Inference of viscosity jump at 670 km depth and lower mantle viscosity structure from GIA observations

Nakada, Masayuki; Okuno, Jun’ichi; Irie, Yoshiya

doi:10.1093/gji/ggx519

Cited by 9 publications

(16 citation statements)

References 42 publications

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“…The nonmonotonic postdeglacial RSL behavior inferred from the sedimentary records worldwide may be explained by a synchronous melting model with T d < 20 kyr and a deep mantle viscosity of ~5 × 10 22 Pa s. A discussion of Neoproterozoic mantle viscosity is challenging if we consider the thermal history of the Earth (e.g., Ganne & Feng, ) and its impact on the mantle viscosity (Karato, ). Nevertheless, a deep mantle viscosity of ~5 × 10 22 Pa s may be consistent with an estimate of ~10 23 Pa s inferred from the recent analyses using GIA data sets pertinent to the last deglaciation (Lau et al, ; Nakada et al, ; Nakada & Okuno, ). According to the results of Ganne and Feng (), for example, the average temperature of the mantle at 0.6–0.7 Gyr was ~50 K higher than at present.…”

Section: Discussionsupporting

confidence: 86%

“…Nakada et al () examined the GIA‐related observations such as RSL changes and secular rate of change of the degree‐two zonal harmonic of the geopotential,

{\dot{J}}_{2}

, based on the temperature‐dependent viscosity model. Although the results are not shown here, the nonmonotonic postdeglacial RSL behavior inferred from the sedimentary records worldwide can be explained based on the viscosity model with temperature distribution ~50 K higher than the deep mantle viscosity of 10 23 Pa s and average upper mantle viscosity of 4 × 10 20 Pa s preferred by Nakada et al (). A postdeglacial RSL drop followed by transgression is also predicted for the viscosity model with an upper mantle viscosity of 10 20 Pa s and lithospheric thickness of 50 km as inferred from the results shown in Figures e–h and e–h.…”

Section: Discussionmentioning

confidence: 99%

“…This may suggest that the Neoproterozoic mantle viscosity is approximately half of the present one for an assumed temperature distribution by Nakada et al (2018). Nakada et al (2018) examined the GIA-related observations such as RSL changes and secular rate of change of the degree-two zonal harmonic of the geopotential, _ J 2 , based on the temperature-dependent viscosity model. Although the results are not shown here, the nonmonotonic postdeglacial RSL behavior inferred from the sedimentary records worldwide can be explained based on the viscosity model with temperature distribution~50 K higher than the deep mantle viscosity of 10 23 Pa s and average upper mantle Finally, we discuss the syndeglacial duration.…”

Section: Journal Of Geophysical Research: Solid Earthmentioning

confidence: 99%

“…The values of η lm = 5 × 10 22 Pa s are consistent with recent estimates from GIA studies based on far‐field sea level data by Lambeck et al () and from LGM sea levels at Barbados and Bonaparte Gulf and the rate of change of degree‐two zonal harmonic of Earth's geopotential due to GIA process by Nakada et al (). More recent analyses using GIA data sets due to the last deglaciation yield a deep mantle viscosity of ~10 23 Pa s (Lau et al, ; Nakada et al, ; Nakada & Okuno, ). We therefore adopt a two‐layer lower mantle viscosity model defined by η 670,1191 = 5 × 10 21 Pa s (viscosity for 670‐ to 1,191‐km depth) and η 1191,2891 = 5 × 10 22 Pa s (viscosity for 1,191‐ to 2,891‐km depth).…”

Section: Model Descriptionsmentioning

confidence: 99%

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Nonmonotonic Postdeglacial Relative Sea Level Changes at the Aftermath of Marinoan (635 Ma) Snowball Earth Meltdown

et al. 2019

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Marinoan snowball Earth offers us a set of sedimentary and geochemical records for exploring glacial isostatic adjustment (GIA) associated with one of the most severe glaciations in Earth history. An accurate prediction of GIA‐based relative sea level (RSL) change associated with a snowball Earth meltdown will help to explore sedimentary records for RSL changes and to place independent constraints on mantle viscosity and on the durations of syndeglaciation (Td) and cap carbonate deposition. Here we mainly examine postdeglacial RSL change characterized by an RSL drop and a resumed transgression inferred from the cap dolostones on the continental shelf in south China. Such a nonmonotonic RSL behavior may be a diagnostic GIA signal for the Marinoan deglaciation resulting from a significantly longer postdeglacial GIA response than that for the last deglaciation. A postdeglacial RSL drop followed by transgression in south China, which is significantly affected by Earth's rotation, is predicted over the continental shelf for models with Td ≤ 20 kyr and a deep mantle viscosity of ~5 × 1022 Pa s regardless of the upper mantle viscosity. The inferred GIA model also explains the postdeglacial RSL changes such as sedimentary‐inferred RSL drops on the continental shelf in northwestern Canada and California at low‐latitude regions insignificantly affected by Earth's rotation. Furthermore, the good match between the predicted and observed RSL changes in south China suggests an approximate duration of ~50 kyr for the Marinoan 17O depletion event, an atmospheric event linked to the post‐Marinoan drawdown of CO2 and the concurrent rise of O2.

