The emergence of subaerial crust and onset of weathering 3.7 billion years ago

2020 ◽  
Author(s):  
Desiree Roerdink ◽  
Yuval Ronen ◽  
Harald Strauss ◽  
Paul Mason
Keyword(s):  
Isotopic Composition ◽  
Marine Sediments ◽  
Carbonate Rocks ◽  
Plate Tectonics ◽  
Chemical Weathering ◽  
Sr Isotope ◽  
O Isotope ◽  
Marine Biosphere ◽  
Biosphere Evolution ◽  
Evolution Trend

Abstract Reconstructing the emergence and weathering of continental crust in the Archean is crucial for our understanding of early ocean chemistry, biosphere evolution and the onset of plate tectonics. However, considerable disagreement exists between the elemental and isotopic proxies that have been used to trace crustal input into marine sediments and data are scarce prior to 3 billion years ago. Here we show that chemical weathering modified the Sr isotopic composition of seawater as recorded in 3.52-3.20 Ga stratiform barite deposits from three different cratons. Using a combination of Sr, S and O isotope data, barite petrography and a hydrothermal mixing model, we calculate a novel Sr isotope evolution trend for Paleoarchean seawater that is much more radiogenic than the curve previously determined from carbonate rocks. Our findings require the presence and weathering of subaerial and evolved (high Rb/Sr) crust from 3.7 ± 0.1 Ga onwards. This Eoarchean onset of crustal weathering affected the chemistry of the oceans and supplied nutrients to the marine biosphere 500 million years earlier than previously thought.

scholarly journals The emergence of subaerial crust and onset of weathering 3.7 billion years ago

2021 ◽  
Author(s):  
Desiree Roerdink ◽  
Yuval Ronen ◽  
Harald Strauss ◽  
Paul Mason
Keyword(s):  
Carbonate Rocks ◽  
Hydrothermal Fluid ◽  
Plate Tectonics ◽  
Chemical Weathering ◽  
Crystal Morphology ◽  
Sr Isotope ◽  
Fluid Mixtures ◽  
Mixing Ratios ◽  
Biosphere Evolution ◽  
Evolution Trend

<p>Reconstructing the emergence and weathering of continental crust in the Archean is crucial for our understanding of early ocean chemistry, biosphere evolution and the onset of plate tectonics. However, considerable disagreement exists between the various elemental and isotopic proxies that have been used to trace crustal input into marine sediments, and data are scarce prior to 3 billion years ago. Here we show that chemical weathering modified the Sr isotopic composition of Archean seawater as recorded in 3.52 to 3.20 Ga stratiform marine-hydrothermal barite deposits from three different cratons. We use a combination of barite crystal morphology, oxygen, multiple sulfur and strontium isotope data to select barite samples with the most seawater-like isotopic compositions, and subsequently use these in a hydrothermal mixing model to calculate a plausible seawater Sr isotope evolution trend from measured <sup>87</sup>Sr/<sup>86</sup>Sr data. From modeled mixing ratios between seawater and hydrothermal fluids required for barite precipitation and comparison of <sup>87</sup>Sr/<sup>86</sup>Sr in theoretical seawater-hydrothermal fluid mixtures with those recorded in the barite, we obtain a novel seawater Sr isotope evolution trend for Paleoarchean seawater that is much more radiogenic than the curve previously determined from carbonate rocks. Our findings require the presence and weathering of subaerial and evolved (high Rb/Sr) crust from 3.7 ± 0.1 Ga onwards, and demonstrate that crustal weathering affected the chemistry of the oceans 500 million years earlier than previously thought.</p>

scholarly journals Sr isotopic characteristics in two small watersheds draining typical silicate and carbonate rocks: implication for the studies on seawater Sr isotopic evolution

