scholarly journals Features of the velocity structure of the mantle under the Precambrian structures on the example of the Indian platform (according to seismic tomography)

2021 ◽  
Vol 43 (1) ◽  
pp. 211-226
Author(s):  
L.N. Zaiets ◽  
I.V. Bugaienko ◽  
T.A. Tsvetkova
Keyword(s):  
Transition Zone ◽  
Seismic Tomography ◽  
Upper Mantle ◽  
Lower Mantle ◽  
Velocity Structure ◽  
Initial Approximation ◽  
Low Velocity ◽  
Tectonic Zone ◽  
Lower Velocity ◽  
Northern Border

The paper presents additional data, approaching to understanding the driving forces in the formation of geological structures and the development of the Indian platform. The results of seismic tomography are attracted here and their analysis is presented. A 3-dimensional P-velocity model of the mantle of the Indian platform was obtained according to the Taylor approximation method developed by V. Geyko. The undeniable advantages of the method are independence from the initial approximation (reference model) and the best approximation of nonlinearity. According to the data, the mantle under the Indian platform is influenced by both plumes and fluid systems. The influence of plumes is observed in the form of low-velocity subvertical exits from the lower mantle to the transition zone; fluids — in the form of interbedding of high and low velocity anomalies from the lower mantle (or from the transition zone of the upper mantle) to the upper mantle. An analysis is presented of both general velocity structure of the platform mantle and the velocity structure of the mantle under individual cratons (Bandelkand, Singhbum, Bastar and Darvar), the totality of which forms the Indian platform and the trap provinces. At lower velocity, an area is distinguished in the mantle that corresponds to the surface of the Narmada-Son lineament moving into the Central Indian Tectonic Zone. The mantle high-velocity structures under the Deccan trap province, together with their spreading area in the transitional zone of the mantle, subdivide the platform into two parts at depths of 375 km. Areas in the mantle with inclined layers were identified and analyzed: under the cratons Bandelkand and Singbum, the Rajmahal traps and the northern border of the Deccan traps. According to the model, an area bordering the Himalayas is well distinguished in the mantle. It is shown how, when the Indian platform collides with the Eurasian margin, the upper mantle stratifies into plates capable of independent motions, including subduction.

Prominent thermal anomalies in the mantle transition zone beneath the Transantarctic Mountains

Geology ◽  
2020 ◽  
Vol 48 (7) ◽  
pp. 748-752
Author(s):  
Erica L. Emry ◽  
Andrew A. Nyblade ◽  
Alan Horton ◽  
Samantha E. Hansen ◽  
Jordi Julià ◽  
...  
Keyword(s):  
Transition Zone ◽  
Upper Mantle ◽  
Lower Mantle ◽  
Low Velocity ◽  
Mantle Transition Zone ◽  
Thermal Anomalies ◽  
Victoria Land ◽  
Convective Thermal ◽  
Mantle Processes ◽  
Transantarctic Mountains

Abstract The Transantarctic Mountains (TAMs), Antarctica, exhibit anomalous uplift and volcanism and have been associated with regions of thermally perturbed upper mantle that may or may not be connected to lower mantle processes. To determine if the anomalous upper mantle beneath the TAMs connects to the lower mantle, we interrogate the mantle transition zone (MTZ) structure under the TAMs and adjacent parts of East Antarctica using 12,500+ detections of P-to-S conversions from the 410 and 660 km discontinuities. Our results show distinct zones of thinner-than-global-average MTZ (∼205–225 km, ∼10%–18% thinner) beneath the central TAMs and southern Victoria Land, revealing throughgoing convective thermal anomalies (i.e., mantle plumes) that connect prominent upper and lower mantle low-velocity regions. This suggests that the thermally perturbed upper mantle beneath the TAMs and Ross Island may have a lower mantle origin, which could influence patterns of volcanism and TAMs uplift.

