Deep subduction in Earth history: Seeking for traces in the sedimentary record
Mineralogy, Petrology and Geochemistry
Final Report Abstract
The project aimed at evaluating whether modern-style plate tectonics including deep subduction and formation of ultrahigh-pressure (UHP) rocks operated already prior to Neoproterozoic or not. This fundamental and vitally discussed question in Earth sciences was tackled by an entirely new approach, a detrital screening technique essentially based on the preservation and detection of coesite inclusions in detrital garnet. While the first part of the project was dedicated to methodological improvements and a ‘test case’ in the Erzgebirge in Germany, the second part focused on Paleoproterozoic belts in W Greenland and NE Canada. For the second part, we have so far only partial results, as fieldwork in Canada could not take place earlier than 9/2022 due to Covid-19 travel restrictions. The methodological improvements include (i) proof of concept for larger catchments >500 km2, (ii) detailed investigation of inclusion type and frequency relations to garnet grain size, (iii) better understanding of coesite inclusion size, characteristics and preservation potential in relation to host-rock type and inclusion density, and (iv) better understanding of inclusion type – host rock – garnet chemistry relations, mainly based on a new machinelearning aided discrimination scheme for host rocks based on garnet chemistry. The improvements allow for a much more efficient screening for UHP garnets in sediments and sedimentary rocks. For the test case in the Erzgebirge, we could demonstrate that besides the well-known UHP lenses significant parts of the felsic country rocks must have experienced UHP metamorphism, too. We further applied the approach to the convergent plate boundary zone in Papua New Guinea, where the youngest UHP rocks on Earth occur. There, we could show that single detrital garnet grains may record a complete rock cycle, including subduction of sedimentary protoliths to UHP conditions, partial melting, rapid exhumation, surface uplift, and erosion. For the Paleoproterozoic belts, our results from the Nordre Strømfjord shear zone in the Nagssugtoqidian Orogen of western Greenland indicate that previously reported extremely high pressures and low T/P ratios are very unlikely. Therefore, the area does not serve as a reliable example or proof for modern-style plate tectonics operating already in Paleoproterozoic time.
Publications
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Diamond and coesite inclusions in detrital garnet of the Saxonian Erzgebirge, Germany. Geology, 47(8), 715-718.
Schönig, Jan; von Eynatten, Hilmar; Meinhold, Guido & Lünsdorf, N. Keno
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Dispersed occurrence of mafic and felsic ultrahigh-pressure rocks in the central Saxonian Erzgebirge (Germany) revealed by diamond and coesite inclusions in detrital garnet. GeoMünster 2019, University of Münster, Germany (oral presentation).
Schönig J, von Eynatten H, Meinhold G & Lünsdorf NK
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Inclusions in detrital garnet as tracer of UHP metamorphism. WAGGS 2019, Syracuse University, New York, USA (oral presentation).
Schönig J, von Eynatten H, Meinhold G & Lünsdorf NK
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The 'life cycle' of coesite-bearing garnet. GeoMünster 2019, University of Münster, Germany (poster presentation).
Schönig J, von Eynatten H, Meinhold G & Lünsdorf NK
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Deep subduction of felsic rocks hosting UHP lenses in the central Saxonian Erzgebirge: Implications for UHP terrane exhumation. Gondwana Research, 87, 320-329.
Schönig, Jan; von Eynatten, Hilmar; Meinhold, Guido; Lünsdorf, N. Keno; Willner, Arne P. & Schulz, Bernhard
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The potential of detrital garnet in UHP research as exemplified by the central Saxonian Erzgebirge. GeoUtrecht 2020, University of Utrecht, Netherlands (oral presentation).
Schönig J, von Eynatten H, Meinhold G & Lünsdorf NK
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Garnet major-element composition as an indicator of host-rock type: a machine learning approach using the random forest classifier. Contributions to Mineralogy and Petrology, 176(12).
Schönig, Jan; von Eynatten, Hilmar; Tolosana-Delgado, Raimon & Meinhold, Guido
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Garnet sand reveals rock recycling processes in the youngest exhumed high- and ultrahigh-pressure terrane on Earth. Proceedings of the National Academy of Sciences, 118(3).
Baldwin, Suzanne L.; Schönig, Jan; Gonzalez, Joseph P.; Davies, Hugh & von, Eynatten Hilmar
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Life-cycle analysis of coesite-bearing garnet. Geological Magazine, 158(8), 1421-1440.
Schönig, Jan; von Eynatten, Hilmar; Meinhold, Guido & Lünsdorf, N. Keno
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Mineral inclusions in detrital garnet: An excellent petrogenetic tool. GeoKarlsruhe 2021, Karlsruhe Institute for Technology, Germany (oral presentation).
Schönig J.
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Reply to comment on “Deep subduction of felsic rocks hosting UHP lenses in the central Saxonian Erzgebirge: Implications for UHP terrane exhumation”. Gondwana Research, 98, 320-323.
Schönig, Jan; von Eynatten, Hilmar; Meinhold, Guido; Lünsdorf, N. Keno; Willner, Arne P. & Schulz, Bernhard
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Mineral inclusions in detrital garnet – A complementary tool in ultrahigh-pressure research. EGU General Assembly, Vienna, Austria (oral presentation).
Schönig J, von Eynatten H, Meinhold G, Lünsdorf NK & Baldwin SL
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Random forests in single-grain provenance analysis: The garnet showcase. 5th Meeting of the Working Group on Sediment Generation, University of Milano-Bicocca, Italy (oral presentation).
Schönig J., von Eynatten H., Tolosana-Delgado R. & Meinhold G.
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The sedimentary record of ultrahigh-pressure metamorphism: a perspective review. Earth-Science Reviews, 227, 103985.
Schönig, Jan; von Eynatten, Hilmar; Meinhold, Guido & Lünsdorf, Nils Keno
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Detrital garnet petrology challenges Paleoproterozoic UHP metamorphism in Western Greenland. EGU General Assembly, Vienna, Austria (oral presentation).
Schönig J, Benner C, Meinhold G, von Eynatten H & Lünsdorf NK
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Detrital garnet petrology challenges Paleoproterozoic ultrahigh-pressure metamorphism in western Greenland. European Journal of Mineralogy, 35(4), 479-498.
Schönig, Jan; Benner, Carsten; Meinhold, Guido; von Eynatten, Hilmar & Lünsdorf, N. Keno