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Section: Discussionsupporting

confidence: 86%

“…Nakada et al () examined the GIA‐related observations such as RSL changes and secular rate of change of the degree‐two zonal harmonic of the geopotential,

{\dot{J}}_{2}

Section: Discussionmentioning

confidence: 99%

Section: Journal Of Geophysical Research: Solid Earthmentioning

confidence: 99%

Section: Model Descriptionsmentioning

confidence: 99%

See 2 more Smart Citations

Nonmonotonic Postdeglacial Relative Sea Level Changes at the Aftermath of Marinoan (635 Ma) Snowball Earth Meltdown

et al. 2019

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“…The width of the anomalous mantle block has been taken to be 200 km with a base at 160 km, as in the purely conductive model. In order to simplify our calculations, constant values of dynamic viscosity from 5E20 to 1E21 Pa·s have been tested, representing the most reasonable range in the upper‐mantle dynamic viscosity (Argus, Peltier, Drummond, & Moore, ; Nakada, Okuno, & Irie, ).…”

Section: Impact Of Anomalously Hot Mantle Lithospherementioning

confidence: 99%

Radiogenic trigger and driver for continental rifting and initial ocean spreading

Maystrenko

Slagstad

2019

Terra Nova

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Closure and opening of oceans on time‐scales of a few hundred million years is a fundamental tectonic process on Earth, typically referred to as a “Wilson cycle”. Subduction of oceanic and continental crust leading up to and during continent–continent collision can refertilize and enrich the orogenic continental lithospheric mantle in heat‐producing elements. The resulting thermal anomaly weakens the lithosphere and, along with structural weaknesses (e.g. sutures), make this orogenic lithosphere more prone to rifting given an extensional stress field. Thermal modelling shows that anomalously hot lithosphere can focus asthenospheric upwellings over time‐scales of a few hundred million years. Processes related to closure of oceans thus provide a mechanism for later localization of rifting and an extensional driving force.

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Revised mantle viscosity profile based on global GPS uplift rates and glacial isostatic adjustment model ICE-6G_D(VM5a)

Chen

Liu

Ray

et al. 2022

Preprint

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Crustal motion observations from Global Positioning System (GPS) networks have not yet been fully exploited in previous studies on glacial isostatic adjustment (GIA) and mantle rheology structure. In this study, we have isolated GIA signals from vertical velocity observations at rigorously selected (over 2,000) GPS stations from the Nevada Geodetic Laboratory (NGL) by removing the effects of atmospheric and oceanic loading, as well as changes in the contemporary glaciers. We have also attempted to include hydrological and sea-level loading corrections based on the most updated model products, but found them still not accurate enough for GIA-related studies. Therefore, we recommend the GPS-derived global GIA uplift rate dataset MIDAS-AO without hydrological and sea-level loading corrections applied. Under the constraints of MIDAS-AO uplift rates, we refined the VM5a viscosity model and obtained two revised viscosity profiles, VM5aR AO1 and VM5aR AO2, that differ by an extra layer in the transition zone of the latter profile. With respect to VM5a, VM5aR AO1 indicates a slight increase of viscosity within the upper mantle, while VM5aR AO2 favors a softer upper part of the upper mantle and a stiffer transition zone. Maps of the variations of model-dataset misfits show that our new viscosity profiles commonly recover a better fit for sites located at the Scandinavian Peninsula and south of the Hudson Bay.

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Inference of viscosity jump at 670 km depth and lower mantle viscosity structure from GIA observations

Cited by 9 publications

References 42 publications

Nonmonotonic Postdeglacial Relative Sea Level Changes at the Aftermath of Marinoan (635 Ma) Snowball Earth Meltdown

Nonmonotonic Postdeglacial Relative Sea Level Changes at the Aftermath of Marinoan (635 Ma) Snowball Earth Meltdown

Radiogenic trigger and driver for continental rifting and initial ocean spreading

Revised mantle viscosity profile based on global GPS uplift rates and glacial isostatic adjustment model ICE-6G_D(VM5a)

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