Occurrence of the ophiolitic complexes along the Indoburman orogenic belt

1983 ◽  
Vol 120 (2) ◽  
pp. 175-182 ◽  
Author(s):  
R. Duarah ◽  
M. M. Saikia ◽  
C. C. Bhattacharjee
Keyword(s):  
Upper Mantle ◽  
Deep Sea ◽  
Lower Cretaceous ◽  
Late Jurassic ◽  
Orogenic Belt ◽  
Indian Plate ◽  
Mantle Material ◽  
Crust And Upper Mantle ◽  
Thrust Sheets ◽  
Ophiolitic Belt

SummaryThe ophiolitic complexes within the Indoburman orogenic belt form a conspicuous N-S line along the eastern margins of Manipur and Nagaland. The rock assemblages consisting of mafic-ultramafics are associated with deep sea pelagic sediments of the Disang Group (Lower Cretaceous-Eocene). The ultramafics in part, represent the oceanic crust and upper mantle material that formed the basement on which the radiolarites and other pelagic sediments were deposited. The fossil radiolaria present in the cherts suggest that the orogen took its foundation during late Jurassic-Lower Cretaceous time. The westward obduction of the flysch ophiolites in the form of large thrust sheets was possible during underthrusting of the Indian plate beneath the Burmese. The position of the ophiolitic belt defines the Indoburman suture zone.

A suite of alkali basalts and gabbros associated with the Hare Bay Allochthon of western Newfoundland

1977 ◽  
Vol 14 (3) ◽  
pp. 346-356 ◽  
Author(s):  
R. A. Jamieson
Keyword(s):  
Oceanic Crust ◽  
Continental Margin ◽  
Upper Mantle ◽  
Ultramafic Rocks ◽  
Alkali Basalts ◽  
Crust And Upper Mantle ◽  
Bay Area ◽  
Close Proximity ◽  
Thrust Sheets

The Hare Bay Allochthon of northwestern Newfoundland consists of a series of sedimentary, volcanic, metamorphic, and ultramafic rocks which was emplaced over a Cambro-Ordovician continental margin as several thrust sheets. It probably represents a continental margin sequence overridden by oceanic crust and upper mantle. The Partridge Point gabbro, Cape Onion volcanics, and Ireland Point Volcanics, which now occur in the Maiden Point, Cape Onion, and St. Anthony tectonic slices respectively, appear to be closely related on petrographic and chemical grounds. Olivine, titanaugite, kaersutite, and plagioclase indicate that these rocks formed as a single suite of hydrous alkali basalts, possibly as part of a seamount near a continental margin. This relationship provides a link between the lower sedimentary and the upper igneous-metamorphic structural slices of the allochthon and implies that most of the transported rocks in the Hare Bay area evolved in close proximity to each other.

Seismic evidence for the subduction of North China Block to Yangtze Block beneath Tongbai-Dabie Orogenic belt

2020 ◽  
Author(s):  
Hongwei Zheng
Keyword(s):  
Upper Mantle ◽  
High Velocity ◽  
North China ◽  
Orogenic Belt ◽  
Late Triassic ◽  
Yangtze Block ◽  
North China Block ◽  
Crust And Upper Mantle ◽  
Dabie Orogenic Belt ◽  
Velocity Anomalies

<p>The Tongbai-Dabie Orogenic belt formed in the Middle-to-Late Triassic through a collision between the Yangtze Block (YB) and North China Block (NCB) and is a key component of the Central Orogen of China, which is famous on the most extensive high and ultrahigh pressure (HP/UHP) metamorphic zone in the world and marks the irregular suture between the YB and NCB. It is an ideal place to study the ancient orogenic processes between collided continents. In this study, we used a large number of P-wave arrival times recorded by portable and permanent seismic stations to reveal the structure of the crust and upper mantle beneath the Tongbai-Dabie orogenic belt and its adjacent region. Our images show the south-dipping high-velocity anomalies beneath the Tongbai-Dabie orogenic belt and the east-dipping high-velocity anomalies beneath the Tanlu Fault, which represent the southeastward subducted NCB in Mesozoic. While a huge high-velocity anomaly beneath the Wudang Moutin region extending down to 250 km is possible the ancient lithosphere of the Yangtze Craton remnant since the Paleoproterozoic. The northward subducted YB is only limited in the Eastern Dabie terrane and Yangtze foreland. Break-off retained Paleo-Tethyan oceanic slab are revealed at depths from the upper mantle 250 to 400 km. The structure of the crust and upper mantle suggests that the southeastward subduction of NCB resulted in the collision of NCB with YB.</p>

scholarly journals Lithospheric dynamics in the vicinity of the Tengchong volcanic field (southeastern margin of Tibet): an investigation using P receiver functions

2020 ◽  
Vol 224 (2) ◽  
pp. 1326-1343
Author(s):  
Hengchu Peng ◽  
José Badal ◽  
Jiafu Hu ◽  
Haiyan Yang ◽  
Benyu Liu
Keyword(s):  
Upper Mantle ◽  
Lower Crust ◽  
Volcanic Field ◽  
Receiver Functions ◽  
Indian Plate ◽  
Fast Wave ◽  
Low Velocity ◽  
Crust And Upper Mantle ◽  
Velocity Anomaly ◽  
Lateral Extrusion

SUMMARY Tengchong volcanic field (TVF) in the northern Indochina block lies in a critical area for understanding complex regional dynamics associated with continent–continent convergence between the Indian and Eurasian plates, including northeastward compression generated by subduction of the Indian Plate beneath the Burma Arc, and southeastward lateral extrusion of the crust from below central Tibet. We gathered 3408 pairs of P receiver functions with different frequencies and calculated the splitting parameters of the Moho-converted Pms phase. An anisotropic H-κ stacking algorithm was used to determine crustal thickness and Vp/Vs ratios. We also inverted for the detailed S-velocity structure of the crust and upper mantle using a two-step inversion technique. Finally, we mapped the topography of the lithosphere–asthenosphere boundary. Results show fast-wave polarization directions with a dominant NE–SW orientation and delay times varying between 0.19 and 1.22 s, with a mean of 0.48 ± 0.07 s. The crustal Vp/Vs ratio varies from 1.68 to 1.90 and shows a maximum value below the central part of the TVF, where there is relatively thin crust (∼35–39 km) and a pronounced low-velocity anomaly in the middle–lower crust. The depth of the lithosphere–asthenosphere boundary ranges from 53 to 85 km: it is relatively deep (∼70–85 km) in the vicinity of the TVF and relatively shallow in the south of the study area. In the absence of low shear wave velocity in the upper mantle below the TVF, we propose that the low-velocity anomaly in the lower crust beneath the TVF derives from the upper mantle below the neighbouring Baoshan block.

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