“…The zircon in the resulting magmas exhibit elevated δ 18 O values due to incorporation of sediments. While elevated zircon δ 18 O occurs as early as 4.27 Gyr ago 40,41 , critically the coupling between radiogenic isotope systematics (Lu-Hf, U-Pb) and δ 18 O in zircon is absent until after 430 Myr ago.…”
Section: Connecting Land Plants and Zirconmentioning
confidence: 99%
“…The influence of sediment on magmatic systems is most commonly tracked through geologic time using δ 18 O and U-Pb geochronology of the mineral, zircon 39 . It is understood that any igneous rocks with δ 18 O values divergent from the average mantle (~5.5‰) must have been in part or wholly derived from supracrustal material 39 and that the presence of a sedimentary δ 18 O signature in magmatic zircon can be traced from some of the oldest terrestrial zircon (~4.27 Gyr ago) 40,41 to the youngest exposed granites (818.5±9.6 kyr ago) 42 . Another powerful isotopic tool in zircon is Lu-Hf, where the radioactive β-decay of 176 Lu to 176 Hf allows for comparison of the Lu-Hf isotopic composition of zircon at formation with the chondrite uniform reservoir and depleted mantle.…”
Section: Sediment Recycling In Magmatic Systemsmentioning
The evolution of land plants during the Palaeozoic Era transformed Earth's biosphere. Because the Earth's surface and interior are linked by tectonic processes, the linked evolution of the biosphere and sedimentary rocks should be recorded as a nearcontemporary shift in the composition of the continental crust. To test this hypothesis, we assessed the isotopic signatures of zircon formed at subduction zones where marine sediments are transported into the mantle, thereby recording interactions between surface environments and the deep Earth. Using oxygen and lutetium-hafnium isotopes of magmatic zircon that respectively track surface weathering (time-independent) and radiogenic decay (time-dependent), we find a correlation in the composition of continental crust after 430 Myr ago, which is coeval with the onset of enhanced complexity and stability in sedimentary systems related to the evolution of vascular plants. The expansion of terrestrial vegetation brought channelled sand-bed and meandering rivers, muddy floodplains, and thicker soils, lengthening the duration of weathering before final marine deposition. Collectively, our results suggest that the evolution of vascular plants coupled the degree of weathering and timescales of sediment routing to depositional basins where they were subsequently subducted and melted. The late Palaeozoic isotopic shift of zircon indicates that the greening of the continents was recorded in the deep Earth.
“…The zircon in the resulting magmas exhibit elevated δ 18 O values due to incorporation of sediments. While elevated zircon δ 18 O occurs as early as 4.27 Gyr ago 40,41 , critically the coupling between radiogenic isotope systematics (Lu-Hf, U-Pb) and δ 18 O in zircon is absent until after 430 Myr ago.…”
Section: Connecting Land Plants and Zirconmentioning
confidence: 99%
“…The influence of sediment on magmatic systems is most commonly tracked through geologic time using δ 18 O and U-Pb geochronology of the mineral, zircon 39 . It is understood that any igneous rocks with δ 18 O values divergent from the average mantle (~5.5‰) must have been in part or wholly derived from supracrustal material 39 and that the presence of a sedimentary δ 18 O signature in magmatic zircon can be traced from some of the oldest terrestrial zircon (~4.27 Gyr ago) 40,41 to the youngest exposed granites (818.5±9.6 kyr ago) 42 . Another powerful isotopic tool in zircon is Lu-Hf, where the radioactive β-decay of 176 Lu to 176 Hf allows for comparison of the Lu-Hf isotopic composition of zircon at formation with the chondrite uniform reservoir and depleted mantle.…”
Section: Sediment Recycling In Magmatic Systemsmentioning
The evolution of land plants during the Palaeozoic Era transformed Earth's biosphere. Because the Earth's surface and interior are linked by tectonic processes, the linked evolution of the biosphere and sedimentary rocks should be recorded as a nearcontemporary shift in the composition of the continental crust. To test this hypothesis, we assessed the isotopic signatures of zircon formed at subduction zones where marine sediments are transported into the mantle, thereby recording interactions between surface environments and the deep Earth. Using oxygen and lutetium-hafnium isotopes of magmatic zircon that respectively track surface weathering (time-independent) and radiogenic decay (time-dependent), we find a correlation in the composition of continental crust after 430 Myr ago, which is coeval with the onset of enhanced complexity and stability in sedimentary systems related to the evolution of vascular plants. The expansion of terrestrial vegetation brought channelled sand-bed and meandering rivers, muddy floodplains, and thicker soils, lengthening the duration of weathering before final marine deposition. Collectively, our results suggest that the evolution of vascular plants coupled the degree of weathering and timescales of sediment routing to depositional basins where they were subsequently subducted and melted. The late Palaeozoic isotopic shift of zircon indicates that the greening of the continents was recorded in the deep Earth.
“…Sedimentary sulphur isotope data are from the compilation of Caruso et al (2017). Global zircon δ 18 O data are from the compilation of Spencer et al (2022) and shown as moving average (dark line) and binned average with 1σ envelope (white line and grey boxes). The seawater 87 Sr/ 86 Sr curve is from Chen et al (2022).…”
et al., 2001) indicate that Archean continents (e.g. the Pilbara and Kaapvaal cratons) were at least locally raised above sea level. In the Sighbhum craton, continental emergence above sea level may have begun as early as 3.3.-3.2 Ga (Chowdhury et al., 2021). However, on a global scale, Precambrian sedimentation patterns indicate deposition in predominantly oceanic settings or epeiric seas, and generally low-freeboard conditions (freeboard refers to the average elevation of continents above sea level) until the Neoarchean to early Proterozoic (Campbell & Davies, 2017; Eriksson et al., 2005; Eriksson & Condie, 2014). Limited exposure of Archean continents is supported by geochemical proxies and numerical models (Flament
“… Fig. 6 Co-evolution of the continental lithospheric mantle (CLM, this work) and the Earth’s crust as expressed by three proxies: granites, bulk shales 57 , and zircons 67 . Note change in δ 18 O scale.…”
Oxygen isotopic ratios are largely homogenous in the bulk of Earth’s mantle but are strongly fractionated near the Earth’s surface, thus these are robust indicators of recycling of surface materials to the mantle. Here we document a subtle but significant ~0.2‰ temporal decrease in δ18O in the shallowest continental lithospheric mantle since the Archean, no change in Δ′17O is observed. Younger samples document a decrease and greater heterogeneity of δ18O due to the development and progression of plate tectonics and subduction. We posit that δ18O in the oldest Archean samples provides the best δ18O estimate for the Earth of 5.37‰ for olivine and 5.57‰ for bulk peridotite, values that are comparable to lunar rocks as the moon did not have plate tectonics. Given the large volume of the continental lithospheric mantle, even small decreases in its δ18O may explain the increasing δ18O of the continental crust since oxygen is progressively redistributed by fluids between these reservoirs via high-δ18O sediment accretion and low-δ18O mantle in subduction zones.
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