Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


This content will become publicly available on May 1, 2027

Title: Tracking Archean crustal evolution of the Zimbabwe Craton through U-Pb geochronology and Hf isotopes
Not AvailableThe ancient history of the Earth is marked by pivotal times recorded in Precambrian terrains, providing crucial insight into the evolution of the crust-mantle system and the geodynamic processes operating in the evolving Earth. This research focuses on the Zimbabwe craton, an important ancient terrain where fundamental concepts of Archean tectonics were first defined and that remains largely uncharacterized by high-precision isotope studies. We integrate in-situ LA-ICPMS zircon U-Pb ages and Hf isotope compositions of magmatic samples and river sands to investigate the Paleo- and Meso-Neoarchean (∼3.6–3.3 Ga and ∼2.9–2.7 Ga) crustal evolution of the craton. Zircon U-Pb data from gneiss complexes and granites within the central part of the craton, which encompasses the Sebakwe proto-craton that experienced tectonic stability temporarily between 3.3 and 3.0 Ga ago, define a main magmatic event at 3.6–3.5 Ga and minor components at ∼3.3 Ga, ∼2.9 Ga, and 2.7 Ga. Outside of the central part of the craton within the Odzi-Mutare area the magmatic record is dominated by zircon U-Pb ages between 2.9 and 2.8 Ga. A similar age distribution is recorded by detrital zircon from modern sediments with age clusters in the Paleoarchean at 3.6–3.5 Ga and 3.4–3.3 Ga, with the latter being more prominent, and in the Meso-Neoarchean at 2.9–2.8 Ga and 2.6 Ga. The Paleoarchean magmatic components yield Hf isotope compositions within 4 epsilon units of CHUR (ƐHf(3.6-3.3Ga) + 2 to –4), similar to the isotope compositions of detrital zircons (ƐHf(3.6-3.3Ga) + 2 to –6). Meso-Neoarchean magmatic components yield Hf isotope compositions with ƐHf(i) between CHUR and +2 at ∼2.9–2.8 Ga, while detrital zircons range from ƐHf(i) + 4 to –9 at ∼2.9–2.6 Ga. Data from the Zimbabwe craton indicate crust formation in the Paleoarchean (3.6–3.3 Ga) that involved juvenile magma additions and a possible derivation from a ∼3.8 Ga chondritic source and craton-wide crust forming episodes between ∼2.9 and 2.6 Ga that involved crustal reworking in various degrees along with new additions of juvenile material. The Hf isotope record of the Zimbabwe craton aligns with the global isotope record—with chondritic to sub-chondritic Hf isotope compositions at ∼3.7–3.6 Ga, the appearance of juvenile additions after ∼3.5 Ga, and mixing trends after ∼3.0 Ga—supporting formation of a long-lived depleted mantle reservoir after ∼3.6 Ga.  more » « less
Award ID(s):
2222254
PAR ID:
10688583
Author(s) / Creator(s):
; ;
Publisher / Repository:
Elsevier
Date Published:
Journal Name:
Geochimica et Cosmochimica Acta
ISSN:
0016-7037
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; (, 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. 
    more » « less
  2. ; ; ; ; (, 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. 
    more » « less
  3. ; ; (, Earth and Planetary Science Letters)
    The Hf and Nd isotope records from Earth’s earliest history are essential for understanding the processes of crustmantle evolution in the early Earth. These records, however, have been largely obtained from bulk-rock samples that have often been compromised by post-crystallization processes. Complexities resulting from open-system behavior and mixing of different components are reflected in heterogeneous Eo-Paleoarchean bulk-rock Hf and Nd isotope records. In this study, we integrate in-situ Sm-Nd isotope analyses of REE-rich minerals with U-Pb titanite geochronology to assess the reliability of the bulk-rock isotope record in ~3.6 Ga gneisses from the northern S˜ao Francisco Craton (NSFC). Our results demonstrate that Nd isotope compositions of minerals controlling the elemental budget in rocks provide a more robust record of the early Earth. The NSFC mineral phases preserving primary signatures have chondritic ƐNd(i) (0.0 to +0.3) at their crystallization ages (~3.6 Ga). In contrast, bulk-rock Hf and Nd isotope compositions exhibit extreme heterogeneity (i.e. ƐNd(i) +4 to −12 ƐHf(i) +8 to −14) reflecting post-crystallization disturbances at 2.5–2.0 Ga. When mineral phases in these rocks have Sm- Nd isochron ages that agree with their U-Pb crystallization ages, their initial Nd isotope compositions are consistent with the zircon Hf isotope data. These findings align with global zircon Hf isotope data, which indicate a chondritic mantle reservoir until ~3.8 Ga, with evidence of significant mantle depletion and crustal differentiation emerging in the isotope record thereafter. This study underscores the importance of mineral-scale isotope investigations in refining interpretations of early crust-mantle evolution and the mechanisms affecting bulk-rock isotope records in Precambrian terranes. 