2013 ◽  
Vol 10 (6) ◽  
pp. 8031-8069 ◽  
Author(s):  
W. H. Wu ◽  
H. B. Zheng ◽  
J. D. Yang
Keyword(s):  
Carbonate Rocks ◽  
Chemical Weathering ◽  
Silicate Weathering ◽  
86Sr Ratio ◽  
Sr Isotope ◽  
River Catchment ◽  
Weathering Rates ◽  
Isotopic Compositions ◽  
Isotopic Evolution ◽  
The Pearl River

Abstract. We systematically investigated Sr isotopic characteristics of small silicate watershed – the tributary Xishui River of the Yangtze River, and small carbonate watershed – the tributary Guijiang River of the Pearl River. The results show that the Xishui River has relatively high Sr concentrations (0.468–1.70 μmol L−1 in summer and 1.30–3.17 μmol L−1 in winter, respectively) and low 87Sr/86Sr ratios (0.708686–0.709148 in summer and 0.708515–0.709305 in winter), which is similar to the characteristics of carbonate weathering. The Guijiang River has low Sr concentrations (0.124–1.098 μmol L−1) and high 87Sr/86Sr ratios (0.710558–0.724605), being characterized by silicate weathering. In the Xishui River catchment, chemical weathering rates in summer are far higher than those in winter, indicating significant influence of climate regime. However, slight differences of 87Sr/86Sr ratios between summer and winter show that influence of climate on Sr isotope is uncertainty owing to very similar Sr isotope values in silicate and carbonate bedrocks. As 87Sr/86Sr ratios in the Xishui River are lower than those in seawater, they will decrease 87Sr/86Sr ratio of seawater after transported into oceans. Previous studies also showed that some basaltic watersheds with extremely high chemical weathering rates reduced the seawater Sr isotope ratios. In other words, river catchments with high silicate weathering rates do not certainly transport highly radiogenic Sr into oceans. Therefore, it may be questionable that using the variations of seawater 87Sr/86Sr ratio to indicate the continental silicate weathering intensity. In the Guijiang River catchment, 87Sr/86Sr ratios of carbonate rocks and other sources (rainwater, domestic and industrial waste water, and agricultural fertilizer) are lower than 0.71. In comparison, some non-carbonate components, such as, sand rocks, mud rocks, shales, have relatively high Sr isotopic compositions. Moreover, granites accounted for only 5% of the drainage area have extremely high 87Sr/86Sr ratios with an average of over 0.8. Therefore, a few silicate components contained in carbonate rocks obviously increases the Sr isotopic compositions of the river water, and results in a positive effect on the rise of 87Sr/86Sr ratio of seawater. Therefore, the relation between Sr isotope evolution of seawater and continental weathering rate is complex, 87Sr/86Sr ratios of underlying bedrock in catchment could be an important controlling factors.

ISOTOPE-GEOCHEMICAL FEATURES OF AUTHENIC CARBONATES OF THE YU1 PRODUCING HORIZON OF THE VERKH-TARSKOYE OIL FIELD (SOUTH OF WESTERN SIBERIA)

2020 ◽  
pp. 20-28
Author(s):  
L. G. Vakulenko ◽  
◽  
O. D. Nikolenko ◽  
D. A. Novikov ◽  
P. A. Yan ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Carbonate Rocks ◽  
Western Siberia ◽  
Oil Field ◽  
Third Generation ◽  
The Third ◽  
First Time ◽  
Different Sources ◽  
Sources Of Co2 ◽  
Comprehensive Study

A comprehensive study of the composition of sand and silt deposits of the Yu1 horizon of the Vasyuganskaya Formation upper part of the Verkh-Tarskoye oil field has been carried out. Associations of authigenic minerals have been determined in their cement, among which the calcite is the most widespread. According to petrographic parameters, three generations of calcite have been identified for which detailed isotopicgeochemical and ultramicroscopic studies were carried out for the first time. Wide and multi directional changes in the isotopic composition of carbon and oxygen and in the chemical composition of carbonate minerals were recorded, they indicate significant variations in the conditions of diagenesis and catagenesis, primarily temperature, and different sources of CO2. Significant variations in the isotopic composition of formation waters and its relationship with the isotopic composition of carbonates have been established. Thus, a narrow interval of close δ13C values was revealed, amounting to –10.5 to –9.1 ‰ in the formation waters of group II, and from –10.7 to –9.1 ‰ in calcites of the third generation. The source of CO2 in this system should be considered a carbon dioxide, which is formed in the process of metamorphism of carbonate rocks of the Paleozoic age.

