Dynamik av magma-sediment samspelet och dess betydelse för paläoklimatförändringar

Tidsperiod: 2016-01-01 till 2019-12-31

Projektledare: Steffi Burchardt

Medarbetare: Valentin Troll, Frances Deegan

Finansiär: Vetenskapsrådet

Bidragstyp: Projektbidrag

Budget: 2 900 000 SEK

The Paleocene-Eocene Thermal Maximum (PETM), a period of global warming some 55 Ma, was triggered by multiple injections of isotopically light carbon into the atmosphere. Methane venting due to magma intrusion into organic carbon-bearing sediments in the North Sea has been suggested as the causal mechanism for the PETM. New experimental results by the proposal-team, however, show that isotopically light carbon can be released via magmatic activity from a relatively wide range of common continental sediments during short time-scale magma-crust interaction. The Mourne granites (Northern Ireland) were intruded into continental, volatile-bearing sediments at the PETM and thus represent an ideal case study to test the hypothesis that continentally-sourced light carbon could have helped to drive paleo-climate change. Magma-crust interaction is characterised by interlinked mechanical, thermal, and chemical processes, prompting a multi-disciplinary project combining the PI’s and the collaborators’ expertise in structural geology, petrology, and geochemistry. Three work packages (WP) will systematically assess interaction between sedimentary rocks and magma at our test locality, the Mourne Mountains, to produce a fully quantitative assessment of magma-sediment interaction processes and their contribution to paleo-climate change.WP1 aims to identify the physical controls on magma-sediment interaction and assess the volume of sedimentary rock affected by thermo-mechanical interaction with magma. This will be achieved through quantitative mapping of multiple traverses extending from within the Mourne granites, through the metamorphic contact aureole, and into the surrounding pristine sedimentary rocks. Field data and rock samples for microstructural analysis of volatile escape structures will be included into 3D structural models to accurately quantify the volume of rock affected by magma-sediment interaction in the Mourne Mountains.WP2 targets the petrological and geochemical evolution of magma-sediment interaction and aims to quantify the exact processes and rates of sedimentary rock degassing from the contact aureole. For this purpose, pristine granite and a range of variably metamorphosed to pristine sedimentary rock samples will be collected for major and trace element, volatile, and stable and radiogenic isotope analyses. Crucially, we will also conduct heating-and-degassing experiments to quantify the amount and the isotope composition of the volatiles released from pristine and metamorphosed sedimentary rocks to assess the volatiles lost from the contact aureole during magma emplacement.WP3 will integrate the results of WP1 and 2 to fully characterise the mechanical, thermal, and chemical processes of magma-sediment interaction in the Mourne Mountains and to assess the contribution of continental degassing to paleo-climate change during the PETM. WP3 will combine affected rock volumes from the 3D models (WP1) with the amount of degassing recorded in the aureole to the Mourne granites (WP2). The results of the sediment-degassing experiments will constrain the isotopic character of the gas liberated from continental sedimentary rock and assess the relevance for climate change during the PETM. WP3 will also deliver fully quantitative constraints on crustal assimilation and associated degassing during emplacement of the Mourne granites, which will allow us to evaluate their complete role in the PETM. As the PETM is thought to be analogous to present-day climate warming, this proposal will contribute to our overall understanding of climate dynamics on both a geological and human timescale. Moreover, ore and hydrocarbon deposits can form due to magma-sediment interaction (e.g. skarn-type iron deposits in Sweden; oil and gas in the North Sea Basin), making our research of wide relevance to society.