<abstract xmlns="http://www.w3.org/1999/xhtml">

<p>For a long time, the 1.38 Ga old Dobra Gneiss (Type A) from the Lower Austrian Drosendorf Unit (Moldanubian Zone, Bohemian Massif) was considered the oldest rock of Austria. We now have dated zircons from a local mafic inlayer in the Dobra Gneiss Type A, termed Hauergraben Gneiss. This small-scale amphibole-bearing orthogneiss has a magmatic formation age of 1.40 Ga, and is, thus, to the present state of knowledge, the oldest rock of Austria. Based on geochemical investigations, the protolith of the Hauergraben Gneiss was a quartz-monzonite. It probably originated in a volcanic arc setting like the Dobra Gneiss, but shows distinctively higher transitional metal contents (especially Cr and Co), higher Ba and Sr, and higher light rare earth element contents, which hint at a lithospheric mantle input. This 1.40 Ga old mafic arc material was then incorporated into the 1.38 Ga old intrusive protolith of the Dobra Gneiss, probably in the form of enclaves. Considering the model that the Drosendorf Unit was part of Amazonia until the late Neoproterozoic, we propose that both, Dobra Gneiss Type A and Hauergraben Gneiss, originated at the western margin of the Columbia super-continent, where several long-lived Mesoproterozoic volcanic arcs existed and accreted over time. During the Variscan orogeny, the Hauergraben Gneiss experienced peak metamorphic temperatures of ~620 °C at pressures of ~6 kbar, as can be deduced from amphibole thermobarometry. This is in line with published peak-<italic>PT</italic> estimates from other parts of the Drosendorf Unit. Formation of secondary low-Al magnesiohornblende at the expense of the earlier edenitic/pargasitic peak amphibole indicates a subsequent retrograde overprint.</p>
</abstract>

For a long time, the 1.38 Ga old Dobra Gneiss (Type A) from the Lower Austrian Drosendorf Unit (Moldanubian Zone, Bohemian Massif) was considered the oldest rock of Austria. We now have dated zircons from a local mafic inlayer in the Dobra Gneiss Type A, termed Hauergraben Gneiss. This small-scale amphibole-bearing orthogneiss has a magmatic formation age of 1.40 Ga, and is, thus, to the present state of knowledge, the oldest rock of Austria. Based on geochemical investigations, the protolith of the Hauergraben Gneiss was a quartz-monzonite. It probably originated in a volcanic arc setting like the Dobra Gneiss, but shows distinctively higher transitional metal contents (especially Cr and Co), higher Ba and Sr, and higher light rare earth element contents, which hint at a lithospheric mantle input. This 1.40 Ga old mafic arc material was then incorporated into the 1.38 Ga old intrusive protolith of the Dobra Gneiss, probably in the form of enclaves. Considering the model that the Drosendorf Unit was part of Amazonia until the late Neoproterozoic, we propose that both, Dobra Gneiss Type A and Hauergraben Gneiss, originated at the western margin of the Columbia super-continent, where several long-lived Mesoproterozoic volcanic arcs existed and accreted over time. During the Variscan orogeny, the Hauergraben Gneiss experienced peak metamorphic temperatures of ~620 °C at pressures of ~6 kbar, as can be deduced from amphibole thermobarometry. This is in line with published peak-PT estimates from other parts of the Drosendorf Unit. Formation of secondary low-Al magnesiohornblende at the expense of the earlier edenitic/pargasitic peak amphibole indicates a subsequent retrograde overprint.

In search of the oldest rock of Austria: The Hauergraben Gneiss, a 1.40 Ga old mafic quartz-monzonitic inlayer in the Dobra Gneiss (Drosendorf Unit, Bohemian Massif) as a new candidate

Department of Chemistry and Physics of Materials

Austrian Journal of Earth Sciences

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

For a long time, the 1.38 Ga old Dobra Gneiss (Type A) from the Lower Austrian Drosendorf Unit (Moldanubian Zone, Bohemian Massif) was considered the oldest...

In search of the oldest rock of Austria: The Hauergraben Gneiss, a 1.40 Ga old mafic quartz-monzonitic inlayer in the Dobra Gneiss (Drosendorf Unit, Bohemian Massif) as a new candidate

Published Online: Apr 22, 2021

Page range: 29 - 45

Received: Nov 22, 2020

Accepted: Jan 20, 2021

DOI: https://doi.org/10.17738/ajes.2021.0002

Keywords
Bohemian Massif, Avalonian Basement, Oldest Rock of Austria, Dobra Gneiss, Drosendorf Unit

© 2021 Martin Lindner et al., published by Sciendo

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

In search of the oldest rock of Austria: The Hauergraben Gneiss, a 1.40 Ga old mafic quartz-monzonitic inlayer in the Dobra Gneiss (Drosendorf Unit, Bohemian Massif) as a new candidate

Published Online: Apr 22, 2021

Page range: 29 - 45

Received: Nov 22, 2020

Accepted: Jan 20, 2021

DOI: https://doi.org/10.17738/ajes.2021.0002

KeywordsBohemian Massif, Avalonian Basement, Oldest Rock of Austria, Dobra Gneiss, Drosendorf Unit

© 2021 Martin Lindner et al., published by Sciendo

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 3.0 License.

Keywords
Bohemian Massif, Avalonian Basement, Oldest Rock of Austria, Dobra Gneiss, Drosendorf Unit