PICO
In this session, we encourage the presentation of new approaches that improve our understanding on the formation, structure, and evolution of the early Earth ranging from the mantle and lithosphere to the atmosphere, oceans and biosphere, and interactions between these reservoirs.
This session aims to bring together scientists from a large range of disciplines to provide an interdisciplinary and comprehensive overview of the field. This includes, but is not limited to, fields such as early mantle dynamics, the formation, evolution and destruction of the early crust and lithosphere, early surface environments and the evolution of the early biosphere, mineral deposits, and how possible tectonic regimes impacted across the early Earth system.
PICO: Wed, 30 Apr | PICO spot 1
Kimberlites are exclusively found on cratons, some of which have remained stable for more than 3 billion years. Kimberlite melts are generated at temperatures of at least 1300°C and pressures of 5–7 GPa, corresponding to depths of 160–250 km. Cratons, being thicker than normal lithosphere, are thus natural hosts for kimberlite melts. Analyzing the frequency of kimberlite eruptions over time, we found that their frequency gradually increased after 1.5 Gyr. Notably, before 2 Gyr, only 4-5 records of kimberlite eruptions have been documented. As kimberlites are found on stable cratons, preservation bias due to tectonic or erosional destruction may not fully explain the scarcity of older kimberlites. This paucity motivated us to explore a potential correlation between craton thickness and kimberlite frequency. Analysing previous studies we hypothesize that, initially, cratons were less than 150 km thick — below the kimberlite stability depth – and they have thickened over time, eventually reaching depths conducive to kimberlite stability. Mechanisms for craton growth remain poorly understood, although gravitational thickening and self-compressive thickening have been proposed. To investigate these mechanisms within the context of supercontinental cycles, we developed 2D box models using the finite element code ASPECT. Starting with a 150 km thick craton, we allowed mantle flow to evolve over 3 Gyr. Due to their high viscosity and thickness, cratons can divert mantle flow, creating a self-compressive environment during supercontinental assembly. During supercontinental breakup, mantle flow generates an extensional environment that thins the craton. We simulated four supercontinental cycles corresponding to Superia, Columbia, Rodinia, and Pangea. Our results show that cratons became progressively thicker during each cycle. After 1.5 Gyr, craton thickness increased to approximately 160 km, entering the kimberlite stability field. By the time of the Rodinia assembly, craton thickness had reached levels suitable for diamondiferous kimberlite formation, potentially explaining the sudden increase in kimberlite eruptions around 1.1 Ga. We tested various parameters, including viscosity, density, initial thickness, and craton width, against different background mantle flow velocities. Our preliminary results suggest that the gradual thickening of cratons after 1.5 Gyr increased the likelihood of kimberlite eruptions on Earth.
How to cite: Paul, J. and Conrad, C. P.: Slow Thickening of Cratons Has Increased Kimberlite Frequency Over Time, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6167, https://doi.org/10.5194/egusphere-egu25-6167, 2025.
The dynamics of Earth’s early mantle and the timing of the onset of plate tectonics remain a topic of debate. Proposed hypotheses for the Archaean eon range from a stagnant-lid Earth all the way to modern-style plate tectonics. Here, we estimate temperatures and depths of melt generation in the late Archaean mantle using a new geochemical data compilation of mafic igneous rocks from the Yilgarn craton, Australia. We combine these results with stratigraphic and geodynamic constraints to resolve the tectonic regime and upper mantle dynamics at the time.
Primitive volcanic rocks can preserve signatures of the melting processes in the mantle: depth and temperature of melting are recorded in magma major and trace element chemistry. We have collated a data compilation of mafic volcanic samples from the Archaean Yilgarn craton in Western Australia. In order to identify those samples most representative of melting conditions in the convecting mantle, the data were screened to minimise the effects of crystal fractionation and assimilation of crustal or cumulate material (9 wt% < MgO < 15 wt%; no Eu anomalies, no positive Pb anomalies; Nb/U > 30). We further correct these screened compositions for olivine fractionation. This screened dataset predominantly comprises tholeiitic basalts in the Kalgoorlie terrane that erupted prior to the main komatiite sequence and the felsic magmas that make up the bulk of the Yilgarn cratonic crust. The mafic compositions investigated here therefore represent melting conditions immediately before the onset of cratonisation.
