Formation of the North–South Seismic Zone and Emeishan Large Igneous Province in Central China: Insights from P-Wave Teleseismic Tomography

2020 ◽  
Vol 110 (6) ◽  
pp. 3064-3076
Author(s):  
Chuansong He ◽  
M. Santosh
Keyword(s):  
High Velocity ◽  
Large Scale ◽  
P Wave ◽  
Large Igneous Province ◽  
Seismic Zone ◽  
Teleseismic Tomography ◽  
Emeishan Large Igneous Province ◽  
The North ◽  
Igneous Province ◽  
Stress Accumulation

ABSTRACT The geodynamic features of the north–south seismic zone (NSSZ) and the formation of the Emeishan large igneous province (ELIP) in China remain controversial. In this study, we conducted detailed P-wave teleseismic tomography studies in the NSSZ and adjacent regions. The results revealed large high-velocity anomalies beneath the Songpan–Ganzi Block and the South China Block, possibly representing large-scale lithospheric delamination. We further identified low-velocity structures at 50–200 km depths in the western and southern parts of the NSSZ, suggesting an upwelling asthenosphere induced by delamination and the absence of a rigid lithosphere. Two high-velocity structures beneath the Sichuan basin and the Alashan block were also revealed, which may represent the lithospheric roots of these structures. These rigid lithospheric roots may have obstructed the eastward extrusion of the Tibetan plateau and led to stress accumulation and release (triggering earthquakes) in the Longmenshan Orogenic Belt and the northern part of the NSSZ. Because of this obstruction, the eastward extrusion was redirected southeastward to Yunnan in the southern part of the NSSZ, which led to stress accumulation and release causing earthquakes along the Honghe and Xiaojiang faults. The results from this study reveal a high-velocity structure with a subducted slab-like appearance that may represent vestiges of the Paleo-Tethys oceanic lithosphere, which subducted beneath the ELIP and initiating large-scale mantle return flow or mantle upwelling, contributing to the formation of the ELIP.

scholarly journals The formation of North-South Seismic Zone and Emeishan large igneous province in Western China: Insight from teleseismic tomography

2019 ◽  
Author(s):  
Chuansong He
Keyword(s):  
High Velocity ◽  
Large Scale ◽  
Western China ◽  
Large Igneous Province ◽  
The Tibetan Plateau ◽  
Seismic Zone ◽  
Study Region ◽  
Teleseismic Tomography ◽  
Emeishan Large Igneous Province ◽  
Igneous Province

Abstract. Several models have been suggested to explain the earthquake mechanism of the North-South Seismic Zone (NSSZ) and the formation of the Emeishan Large Igneous Province (ELIP). In this study, I extended the study region and carried out detailed teleseismic tomography in the NSSZ and near-by regions. Results identified by this study reveal large plate-like high-velocity anomalies beneath the Songpan-Ganzi Block and the South China Block, which may be associated with large-scale lithospheric delamination, and low-velocity structures at 50–200 km depths in the western and southern parts of this study region, which imply upwelling asthenosphere induced by delamination and the absence of the rigid lithosphere there. Two high-velocity structures beneath the Sichuan Basin and the Alashan Block are revealed, which might be the lithospheric roots of these structures. These rigid lithospheric roots obstructed the eastward extrusion of the Tibetan Plateau and led to stress accumulations and releases (earthquakes) in the Longmenshan Orogenic Belt and the northern part of the NSSZ. Due to obstruction by the Sichuan Basin’s lithosphere, eastward extrusion was redirected southeastward to Yunnan in the southern part of the NSSZ, which led to stress accumulations and releases (earthquakes) along the Honghe and Xiaojiang Faults. This study provide velocity images reveal a slab-like high-velocity structure, which might be associated with the lithospheric vestige of the Paleo-Tethys Ocean that subducted beneath the ELIP, which resulted in large-scale return mantle flow or mantle upwelling and contribute to the LIP formation in early Mesozoic.