Crust-mantle velocity structure in Shanxi rift, Central North China Craton

2020 ◽  
Author(s):  
Yan Cai ◽  
Jianping Wu
Keyword(s):  
Upper Mantle ◽  
High Velocity ◽  
North China Craton ◽  
Lower Crust ◽  
North China ◽  
Velocity Structure ◽  
Low Velocity ◽  
Crust And Upper Mantle ◽  
The North ◽  
Shanxi Rift

<p>North China Craton is the oldest craton in the world. It contains the eastern, central and western part. Shanxi rift and Taihang mountain contribute the central part. With strong tectonic deformation and intense seismic activity, its crust-mantle deformation and deep structure have always been highly concerned. In recent years, China Earthquake Administration has deployed a dense temporary seismic array in North China. With the permanent and temporary stations, we obtained the crust-mantle S-wave velocity structure in the central North China Craton by using the joint inversion of receiver function and surface wave dispersion. The results show that the crustal thickness is thick in the north of the Shanxi rift (42km) and thin in the south (35km). Datong basin, located in the north of the rift, exhibits large-scale low-velocity anomalies in the middle-lower crust and upper mantle; the Taiyuan basin and Linfen basin, located in the central part, have high velocities in the lower crust and upper mantle; the Yuncheng basin, in the southern part, has low velocities in the lower crust and upper mantle velocities, but has a high-velocity layer below 80 km. We speculate that an upwelling channel beneath the west of the Datong basin caused the low velocity anomalies there. In the central part of the Shanxi rift, magmatic bottom intrusion occurred before the tension rifting, so that the heated lithosphere has enough time to cool down to form high velocity. Its current lithosphere with high temperature may indicate the future deformation and damage. There may be a hot lithospheric uplift in the south of the Shanxi rift, heating the crust and the lithospheric mantle. The high-velocity layer in its upper mantle suggests that the bottom of the lithosphere after the intrusion of the magma began to cool down.</p>

High temperature in the upper mantle beneath Cape Verde as a possible cause for the oceanic lithosphere rejuvenation inferred from Rayleigh-wave phase-velocity measurements.

2020 ◽  
Author(s):  
Joana Carvalho ◽  
Raffaele Bonadio ◽  
Graça Silveira ◽  
Sergei Lebedev ◽  
Susana Custódio ◽  
...  
Keyword(s):  
Phase Velocity ◽  
Upper Mantle ◽  
Lower Mantle ◽  
Oceanic Lithosphere ◽  
Cape Verde ◽  
Seismic Velocities ◽  
Low Velocity ◽  
Period Range ◽  
Rayleigh Wave Phase Velocity ◽  
Central Atlantic

<p>Cape Verde is an intraplate archipelago located in the Atlantic Ocean about 560 km west of Senegal, on top of a ~130 Ma sector of the African oceanic lithosphere. Until recently, due to the lack of broadband seismic stations, the upper-mantle structure beneath the islands was poorly known. In this study we used data from two temporary deployments across the archipelago, measuring the phase velocities of Rayleigh-waves fundamental-modes in a broad period range (8–250 s), by cross-correlating teleseismic earthquake data between pairs of stations. Deriving a robust average, phase-velocity curve for the Cape Verde region, we inverted it for a shear-wave velocity profile using non-linear gradient search.</p><p>Our results show anomalously low velocities of ∼4.2 km/s in the asthenosphere, indicating the presence of high temperatures and, eventually, partial melting. This temperature anomaly is probably responsible for the thermal rejuvenation of the oceanic lithosphere to an age as young as about 30 Ma, which we inferred from the comparison of seismic velocities beneath Cape Verde and the ones representing different ages in the Central Atlantic.</p><p>The present results, together with previously detected low-velocity anomalies in the lower mantle and relatively He-unradiogenic isotopic ratios, also suggest a hot plume deeply rooted in the lower mantle, as the origin of the Cape Verde hotspot.</p><p><span>The author</span><span>s</span><span> would like to acknowledge the financial support FCT through project</span> <span>UIDB/50019/2020</span> <span>– IDL</span><span> and FIRE project Ref. PTDC/GEO- GEO/1123/2014.</span></p>

scholarly journals Speed structure of the mantle of the border of the Eastern European and West European platforms

