Combined phase diagram modelling and quartz-in-garnet barometry of HP metapelites from the Kamieniec Metamorphic Belt (NE Bohemian Massif)

The Kamieniec Metamorphic Belt belongs to the Variscan Belt of Europe as the NE part of the Bohemian Massif. It comprises a supracrustal succession dominated by micaschists that has not been yet recognized as a high-P, low-T (HP-LT) metamorphic unit. Our work demonstrates the significance of metapelites in the study of HP metamorphism of the NE part of the Bohemian Massif. To reconstruct the P-T history of the Kamieniec Metamorphic Belt, we have investigated three samples using independent geothermobarometric techniques including phase diagram modelling, Si4+ content in white mica and quartz-in-garnet elastic barometry. Two samples con tain mineral assemblages bearing a record of HP metamorphism followed by an LP event. The oldest assemblage is mostly preserved in the first generation of garnet and it, comprises phengitic white mica and rutile. In one of the investigated samples, we also recognized chloritoid and inferred pseudomorphs after lawsonite composed of quartz, clinozoisite associated with margarite. The third of the investigated samples is strongly retrogressed and only contains the relics of phengitic white mica. All three samples contain a younger mineral assemblage comprising white mica with low Si4+ content and ilmenite. Mineral equilibria modelling indicates the P T conditions of the HP event culminated at similar to 15.5-18 kbar and similar to 470-570 degrees C, while the LP episode occurred at similar to 5-7 kbar and similar to 530-570 degrees C. The Raman shift measured in quartz inclusions in garnet in samples with a well-preserved record of the HP stage points to their entrapment at pressures between 11 and 16 kbar. The quartz inclusions within the strongly retrogressed micaschist sample exhibit Raman shifts corresponding to the LP episode at similar to 5-8 kbar. Discrepant results obtained for one of the samples are discussed in detail. Our investigations show that the supracrustal succession of the Kamieniec Metamorphic Belt contains a record of HP-LT metamorphism typical for subduction systems. A recently established tectonic model for the crystalline complexes exposed in the Bohemian Massif suggests that they were formed via the collision of the Saxothuringian, Tepla-Barrandian, and Brunovistulian domains. Therefore, we interpret the Kamieniec Metamorphic Belt as representing fragments of the Saxothuringian crust that experienced cold extrusion from below the Tepid- Barrandian domain in front of the rigid Brunovistulian indenter.

Automated summary

The Kamieniec Metamorphic Belt in the NE part of the Bohemian Massif is a supracrustal succession dominated by micaschists that has not been recognized as a high-P, low-T metamorphic unit. Investigation of samples from the belt reveals high-pressure metamorphism followed by a low-pressure event, typical for subduction systems. This suggests that the belt likely represents fragments of the Saxothuringian crust affected by cold extrusion within a tectonic model involving multiple domains in the Bohemian Massif.