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The Mecsekalja Zone is a strike-slip fault zone that plays an essential role in the structural framework of South Transdanubia. The metamorphic and deformation history of the crystalline basement of the Mecsekalja Zone has been determined thus far based exclusively on a few surface outcrops and near-surface samples. The Szentlőrinc-1 (Sztl-1) well penetrated the shear zone at a depth of approximately 2 km and brought drilling chips from a 220-m-long section of the basement to the surface. The aim of this study is to reconstruct the metamorphic and deformation history of the Mecsekalja Zone along the Sztl-1 well using these tiny samples. These drilling chips consist of single mineral and rock pieces that are dominated by quartz grains. This study concentrates on the detailed analysis of quartz grains utilizing the physical conditions of metamorphic evolution as well as ductile and brittle deformation to determine the chemical composition and rheology of quartz. The evolution of the studied area can be determined by evaluating analytical data measured by Raman spectroscopy, LA-ICP-MS, and FTIR spectroscopy. These data suggest that the maximum temperature of the early regional metamorphism was 500–575 °C, the temperature of the subsequent ductile deformation was below 500 °C including recrystallization occurred between 400 and 475 °C. During the structural evolution of the study area, two independent, single deformation events occurred. The earlier ductile deformation event was followed by a brittle event through the reactivation of the former ductile shear zone. Our model is in accordance with previous results concerning the evolution of the Mecsekalja Zone, thus, the shear zone, with an identical evolution, can be extended toward the southwest at least to the Sztl-1 well.

Open access
Central European Geology
Authors: Zsófia Pálos, István János Kovács, Dávid Karátson, Tamás Biró, Judit Sándorné Kovács, Éva Bertalan, Anikó Besnyi, György Falus, Tamás Fancsik, Martina Tribus, László Előd Aradi, Csaba Szabó, and Viktor Wesztergom

The past decade has seen a great number of studies dealing with magmatic water contents and how these could be retrieved by the nominally anhydrous minerals’ (NAMs) trace structural hydroxyl (water) contents. Constraints have been made to magmatic hygrometry with clinopyroxene and plagioclase. Although results suggest that the method is more flexible and reliable than melt inclusion studies, they also indicate that the trace hydroxyl contents could still be overprinted by syn- and post-eruptive processes. Clinopyroxenes can hold more structural hydroxyl than plagioclases. A comprehensive review is presented with the inclusion of all published results so far to compile the available pieces of information. As a case study, micro-FTIR measurements are made of a representative set of plagioclase phenocrysts from the Börzsöny Mts. (Carpathian–Pannonian Region). The samples were selected to represent the progress of the volcanic activity in time and space, considering the petrologic and geochemical evolution of volcanic products in well-defined volcanostratigraphic positions. The syn- and post-eruptive cooling rate seems to have the greatest effect on water retention. This means that the systematic investigation of water in volcanic phenocrysts can contribute to distinguish the slowly and rapidly cooling parts of the volcanostratigraphic units.

Open access