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1. An optimized chromatography method and MC-ICP-MS technique for apatite Lu–Hf geochronology

   https://doi.org/10.1039/d3ja00203a  

   Zhang, Chao; Chen, Tsai-Wei; Vervoort, Jeffrey D (November 2023, Journal of Analytical Atomic Spectrometry)

   By using specialized extraction chromatography columns, we have developed an innovative approach that effectively separates Lu and Hf from apatite with high yields and minimal interference, addressing the challenges associated with dating apatite using the Lu–Hf isochron technique. 

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2. Deciphering complex Hf-Nd records of polymetamorphic terranes through multiple isotope systems

   https://doi.org/10.1016/j.gca.2025.09.022  

   Chen, Tsai-Wei; Vervoort, Jeffrey D; Baldwin, Julia A (November 2025, Geochimica et Cosmochimica Acta)

   Understanding the history of polymetamorphic terranes requires integrating multiple analytical techniques to reveal different aspects of crustal evolution. This approach includes geochronological analyses to establish a timeline of geological events as well as isotopic analyses to understand the nature of source rocks. In this study, we analyze Sm-Nd isotopes in apatite and titanite and U-Pb ages in monazite and titanite from metaigneous samples in the northwest Wyoming Province. We integrate these new data with our previously published zircon U-Pb ages and Lu-Hf isotopes with garnet Lu-Hf and Sm-Nd dates from the same samples. This dataset allows us to reconstruct a complete history from magmatic crystallization through metamorphism to isotopic reequilibration. The U-Pb ages from monazite and titanite complement our existing garnet geochronology, constraining peak metamorphism and subsequent cooling at 1.78 Ga (billion years ago) and 1.71 Ga, respectively. Multi-phase Sm-Nd isotope data indicate that isotopic re-equilibration occurred between 1.82 Ga and 1.68 Ga, coinciding with the hypothesized occurrence of the Big Sky orogeny in the region. Notably, the Sm-Nd system reveals a bimodal initial isotopic composition—with one endmember with a near-chondritic composition (εNd(i) ~ −1.7) and the other with strongly subchondritic signatures (εNd(i) ~ −12)—indicating mixing between juvenile and reworked crustal components during orogenesis. The preservation of primary Hf isotopic signatures in zircon—in contrast to the disturbed and reset Nd isotopic compositions in other minerals (apatite, garnet, and titanite)—provides insights into the region’s tectonothermal evolution. These results demonstrate significant Sm- Nd re-equilibration during post-crystallization processes, similar to observations from other ancient terranes, highlighting the importance of multi-isotope approaches in unraveling early Earth evolution. 

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3. Magnetite-apatite deposits of the New Jersey Highlands, USA: Geochronological evidence for orogen-scale Fe-P-(Ti) mineralization during the Grenvillian Orogeny

   https://doi.org/10.1130/B38511.1  

   McKanna, Alyssa J; Koran, Isabel; Schoene, Blair; Guevara, Victor E; Hanchar, John M; Volkert, Richard A; Maeder, James; Mueller-Harder, Cameron (November 2025, Geological Society of America Bulletin)

   Abstract Magnetite-apatite (MtAp) ore deposits are broadly distributed within Mesoproterozoic rocks of the New Jersey Highlands (USA); however, the age and origins of the ores, and relationships to other Fe-P-(Ti) ore deposits in the Grenvillian Orogen are presently unknown. We use zircon U-Pb geochronology and isotope geochemistry to (1) constrain the timing of MtAp mineralization in the New Jersey Highlands, (2) evaluate the relationship between the MtAp ores and associated lithologies, (3) develop a magmatic model for ore genesis, and (4) place the New Jersey ores within the context of Grenville tectonics and regional mineralization. Ore-body zircon crystals exhibit complex, magmatic textures that record episodic or prolonged crystallization over an extended duration from ca. 1074 Ma to 905 Ma, suggesting that MtAp mineralization occurred during Ottawan to post-Ottawan orogenesis. Cumulate textures of MtAp ores and a close spatial and temporal association among ores, pegmatitic granitoids (ca. 1058 Ma to ca. 986 Ma regionally), and clinopyroxene syenites (most dates ca. 1097 Ma to ca. 926 Ma at one mine) suggest that MtAp mineralization and intrusive magmatism reflect co-magmatic processes. Zircon O isotope data indicate that the MtAp deposits and associated lithologies formed from crustal melts (δ18O = 7.66‰–9.24‰ for the orthogneiss-hosted deposits and δ18O = 5.40‰–6.29‰ for the amphibolite-hosted deposit). Zircon Hf isotope data are more complex. Some MtAp deposits and associated lithologies record Hf signatures consistent with a crustal melt source (εHfi = 0.6–11.1). Whereas other MtAp deposits have extremely radiogenic signatures (εHfi = 29–542) due to the high modal abundance of apatite and monazite in the ores and, consequently, high Lu/Hf ratios. MtAp mineralization in the New Jersey Highlands is broadly coeval with MtAp mineralization in the Adirondack Highlands of New York (USA), rare earth element (REE) mineralization in the Hudson Highlands of New York, and nelsonite mineralization at Lac à l’Orignal and Lac Mirepoix in Québec (Canada). Collectively, these results indicate that orogen-scale, Fe-P-(Ti) and REE mineralization processes operated during Ottawan to post-Ottawan orogenesis throughout the Grenville orogen. 