The screened data display depleted, MORB-like rare earth element patterns with no evidence of a garnet signature. Forward and inverse geochemical modelling of these compositions, assuming a primitive mantle source, predicts melting at depths as shallow as ~40 km and mantle potential temperatures elevated by ~200 °C compared to present-day ambient mantle. These results are consistent with melting of a rising plume head combined with moderate extension of the pre-existing lithospheric lid.
How to cite: Klöcking, M., Czarnota, K., Campbell, I. H., Smithies, H., Champion, D. C., and Davies, D. R.: Late Archaean basalts from the Yilgarn craton record evidence of thin lithosphere prior to cratonisation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10905, https://doi.org/10.5194/egusphere-egu25-10905, 2025.
The initiation of plate tectonics marks a pivotal moment in Earth's geological history, shaping its surface dynamics and influencing its habitability. Despite its significance, the mechanisms that triggered the onset of plate tectonics during the early Earth remain a subject of active debate, with several mechanisms that may have existed prior to Plate tectonics (PT), and might have gradually evolved into or abruptly triggered PT., e.g. crustal resurfacing, crustal overturn, sagduction, plume induced subduction, formation of reworked crust, damage induced plate boundary formation and plutonic squishy lid regime. In this study, we investigate how localized lithospheric weakening, potentially driven by mantle plumes and/or melt, could have contributed to the emergence of plate tectonics. Using 2D numerical simulations developed with the ASPECT geodynamic code, we explore the conditions under which these mechanisms may operate. To investigate these processes, a parameter sensitivity study that explores the effects of mantle and crustal rheological properties and ambient mantle temperature have been carried out. We will present the preliminary results of this work which provides new insights into the complex interplay of lithosphere and mantle processes that could have driven the emergence of plate tectonics, offering a framework for reconciling diverse hypotheses.
How to cite: Roy, P., van Hunen, J., Pons, M., and Chakraborty, A.: Lithosphere-Mantle Interactions and Weakening Processes in Early Earth: Implications on the onset of Plate Tectonics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11656, https://doi.org/10.5194/egusphere-egu25-11656, 2025.
Plate tectonics is central to the long-term release of heat from Earth’s deep interior, which ultimately maintains habitability, but its time of onset is highly debated. Early Archean granitic domes surrounded by greenstones provide evidence for gravitational reorganization of the crust and dominance of vertical tectonics distinct from plate tectonics. However, because plate tectonics is a kinematic framework, a measure of motion such as that provided by paleomagnetism is needed for direct tests. The East Pilbara craton (Western Australia) preserves classic Paleoarchean to Mesoarchean granite-greenstone geology, but paleomagnetic data from these rocks have been interpreted as tracing modern plate tectonic velocities. Herein, we report new paleomagnetic data from granite, basalt and dacite ranging in age from 3.49 to 3.2 Ga from the East Pilbara craton and find that these carry a 2.7 Ga reset magnetization, a pattern seen in data throughout the craton. The recognition of this resetting resolves the conflict with the geological record, and together with other paleomagnetic results from the Kaapvaal (South Africa) and the Yilgarn (Western Australia) cratons define a 600 myr-long transition between stagnant lid tectonics and modern plate tectonic motions, the latter beginning ca. 3.0 to 2.7 billion years ago.
How to cite: Cottrell, R., Bono, R., and Tarduno, J.: Modern plate tectonic motions commenced after formation of voluminous Paleoarchean to Mesoarchean TTG crust , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7331, https://doi.org/10.5194/egusphere-egu25-7331, 2025.
