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

Abstract

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 contain 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 ~15.5–18 kbar and ~470–570℃, while the LP episode occurred at ~5–7 kbar and ~530–570℃. 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 ~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, Teplá–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 Teplá–Barrandian domain in front of the rigid Brunovistulian indenter.

Large-strain Elastic and Elasto-Plastic Formulations for Host-Inclusion Systems and Their Applications in Thermobarometry and Geodynamics

“…Mineral inclusions can provide both mineralogical and compositional data that can be of value for the petrogenetic interpretation of metamorphic rocks (e.g., Chopin & Sobolev, 1995;Spear & Selverstone, 1983). Due to the increasingly developed spectroscopic and diffraction techniques, the mechanical effects of mineral host-inclusion systems have been commonly used as independent means for the determination of pressure (sometimes also temperature) in metamorphic phase equilibria interpretations (Alvaro et al, 2020;Castro & Spear, 2017;Moulas et al, 2020;Szczepański et al, 2022;, 2019). So far, most of the solutions employed in the calculation of residual inclusion pressure assume spherically symmetric systems and materials which are elastically isotropic (Guiraud & Powell, 2006;Van der Molen & Van Roermund, 1986;Y.…”

Provenance of the early Palaeozoic volcano-sedimentary successions from eastern part of the Central Sudetes: implications for the tectonic evolution of the NE Bohemian Massif

“…4, Tables 2–6). Petrography, mineral assemblages and the P-T history of mica schists from the KMB were described in detail by Szczepański et al (2022) and Szczepański and Goleń (2022). In this study, we used the same set of samples, and therefore here only a brief description of the mica schist from the KMB used for the geochronological study is given.…”

“…Schulmann et al . 2009; Chopin et al 2012; Jastrzębski et al 2020; Szczepański et al 2022; Szczepański & Goleń, 2022). However, the metamorphic records preserved in the KMB and DMC are strikingly different.…”

“…However, the metamorphic records preserved in the KMB and DMC are strikingly different. The mica schists of the KMB underwent HP-LT metamorphism at c. 490 o C and 18 kbar which was overprinted by LP-HT episode at c. 530–580 o C and 3–7 kbar (Szczepański et al 2022; Szczepański & Goleń, 2022). On the other hand, the migmatized Chałupki paragneiss bears record of HT metamorphism at max.…”

Measurement of crystallographic orientation of quartz crystal using Raman spectroscopy: application to entrapped inclusions

“…The quartz-in-garnet elastic barometry technique is a good example of this. Recently this technique has become more and more popular and has been widely applied in many petrological studies on metamorphic rocks (e.g., Korsakov et al 2009;Ashley et al 2014;Kohn 2014;Kouketsu et al 2014;Zhong et al 2021b;Taguchi et al 2019;Zhong et al 2019;Alvaro et al 2020;Dunkel et al 2020;Schwarzenbach et al 2021;Szczepański et al 2021). The main advantage of the Raman elastic thermobarometry is that it is not relying on interpretations of the complex history of phase relations during the bulk chemical equilibrium evolution, and Communicated by Daniela Rubatto.…”