    more » « less
  4. ; ; (, Geological Society of America Bulletin)
    The Montana metasedimentary terrane in the northern Wyoming Province provides valuable insight into crustal formation and reworking processes along the cratonic margin and offers a unique opportunity to decipher the complex Neoarchean−Paleoproterozoic terrane assembly in southwestern Laurentia. We report new zircon U-Pb dates and Hf isotopes from seven metaigneous samples in the northwestern Montana metasedimentary terrane. The internal textures of zircon in this study are complex; some lack inherited cores and metamorphic overgrowths, while others exhibit core-rim relationships. Based on the cathodoluminescence (CL) features, we interpret these grains to be magmatic populations. These data demonstrate discrete igneous pulses at 2.7 Ga, 2.4 Ga, and 1.7 Ga, which indicate significant crustal formation intervals in the Montana metasedimentary terrane. Zircons at 2.7 Ga have positive εHf values (+2.4 to +0.9) that indicate a depleted mantle source. Most 2.4 Ga and 1.7 Ga samples have negative εHf values (−1.6 to −15.5), which indicate significant contributions from preexisting crust. Two 1.7 Ga samples, however, have near-chondritic εHf values (+0.4 to +0.3) that indicate larger juvenile contributions. The time-integrated Hf isotope trend suggests that the Paleoproterozoic zircons were produced from a mixture of older crust and juvenile mantle inputs. Additionally, the isotopic age fingerprint of the Montana metasedimentary terrane suggests that it differs from northern-bounding terranes. Viewed more broadly, the 2.7 Ga and 1.7 Ga age peaks that the Montana metasedimentary terrane shares with the global zircon age spectrum suggest that the drivers of these events in the Montana metasedimentary terrane were common throughout the Earth and may be associated with the assembly of supercontinents Kenorland and Nuna. 
    more » « less
  5. ; ; ; (, Geochimica et Cosmochimica Acta)
    Iizuka, Tsuyoshi (Ed.)
    Zircon trace element geochemistry has become an increasingly popular tool to track crustal evolution through time. This has been especially important in early-Earth settings where most of the crust has been lost, but in some fortuitous instances detrital zircons derived from that lost crust have been preserved in younger sediments. To study the formation and geochemical evolution of continental crust from the Hadean to the Paleoarchean, the 3.6 to 3.2 Ga Barberton Greenstone Belt in southern Africa is an excellent target due to its outstanding preservation and presence of detrital zircons that span almost a billion years. Here, we use trace elements, in combination with hafnium and oxygen isotopes, of 3.65 to 3.22 Ga detrital and tuffaceous zircons of the Moodies and Fig Tree groups and compare their geochemistry to previously studied 4.2 to 3.3 Ga detrital zircons from the Green Sandstone Bed of the Onverwacht Group. The major detrital zircon age clusters in the former at 3.55 Ga, 3.46 Ga, and 3.26–3.23 Ga overlap with episodes of TTG emplacement and felsic volcanism in the Barberton area, suggesting a local provenance. In contrast, age clusters at 3.65 Ga and 3.29 Ga of the Moodies and Fig Tree groups as well as 4.2 to 3.3 Ga detrital zircons from the Green Sandstone Bed do not have known intrusive sources and were likely derived from outside the present-day Barberton belt. This indicates that more than half of the felsic igneous events in the detrital zircon record do not have a whole-rock representation that can be directly studied. The similar compositions and inferred crustal evolution histories recorded in zircons from the Fig Tree and Moodies groups, as well as from the Green Sandstone Bed, suggest that they were derived from connected terranes experiencing similar crustal processes diachronously. Together, they show three phases of felsic continent formation, reflecting different crustal processes: (1) long-lived protocrust formed in the Hadean from undepleted mantle sources. These zircons are vastly different from younger zircons and, hence, Barberton TTGs are not good analogues of Hadean crust formation. (2) At 3.8 Ga, onset of significant crustal growth though cyclic juvenile additions and hydrous melting, possibly within a volcanic plateau setting but an arc-like setting cannot be excluded based on this data. (3) Between 3.4 and 3.3 Ga, felsic crust is generated through a previously unrecognized episode of crustal growth by shallow melting of mafic, mantle-derived sources. This is immediately followed by the onset of crustal thickening through the transport of surface-altered, hydrated materials to deep crustal levels. Since there is geological evidence for extension and shortening at that time this may reflect the onset of horizontal movement. Whether this last geodynamic setting reflects modern-style plate tectonics or not, continent formation and the onset of plate tectonics in the Barberton area occurred through complex multi-stage processes spanning almost a billion years, most of which is only accessible through the detrital zircon record. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Text Encoded Conversion
  • XML
  • Save / Share this Record
  • Send to Email