Stepwise Pb-Pb leaching (PbSL) is a silicate digestion technique based on sequential acid treatment of a mineral, resulting in the selective recovery of radiogenic and common Pb from the crystal lattice. This technique has proven effective for directly dating rock-forming silicates associated with metamorphic reactions that define a PT path. Two Paleoarchean granitoids from the Bastar craton were selected for this study; one is a ~3.5 Ga orthopyroxene-bearing basement tonalite sample near Nagaras, CH13 [1] and the other is the ~3.6 Ga ‘true granite’ sample near Dalli-Rajhara [2], resampled as C30. Orthopyroxene (Opx) and microcline (Mc) grain separates were leached in multiple steps using HBr, HNO3, and HF acids [3]. Lead was separated and purified using 100 µL and 10µL AG1-X8 anion exchange resin using HNO3 – HBr chemistry, and the purified Pb fraction was dissolved in 0.2% HNO3 solution. Lead isotope ratios were measured on a Thermo-Fisher Scientific Neptune Plus MC-ICPMS at the Indian Institute of Technology (IIT) Kharagpur, India, using a novel approach of combining Thallium-doping with sample-standard bracketing. Two multi-grain Opx fractions from sample CH13 yielded a combined Pb-Pb isochron age of 3594±95 Ma (2σ error, MSWD = 8.3, n = 11), which is slightly older than the zircon U-Pb crystallization age of 3453±21 Ma [1]. Therefore, sample CH13 is a Paleoarchean charno-enderbite formed at lower crustal depths. In contrast, Mc separated from sample C30 yielded a Pb-Pb isochron age of 3189±3 Ma (2σ error, MSWD = 1.3, n = 5), which confirms that despite an older zircon U-Pb crystallization age, this sample is not a ~3.6 Ga ‘true granite’ but is a product of a later ~3 Ga partial melting event, related to the Mesoarchean Sukma orogeny [1].
[1] Nandi, A., Mukherjee, S., Sorcar, N., and Vadlamani, R., 2023, Relict Mesoarchean (2.99–2.94 Ga) metamorphism overprinted by late Neoarchean tectonothermal event(s) from the Sukma Group supracrustal rocks, Bastar craton, India: Evidence from new Lu-Hf and Sm-Nd garnet isochron and Th-U-total Pb monazite ages: Precambrian Research, v. 390, p. 107056.
[2] Rajesh, H. M., Mukhopadhyay, J., Beukes, N. J., Gutzmer, J., Belyanin, G. A., and Armstrong, R. A., 2009, Evidence for an early Archaean granite from Bastar craton, India: Journal of Geological Society, London, v. 166, p. 193 – 196.
[3] Frei, R., and Kamber, B. S., 1995. Single mineral Pb-Pb dating. Earth and Planetary Science Letters, 129(1-4), 261 – 268.
How to cite: Nandi, A. and Vadlamani, R.: Constraining timing of early Archean magmatism using stepwise Pb-Pb leaching (PbSL) dating from the Bastar Craton, central India, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-875, https://doi.org/10.5194/egusphere-egu25-875, 2025.
Mount Isa Inlier, located in northwest Queensland, consists of multiple Proterozoic volcano-sedimentary sequences intruded, deformed and metamorphosed during a complex tectonic history between ~1880 Ma and ~1490 Ma. The stratigraphy of the Mount Isa Inlier is generally interpretated to reflect the superposition of three major superbasin events, marked by discontinuities, and deformed and metamorphosed during the Isan Orogeny (1620-1500 Ma). The superbasin model proposes continuation of stratigraphy along the length of the inlier and the existence of corelative units across the inlier. According to this model, the stratigraphy in the Dajarra region (southern part of Western Fold Belt) consists of a series of units that are either continuous with or can be corelated along strike with units that occur further north. The oldest units are the Bottletree Formation and the Lower Haslingden Group, characterized by bimodal volcanics and siliciclastic rocks which were deposited during the 1800-1780 Ma Leichardt Superbasin. These units were unconformably overlain by the Warrina Park Quartzite and the Moondarra Siltstone accumulated during the 1690-1670 Ma Calvert Superbasin. However, there is no geochronological data available from the sedimentary units in the Dajarra region and these correlations remain speculative. In this study, we report new LA-ICP-MS ages from magmatic and detrital zircons that can help constrain the magmatic and sedimentary history of the rocks occurring in this region and evaluate the existing stratigraphic correlations. Two new magmatic events, between 1810-1780 Ma and between 1710-1690 Ma, are identified in the southern part of the Western Fold Belt. The detrital zircon data indicates that (1) siliciclastic rocks mapped as the Mount Guide Quartzite have the youngest detrital populations between 1885 Ma and 1850 Ma; (2) siliciclastic sediments from the Eastern Creek Volcanics and the Jayah Creek Metabasalt have the youngest detrital zircon populations between 1870 and 1850 Ma; (3) siliciclastic rocks mapped as the Timothy Creek Sandstone and as the Mount Isa Group have the youngest detrital populations between 1820 and 1780 Ma. The maximum depositional ages obtained in this study are significantly older compared to the same stratigraphic units mapped to the north indicating either a different source or that these units are indeed much older and represent a different stratigraphy not previously recognized in the Mount Isa Inlier.
