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1. U-Pb and Lu-Hf isotopic evolution of ∼3.6 Ga remnants in NE Brazil – Implications on Eo-Paleoarchean global crustal evolution

   https://doi.org/10.1016/j.chemgeo.2025.122646  

   Botero, Manuela; Vervoort, Jeffrey D; Meira, Vinicius T; Martins_de_Sousa, Daniel F; Santos, Ticiano JS (April 2025, Chemical Geology)

   NA (Ed.)

   Precambrian terrains preserving rocks older than 3.5 Ga contain an essential record of the crustal evolution of the primitive Earth. In this study, we investigated Eo-Paleoarchean rocks from the northern S˜ao Francisco Craton (NSFC) and the Borborema Province in northeastern Brazil to contribute to a more complete global isotopic record of this pivotal time in Earth’s history. Zircon U-Pb ages along with zircon Hf isotope compositions were obtained for migmatitic gneiss complexes in both terrains. Zircon U-Pb data from the NSFC yield well-defined populations with 207Pb/206Pb ages from 3.61 to 3.59 Ga and younger components at ~3.5 and ~3.4 Ga. Similarly, the Borborema Province gneiss yields a main zircon age population of 3.58 Ga and a younger ~3.5 Ga age component. The ~3.6 Ga zircon components yield consistently sub-chondritic Hf isotopic compositions with initial εHf between −1.9 and −3.1 for the NSFC and of εHf −0.5 for the Borborema Province. Gneisses from northeastern Brazil record a main crust forming period at 3.65–3.60 Ga with sub-chondritic Hf isotope compositions that indicate derivation from melting of a ~3.8 Ga source of broadly chondritic isotope composition, similar to that of many Eo-Paleoarchean gneisses worldwide. This Hf isotope record supports the existence of broadly chondritic mantle reservoir in the Eoarchean with development of depleted mantle and the appearance of evolved crust later in the Paleoarchean. 

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2. U-Pb and Lu-Hf isotopic evolution of ~ 3.6 Ga remnants in NE Brazil – Implications on Eo-Paleoarchean global crustal evolution

   Botero, M; Vervoort, J; Meira, V; Martins_de_Sousa, Daniel F; Santos, T (October 2024, Chemical geology)

   NA (Ed.)

   Precambrian terrains preserving rocks older than 3.5 Ga contain an essential record of the crustal evolution of the primitive Earth. In this study, we investigated Eo-Paleoarchean rocks from the northern S˜ao Francisco Craton (NSFC) and the Borborema Province in northeastern Brazil to contribute to a more complete global isotopic record of this pivotal time in Earth’s history. Zircon U-Pb ages along with zircon Hf isotope compositions were obtained for migmatitic gneiss complexes in both terrains. Zircon U-Pb data from the NSFC yield well-defined populations with 207Pb/206Pb ages from 3.61 to 3.59 Ga and younger components at ~3.5 and ~3.4 Ga. Similarly, the Borborema Province gneiss yields a main zircon age population of 3.58 Ga and a younger ~3.5 Ga age component. The ~3.6 Ga zircon components yield consistently sub-chondritic Hf isotopic compositions with initial εHf between −1.9 and −3.1 for the NSFC and of εHf −0.5 for the Borborema Province. Gneisses from northeastern Brazil record a main crust forming period at 3.65–3.60 Ga with sub-chondritic Hf isotope compositions that indicate derivation from melting of a ~3.8 Ga source of broadly chondritic isotope composition, similar to that of many Eo-Paleoarchean gneisses worldwide. This Hf isotope record supports the existence of broadly chondritic mantle reservoir in the Eoarchean with development of depleted mantle and the appearance of evolved crust later in the Paleoarchean. 