Geochronology, isotopic and Platinum-group elemental geochemistry of lavas and dykes from the western Guangxi in outer zone of Emeishan mantle plume, SW China

2021 ◽  
Author(s):  
Bing Zhao ◽  
Xijun Liu ◽  
Zhenglin Li ◽  
Wenmin Huang ◽  
Chuan Zhao
Keyword(s):  
Partial Melting ◽  
Mantle Source ◽  
Large Scale ◽  
Outer Zone ◽  
Large Igneous Province ◽  
Yangtze Block ◽  
Mafic Rocks ◽  
Emeishan Large Igneous Province ◽  
Low Degree ◽  
Igneous Province

<p>The Emeishan flood basalts are part of an important large igneous province along the western margin of the Yangtze Block, Southwest China. The western Guangxi region in southwestern China is geologically a part of the Yangtze Block. Mafic rocks, comprising mainly lavas and dykes in western Guangxi belong to the outer part of the ~260 Ma Emeishan Large Igneous Province (ELIP). Here we present a systematic study of platinum-group elements (PGEs) combined with the LA-ICP-MS zircon U–Pb age, whole-rock geochemical and isotopic data of the lavas and dykes in the Longlin area of outer zone of ELIP to constraints on their origin. On the basis of petrography and major elements characteristics, mafic lavas and dykes display an enrichment of LREE, LILE, HFSE, high (<sup>87</sup>Sr/<sup>86</sup>Sr)<sub>i</sub> ratios (0.704227~0.705754), low ε<sub>Nd</sub><sub>(t)</sub> values(0.42~0.99), high ε<sub>Hf</sub><sub>(t)</sub> values(5.19~6.04), they are similar to those of Permian Emeishan high-Ti basalts and Ocean island basalts (OIB) features. The Longlin mafic rocks was formed in the Late Permian with the zircon U-Pb dated age of 256.3± 1.7 Ma. The age of the Longlin mafic rocks is close to the formation age of the ELIP large-scale magmatism, suggesting that these lavas and dykes probably belongs to part of the ELIP large-scale magmatism. The Longlin mafic rocks have low total PGE contents ranging from 1.56×10<sup>-9 </sup>to 2.28×10<sup>-9</sup>, with Os, Ir, Ru, Rh, Pt and Pd contents of 0.040~0.076, 0.046~0.076, 0.027~0.079, 0.037~0.056, 0.6374~1.053 and 0.715~1.021ppb, respectively. They show left-leaning primitive mantle-normalized PGE patterns with depletion in Iridium group(IPGE) and enrichment in Palladium group, which also have lower contents than mafic rocks from the inner zone of the ELIP, suggesting that a low degree of partial melting of the mantle source plays an important role. The Longlin mafic rocks exhibit a marked increase in Cu/Pd ratios (>10<sup>5</sup>,84655 to 174785) albeit with a narrow range of lower Pd/Ir ratios (<50,13.4 to 18.7), different from the PGE-enriched basalts of the Siberian Traps, Emeishan Large Igneous Province (ELIP), East Greenland CFBs and Deccan Traps, indicating that their parent magmas was significantly depleted in chalcophile elements. Calculations based on the available trace element geochemistry reveal that the basalts were originated by low degree of partial melting(<5%)，with sulfides remain in the mantle during partial melting. Sulfide segregation could not happen during the evolution of the Longlin mafic rocks, due to the fact that neither significant fractional crystallization nor crustal contamination has been involved in their formation. Overall, mafic rocks from the outer zone of the ELIP show lower PGE contents than those in the inner zones, we find that the PGE contents in igneous rocks are related with the degrees of partial melting in the mantle source and the removal of sulfides before their emplacement.</p><p>This study was financially supported by the Guangxi Natural Science Foundation for Distinguished Young Scholars (2018GXNSFFA281009) and the Fifth Bagui Scholar Innovation Project of Guangxi Province (to XU Ji-feng).</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 The Splitting 660 km Discontinuity Associated with Lithospheric Delamination in the Northern Part of the North-South Seismic Zone, China