How to cite: Noptalung, S., Sanislav, I., and McCoy-West, H.: New constraints on the timing of magmatism and sedimentation in the Dajarra region, southern area of Western Fold Belt, Mt Isa Inlier, Australia: implication for stratigraphic successions during Paleoproterozoic , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2666, https://doi.org/10.5194/egusphere-egu25-2666, 2025.
The Namibe Group represents the largest package of immature supracrustal rocks of the Angola Shield (Congo Craton), occupying an area of nearly 10,000 km2 in the Namibe Zone (NZ). It is a folded, steeply dipping, meta-volcanosedimentary sequence essentially comprising immature micaschists and greywackes, felsic metavolcaniclastites, along with intercalated marbles and amphibolites. The metavolcanosedimentary sequence is intruded by ca. 1810–1790 Ma ultramafic to felsic plutonic rocks with magmatic arc geochemical signatures. Despite its importance, key aspects such as its maximum depositional age (MDA), sedimentary provenance, and the detrital zircon (DZ) record of crustal evolution remain unresolved. This study presents LA-ICP-MS U-Pb and Lu-Hf DZ analyses from nine NG samples.
The results reveal a dominant cluster of MDAs between 1840 ± 6 Ma and 1820 ± 5 Ma, with two samples yielding older MDAs of 1867 ± 15 Ma and 1880 ± 13 Ma. These findings establish a late-Orosirian age for the NG, refuting earlier proposals of an Archean age. The DZ age distributions are dominated by a prominent youngest peak, with most ages clustering near the MDA. These patterns resemble those of active magmatic arc basin deposits, indicating a convergent plate margin setting for NG deposition.
The provenance for all DZs can be explained by sources internal to the SW Angolan Shield, apart from a minor (8%) Rhyacian age fraction (~2.08 and ~2.14 Ga), for which no rocks of this age have been identified in the Angolan Shield. Approximately 63% of the DZs are late-Orosirian (1.82–1.90 Ga), with a predominant component at ~1.83 Ga and a minor one at ~1.87 Ga. These zircons were likely sourced from the extensive magnesian, calc-alkaline granitoids of the Epupa Metamorphic Complex (EMC: ~1.86–1.76 Ga), the Kamanjab Inlier (~1.88–1.80 Ga), the NZ (~1.83–1.79 Ga), and/or ~1.84–1.80 Ga plutons intruding the Central Eburnean Zone (CEZ: 2.04–1.95 Ga). Older DZ populations comprise 23% early-Orosirian (Eburnean) ages (peaks at ~1.92, ~1.97, and ~2.01 Ga) and 6% Archean ages (2.50–3.52 Ga). These Eburnean and Archean DZs were likely sourced from the CEZ and/or Cassinga Zone in southern Angola, and/or the Sesfontein-Grootfontein-Tsumkwe-Quangwadum inliers in northern Namibia.
Archean DZs exhibit mostly subchondritic Hf compositions, indicating significant crustal reworking. This trend persisted during Rhyacian to early Orosirian times, with 88% of DZs displaying markedly negative εHf(i) values. In contrast, most late Orosirian DZs (86%) plot above the crustal evolution trend of older ones, reflecting a marked shift toward slightly subchondritic to suprachondritic εHf(i) values and younger TDM2 model ages. This trend indicates a substantial increase in the contribution of juvenile material to magma generation in late-Orosirian times.
This isotopic shift is also observed in late-Orosirian granitoids of the NZ and EMC, likely reflecting a fundamental geodynamic transition from a period dominated by crustal reworking to juvenile accretion within this part of the Angolan Shield. Our data show that significant continental growth took place in the southwestern margin of the Angolan Shield (Congo Craton) in late-Orosirian times, during the assembly of Columbia.
How to cite: Ferreira, E., Lehmann, J., Feliciano Rodrigues, J., Bravo Silva, P., Owen-Smith, T., Garcia Lobón, J. L., Correia, J., Ueckermann, H., Molekwa, M. A., Manuel, J., and da Mata Lourenço Victorino, A.: Namibe Group detrital zircon U-Pb and Lu-Hf isotopes: a testimony of late-Orosirian (1.9–1.8 Ga) crustal growth in the Angolan Shield (Congo Craton), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18911, https://doi.org/10.5194/egusphere-egu25-18911, 2025.