2021 ◽  
Vol 43 (5) ◽  
pp. 181-192
Author(s):  
T. A. Tsvetkova ◽  
I. V. Bugaenko ◽  
L. N. Zaets
Keyword(s):  
Baltic Sea ◽  
Transition Zone ◽  
Upper Mantle ◽  
High Velocity ◽  
Oil And Gas ◽  
The Baltic Sea ◽  
Low Velocity ◽  
East European ◽  
The Baltic ◽  
West European

This work is devoted to studying the velocity structure of the mantle of the border area of the East European and West European platforms in the crust separated by the Teiserre-Tornquist zone. The mantle under the territory of Poland and Western Ukraine is being investigated. The work uses a three-dimensional P-velocity model of the mantle, constructed using the Taylor approximation method developed by V. S. Geyko. The method’s advantages are independent of the initial approximation (reference model) and the best approximation of nonlinearity. In this area, the exploration depth is 2500 km south of 50 °NL and 1700 km north of 50 °NL. A detailed analysis of horizontal sections of a 3D P-velocity model of the mantle up to a depth of 850 km with a step of 50 km has been carried out. The change in the spatial distribution of the zero seismic velocity boundary is analyzed throughout the depths. This boundary separates the high-velocity upper mantle of the East European Platform and the low-velocity upper mantle of the West European Platform. At the depths of the transition zone of the upper mantle, this boundary separates the low-velocity upper mantle of the East European platform and the high-velocity upper mantle of the West European platform (in this geosphere, a velocity inversion has occurred with respect to the upper mantle). In latitudinal sections, two inclined layers are distinguished. One of them is associated with the upper mantle under the DDV and reaches the mantle under the Carpathians, where it begins to plunge into the high-velocity transition zone of the upper mantle. The second layer is associated with the mantle under the northwestern end of the Baltic syneclise, which extends to the mantle under the Presudet monocline, where it also plunges into the high-velocity transition zone of the upper mantle. In longitudinal sections, inclined layers are distinguished, extending from the mantle under the South Scandinavian megablock of the Baltic Shield to the mantle under the Bohemian massif and the Carpathians, where they plunge into the high-velocity transition zone of the upper mantle. In the study area, three super-deep fluids were identified, characterized by increased stratification of the medium (alternation of higher and lower velocities). The first includes the well-known oil and gas fields of the Central European oil and gas basin (Pomorie and Presudet monocline (Poland)). The second is associated with oil and gas fields of the North Ciscarpathian oil and gas basin (southeastern Poland) and the Carpathian oil and gas basin (Western Ukraine). The extracted super-deep fluid in the mantle of the Baltic Sea corresponds to both the Gdansk Gulf of the Baltic Sea and the Kaliningrad fields (southeast of the Baltic Sea).

Lithosphere velocity structure of the Khibiny and Lovozero plutons (Eastern part of the Baltic shield) from receiver functions

2021 ◽  
Author(s):  
Andrey Goev
Keyword(s):  
Baltic Shield ◽  
Upper Mantle ◽  
Velocity Structure ◽  
Deep Structure ◽  
Joint Inversion ◽  
Receiver Functions ◽  
Function Technique ◽  
High Porosity ◽  
Low Velocity ◽  
The Baltic

