Kimberlite from Rajmahal magmatic province: Sr‐Nd‐Pb isotopic evidence for Kerguelen plume derived magmas

Ahmad

2007

Geochem. J.

Chotanagpur Gneissic Complex basement rocks of the Eastern Indian shield has been dissected by numerous mafic dykes, now occurring as amphibolitic dykes and gneissic amphibolites. These dykes are subalkaline, ranging in composition from basalt through basaltic-andesite to andesite. These rocks have enriched incompatible trace element patterns. These are particularly enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE) with depleted high field strength elements (HFSE; Nb, P, Ti) characterisitcs (i). Negative Sr anomaly is conspicuous. Nb/La and Nb/Ce ratios of the dykes are lower compared to the primitive mantle but these values are closer to average crustal values. Incompatible trace element data suggest enriched source characteristics and influence of crustal contamination in their genesis. Trace element ratios such as Gd/Yb of these dykes indicate at least two different sources. They probably represent Precambrian continental rifting in this region.

Section: (B) Geological Map Of Chotanagpur and Singbhum Regions Shomentioning

confidence: 70%

Geochemistry of mafic dykes in part of Chotanagpur gneissic complex: Petrogenetic and tectonic implications

Ahmad

2007

Geochem. J.

“…Major events include wide spread rifting in the Late Jurassic related to the Gondwana break‐up apparently caused by a hotspot [ Talukdar and Murthy , 1970]. This was followed by a massive eruption of the Sylhet flood basalts farther south, about 117 Ma ago due to passage of the Kerguelen hotspot [ Kumar et al , 2003]. Such episodes are capable of generation of melts that could manifest as the observed 300‐km discontinuity following the third mechanism discussed above.…”

Section: Resultsmentioning

confidence: 99%

Moho geometry and upper mantle images of northeast India

Ramesh

Geophysical Research Letters

Devi

et al. 2005

[1] Images of the crust and mantle beneath northeast India obtained by 2D migration of $1000 broadband P-receiver functions clearly trace a northward dipping Moho from the Himalayan foredeep reaching depths up to 50 km further north beneath the Himalayan convergence zone. Also, these images reveal presence of largely coherent 410-km and 660-km discontinuities that conform to the IASP91 model. Marginal variations in the depth of the 410-km interface are observed, that appear region specific. The thickness of the mantle transition zone does not deviate significantly from a global average of $250 km. Interestingly, our results reveal consistent presence of a signal from an interface around 300 km. Origin of such a boundary, known as X-discontinuity and unrelated to the Lehmann discontinuity, is discussed. Possible presence of the X-discontinuity from the Indian region is reported here for the first time. Citation:

“…Various hypotheses have been proposed to explain the Shillong uplift, which include isostatic adjustment (Das Gupta & Biswas 2006), thermal disturbance during Jurassic, which resulted in uplift that is still continuing (Kailasam 1979) and pop‐up due to tectonic forces (Rao & Kumar 1997; Bilham & England 2001). Also, two prominent faults to the south of the Shillong plateau acted as vents to the eruption of Sylhet traps about 116 Ma (Ray et al 2005), as a consequence of the heating of the Indian Plate as it passed over the Kerguelen hotspot (Kumar et al 2004a).…”

Section: Study Regionmentioning

confidence: 99%

Imaging the Indian lithosphere beneath the Eastern Himalayan region

Devi

Geophysical Journal International

2011

SUMMARY Lithospheric thickness is an important parameter to understand the nature of collision and subduction between the Indian and Asian tectonic plates. In this study, we apply the S receiver function technique to data from a network of broad‐band stations in the northeast India and Eastern Himalayan regions and image the geometry of Indian Plate collision. This analysis reveals clear S‐to‐p conversions from the Moho and Lithosphere‐‐Asthenosphere boundary (LAB) in the various tectonic units of the study region. The Indian lithosphere is found to be only 90 km thick beneath the Shillong plateau deepening to 135 km on either side suggestive of a lithospheric upwarp related to the plateau uplift. The lithosphere thickens northward, with values reaching ∼180 km beneath the Eastern Himalaya. The trend of the LAB north of the foredeep region indicates that the Indian Plate plunges beneath the Eastern Himalaya. The consistent northward‐dipping character of the Indian Plate suggests that the Indian Plate is traceable until it gets subducted beneath Tibet just south of Bangong suture zone. The deepening of the LAB and its correlation with the topographic elevation is in agreement with homogeneous thickening of the lithosphere in response to compressive forces due to the continental collision of India with Asia.