Seismic imaging of the deep crustal structure beneath Eastern Ghats Mobile Belt (India): Crustal growth in the context of assembly of Rodinia and Gondwana supercontinents

2019 ◽  
Vol 331 ◽  
pp. 105343
Author(s):  
Arun Singh ◽  
Chandrani Singh
2020 ◽  
Author(s):  
Arun Singh ◽  
Chandrani Singh

<p>We present the first high resolution seismic images illuminating the hitherto-elusive crustal architecture beneath the Eastern Ghats Mobile Belt (EGMB) using teleseismic receiver functions. Data were collected using 27 broadband seismic stations operated in a continuous mode covering two distinct seismic profiles (~550 km long) during 2015–2018. Several interesting observations and inferences are made through analysis of the receiver functions such as (a) a very thick crust (>40 km) with oppositely dipping Moho beneath the EGMB and Archean Bastar Craton, (b) EGMB formed from amalgamation of different crustal domains thrust over one another possibly during the Pan-African orogeny, (c) the Archean Bastar Craton crust extends (~75 km) eastward beneath the EGMB, from its surficial geological boundary, (d) there is a sharp contrast in the crustal structure (with ~20 km Moho offset) at the contact between the Rengali Province and Singhbhum Craton which does not support southward growth of the Singhbhum Craton through accretion, (e) anorthosite complexes may possibly be created by rising diapirs channeled through the weak zones in the crust, from the magma chambers developed by melting of frontal portion of the underthrusting lower crust. We report a significant change in the crustal architecture just east of the most elevated topography observed along the profile covering the Bastar Craton and the EGMB. It requires further careful petrological investigations to ascertain the relationship of high elevation and its linkages with the deep crust, forming a separate domain. Our results do not support or discard a Grenvillian age (~1 Ga) docking of the EGMB with Proto-India, though it is preferred to explain the present day crustal features with intense Pan-African (0.5–0.6 Ga) reorganization.</p>


Author(s):  
J. K. Nanda ◽  
U. C. Pati

While congratulating the authors for the wealth of geochemical data on a very important Precambrian lithological assemblage of India, known commonly as khondalites, which constitute a major part of the Eastern Ghats mobile belt bordering the eastern fringes of the Indian Peninsula, we have a few comments to offer on the hypothesis propounded by the authors (Dash et al. 1987).


2019 ◽  
Vol 289 ◽  
pp. 20-33
Author(s):  
Niptika Jana ◽  
Arun Singh ◽  
Ashwani Kant Tiwari ◽  
Chandrani Singh ◽  
Rahul Biswas

2020 ◽  
Author(s):  
Ritabrata Dobe ◽  
Saibal Gupta

<p>The Remal granite-gneiss is situated close to the tectonic boundary between the Singhbhum Craton and the Rengali Province in the state of Odisha, eastern India. This granite-gneiss contains two prominent fabric elements - a sub-horizontal to gently dipping felsic fabric S<sub>ign</sub>, believed to be of igneous origin that predates a sub-vertical gneissosity S<sub>1</sub> which is of tectonic origin. S<sub>ign</sub> layers have a non-uniform, arcuate geometry and grain-size within the layers show systematic variations. S<sub>1</sub> is defined by metre-scale segregations of biotite-poor and biotite-rich domains whose orientations are constant. S<sub>ign</sub> layers are arranged rhythmically in cross-section and either curve into parallelism with or truncate against layers above and below; the entire assembly resembles cross beds developed in sediments. Some of the layers develop trough cross-bedding similar to those seen in mafic intrusions such as the Skaergaard Complex, indicative of slumping of a crystallizing mush along an inclined depositional plane at the time of crystallization. The S<sub>ign</sub> layers are composed of quartz, K-feldspar and plagioclase with abundant graphic intergrowths and myrmekite, and lack any evidence of compaction. Plagioclase grains are often zoned, and dihedral angles between mineral grains is significantly different from the equilibrium value of 120°, testifying to the preservation of the igneous nature of this fabric without significant solid state modification. In contrast, S<sub>1</sub> is sub-parallel to localized mylonite zones within the granite-gneiss composed of chlorite and epidote, indicative of deformation under greenschist facies conditions. The mylonitized zones contain prominent dextral shear sense indicators and is believed to have originated due to the amalgamation of the Rengali Province with the Eastern Ghats Mobile Belt along the east-west trending, sub-vertical Brahmani Shear Zone further to the south. The S<sub>1</sub> gneissosity appears to have developed as a result of this deformation event. EBSD analyses of quartz grains within the granite-gneiss reveal distinct variations in the distribution of <c> axes in different domains. Close to the mylonite zones, deformation of quartz has been dominantly accommodated by basal <a> slip with a dextral shearing overprint while away from these zones and S<sub>1, </sub>the <c> axes are distributed in clusters without any systematic pattern. The persistence of an earlier igneous layering, despite the subsequent development of a gneissosity concomitant with localised mylonitisation, indicates that the later deformation event has not obliterated the earlier formed igneous fabric. The study also demonstrates that development of a gneissosity does not necessarily require deformation operating at moderate to high temperature, and can stabilize even under greenschist facies conditions.</p>


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