Detrital rutile petrochronology: Assessing metamorphism through time at the global scale

• Applicant: Dr. Jan Schoenig
• Subject Area: Palaeontology ; Mineralogy, Petrology and Geochemistry
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 509465124

Reconstructing metamorphic conditions throughout Earth history is of fundamental importance to understand the long-term evolution of thermal, dynamic, and chemical regimes. A major and apparently insuperable obstacle is marked by the fragmentarily preserved crystalline rock record. Interpretations of whether plate tectonics globally initiated early or late, whether the transition from a preceding non-plate-tectonic regime was abrupt or long lasting, and whether thermal regimes secularly evolved from warm to cold conditions suffer in particular from extrapolating local-scale observations to the global scale. By contrast, detrital mineral grains have remarkable potential to efficiently acquire large datasets from a wide range of sources, including preserved sediments shed from orogens that are lost by erosion, and thus provide a much better representation of the global-scale picture. However, up-to-date, no tool exists which is able to reliably combine age and P–T (pressure–temperature) information from a detrital perspective. Based on a preliminary application of advanced statistical methods on a compiled literature dataset, a multivariate consideration of trace elements in rutile demonstrates high potential to close this gap. The proposed project is subdivided into two phases. In the first phase, a rutile trace-element database will be compiled by acquiring new data from well-defined crystalline rock samples and integration with published data. This will include 17 trace-element concentrations from rutiles of metasomatic, igneous, mantle, and metamorphic origin. The latter will be additionally analyzed for 8 element concentrations. Rutile-bearing samples from metamorphic rocks cover felsic and mafic bulk-rock compositions as well as a broad range of P–T conditions. A multivariate discrimination model will be developed that (i) separates metasomatic, igneous, mantle and metamorphic rutile, and (ii) predicts T/P gradients for metamorphic rutile. In the second phase, the developed discrimination scheme will be combined with U–Pb dating and applied to ~10,000 detrital rutile grains from 33 modern-sand samples of rivers draining considerable parts of S Africa, S America, NE Canada, S India, and W Australia. These rivers mainly sample material sourced from Archean and Proterozoic units as well as reworked sediments from basins recording earlier stages of erosion, which are inaccessible via the crystalline rock record. For samples indicating a contribution from low T/P metamorphic rocks, inclusion assemblages of detrital rutiles will be screened for characteristic low T/P minerals in order to confirm geochemical predictions by mineralogical evidence. A successful project will shed new light on the evolution of metamorphic gradients through time and support or falsify our central hypothesis that “modern-style low T/P gradients were established globally in the Paleoproterozoic”.

• DFG Programme: Research Grants
• International Connection: Sweden
• Co-Investigators: Professor Dr. Hilmar von Eynatten; Professor Dr. Horst Marschall; Privatdozent Dr. Raimon Tolosana-Delgado
• Cooperation Partner: Professor Dr. Thomas Zack