2021 ◽  
Author(s):  
Chuansong S. He
Keyword(s):  
Large Scale ◽  
Receiver Functions ◽  
The Tibetan Plateau ◽  
Seismic Zone ◽  
The North ◽  
Conversion Point ◽  
Teleseismic Data ◽  
Earthquakes In China ◽  
North Part ◽  
Stress Accumulation

Abstract The north-south seismic zone (NSSZ) is a destructive zone of large-scale earthquakes in China, and the earthquake mechanism associated with deep structures remains unclear. Previous studies have indicated that lithospheric delamination or absence of lithospheres in the western part of the NSSZ may facilitate the eastern extrusion of the Tibetan Plateau and lead to stress accumulation and release. However, the deep process of lithospheric delamination needs to be further clarified. In this study, I collect abundant high-quality teleseismic data recorded by permanent seismic stations and perform common conversion point (CCP) stacking of receiver functions in the north part of the NSSZ. The results show that lithospheric delamination might result in the splitting 660 km discontinuity and a thickening region of the mantle transition zone (MTZ).

Deep velocity image of the north Zagros collision zone (Iran) from regional and teleseismic tomography

2019 ◽  
Vol 219 (3) ◽  
pp. 1729-1740 ◽  
Author(s):  
M Rahmani ◽  
K Motaghi ◽  
A Ghods ◽  
F Sobouti ◽  
M Talebian ◽  
...  
Keyword(s):  
Upper Mantle ◽  
High Velocity ◽  
Velocity Structure ◽  
Central Iran ◽  
P Wave ◽  
Arabian Plate ◽  
Zagros Mountains ◽  
Teleseismic Tomography ◽  
The North ◽  
Collision Zone

SUMMARY We inverted 3555 regional and teleseismic P-wave relative time residuals to resolve deep velocity structure beneath the NW part of the Zagros collision zone. The data were gathered by 46 seismic stations installed along a ∼520-km-long seismic profile crossing the Zagros Mountains, Central Iran and the western Alborz Mountains. The obtained tomogram reveals a high velocity lithospheric root beneath the Zagros Mountains and a low velocity wedge in the frontal edge of the Arabian Plate beneath the suture that might be interpreted as beginning of delamination of lower part of the Arabian mantle lithosphere from its upper part. A significant deep (depth >350 km) high velocity feature is observed in the lower part of the upper mantle to the north of the Zagros suture and beneath Central Iran. We interpret this feature as the remains of oceanic slab of the Neotethys lying in the lower portion of the upper mantle and the transition zone.

A subducted slab of the Paleo-Tethys oceanic lithosphere associated with the formation of the Emeishan large igneous province

2020 ◽  
Author(s):  
Chuansong He
Keyword(s):  
Large Scale ◽  
Oceanic Lithosphere ◽  
Receiver Functions ◽  
Large Igneous Province ◽  
Mantle Flow ◽  
Mantle Dynamics ◽  
Tomographic Images ◽  
Emeishan Large Igneous Province ◽  
Velocity Anomaly ◽  
Igneous Province

<p>The formation of large igneous provinces is a focus of geoscientists and is a major scientific issue in mantle dynamics. A broad consensus holds that the Emeishan large igneous province (ELIP) was generated by an upwelling mantle plume. However, recent geological and seismic studies have challenged this notion. In this study, I redraw and reanalyze previous tomographic images and use images of three velocity perturbation profiles crossing the ELIP. I collected abundant high-quality teleseismic data and performed common conversion point (CCP) stacking of receiver functions in the mantle transition zone (MTZ) of the ELIP. The tomographic images show a high-velocity anomaly of a northeastward-subducted slab-like body beneath the ELIP, which might be a relic of the Paleo-Tethys oceanic lithosphere. Images from CCP stacking of receiver functions indicate that the subducted slab of the Paleo-Tethys oceanic lithosphere retained an imprint on the X-discontinuity and the 410 and 660 km discontinuities. Based on my assessment, the subducted slab might have induced return mantle flow or large-scale mantle upwelling, which possibly played an important role in the formation of the ELIP.</p>

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