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4. Completion of lunar magma ocean solidification at 4.43 Ga

   https://doi.org/10.1073/pnas.2413802121  

   Dauphas, Nicolas; Zhang, Zhe J; Chen, Xi; Barboni, Mélanie; Szymanowski, Dawid; Schoene, Blair; Leya, Ingo; McKeegan, Kevin D (January 2025, Proceedings of the National Academy of Sciences)

   Crystallization of the lunar magma ocean yielded a chemically unique liquid residuum named KREEP. This component is expressed as a large patch on the near side of the Moon and a possible smaller patch in the northwest portion of the Moon’s South Pole-Aitken basin on the far side. Thermal models estimate that the crystallization of the lunar magma ocean (LMO) could have spanned from 10 and 200 My, while studies of radioactive decay systems have yielded inconsistent ages for the completion of LMO crystallization covering over 160 My. Here, we show that the Moon achieved >99% crystallization at 4,429 ± 76 Ma, indicating a lunar formation age of ~4,450 Ma or possibly older. Using the¹⁷⁶Lu–¹⁷⁶Hf decay system (t_1/2= 37 Gy), we found that the initial¹⁷⁶Hf/¹⁷⁷Hf ratios of lunar zircons with varied U–Pb ages are consistent with their crystallization from a KREEP-rich reservoir with a consistently low¹⁷⁶Lu/¹⁷⁷Hf ratio of 0.0167 that emerged ~140 My after solar system formation. The previously proposed younger model age of ~4.33 Ga for the source of mare basalts (240 My after solar system formation) might reflect the timing of a large impact. Our results demonstrate that lunar magma ocean crystallization took place while the Moon was still battered by planetary embryos and planetesimals leftover from the main stage of planetary accretion. The study of Lu–Hf model ages for samples brought back from the South Pole-Aitken basin will help to assess the lateral continuity of KREEP and further understand its significance in the early history of the Moon. 

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5. Tectonothermal Evolution of the NW Wyoming Province: Insights From Coupled Garnet Lu‐Hf and Sm‐Nd Geochronology

   https://doi.org/10.1111/jmg.70006  

   Chen, Tsai‐Wei; Vervoort, Jeff; Baldwin, Julia; Baker, Peter (October 2025, Journal of Metamorphic Geology)

   ABSTRACT Understanding how Paleoproterozoic orogenic processes shaped the assembly of Laurentia remains a critical puzzle in deciphering Earth's ancient tectonic history. To address this challenge, the Montana metasedimentary terrane in the northwest Wyoming Province, which preserves a complex record of multiple metamorphic episodes, provides a unique opportunity. In this study, we integrate garnet composition with coupled Lu‐Hf and Sm‐Nd geochronology to unravel the polymetamorphic history of this terrane and constrain the timing and mechanisms of orogenic processes. Our new garnet Lu‐Hf and Sm‐Nd ages reveal three distinct age groups: 2.42, 2.19–2.06 and 1.83–1.70 Ga. Most analysed garnet samples demonstrate typical prograde zoning patterns with enriched Mn and Lu contents in their core, suggesting that the Lu‐Hf ages from these samples reflect the timing of prograde metamorphism. The ~30 Myr younger Sm‐Nd ages for most samples document the cooling process that followed peak metamorphic conditions during the orogenic cycle. One amphibolite sample shows reverse Lu zoning that likely resulted from mineral breakdown reactions, suggesting complex trace‐element incorporation during high‐grade metamorphic processes. By integrating our age data with the estimated peak metamorphic conditions reported by previous studies, we identify a spatial and temporal trend of decreasing metamorphic grade that progressed southeastward from the northwestern boundary of the terrane between 1.8 and 1.7 Ga. This pattern reveals a propagation of orogenic activity during the Big Sky orogeny, providing insights into the thermal evolution and incorporation of terranes during Laurentia assembly. 

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