The Manamedu Ophiolite Complex (MOC) within the Palghat-Cauvery Suture Zone (PCSZ) in southern India comprises metamorphosed equivalents of mafic–ultramafic group of rocks including pyroxenite and dunite with locally cumulate textures; gabbroic rock types including gabbro, gabbronorite, and anorthosite; sheeted mafic dykes of amphibolite to meta-andesite and plagiogranite; a thin layer of ferruginous cherts. The tectonic discrimination of these rocks based on various geochemical plots shows that they were related to island arc tholeiite (IAT) group with tholeiitic to calcalkaline signatures. Most of the samples (hornblendite, anorthosite, and amphibolite) have similar chondrite-normalized rare earth element patterns characterized by light REE enrichment, slightly Eu anomaly, and flat heavy REE profiles, except plagiogranite has a significant Eu anomaly. In the primitive mantle-normalized spidergram, all samples show depletion in HFSE (P, Zr, Sm, Ti, and Y) and enrichment of LILE (Rb, Ba, Th, Sr) with negative Nb anomalies. The petrological and geochemical characteristics of the lithological association of MOC represent the remnants of an oceanic crust, which may be formed in a suprasubduction zone geodynamic environment.
How to cite: Chen, N. H.-C.: Geochemical and petrological study of the Manamedu Ophiolite Complex, Cauvery suture zone, southern India, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4628, https://doi.org/10.5194/egusphere-egu25-4628, 2025.
Original phases of the Proterozoic Iron Formations (IFs) have been considered as essential archives of paleo-seawater geochemistry. It is widely acknowledged that hydrated ferric oxides/hydroxides were the primary precursor phase. However, the significance of high silica concentrations in Precambrian seawater has been receiving increasing attention for understanding the original iron mineralogy. Recent studies have provided compelling evidence that Fe(II)-silicates were the predominant precursor phases of IFs.
In this study, we identified the Fe-illite cortices within ooids from the Paleoproterozoic Chuanlinggou Iron Formation, located on the northern margin of the North China Craton. The Fe-illite, characterized by an Fe(II)/Fetotal ratio of approximately 20%, exhibits tangentially arranged crystals probably formed by wave action in reducing environments. There is considerable hematite within the Fe-illite cortices, which can be categorized into striped and granular types. Striped hematite is tangentially arranged alongside the Fe-illite, and its rare earth element (REE) patterns exhibit heavy rare earth element (HREE) enrichment, similar to Fe-oxide cortices. In contrast, Fe-illite associated with granular hematite exhibits light rare earth element (LREE) enrichments. We propose the Fe-illite cortices reflect the original Fe-smectite precipitation from paleo-seawater under alkaline conditions, and striped hematite represents the original mineral phase during the formation of the Fe-smectite cortices. Furthermore, the Fe-illite cortices exhibit orders-of-magnitude enrichment in biological elements compared to Fe-oxide cortices. It is noticeable that similar clay-hematite association has been reported in the Paleoproterozoic Yunmengshan oolitic ironstone from the southern margin of the North China Craton (Qiu et al., 2020). These findings indicate specific solution chemistry and potential biological influences at the craton margins during the Proterozoic era.
References
Qiu, Y., Zhao, T. and Li, Y. (2020) The Yunmengshan iron formation at the end of the Paleoproterozoic era. Applied Clay Science 199, 105888.
How to cite: Li, Y., Lu, X., Cui, X., Liu, H., Liu, J., and Cai, Y.: Clay-hematite Association in Late Paleoproterozoic Oolitic Ironstones of the North China Craton , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10015, https://doi.org/10.5194/egusphere-egu25-10015, 2025.
The ocean pH is a fundamental property regulating various aspects of Earth system evolution. However, the early ocean pH remains controversial, with estimates ranging from strongly acidic to alkaline. Here we develop a model integrating global carbon cycling with ocean geochemistry, and incorporating continental growth and mantle thermal evolution. By coupling global carbon cycle with ocean charge balance, and by using solid Earth processes of mantle degassing and crustal evolution to specify the history of volatile distribution and ocean chemistry, we show that a rapid increase in ocean pH is likely during the Hadean to the early Archean, with pH evolving from 5 to neutral by approximately 4.0 Ga. This rapid pH evolution is attributed primarily to elevated rates of both seafloor and continental weathering during the Hadean. This acceleration in weathering rates originates in the unique aspects of Hadean geodynamics, including rapid crust formation, different crustal lithology, and fast plate motion. Earth likely transformed from a hostile state to a habitable one by the end of the Hadean, approximately 4.0 Ga, with important implications for planetary habitability and the origin of life.
