128 A Tribute to Rodney C. Ewing: Celebrating a Half-Century of Transformative Contributions to Geoscience, Mineralogy, and Material Science

Honoring Prof. Rodney C. Ewing (1946–2024), this session celebrates over 50 years of groundbreaking contributions to mineralogy, geoscience, and materials science, from atomic-scale processes to field-scale applications.

Monday, 20 October 2025
1:30 PM - 5:30 PM
HBGCC, 217A

Contemporaneous Subduction and Stagnant-Lid Tectonics on the Hadean Earth

Paper number: 128-9
Program: Technical Sessions
Time: 3:45 PM – 4:00 PM

Authors

Abstract

In situ analysis of igneous zircons provides important evidence constraining Hadean and Archean tectonics. Rodney Ewing’s pioneering studies of radiation damage are instrumental to distinguishing altered from pristine zircon and unlocking this record. Many tests can be applied to evaluate fidelity of the ancient zircon record including optics, SEM-CL-BSE, XRD, magnetism, U-Pb-age concordance, water content, trace-element compositions, Raman, TEM, and APT.

Here, we use some of these tools to verify unaltered domains in Hadean/Archean detrital zircons from the Jack Hills, Australia (JHZ, 4.4-3.1Ga) and report new trace-element measurements (including U/Nb and Sc/Yb). The temporal progression of these TE ratios, along with the oxygen and hafnium isotope evolution of the JHZ, yields insights into the timing and setting of early magmatism, which contrast with records from Barberton, South Africa detrital zircons (BZ, 4.1-3.3Ga, Drabon+ 2022). Continental arc-type (CA) zircons are typified by higher Sc/Yb and U/Nb than mantle-type zircons (Grimes+ 2015) and higher d18O (Valley+ 2005).  For zircons older than 3.8Ga, percentages are: 73%/18% (JHZ/BZ) have Sc/Yb>0.1 (N=249/20) and 45%/20% have U/Nb>20 (Valley+ 2025 in review). Oxygen isotope evidence for crustal reworking is also stronger for JHZ; 77% of JHZ have d18O>6.1‰ vs 40% for BZ. BZ show change-points in Sc/Yb and U/Nb vs. age (increased CA-like values in younger zircon) that correlate to eHf (Drabon+ 2022), suggesting onset of subduction at 3.8Ga, but JHZ show these continental/subduction affinities back to before 4.2Ga. These data show great variability among the source rocks of JHZ and between JHZ and BZ. Importantly, this shows that the two suites likely came from distinct Hadean terranes reflecting a spatial diversity of tectonic settings >4Ga. In contrast to the dominance of stagnant-lid magmatism suggested by TE signatures of BZ, most Hadean/Eoarchean JHZ record subduction-related magmatism alternating with periods of magmatic quiescence. Subduction-like sinking of hydrated surface rocks is consistent with geodynamic modelling (Vezinet+ 2025), though plate tectonics is not implied. Hydrous melting promoted reworking of Hadean protocrust to form granitoids. The variable settings for sources of Hadean zircons suggest contemporaneous subduction and locally stagnant lids during generation of Hadean magmas. This indicates a broader diversity of early crustal origins than previously recognized.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-412717

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