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3. Crustal Architecture of the Paleo‐Pacific Rift Margin of East Antarctica: Evidence From U‐Pb Ages and O‐Hf Isotope Compositions of Ross Orogen Granitoids

   https://doi.org/10.1029/2024GC011435  

   Goodge, John W.; Fanning, C. Mark; Fisher, Christopher M.; Vervoort, Jeffrey D. (April 2024, Geochemistry, Geophysics, Geosystems)

   Abstract Granitic batholiths of the ∼500 Ma Ross Orogen in Antarctica are voluminous in scale, reflecting prolific magmatism along the active early Paleozoic convergent margin of Gondwana. New age and isotopic analysis of zircons from a large suite of Ross granitoids spanning >2,000 km along the orogen provide a wealth of geochronologic, tracer, and inheritance information, enabling us to investigate the pace of magmatism, along‐strike temporal and geochemical trends, magmatic sources, and tectonic modes of convergence. Because granitoids penetrate the crust of the earlier Neoproterozoic rift margin, they also provide insight into the age and composition of the largely ice‐covered East Antarctic craton. Zircon U‐Pb ages from these and other samples indicate that active Ross magmatism spanned 475–590 Ma, much longer than generally regarded. Most samples have heavy zircon δ¹⁸O values between 6.5 and 11.5‰ and initial ε_Hfcompositions between 0 and −15; their isotopic co‐variations are independent of age, as in other contemporary continental arcs, and reflect largely crustal melt sources. Samples near Shackleton Glacier have distinctly more mantle‐like isotope composition (i.e., radiogenic ε_Hfand low δ¹⁸O) and separate two regions with distinctive isotopic properties and inheritance patterns—a more juvenile section of Mesoproterozoic crust underlying the southern TAM and an older, more evolved region of Paleoproterozoic and Archean crust in the central TAM. The isotopic discontinuity separating these regions indicates the presence of a cryptic crustal boundary of Grenvillian or younger age within the East Antarctic shield that may be traceable into the western Laurentian part of the Rodinia supercontinent. 

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4. 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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5. Detrital zircon record of Phanerozoic magmatism in the southern Central Andes

   https://doi.org/10.1130/GES02346.1  

   Capaldi, T.N.; McKenzie, N.R.; Horton, B.K.; Mackaman-Lofland, C.; Colleps, C.L.; Stockli, D.F. (May 2021, Geosphere)

   null (Ed.)

   Abstract The spatial and temporal distribution of arc magmatism and associated isotopic variations provide insights into the Phanerozoic history of the western margin of South America during major shifts in Andean and pre-Andean plate interactions. We integrated detrital zircon U-Th-Pb and Hf isotopic results across continental magmatic arc systems of Chile and western Argentina (28°S–33°S) with igneous bedrock geochronologic and zircon Hf isotope results to define isotopic signatures linked to changes in continental margin processes. Key tectonic phases included: Paleozoic terrane accretion and Carboniferous subduction initiation during Gondwanide orogenesis, Permian–Triassic extensional collapse, Jurassic–Paleogene continental arc magmatism, and Neogene flat slab subduction during Andean shortening. The ~550 m.y. record of magmatic activity records spatial trends in magma composition associated with terrane boundaries. East of 69°W, radiogenic isotopic signatures indicate reworked continental lithosphere with enriched (evolved) εHf values and low (<0.65) zircon Th/U ratios during phases of early Paleozoic and Miocene shortening and lithospheric thickening. In contrast, the magmatic record west of 69°W displays depleted (juvenile) εHf values and high (>0.7) zircon Th/U values consistent with increased asthenospheric contributions during lithospheric thinning. Spatial constraints on Mesozoic to Cenozoic arc width provide a rough approximation of relative subduction angle, such that an increase in arc width reflects shallower slab dip. Comparisons among slab dip calculations with time-averaged εHf and Th/U zircon results exhibit a clear trend of decreasing (enriched) magma compositions with increasing arc width and decreasing slab dip. Collectively, these data sets demonstrate the influence of subduction angle on the position of upper-plate magmatism (including inboard arc advance and outboard arc retreat), changes in isotopic signatures, and overall composition of crustal and mantle material along the western edge of South America. 

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