How to cite: Guo, M. and Korenaga, J.: Rapidly evolving ocean pH in the early Earth: Insights from global carbon cycle coupled with ocean chemistry, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11088, https://doi.org/10.5194/egusphere-egu25-11088, 2025.
Clarifying the sedimentary characteristics of the Precambrian microbialite is crucial for understanding the evolution of early life on Earth. In the study, the sedimentary, mineralogical and geochemistry characteristics of microbial dolomite at the Ediacaran in the Upper Yangtze Block are analyzed. The results show that the late Ediacaran in the Upper Yangtze is a rimmed carbonate platform. The microbialite inside the semi-restricted platform is small and sparse, with low residual organic matter, while microbialite at the platform margin is large and dense, with high residual organic matter. The in- situ major elements, rare earth elements, C/O isotopes, and mineral assemble of microbialite indicate significant hydrothermal activity at the platform margin. Under the influence of hydrothermal activity, microbialite at the platform margin are enriched in Fe, Mn, PEF, BaEF, NiEF, CuEF, CoEF, ZnEF, with higher levels of NaEF, KEF, MgEF and UEF, MoEF, VEF, indicating a sedimentary environment with sufficient nutrients, higher salinity, higher seawater temperature and lower oxygen. It can be concluded that environments significantly influenced by hydrothermal activity during the late Neoproterozoic were more suitable for microbial habitation, which may also suggest the origin of early life on Earth.
How to cite: Wang, H.: Sedimentary characteristics of Ediacaran microbialite in the Yangtze Platform, South China: implications for the evolution of early life, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4766, https://doi.org/10.5194/egusphere-egu25-4766, 2025.
The Isua Supracrustal Belt hosts >3.7 Ga old detrital meta-sediments that consist of turbiditic and pelagic pelites. These meta-sediments contain some of the oldest evidence for life in the form of abundant graphite with low δ13C. The continuous occurrence of this graphite throughout these meta-sediments is consistent with their formation in a basin with a continued pelagic biomass productivity, fueled by a consistent source of nutrients. Understanding the environment in which these early life-forms thrived is fundamental to our understanding of which conditions are conducive to life on Earth. In order to trace the tectonic and compositional development of the basin and proximal terranes, we have characterized a ca. 80 m rock core that samples the basaltic basement, iron-rich meta-sediments, detrital meta-sediments and contacts between these lithologies. The basement consists of basalts with major and trace elemental compositions that are similar to boninites and are conformably overlain by iron rich mixed chemical and detrital sediments. Iron concentrations fall gradually upwards in the core, with sporadic reoccurring iron-rich layers occurring in the upper core. The gradual change in iron concentrations shows that the core contains a broadly conformable and coherent stratigraphy that records the formation of the volcanic basement, followed by iron deposition enhanced by post-volcanic hydrothermal circulation. Detrital sediments were being deposited as soon as the basin floor was formed, indicating that proximal erodible terranes were already present. A combination of proxies, consisting of La/Yb, Ti/Zr and petrographic observations show that this detrital component was derived from ca. 60 % tonalities and 40 % non-boninitic basalts. These conditions are best explained by the formation of a volcanic fore-arc basin in front of a pre-existing differentiated terrane formed by melting of hydrated basalts. This sequence of events is consistent with cumulative zircon ages in surrounding gneisses that suggest episodic collisions of primitive arcs, followed by re-initiation of subduction. The active volcanism, tectonism and formation of (semi)restricted basins in this environment likely allowed the accumulation of nutrients required for the proliferation of life.
How to cite: Boyd, A. J., Rosing, M., Harding, M., Canfield, D., and Hassenkam, T.: 3.7 Ga Isua Supracrustal Belt sediments record formation of fore-arc basin with conditions conducive to proliferation of life, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16055, https://doi.org/10.5194/egusphere-egu25-16055, 2025.
