TY - JOUR

T1 - Hf-Nd isotopes in archean marine chemical sediments

T2 - Implications for the geodynamical history of early earth and its impact on earliest marine habitats

AU - Viehmann, Sebastian

N1 - Funding information: and innovation program of the Marie Sklodowska-Curie grant agreement No. 746033 for project ELEMIN. This project and the open access costs are funded from the European Union’s Horizon 2020 research and innovation program of the Marie Sklodowska-Curie grant agreement No. 746033 for project ELEMIN. Funding: This project and the open access costs are funded from the European Union’s Horizon 2020 research

PY - 2018/7/16

Y1 - 2018/7/16

N2 - The Hf-Nd isotope systems are coupled in magmatic systems, but incongruent Hf weathering (‘zircon effect’) of the continental crust leads to a decoupling of the Hf-Nd isotope systems in low-temperature environments during weathering and erosion processes. The Hf-Nd isotope record was recently dated back from the Cenozoic oceans until the Archean, showing that both isotope systems were already decoupled in seawater 2.7 Ga ago and potentially 3.4 Ga and 3.7 Ga ago. While there might have existed a hydrothermal pathway for Hf into Archean seawater, incongruent Hf weathering of more evolved, zircon-bearing uppermost continental crust that was emerged and available for subaerial weathering accounts for a significant decoupling of Hf-Nd isotopes in the dissolved (<0.2 µm) and suspended (>0.2 µm) fractions of Early Earth’s seawater. These findings contradict the consensus that uppermost Archean continental crust was (ultra)mafic in composition and predominantly submerged. Hence, Hf-Nd isotopes in Archean marine chemical sediments provide the unique potential for future research to trace the emergence of evolved continental crust, which in turn has major implications for the geodynamical evolution of Early Earth and the nutrient flux into the earliest marine habitats on Earth.

AB - The Hf-Nd isotope systems are coupled in magmatic systems, but incongruent Hf weathering (‘zircon effect’) of the continental crust leads to a decoupling of the Hf-Nd isotope systems in low-temperature environments during weathering and erosion processes. The Hf-Nd isotope record was recently dated back from the Cenozoic oceans until the Archean, showing that both isotope systems were already decoupled in seawater 2.7 Ga ago and potentially 3.4 Ga and 3.7 Ga ago. While there might have existed a hydrothermal pathway for Hf into Archean seawater, incongruent Hf weathering of more evolved, zircon-bearing uppermost continental crust that was emerged and available for subaerial weathering accounts for a significant decoupling of Hf-Nd isotopes in the dissolved (<0.2 µm) and suspended (>0.2 µm) fractions of Early Earth’s seawater. These findings contradict the consensus that uppermost Archean continental crust was (ultra)mafic in composition and predominantly submerged. Hence, Hf-Nd isotopes in Archean marine chemical sediments provide the unique potential for future research to trace the emergence of evolved continental crust, which in turn has major implications for the geodynamical evolution of Early Earth and the nutrient flux into the earliest marine habitats on Earth.

KW - Archean

KW - Early life

KW - Emergence of continents

KW - Hf-nd decoupling

KW - Hf-nd isotopes

KW - Incongruent weathering

KW - Seawater

KW - Zircon effect

UR - http://www.scopus.com/inward/record.url?scp=85050561258&partnerID=8YFLogxK

U2 - 10.3390/geosciences8070263

DO - 10.3390/geosciences8070263

M3 - Review article

AN - SCOPUS:85050561258

VL - 8

JO - Geosciences (Switzerland)

JF - Geosciences (Switzerland)

IS - 7

M1 - 263

ER -