Zircon has long been used as a geochronological tool for determining the age of rock formations. However, our discovery of anomalously ‘young’ zircon grains (<81 Ma) within igneous rocks from the Troodos ophiolite in Cyprus challenges conventional interpretations. These chronologically younger zircon grains, hosted in rocks dated to 95–81 Ma, are ubiquitously distributed across all mafic lithologies, including gabbros, diabases and pillow lavas. Their morphology, trace element signatures and Hf isotope compositions differ markedly from the magmatic zircon grains formed between 95 and 81 Ma, as well as the hydrothermal zircons. Instead, they exhibit inherited characteristics akin to older detrital zircon grains dating from 3300 to 95 Ma. Notably, the <81 Ma zircon grains show a progressive decrease in trace element concentrations (except for U and Hf) and Hf(t) values correlating with younger apparent ages. These trends suggest that their anomalously ‘young’ U–Pb ages reflect secondary processes involving Pb loss and U gain. We propose that these zircon grains underwent variable degrees of modification of the characteristics inherited from detrital precursors during the earliest stages of subduction initiation. Based on the chondrite-like rare earth element patterns, Hf isotope heterogeneities, mineral inclusions and the ophiolite's circular outcrop pattern, we further hypothesize that a meteorite impact event occurred during this modification phase. The associated high-pressure/high-temperature conditions extensively reset the U–Pb system while minimally affecting the Lu–Hf system of pre-existing zircon grains in the oceanic crust. These modified grains were subsequently incorporated into magmatic systems during subduction-related melting. The resultant mixture of meteoritic components, marine sediments and mantle materials explains the unique geochemical signatures observed in Troodos magmatic zircon grains and their host rocks. This model may also account for the ancient signatures (e.g. Proterozoic to Archean Os model ages and inherited zircon in peridotites and chromitites) documented in many Neotethyan ophiolites, offering a unifying framework for reconciling disparate geochronological records in supra-subduction zone settings.
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June 10, 2025
Impact-induced ‘young’ zircon in old rocks from Troodos ophiolite, Cyprus Available to Purchase
Ben-Xun Su;
Ben-Xun Su
*
1
State Key Laboratory of Lithospheric and Environmental Coevolution
, Institute of Geology and Geophysics, Chinese Academy of Sciences
, Beijing 100029, China
2
College of Earth and Planetary Sciences
, University of Chinese Academy of Sciences
, Beijing 100049, China
*
Correspondence: [email protected]
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Jing Wang;
Jing Wang
1
State Key Laboratory of Lithospheric and Environmental Coevolution
, Institute of Geology and Geophysics, Chinese Academy of Sciences
, Beijing 100029, China
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Qi-Qi Pan;
Qi-Qi Pan
1
State Key Laboratory of Lithospheric and Environmental Coevolution
, Institute of Geology and Geophysics, Chinese Academy of Sciences
, Beijing 100029, China
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Yan Xiao;
Yan Xiao
1
State Key Laboratory of Lithospheric and Environmental Coevolution
, Institute of Geology and Geophysics, Chinese Academy of Sciences
, Beijing 100029, China
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Meng-Meng Cui
Meng-Meng Cui
1
State Key Laboratory of Lithospheric and Environmental Coevolution
, Institute of Geology and Geophysics, Chinese Academy of Sciences
, Beijing 100029, China
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Ben-Xun Su
*
1
State Key Laboratory of Lithospheric and Environmental Coevolution
, Institute of Geology and Geophysics, Chinese Academy of Sciences
, Beijing 100029, China
2
College of Earth and Planetary Sciences
, University of Chinese Academy of Sciences
, Beijing 100049, China
Jing Wang
1
State Key Laboratory of Lithospheric and Environmental Coevolution
, Institute of Geology and Geophysics, Chinese Academy of Sciences
, Beijing 100029, China
Qi-Qi Pan
1
State Key Laboratory of Lithospheric and Environmental Coevolution
, Institute of Geology and Geophysics, Chinese Academy of Sciences
, Beijing 100029, China
Yan Xiao
1
State Key Laboratory of Lithospheric and Environmental Coevolution
, Institute of Geology and Geophysics, Chinese Academy of Sciences
, Beijing 100029, China
Meng-Meng Cui
1
State Key Laboratory of Lithospheric and Environmental Coevolution
, Institute of Geology and Geophysics, Chinese Academy of Sciences
, Beijing 100029, China
*
Correspondence: [email protected]
Publisher: Geological Society of London
Received:
16 Sep 2024
Revision Received:
29 Apr 2025
Accepted:
01 May 2025
First Online:
13 May 2025
Online ISSN: 2041-479X
Print ISSN: 0016-7649
Funding
- Funder(s):National Natural Science Foundation of China
- Award Id(s): 42350001
- Award Id(s):
© 2025 The Author(s). Published by The Geological Society of London. All rights, including for text and data mining (TDM), artificial intelligence (AI) training, and similar technologies, are reserved. For permissions: https://www.lyellcollection.org/publishing-hub/permissions-policy. Publishing disclaimer: https://www.lyellcollection.org/publishing-hub/publishing-ethics
© 2025 The Author(s)
Journal of the Geological Society (2025) 182 (5): jgs2024-192.
Article history
Received:
16 Sep 2024
Revision Received:
29 Apr 2025
Accepted:
01 May 2025
First Online:
13 May 2025
Funding
This work was funded by the National Natural Science Foundation of China (42350001).
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CitationBen-Xun Su, Jing Wang, Qi-Qi Pan, Yan Xiao, Meng-Meng Cui; Impact-induced ‘young’ zircon in old rocks from Troodos ophiolite, Cyprus. Journal of the Geological Society 2025;; 182 (5): jgs2024–192. doi: https://doi.org/10.1144/jgs2024-192
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