Leucogranite zircon: An analogue for Hadean zircons from Jack Hills, Western Australia
Abstract
Much of our current knowledge of the Hadean has been gleaned from the geochemical characterization of detrital zircons, some as old as nearly 4.4 Ga, predominantly from Jack Hills, Western Australia. This analysis has led to a profound paradigm shift from an early hellish, uninhabitable environment to a much cooler early Earth with water-rock interactions and the possible origin of life. Although multiple formation scenarios for Earths earliest crust have been proposed, there is no consensus as to the magmatic environment in which these seemingly unique grains crystallized. Partly this reflects a paucity of modern analogs, particularly zircons containing muscovite and quartz inclusions which dominate Hadean populations, Ti-in-zircon crystallization temperatures with a narrow distribution around a peak of 680°C, and formation pressures of 5-15 kbars. Harrison and Wielicki (2016) identified a modern-day analog in zircons of the 22 Ma Arunachal leucogranite in eastern Himalaya, which they interpreted grew under wet basement melting conditions in the hanging wall of a continental collision - a melting environment that might be broadly similar to a Hadean ocean-continent subduction zone. To test the robustness of this similarity and the uniformity within the population of zircons formed in leucogranites, we are investigating grains from Harney Peak, Black Hills, South Dakota and the Phillips Pluton, Maine, both well-studied leucogranites, to assess the similarity of these grains to those of the Arunachal and Jack Hills populations. Results from this study provide new information about the presence and abundance of felsic, continental crust-like material during the Hadean and the interactions of such materials in convergent margins, possibly reflective of early plate tectonics. Due to the lack of a >4 Ga rock record, identification of modern analogs for the Hadean zircon population offers a path to further understanding the near surface conditions associated with their formation and provides valuable constraints to our understanding of this fundamental period in Earth evolution.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.V31G0129W
- Keywords:
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- 1020 Composition of the continental crust;
- GEOCHEMISTRY;
- 3660 Metamorphic petrology;
- MINERALOGY AND PETROLOGY;
- 8110 Continental tectonics: general;
- TECTONOPHYSICS;
- 8178 Tectonics and magmatism;
- TECTONOPHYSICS