Significant Increase of Continental Freeboard During the Early Paleoproterozoic: Insights From Metasediment‐Derived Granites

• Published in: Geophysical research letters 2021-11, Vol.48 (22), p.n/a
• Main Authors: Lu, Gui‐Mei, Spencer, Christopher J., Tian, Yang, Wang, Wei
• Format: Article
• Language: English
• Subjects: Biosphere; Composition; Continental crust; Emergence; Freeboard; Isotope composition; Isotopes; Lithosphere; Oxygen; Reservoirs; Sea level; Sediments; Statistical analysis; Statistical methods; Statistics; Tectonics; Zircon
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL096049

Subaerial continental crust plays a fundamental role in modulating the composition of the ocean, atmosphere, and biosphere, but the timing and rate of continental emergence above sea level remain unclear. Here, we use the zircon oxygen isotopic compositions of early Paleoproterozoic metasediment‐derived granitoids from the southwestern Yangtze Block to constrain the rapidity of continental emergence. Statistical analyses of compiled igneous and detrital zircon oxygen isotopic database show a rapid increase in zircon δ18O at ∼2.36 Ga. We suggest that this isotopic shift is best explained by a significant increase of continental freeboard between ∼2.43 and ∼2.36 Ga due to the increasing strength of the continental lithosphere since the late Archean, concomitantly yielding a high‐δ18O sedimentary reservoir. Subsequent melting of these high‐δ18O sediments in a variety of tectonic regimes results in high zircon δ18O. Plain Language Summary The timing and pattern of continental emergence are highly debated due to the lack of associated geological records back into Earth deep time, particularly for the early Paleoproterozoic era, when the earth likely experienced a “tectono‐magmatic lull” period. In this study, the early Paleoproterozoic high δ18O (>7.5‰) metasediment‐derived granitoids are identified in the SW Yangtze Block. Statistical analyses were carried out on the globally compiled igneous and detrital zircon δ18O database, detecting that a rapid increase in zircon δ18O at ∼2.36 Ga. We propose a geodynamic driver for the formation of a high‐δ18O sedimentary reservoir during the early Paleoproterozoic due to significant continental emergence at that time could geodynamically account for this isotopic shift. Key Points Early Paleoproterozoic high δ18O metasediment‐derived granites were identified in the SW Yangtze The rapid increase in zircon δ18O at ∼2.36 Ga was related to a high‐δ18O sedimentary reservoir Continental crust was significantly emerged above sea level since the early Paleoproterozoic