<p>The Kola region of the Russian Arctic is located in the northeast of the Baltic Shield and is widely known for its unique geology in regards to the presence of massive Paleozoic intrusions. Multidisciplinary researches have been carried out to provide a comprehensive reconstruction of Khibiny and Lovozero plutons’ formation and their structure models The main source of geochronological data comes from isotope analysis of the arrays’ rocks. The amount of research focuses on the deep structure beneath the Khibiny pluton is scarce. To investigate velocity structure of the investigated region we used receiver function technique. Essence of the method is to analyze P-S (PRF) and S-P (SRF) converted waves form seismic boundaries along with their multiples. For the given research we used seismograms of the teleseismic events recorded by the Apatity (APA) and Lovozero (LVZ) broadband seismic stations since 2000. We selected 220 and 232 individual PRF;147 and 122 individual SRF for LVZ and APA station respectively. As both LVZ and APA are located relatively close to each other, we combined all 452 PRF to get a robust estimation of delay times of P410s and P660s phases. Our estimations of P410s and P660s phases are 43.6 and 67.6 sec respectively. Delay time between these phases is 24 sec that is close to “standard” according to the IASP91 model. The individual times of each phase are slightly less than predicted by IASP91 (by 0.4 sec) and could indicate an increase of velocities in the upper mantle, but it is not unusual for cratonic regions. Joint inversion of PRF and SRF was used to restore velocity sections for the depth up to 300 km. All models have shown a gradient increase in velocities in the earth's crust and sharp crust-mantle boundary at depth of 40 ± 1 km with a velocity jump from 3.9 to 4.4 km/s. The most prominent feature of the upper mantle structure is the presence of the low-velocity zone at a depth from 90 to 140 km. One of the possible explanation of this discontinuity could be the presence of deep fluids and the high porosity of this zone. This study was partially supported by the RFBR grant 18-05-70082 and the SRW theme No. АААА-А19-119022090015-6.</p>

2D crust-upper mantle velocity structure along a seismic section in Nanling, South China

2020 ◽  
Author(s):  
Jia-ji xi ◽  
Guo-ming jiang ◽  
Gui-bin zhang ◽  
Xiao-long he
Keyword(s):  
Upper Mantle ◽  
Velocity Structure ◽  
Ore Deposits ◽  
Low Velocity ◽  
Seismic Section ◽  
Late Mesozoic ◽  
Velocity Anomaly ◽  
Metallogenic Belt ◽  
Velocity Anomalies ◽  
Mantle Velocity

<p>    There exists an important polymetallic ore belt in Nanling of the southeastern China. Previous studies suggest that the mineralization of Nanling is probably related to the bottom intrusion of magmatic rocks in the late Mesozoic. In this study, a natural seismic section was installed by using 81 portable stations with an interval of 5 km from July 2017 to August 2019, which runs across the Nanling belt in the south of Fujian and Jiangxi provinces. As a result, we have picked up 3,818 relative residual data from 215 teleseismic events with magnitude greater than 5.5. And we have applied the teleseismic full-waveform tomography and the teleseismic travel-time tomography to study the crust and the mantle velocity structure beneath the Nanling metallogenic belt, respectively. Our preliminary results show that: (1) a clear low-velocity anomaly exists in the crust beneath the Zhenghe-Dapu fault and its east side, which might be related to the rich ore deposits in Nanling; (2) some high-velocity anomalies in the uppermost mantle beneath the Wuyi metallogenic belt may be relevant to the igneous rock cooling and the lithospheric thickening; (3) there are obvious low-velocity anomalies at the upper mantle beneath the Wuyi and Nanling metallogenic belts, which are speculated to be hot materials from asthenosphere upwelling into the bottom of the lithosphere. Our results provide a new insight for investigating the deep structures and deep dynamic processes of Nanling tectonic belt.</p>

A comparison of the receiver structure beneath stations of the Canadian National Seismograph Network

1995 ◽  
Vol 32 (7) ◽  
pp. 938-951 ◽  
Author(s):  
John F. Cassidy
Keyword(s):  
Northwest Territories ◽  
Upper Mantle ◽  
Velocity Structure ◽  
Receiver Functions ◽  
Canadian Shield ◽  
Low Velocity ◽  
Low Velocity Zone ◽  
Appalachian Orogen ◽  
Seismograph Network ◽  
Velocity Zone

