scholarly journals UPPER MANTLE CONVECTION RELATED TO SUBDUCTION ZONE AND APPLICATION OF THE MODEL TO INVESTIGATE THE CRETACEOUS-CENOZOIC GEODYNAMICS OF CENTRAL EAST ASIA AND THE ARCTIC

2021 ◽  
Vol 12 (3) ◽  
pp. 455-470
Author(s):  
L. I. Lobkovsky ◽  
M. M. Ramazanov ◽  
V. D. Kotelkin
Keyword(s):  
East Asia ◽  
Subduction Zone ◽  
Upper Mantle ◽  
Mantle Convection ◽  
Stationary Problem ◽  
Convective Cell ◽  
The Arctic ◽  
The Pacific ◽  
Mantle Layer ◽  
Rayleigh Numbers

A geodynamic model of upper mantle convection related to the Pacific subduction zone is mathematically substantiated and applied to investigate the Cretaceous-Cenozoic evolution of Central East Asia (CEA) and the Arctic. We present a solution for the two-dimensional stationary problem of thermal convection in the upper mantle layer, considering different Rayleigh numbers and taking into account the influence of the subduction process and lithospheric movements along the upper mantle base. We describe the results of 3D modeling of nonstationary upper mantle convection in a subduction zone. Our data give grounds to propose explanations for the entire spectrum of tectonic-magmatic processes developing within CEA in the Cenozoic and the Arctic in the Upper Cretaceous and Cenozoic. We discuss the reasons why the lithosphere in CEA and the Arctic is generally shifting towards the Pacific subduction zone, considering the presence of separate magmatic provinces and rift zones. In our opinion, this is due to the existence of a large horizontally elongated convective cell, which interior is composed of smaller isometric cells. This long cell creates the effect of conveyor dragging of the lithosphere, while its internal cells produce the effect of upper mantle plumes.

scholarly journals Influence of the upper-mantle convective cell and related Pacific plate subduction on Arctic tectonics in the late Cretaceous–Cenozoic

2019 ◽  
pp. 27-45
Author(s):  
M. V. Kononov ◽  
L. I. Lobkovsky
Keyword(s):  
Pacific Ocean ◽  
Subduction Zone ◽  
Upper Mantle ◽  
Convective Cell ◽  
Pacific Plate ◽  
The Arctic ◽  
The Pacific ◽  
Eurasian Basin ◽  
Pacific Plate Subduction ◽  
Plate Subduction

Abstract The paper considers the history of the spreading of the Eurasian basin. The sharp deceleration of the spreading rate in the Eocene about 46 million years ago, which is fixed by the distribution of linear magnetic anomalies, is noted. That jump in velocity is clarified from the perspective of the geodynamic model but shouldnt be explained by the northern motion of Greenland. The geodynamic processes of the Pacific subduction zone generate an upper mantle convective cell with return flow dragging the Arctic continental lithosphere in the direction of the Pacific subduction zone. The geodynamic mechanism is confirmed by seismic tomographic mantle sections of the northeastern margin of Asia and the numerical model of the upper mantle convection of the active continental margin. It is the activity of the upper mantle convective return cell, which is determined by the runoff volume and, ultimately, the speed and direction of the Kula plate and Pacific plate subduction vectors in the subduction zone, affects tectonics and kinematics of the plates of the Eurasian basin. In the Middle CretaceousMiddle Eocene and for about 73 Ma the return cell has been active, since the Kula and Pacific plates move north and submerged orthogonally beneath the Central Arctic. After the Middle Eocene geodynamic reorganization about 47.5 million years ago, oceanic plates in the Pacific Ocean begin to move to the northwest. As a result, the transport of the oceanic Pacific Ocean lithospheric substance to the arctic convective return cell has practically ceased. After the restructuring, the spreading of the Eurasian basin slowed down about 46 million years ago to an ultra-slow regime. The main tectonic and geodynamic consequences of applying the proposed geodynamic model for the Arctic in the Late CretaceousCenozoic are considered.

scholarly journals A subduction influence on ocean ridge basalts outside the Pacific subduction shield

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
A. Y. Yang ◽  
C. H. Langmuir ◽  
Y. Cai ◽  
P. Michael ◽  
S. L. Goldstein ◽  
...  
Keyword(s):  
Upper Mantle ◽  
The Arctic ◽  
Mantle Flow ◽  
Mantle Heterogeneity ◽  
Gakkel Ridge ◽  
The Pacific ◽  
Mid Ocean Ridge ◽  
The Pacific Ocean ◽  
Back Arc ◽  
Ocean Ridge

