Historical Mine Plans meet Modern Remote Sensing Data – Knowledge and Geodata Management at the Research Center of Post-Mining
Benjamin Haske, Julia Tiganj, Laura Klein
Technische Hochschule Georg Agricola, Germany
With the establishment of the Research Center of Post-Mining (FZN) at the Technische Hochschule Georg Agricola University in Bochum in 2015, the development of an extensive archive for the systematic collection and evaluation of all post-mining related information began. In addition to the current collection of more than 4500 books and journals, over 1000 maps, as well as slides, photographs and lecture notes, a Thesaurus Post-Mining is currently being created.
The combination of historic data and modern geomonitoring techniques such as remote sensing via satellite and unmanned aerial systems, allows the contemporary handling of post-mining issues. Based in concepts of various mining companies an adjusted approach is currently developed to integrate the variety of different datasets within a spatial data infrastructure (SDI). All this information not only supports the researchers of the FZN in their work, but also creates transparency in dealing with the legacy of mining and its significance for the present and the orientation towards a more sustainable future in post-mining regions. The goal is therefore not only the ongoing digitization of existing materials, but also the creation of an open-access database on the subject of post-mining and the establishment of a server-based spatial data infrastructure for internal and external users. In the long run, this step will ensure a transdisciplinary and inter-institutional evaluation of spatial data, while the research results as well as the already existing historical information can be made easily accessible to the public within the framework of the EU INSPIRE directive.
Fluid metasomatism in the cold nose of the Mariana subduction zone
Elmar Albers1, Christian T. Hansen1, John Shervais2, Yuji Ichiyama3
1MARUM – Center for Marine Environmental Sciences, University of Bremen, Germany; 2Department of Geology, Utah State University, USA; 3Graduate School of Science, Chiba University, Japan
Fluid-mediated mass transfer in subduction zones is crucial for chemical cycling on Earth. Particularly little is, however, known about such processes at shallow subduction levels.
We used thermodynamic models to reproduce the metamorphic history of ocean island basalt (OIB) clasts recovered from the Mariana forearc during IODP Expedition 366. The OIBs were subducted to ~30 km depth, metamorphosed/metasomatized, and subsequently recycled to the seafloor via mud volcanism (Fryer et al., 2020). The rocks exhibit K2O contents (median = 4.6 wt.%) and H2O (median = 5.3 wt.%) much higher than OIBs situated on the Pacific plate (Deng et al., 2021), suggesting that these have been added during subduction. This interpretation is in line with the presence of abundant phengite in the samples. Additionally, mass balance calculations point to the addition of SiO2, and high Cs, Rb, Th, and U concentrations imply an uptake whereas low Ba and Sr contents indicate the removal of trace elements.
We show that the metasomatic change in composition and the formation of phengite can be explained by (i) the dehydration of altered oceanic crust releasing K2O-rich fluids and (ii) the subsequent reaction of such fluids with OIB. These processes are predicted to initiate at temperatures of <200°C and pressures of <5 kbar.
Our study provides direct evidence for fluid–rock interactions and metasomatism in an active subduction zone. We demonstrate that mass transfer from subducted oceanic crust initiates at low pressure/temperature conditions. Subducted volcanics can hence undergo significant compositional changes even at shallow depths.
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