^1,2Yao Sun, ²Jonas Tusch, ¹Xiaorui Fan, ¹Jifeng Xu, ³Chao Li, ⁴Kristoffer Szilas, ²Carsten Münker, ¹Jingao Liu, ²Mario Fischer-Gödde
Earth and Planetary Science Letters 684, 120012 Link to Article [https://doi.org/10.1016/j.epsl.2026.120012]
¹State Key Laboratory of Geological Processes and Mineral Resources, and Frontiers Science Center for Deep‐time Digital Earth, China University of Geosciences, Beijing 100083, China
²Institut für Geologie und Mineralogie, Universität zu Köln, Cologne 50674, Germany
³National Research Center for Geoanalysis, Beijing 100037, China
⁴Natural History Museum of Denmark, University of Copenhagen, Copenhagen 1350, Denmark
Copyright Elsevier

The mass-independent Mo isotope composition of the Bulk Silicate Earth (BSE) bears great potential to investigate the origin of the Earth’s latest 10–20% planetary building blocks. However, currently different estimates for the Mo isotope composition of the BSE render constraints on the composition of late-stage accretionary materials difficult. To address this issue and to revisit the Mo isotope composition of the BSE, we report high-precision molybdenum isotope data for a comprehensive set of terrestrial molybdenites from different locations around the globe covering mineralization ages that extend from the Archean to the Phanerozoic. The molybdenite results are used to constrain the Mo isotope composition of the BSE as follows: ε92Mo = 0.04 ± 0.06, ε94Mo = 0.03 ± 0.03, ε95Mo = 0.01 ± 0.01, ε97Mo = 0.02 ± 0.02, ε100Mo = 0.05 ± 0.06 (n = 16, 95% confidence interval, relative to the NIST SRM 3134 Mo standard). In contrast to previous studies, no resolvable ε94Mo and ε95Mo anomalies were observed, suggesting a BSE composition with predominantly non-carbonaceous chondrite provenance. Considering the analytical uncertainties of our new BSE estimate and literature data for carbonaceous and non-carbonaceous meteorites, it remains a viable option that 12±10% of the present-day Mo budget in the BSE derives from carbonaceous meteorite material delivered during late-stage accretion. This amount of Mo is consistent with the fraction of Mo that was delivered to Earth during its final 0.5% of accretion by the late veneer.

¹Roger L. Gibson,¹S’lindile S. Wela,¹Leonidas C. Vonopartis,¹Marco A. G. Andreoli
Meteoritics & Planetary Science (in Press) Open Access Link to Articles [https://doi.org/10.1111/maps.70136]
¹School of Geosciences, University of the Witwatersrand, Johannesburg, South Africa
Published by arrangement with John Wiley & Sons

A core drilled through shocked and faulted Archean granitoid gneisses and dolerites in the eroded peak ring of the 70–80 km diameter Morokweng impact structure intersects multiple centimeter- to meter-wide clastic-matrix breccias containing a polymict clast population of lithic and mineral clasts and altered, millimeter- to centimeter -size, melt clasts. These polymict melt-bearing (PMB) breccias occur both as discrete dikes and in meter- to decameter-wide composite breccia intersections where they are intimately associated with cataclasite and pseudotachylite. Petrographic and bulk-rock geochemical analysis confirms that the PMB breccias comprise fragmental and melt material derived exclusively from the granitoid and doleritic wallrocks, with local geochemical deviations attributable to metasomatic hydrothermal alteration. Notwithstanding their almost complete replacement by smectite and zeolite assemblages, the melt clasts display textural and compositional characteristics identical to the pseudotachylite dikes. Composite lithic-melt clasts indicate an intimate association of melting with cataclasis and comminution prior to their incorporation into the PMB breccias. While most melt clasts display sharp, angular shapes, indicating brittle fracturing, local preservation of delicate filaments intruding the adjacent clastic matrix and bulbous to cuspate-lobate melt clast margins against the matrix indicate incorporation into the breccias while still molten and/or plastic. We propose that the PMB breccias formed by a combination of dynamic injection of friction melt into the cataclasite portions of large fault zones and the development of shear-induced Kelvin–Helmholz instabilities along the melt-cataclasite interface during ongoing fault slip. Melt injection into brecciated wallrock and smaller fractures hosting incoherent cataclasite may have been assisted by a pumping-suction mechanism driven by complex, rapidly changing, block movements during crater wall collapse and peak ring formation. Cooling of the pseudotachylite melts during continued shear or compression of the breccia zones led to their embrittlement and mechanical entrainment as fragments into the incohesive cataclastic fault material, producing the hybrid PMB breccia type. Although the complex strain patterns during peak ring formation could have played a role in extending the duration of shear movements affecting the breccias, we propose that the sequence of cataclasis, frictional melting, melt injection, quenching, brecciation of quenched melt, and melt clast entrainment necessary to produce the PMB breccias can be reconciled with a single, continuous, long-duration, large-magnitude, slip event during collapse of the transient crater wall.