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No evidence of supracrustal recycling in Si-O isotopes of Earth's oldest rocks 4 Ga ago.

ABSTRACT: Identifying the oldest evidence for the recycling of hydrated crust into magma on Earth is important because it is most effectively achieved by subduction. However, given the sparse geological record of early Earth, the timing of first supracrustal recycling is controversial. Silicon and oxygen isotopes have been used as indicators of crustal evolution on Archean igneous rocks and minerals to trace supracrustal recycling but with variable results. We present Si-O isotopes of Earth's oldest rocks [4.0 billion years ago (Ga)] from the Acasta Gneiss Complex, northwest Canada, obtained using multiple techniques applied to zircon, quartz, and whole rock samples. Undisturbed zircon is considered the most reliable recorder of primary Si signatures. By combining reliable Si isotope data from the Acasta samples with filtered data from Archean rocks globally, we observe that widespread evidence for a heavy Si signature is recorded since 3.8 Ga, marking the earliest record of surface silicon recycling.

SUBMITTER: Zhang Q

PROVIDER: S-EPMC10313171 | biostudies-literature | 2023 Jun

REPOSITORIES: biostudies-literature

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No evidence of supracrustal recycling in Si-O isotopes of Earth's oldest rocks 4 Ga ago.

Zhang Qing Q Zhao Lei L Zhou Dawn D Nutman Allen P AP Mitchell Ross N RN Liu Yu Y Li Qiu-Li QL Yu Hui-Min HM Fan Billy B Spencer Christopher J CJ Li Xian-Hua XH

Science advances 20230630 26

Identifying the oldest evidence for the recycling of hydrated crust into magma on Earth is important because it is most effectively achieved by subduction. However, given the sparse geological record of early Earth, the timing of first supracrustal recycling is controversial. Silicon and oxygen isotopes have been used as indicators of crustal evolution on Archean igneous rocks and minerals to trace supracrustal recycling but with variable results. We present Si-O isotopes of Earth's oldest rocks ...[more]

PMID: 37390214

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Project description:Concentrations of highly siderophile elements (HSE) and 187Os/188Os isotopic compositions for eleven impact related rocks from the Apollo 15 and 16 landing sites are reported and combined with existing geochronological data to investigate the chemical nature and temporal changes in the large impactors implicated in the formation of the lunar basins. Data for the samples all define linear trends on plots of HSE versus Ir concentrations, whose slopes likely reflect the relative HSE compositions of the dominant impactors that formed the rocks. The inferred Imbrium basin impactor that generated Apollo 15 impact melt rocks 15445 and 15455 was characterized by modestly suprachondritic 187Os/188Os, Ru/Ir, Pt/Ir and Pd/Ir ratios. Diverse impactor components are revealed in the Apollo 16 impact melt rocks. The 187Os/188Os and HSE/Ir ratios of the impactor components in melt rocks 60635, 63595 and 68416, with reported ages < 3.84 Ga, are within the range of chondritic meteorites, but slightly higher than ratios characterizing previously studied granulitic impactites with reported ages > 4.0 Ga. By contrast, the impactor components in melt rocks 60235, 62295 and 67095, with reported ages of ~3.9 Ga, are characterized by suprachondritic 187Os/188Os and HSE/Ir ratios similar to the Apollo 15 impact melt rocks, and may also sample the Imbrium impactor. Three lithic clasts from regolith breccias 60016 and 65095, also with ~3.9 Ga ages, contain multiple impactor components, of which the dominant composition is considerably more suprachondritic than those implicated for Imbrium and Serenitatis (Apollo 17) impactors. The dominant composition recorded in these rocks was most likely inherited from a pre-Imbrium impactor. Consideration of composition versus age relations among lunar impact melt rocks reveals no discernable trend. Virtually all lunar impact melt rocks sampled by the Apollo missions, as well as meteorites, are characterized by 187Os/188Os and HSE/Ir ratios that, when collectively plotted, define linear trends ranging from chondritic to fractionated compositions. The impact melt rocks with HSE signatures within the range of chondritic meteorites are interpreted to have been derived from impactors that had HSE compositions similar to known chondrite groups. By contrast, the impact melt rocks with non-chondritic relative HSE concentrations could not have been made by mixing of known chondritic impactors. These signatures may instead reflect contributions from early solar system bodies with bulk chemical compositions that have not yet been sampled by primitive meteorites present in our collections. Alternately, they may reflect the preferential incorporation of evolved metal separated from a fractionated planetesimal core. Pre-3.9 Ga ages for at least some impactor components with both chondritic and fractionated HSE raise the possibility that the bulk of the HSE were added to the lunar crust prior to the later-stage basin-forming impacts, such as Imbrium and Serenitatis, as proposed by Fischer-Gödde and Becker (2012). For this scenario, the later-stage basin-forming impacts were more important with respect to mixing prior impactor components into melt rocks, rather than contributing much to the HSE budgets of the rocks themselves.

Project description:Understanding how mutations arise and spread through individuals and populations is fundamental to evolutionary biology. Most organisms have a life cycle with unicellular bottlenecks during reproduction. However, some organisms like plants, fungi, or colonial animals can grow indefinitely, changing the manner in which mutations spread throughout both the individual and the population. Furthermore, clonally reproducing organisms may also achieve exceedingly long lifespans, making somatic mutation an important mechanism of creating heritable variation for Darwinian evolution by natural selection. Yet, little is known about intra-organism mutation rates and evolutionary trajectories in long-lived species. Here, we study the Pando aspen clone, the largest known quaking aspen (Populus tremuloides) clone founded by a single seedling and thought to be one of the oldest studied organisms. Aspen reproduce vegetatively via new root-borne stems forming clonal patches, sometimes spanning several hectares. To study the evolutionary history of the Pando clone, we collected and sequenced over 500 samples from Pando and neighboring clones, as well as from various tissue types within Pando, including leaves, roots, and bark. We applied a series of filters to distinguish somatic mutations from the pool of both somatic and germline mutations, incorporating a technical replicate sequencing approach to account for uncertainty in somatic mutation detection. Despite root spreading being spatially constrained, we observed only a modest positive correlation between genetic and spatial distance, suggesting the presence of a mechanism preventing the accumulation and spread of mutations across units. Phylogenetic models estimate the age of the clone to between ~16,000-80,000 years. This age is generally corroborated by the near-continuous presence of aspen pollen in a lake sediment record collected from Fish Lake near Pando. Overall, this work enhances understanding of mutation accumulation and dispersal within and between ramets of long-lived, clonally-reproducing organisms.

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No evidence of supracrustal recycling in Si-O isotopes of Earth's oldest rocks 4 Ga ago.

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No evidence of supracrustal recycling in Si-O isotopes of Earth's oldest rocks 4 Ga ago.

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