Three-component broadband data from the recently deployed Canadian National Seismograph Network provide a new opportunity to examine the structure of the crust and upper mantle beneath the Canadian landmass. Receiver function analysis is an ideal method to use with this data set, as it can provide constraints on the S-velocity structure beneath each station of this seismograph network. This analysis method is particularly useful in that it provides site-specific information (i.e., within 5–15 km of the station), low-velocity layers can be identified, and it is possible to examine structure to upper mantle depths. In this study, receiver functions were computed for each of the 19 stations that made up the seismograph network in June 1994. Five stations, sampling a variety of tectonic environments, including the Appalachian Orogen, the Canadian Shield, the Western Canadian Sedimentary Basin, and the Cascadia subduction zone, were chosen for detailed modelling. The results presented here are the first estimates of the S-velocity structure beneath these five stations. For those stations where comparisons can be made with seismic reflection and refraction results, there is excellent agreement. In eastern Canada, simple receiver functions and clear Moho Ps conversions at most stations indicate a relatively transparent crust and a Moho depth of 40–45 km. In northwestern Canada, Moho Ps phases indicate a crustal thickness of 33–38 km. Beneath Inuvik, Northwest Territories, the Moho is interpreted as two velocity steps separated in depth by 5 km, and an upper mantle low-velocity zone is near 47 km depth. In western Canada, the data indicate a mid-crustal low-velocity zone beneath Edmonton. The Moho of the subducting Juan de Fuca plate is interpreted at 52 km depth beneath southern Vancouver Island. Several stations exhibiting complex receiver functions warrant further study. They include stations at Schefferville, Quebec, in the Canadian Shield; Deer Lake, Newfoundland, on the boundary of the Grenville Province and the Appalachian Orogen; and Yellowknife, Northwest Territories, at the intersection of the Churchill and Slave provinces and the Western Plains.

scholarly journals Teleseismic Tomography for Imaging the Upper Mantle Beneath Northeast China

2020 ◽  
Vol 10 (13) ◽  
pp. 4557
Author(s):  
Zhuo Jia ◽  
Gongbo Zhang
Keyword(s):  
Travel Time ◽  
Transition Zone ◽  
Upper Mantle ◽  
Northeast China ◽  
Time Data ◽  
Low Velocity ◽  
Mantle Transition Zone ◽  
Teleseismic Tomography ◽  
Travel Time Data ◽  
Velocity Anomalies

Tomographic imaging technology is a geophysical inversion method. According to the ray scanning, this method carries on the inversion calculation to the obtained information, and reconstructs the image of the parameter distribution rule of elastic wave and electromagnetic wave in the measured range, so as to delineate the structure of the geological body. In this paper, teleseismic tomography is applied by using seismic travel time data to constrain layered crustal structure where Fast Marching Methods (FMM) and the subspace method are considered as forward and inverse methods, respectively. Based on the travel time data picked up from seismic waveform data in the study region, the P-wave velocity structure beneath Northeast China down to 750 km is obtained. It can be seen that there are low-velocity anomalies penetrating the mantle transition zone under the Changbai volcano group, Jingpohu Volcano, and Arshan Volcano, and these low-velocity anomalies extend to the shallow part. In this paper, it is suggested that the Cenozoic volcanoes in Northeast China were heated by the heat source provided by the dehydration of the subducted Pacific plate and the upwelling of geothermal matter in the lower mantle. The low-velocity anomaly in the north Songliao basin does not penetrate the mantle transition zone, which may be related to mantle convection and basin delamination. According to the low-velocity anomalies widely distributed in the upper mantle and the low-velocity bodies passing through the mantle transition zone beneath the volcanoes, this study suggests that the Cenozoic volcanoes in Northeast China are kindred and have a common formation mechanism.

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