Secular change in the age of TTG sources during the Archean from in-situ Sr and Hf isotope analysis by LA-MC-ICPMS
- 1Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, 2020-2207 Main Mall, Vancouver, British Columbia, V6T 1Z4, Canada (kmusiyachenko@eoas.ubc.ca)
- 2School of Earth and Atmospheric Sciences, Queensland University of Technology, 2 George Street, Brisbane, QLD 4000, Australia
- 3Department of Geosciences, Swedish Museum of Natural History, Frescativägen 40, SE-104 05 Stockholm, Sweden
- 4Department of Geology, Lund University, Sölvegatan 12, SE-223 62, Lund, Sweden
- 5Geological Museum, Finnish Museum of Natural History, Pohjoinen Rautatiekatu 13, FIN-00100, Helsinki, Finland
- 6Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, K1A 0E8, Canada
- 7Institut für Geologische Wissenschaften, Freie Universität Berlin, Malteserstraße 74-100, D-12249, Berlin, Germany
- 8Department of Earth Sciences and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal 23955, Saudi Arabia
- 9Department of Earth Sciences, Eidgenössische Technische Hochschule, Clausiusstrasse 25, CH-8092, Zürich, Switzerland
- 10Institut für Geologie, Universität Bern, Baltzerstrasse 1+3, CH-3012, Bern, Switzerland
Much of the continental lithosphere developed during the Archean, which was an Eon of change in terms of global geodynamics and geochemical cycles. Uncovering the causal links between crust forming processes and prevailing geodynamic mechanisms is crucial for understanding the origins and composition of the present-day continental lithosphere. Pristine Archean crust is scarce yet can be found in cratons worldwide. Many of these occurrences comprise rocks of the tonalite-trondhjemite-granodiorite (TTG) suite, which represent a prevalent component of the Archean continental crust. TTGs are generally considered to have formed by partial melting of amphibolite or eclogite source rocks that had basaltic precursors originally extracted from a depleted mantle (e.g., [1]). The age of the source rocks (i.e., the time between the basalt extraction from the mantle and TTG formation) can be determined from the initial radiogenic isotope compositions of TTGs, provided that the P/D ratio of the source can be reliably estimated and is significantly different from that of the depleted mantle.
Based on this principle, we estimated the age of basaltic sources of TTGs from cratons of different age and paleogeography from initial 87Sr/86Sr compositions determined by in-situ Sr isotope analysis of primary igneous apatite (LA-MC-ICPMS). The 87Sr/86Sr of these apatites show that prior to 3.4 Ga TTGs were derived from relatively old mafic sources and that the average time between formation of basaltic material from the mantle and subsequent remelting under amphibolite to eclogite facies conditions decreased drastically during the Paleoarchean. This secular change indicates a rapid global increase in the efficiency of TTG production or the emergence of a new TTG-forming process at c. 3.4 Ga [2].
In this contribution we explore this hypothesis by comparing the 87Sr/86Sr signature of the TTGs with their trace-element compositions, as well as with 176Hf/177Hf zircon data for these rocks and contemporary TTGs from other studies. This combined geochronological, isotope and geochemical analyses will provide new constraints on the age of TTG sources during the Archean and will allow investigation into the nature and probable causes of the apparent rejuvenation at 3.4 Ga, as indicated by Sr isotopes.
[1] Hoffmann, J.E. et al. (2011) Geochim. Cosmochim. Acta 75, 4157-4178.
[2] Caton, S., et al., (in review) Chem. Geol.
How to cite: Musiyachenko, K., Smit, M., Caton, S., B. Emo, R., Kielman-Schmitt, M., Kooijman, E., Scherstén, A., Halla, J., Bleeker, W., Hoffmann, J. E., Prakash Pandey, O., Ravindran, A., Maltese, A., and Mezger, K.: Secular change in the age of TTG sources during the Archean from in-situ Sr and Hf isotope analysis by LA-MC-ICPMS, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3181, https://doi.org/10.5194/egusphere-egu22-3181, 2022.