Cryptic Sr and Nd isotopic variation across the Leinster Granite, southeast Ireland

1991 ◽  
Vol 128 (3) ◽  
pp. 251-256 ◽  
Author(s):  
Peter Mohr
Keyword(s):  
Isotopic Composition ◽  
Old Age ◽  
Sampling Scheme ◽  
Sr Isotope ◽  
Isotopic Variation ◽  
Geographic Position ◽  
Isotopic Pattern ◽  
Wide Range ◽  
Isotopic Variations ◽  
Range Of Values

AbstractRb–Sr isotope whole-rock data from the end-Caledonian Leinster Batholith define an errorchron age of 464±26 Ma, appreciably older than the accepted emplacement age of c. 405 Ma. This anomalously old age is the consequence of a highly variable initial Sr isotopic composition. Initial Nd ratios and TDM model ages also show a wide range of values. However, these isotopic variations are neither randomly distributed nor related to petrographic changes but instead reflect, in a simple way, geographic position about the axis of the batholith. The isotopic pattern revealed in the Leinster Batholith means that isochron ages obtained from S-type granites may be largely dependent on the sampling scheme adopted. The variable isotopic composition of the granite most likely resulted from either a heterogeneous metasedimentary source or hybridization of coeval, dominantly crustal melts.

Mo mobility in lateritic weathering profiles overlying ultramafic rocks of the East Sulawesi Ophiolite, Indonesia

2021 ◽  
Author(s):  
Adrianus Damanik ◽  
Martin Wille ◽  
Martin Grosjean ◽  
Sri Yudawati Cahyarini ◽  
Hendrik Vogel
Keyword(s):  
Isotopic Composition ◽  
Chemical Weathering ◽  
Isotopic Fractionation ◽  
Reduced Form ◽  
Ultramafic Rocks ◽  
Early Earth ◽  
Atmospheric Input ◽  
First Time ◽  
Weathering Process ◽  
Mo Isotopes

<p>Molybdenum (Mo) isotopes are known as sensitive recorders for changes in redox conditions because the oxidized form of Mo (Mo VI) is more soluble, whereas its reduced form is more particle reactive. Previous studies suggest that Mo isotopic fractionation during the weathering process is controlled by atmospheric input, Mo host, and bedrock composition. However, Mo isotopic variation and processes influencing fractionation in weathering profiles overlying ultramafic bedrock, the early Earth analog, have yet to be explored. This study explores for the first time (1) Mo behavior and (2) isotopic fractionation in two representative and intensely-weathered lateritic profiles overlying ultramafic bedrock of the East Sulawesi Ophiolite, Indonesia. Mo concentrations measured on samples obtained from laterite successions studied here range between 60 - 537 ppb and are overall higher compared to bedrock values ranging between 9 - 45 ppb. The Mo isotope compositions of laterite samples vary between -0.043‰ to -0.161‰ δ<sup>98</sup>Mo<sub>NIST3134</sub>. The overall close to mantle Mo isotopic composition of the laterite samples, their small Mo isotope variability, and the covariation between Mo and Ti concentrations suggest low mobility of Mo during chemical weathering and laterite formation. This low Mo mobility is likely a consequence of a) the low Mo concentration of the ultramafic protolith and b) adsorption of Mo to secondary Fe-Oxides during laterite formation under oxic weathering conditions.</p>

Sr isotope evolution during chemical weathering of granites

2001 ◽  
Vol 44 (8) ◽  
pp. 726-734 ◽  
Author(s):  
Yingjun Ma ◽  
Congqiang Liu
Keyword(s):  
Chemical Weathering ◽  
Sr Isotope
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