AbstractThe plate tectonic cycle produces chemically distinct mid-ocean ridge basalts and arc volcanics, with the latter enriched in elements such as Ba, Rb, Th, Sr and Pb and depleted in Nb owing to the water-rich flux from the subducted slab. Basalts from back-arc basins, with intermediate compositions, show that such a slab flux can be transported behind the volcanic front of the arc and incorporated into mantle flow. Hence it is puzzling why melts of subduction-modified mantle have rarely been recognized in mid-ocean ridge basalts. Here we report the first mid-ocean ridge basalt samples with distinct arc signatures, akin to back-arc basin basalts, from the Arctic Gakkel Ridge. A new high precision dataset for 576 Gakkel samples suggests a pervasive subduction influence in this region. This influence can also be identified in Atlantic and Indian mid-ocean ridge basalts but is nearly absent in Pacific mid-ocean ridge basalts. Such a hemispheric-scale upper mantle heterogeneity reflects subduction modification of the asthenospheric mantle which is incorporated into mantle flow, and whose geographical distribution is controlled dominantly by a “subduction shield” that has surrounded the Pacific Ocean for 180 Myr. Simple modeling suggests that a slab flux equivalent to ~13% of the output at arcs is incorporated into the convecting upper mantle.

Mantle convection beneath East Asia under global mantle convection spherical framework

2020 ◽  
Author(s):  
Qunfan Zheng ◽  
Huai Zhang
Keyword(s):  
Tibetan Plateau ◽  
East Asia ◽  
Upper Mantle ◽  
Mantle Convection ◽  
Mantle Flow ◽  
The Tibetan Plateau ◽  
Mantle Structure ◽  
Lithospheric Deformation ◽  
Mantle Dynamics ◽  
Flow Models

<p>East Asia is a tectonically active area on earth and has a complicated lithospheric deformation due to the western Indo-Asian continental collision and the eastern oceanic subduction mainly from Pacific plate. Till now, mantle dynamics beneath this area is not well understood due to its complex mantle structure, especially in the framework of global spherical mantle convection. Hence, a series of numerical models are conducted in this study to reveal the key controlling parameters in shaping the present-day observed mantle structure beneath East Asia under 3-D global mantle flow models. Global mantle flow models with coarse mesh are firstly applied to give a rough constraint on global mantle convection. The detailed description of upper mantle dynamics of East Asia is left with regional refined mesh. A power-law rheology and absolute plate field are applied subsequently to get a better constraint on the related regional mantle rheological structure and surficial boundary conditions. Thus, the refined and reasonable velocity and stress distributions of upper mantle beneath East Asia at different depths are retrieved based on our 3-D global mantle flow simulations. The derived large shallow mantle flow beneath the Tibetan Plateau causes significant lithospheric shear drag and dynamic topography that result in prominent tectonic evolution of this area. And the Indo–Asian collision may have induced mantle flow beneath the Indian plate and the different velocity structures between the asthenosphere and lithosphere indicate the shear drag of asthenospheric mantle. That may explain the reason that Indo–Asian collision has occurred for 50 Ma, and this collision can still continue to accelerate uplift in the Tibetan plateau. Finally, we also consider the possible implementations of 3-D numerical simulations combined with global lithosphere and deep mantle dynamics so as to discuss the relevant influences.</p>

scholarly journals S WAVE VELOCITY STRUCTURE IN NONTECTONIC SE ASIA BY SEISMOGRAM ANALYSIS OF THE EARTHQUAKES IN SUMATRA–JAVA AT TATO STATION, TAIWAN

2010 ◽  
Vol 04 (03) ◽  
pp. 181-195
Author(s):  
BAGUS JAYA SANTOSA
Keyword(s):  
East Asia ◽  
Subduction Zone ◽  
Wave Velocity ◽  
Upper Mantle ◽  
Arrival Time ◽  
Velocity Structure ◽  
Synthetic Seismogram ◽  
Earth Model ◽  
South East Asia ◽  
S Wave

