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.

Travel-time curves and upper-mantle structure from long period S waves

1967 ◽  
Vol 57 (5) ◽  
pp. 1063-1092 ◽  
Author(s):  
Abou-Bakr K. Ibrahim ◽  
Otto W. Nuttli
Keyword(s):  
Travel Time ◽  
Upper Mantle ◽  
Earth Model ◽  
S Wave ◽  
Time Data ◽  
Low Velocity ◽  
S Waves ◽  
Long Period ◽  
Travel Time Data ◽  
Proposed Model

abstract Long-period S-wave travel-time data, including second and later arrivals, are presented for distances of 3° to 65° for focal depths of 33 and 120 km. Onset times were determined on the basis of particle motion diagrams and the product of the horizontal radial and vertical components of motion. Because the recording stations principally were LRSM units, the travel times represent data for an “average” United States earth model. An S-wave velocity distribution calculated for the upper mantle provides a satisfactory fit to the empirical travel-time data for focal depths of both 33 and 120 km. The proposed model contains a pronounced low-velocity layer at a depth of about 150-200 km, and secondary low-velocity layers at depths of 340-370 km and of 670-710 km. In addition, there are regions of rapidly increasing velocity beginning at depths of about 400 and 750 km, and constant velocity zones at 220-350 km and 400-670 km.

Intraplate and petit-spot volcanism originating from hydrous mantle transition zone

2020 ◽  
Author(s):  
Jianfeng Yang ◽  
Manuele Faccenda
Keyword(s):  
Transition Zone ◽  
Northeast China ◽  
Subduction Zones ◽  
Japan Trench ◽  
Low Velocity ◽  
Iranian Plateau ◽  
Mantle Transition Zone ◽  
Mantle Minerals ◽  
Ocean Ridges ◽  
Pacific Slab

<p>Most magmatism occurring on Earth is conventionally attributed to passive mantle upwelling at mid-ocean ridges, slab devolatilization at subduction zones, and mantle plumes. However, the widespread Cenozoic intraplate volcanism in northeast China and the peculiar petit-spot volcanoes offshore the Japan trench cannot be readily associated with any of these mechanisms. Furthermore, the seismic tomography images show remarkable low velocity zones (LVZs) sit above and below the mantle transition zone which are coincidently corresponding to the volcanism. Here we show that most if not all the intraplate/petit-spot volcanism and LVZs present around the Japanese subduction zone can be explained by the Cenozoic interaction of the subducting Pacific slab with a hydrous transition zone. Numerical modelling results indicate that 0.2-0.3 wt.% H<sub>2</sub>O dissolved in mantle minerals which are driven out from the transition zone in response to subduction and retreat of a stagnant plate is sufficient to reproduce the observations. This suggests that critical amounts of volatiles accumulated in the mantle transition zone due to past subduction episodes and/or delamination of volatile-rich lithosphere could generate abundant dynamics triggered by recent subduction event. This model is probably also applicable to the circum-Mediterranean and Turkish-Iranian Plateau regions characterized by intraplate/petit-spot volcanism and LVZs in the underlying mantle.</p>

scholarly journals Insights from the P Wave Travel Time Tomography in the Upper Mantle Beneath the Central Philippines

2021 ◽  
Vol 13 (13) ◽  
pp. 2449
Author(s):  
Huiyan Shi ◽  
Tonglin Li ◽  
Rui Sun ◽  
Gongbo Zhang ◽  
Rongzhe Zhang ◽  
...  
Keyword(s):  
Travel Time ◽  
Upper Mantle ◽  
High Velocity ◽  
Velocity Structure ◽  
The Philippines ◽  
P Wave ◽  
The South ◽  
Teleseismic Tomography ◽  
The North ◽  
Velocity Anomalies

In this paper, we present a high resolution 3-D tomographic model of the upper mantle obtained from a large number of teleseismic travel time data from the ISC in the central Philippines. There are 2921 teleseismic events and 32,224 useful relative travel time residuals picked to compute the velocity structure in the upper mantle, which was recorded by 87 receivers and satisfied the requirements of teleseismic tomography. Crustal correction was conducted to these data before inversion. The fast-marching method (FMM) and a subspace method were adopted in the forward step and inversion step, respectively. The present tomographic model clearly images steeply subducting high velocity anomalies along the Manila trench in the South China Sea (SCS), which reveals a gradual changing of the subduction angle and a gradual shallowing of the subduction depth from the north to the south. It is speculated that the change in its subduction depth and angle indicates the cessation of the SCS spreading from the north to the south, which also implies that the northern part of the SCS opened earlier than the southern part. Subduction of the Philippine Sea (PS) plate is exhibited between 14° N and 9° N, with its subduction direction changing from westward to eastward near 13° N. In the range of 11° N–9° N, the subduction of the Sulu Sea (SS) lies on the west side of PS plate. It is notable that obvious high velocity anomalies are imaged in the mantle transition zone (MTZ) between 14° N and 9° N, which are identified as the proto-SCS (PSCS) slabs and paleo-Pacific (PP) plate. It extends the location of the paleo-suture of PSCS-PP eastward from Borneo to the Philippines, which should be considered in studying the mechanism of the SCS and the tectonic evolution in SE Asia.

scholarly journals Seismic structure of the lithosphere and upper mantle beneath the ocean islands near mid-oceanic ridges

Solid Earth ◽  
2014 ◽  
Vol 5 (1) ◽  
pp. 327-337 ◽  
Author(s):  
C. Haldar ◽  
P. Kumar ◽  
M. Ravi Kumar
Keyword(s):  
Transition Zone ◽  
Upper Mantle ◽  
Hot Spot ◽  
Quality Data ◽  
Moho Depth ◽  
Seismic Structure ◽  
Low Velocity ◽  
Mantle Transition Zone ◽  
Lithospheric Thickness ◽  
Ocean Islands

Abstract. Deciphering the seismic character of the young lithosphere near mid-oceanic ridges (MORs) is a challenging endeavor. In this study, we determine the seismic structure of the oceanic plate near the MORs using the P-to-S conversions isolated from quality data recorded at five broadband seismological stations situated on ocean islands in their vicinity. Estimates of the crustal and lithospheric thickness values from waveform inversion of the P-receiver function stacks at individual stations reveal that the Moho depth varies between ~ 10 ± 1 km and ~ 20 ± 1 km with the depths of the lithosphere–asthenosphere boundary (LAB) varying between ~ 40 ± 4 and ~ 65 ± 7 km. We found evidence for an additional low-velocity layer below the expected LAB depths at stations on Ascension, São Jorge and Easter islands. The layer probably relates to the presence of a hot spot corresponding to a magma chamber. Further, thinning of the upper mantle transition zone suggests a hotter mantle transition zone due to the possible presence of plumes in the mantle beneath the stations.

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.

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