gneisses in the region, at Kinkhyttan they have a characteristic, massive appearance, while the rocks at Nygården are mobilized and back-vein a norite. A thermal metamorphic peak is present in the area, displayed by the Kinkhyttan samples which, according to the garnet-cordierite thermometers, have reached temperatures of at least 650–700°C. This metamorphism is most likely associated with a near lobe of Småland-Värmland granitoids. Along the western contact of this lobe, the granulite facies conditions prevail. A comparison between the results of the present investigation and those from the granulite facies area demonstrates that the garnet-cordierite thermometers show only minor differences for the peak metamorphism while the garnet-biotite thermometers indicate more pronounced retrograde metamorphism in the studied area.