The S wave velocity structure beneath South-East Asia and South China Sea due to earthquakes in Sumatra–Java subduction zone has been investigated through seismogram analysis in time domain and three components simultaneously, using data recorded in TATO, Taiwan seismological station. The synthetic seismogram was calculated using the GEMINI method, which consists of the earth model and the CMT solution of the earthquake. A low-pass filter with corner frequency of 20 mHz is imposed to the seismograms. Response file inversion subjected on the measured seismogram will compare the measured and the synthetic seismogram in the same unit. The seismogram comparison indicated that the synthetic seismogram constructed from PREMAN earth model deviates greatly from the measured one. The deviation occurred on the arrival time of surface wave of Rayleigh and Love as well as S body waves. The S, Love, and Rayleigh waveform deviations on arrival time or oscillation number are solved by changing the gradient of βh into positive in the upper mantle layers, and corrections for zero-order coefficients of β speed polynomial in every earth mantle layers. The interpretation results of seismogram analysis using waveform comparison indicate that the nontectonic South-East Asia area in front of subduction zone has strong negative correction of βv in the upper mantle and with smaller factor also at earth layers below. This result shows stronger vertical anisotropy than that indicated by the PREMAN earth model.

The subduction influence on ocean ridge basalts and its significance

2021 ◽  
Author(s):  
Alexandra Yang Yang ◽  
Charles Langmuir ◽  
Yue Cai ◽  
Steven Goldstein ◽  
Peter Michael ◽  
...  
Keyword(s):  
Pacific Ocean ◽  
Upper Mantle ◽  
The Arctic ◽  
Plate Tectonic ◽  
Gakkel Ridge ◽  
The Pacific ◽  
Mid Ocean Ridge ◽  
The Pacific Ocean ◽  
Back Arc ◽  
Ocean Ridge

Abstract The plate tectonic cycle produces chemically distinct mid-ocean ridge basalts (MORB) and arc volcanics, with the latter enriched in fluid-mobile elements and depleted in Nb owing to fluxes from the subducted slab. Basalts from back-arc basins (BABB), with intermediate compositions, show that the subduction flux can escape the arc. Hence it is puzzling why arc signatures have rarely been recognized in MORB. Here we report the first MORB samples with distinct arc signatures, akin to BABB, from the Arctic Gakkel Ridge. A new high precision dataset for 576 Gakkel samples suggests a pervasive subduction influence. This influence can also be identified in Atlantic and Indian MORB with a “BABB filter”, but is nearly absent in Pacific MORB. This global distribution reflects the control of a “subduction shield” that has surrounded the Pacific Ocean for 180Myr. Statistics suggest that a flux equivalent to ~ 13% of output at arcs is incorporated into the convecting upper mantle.

scholarly journals A Synergistic Effect of Blockings on a Persistent Strong Cold Surge in East Asia in January 2018

Atmosphere ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 215 ◽  
Author(s):  
Wei Dong ◽  
Liang Zhao ◽  
Shunwu Zhou ◽  
Xinyong Shen
Keyword(s):  
Synergistic Effect ◽  
East Asia ◽  
Air Temperature ◽  
Western Europe ◽  
The Arctic ◽  
West Siberian Plain ◽  
Near Surface ◽  
Cold Surge ◽  
Cold Air ◽  
The Pacific

A persistent strong cold surge occurred in East Asia in late January 2018, causing mean near-surface air temperature in China to hit the second lowest since 1984. Moreover, the daily mean air temperature remained persistently negative for more than 20 days. Here, we find that a synergistic effect of double blockings in Western Europe and North America plays an important accelerating role in the rapid phase transition of Arctic Oscillation and an amplifying role in the strength of cold air preceding to the cold surge outbreaks by the use of an isentropic potential vorticity analysis. In mid-January, an Atlantic mid-latitude anticyclone merged with Western Europe blocking, which led to a strengthening of the blocking. Simultaneously, the Pacific-North American blocking was also significantly strengthened. The two blockings synchronously deeply stretched towards the Arctic, which resulted in, on the one hand, warm and moist air of the Pacific and the Atlantic being excessively transported into the Arctic, and on the other hand, the polar vortex being split and cold air being squeezed southwards and accumulating extensively on the West Siberian Plain. After the breakdown of the double blocking pattern, which lasted for about 10 days, the record-breaking cold surge broke out in East Asia. It was discovered that the synergistic effect of double blockings extending into the Arctic, which is conducive to extreme cold events, has been rapidly increasing in recent years.

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