Khan Z.A.,Directorate of Geology and Mining |
Tewari R.C.,P.A. College
Journal of Asian Earth Sciences | Year: 2011
The quantitative relationships between lithological variables from the Late Paleozoic coal bearing cycles have been investigated using factor analysis in an attempt to analyze net subsidence during the deposition of these cycles. The results suggest that there are only two non-zero eigenvalues in varimax matrix which indicate that the hyper ellipsoid enclosing the data points have seven axes of zero length and exists an ordinary two dimensional ellipsoid. The data points can be located with reference to two mutually perpendicular axes. Loading on thickness of sandstones, thickness of shale, number of sandstone beds and number of shale beds are extremely high on RF-I and low on the other factor. This would lead to the interpretation that a balance was maintained throughout the Barakar sedimentation between the rate of deposition and the rate of subsidence. On the other hand, loading on number of coal beds is high on ' suggesting that the development of peat swamps (coal beds) is not a normal feature during the Late Paleozoic Barakar sedimentation in this Gondwana sub-basin. © 2010 Elsevier Ltd.
Tewari R.,University of Lucknow |
Awatar R.,University of Lucknow |
Pandita S.K.,Jammu University |
McLoughlin S.,Swedish Museum of Natural History |
And 5 more authors.
Earth-Science Reviews | Year: 2015
This first palynological study of the Permian-Triassic succession in the Guryul Ravine, Kashmir, India, reveals impoverished latest Permian spore-pollen assemblages in the uppermost Zewan Formation, a rich palynoassemblage from the basal Khunamuh Formation characteristic of the Permian-Triassic transition zone and depleted Triassic assemblages from higher in the Khunamuh Formation. The collective assemblages can be broadly correlated to the Densipollenites magnicorpus and Klausipollenites decipiens palynozones of peninsular India and to palynofloras spanning the Permian-Triassic boundary elsewhere in Gondwana. Generally, low spore-pollen yields and poor preservational quality of the studied assemblages hinder more precise correlations and are inferred to be a function of an offshore marine depositional setting on the margin of the Neotethys Ocean, and thermal alteration associated with Cenozoic collisional tectonism between India and Asia. © 2014 Elsevier B.V.
Ghose N.C.,G 608 |
Ghose N.C.,Patna University |
Agrawal O.P.,Directorate of Geology and Mining |
Chatterjee N.,Massachusetts Institute of Technology
Island Arc | Year: 2010
A variety of low- to high-pressure metamorphic assemblages occur in the metabasic rocks and metachert in the Upper Cretaceous-Eocene ophiolite belt of the central part of the Naga Hills, an area in the northern sector of the Indo-Myanmar Ranges in the Indo-Eurasian collision zone. The ophiolite suite includes peridotite tectonite containing garnet lherzolite xenoliths, layered ultramafic-mafic cumulates, metabasic rocks, basaltic lava, volcaniclastics, plagiogranite, and pelagic sediments emplaced as dismembered and imbricated bodies at thrust contacts between moderately metamorphosed accretionary rocks/basement (Nimi Formation/Naga Metamorphics) and marine sediments (Disang Flysch). It is overlain by coarse clastic Paleogene sediments of ophiolite-derived rocks (Jopi/Phokphur Formation). The metabasic rocks, including high-grade barroisite/glaucophane-bearing epidote eclogite and glaucophane schist, and low-grade greenschist and prehnite-clinochlore schist, are associated with lava flows and ultramafic cumulates at the western thrust contact. Chemically, the metabasites show a low-K tholeiitic affinity that favors derivation from a depleted mantle source as in the case of mid-ocean ridge basalt. Thermobarometry indicates peak P-T conditions of about 20 kb and 525°C. Retrogression related to uplift is marked by replacement of barroisite and omphacite by glaucophane followed by secondary actinolite, albite, and chlorite formation. A metabasic lens with an eclogite core surrounded by successive layers of glaucophane schist and greenschist provides field evidence of retrogression and uplift. Presence of S-C mylonite in garnet lherzolite and 'mica fish' in glaucophane schist indicates ductile deformation in the shear zone along which the ophiolite was emplaced. © 2010 Blackwell Publishing Asia Pty Ltd.
Chalapathi Rao N.V.,Banaras Hindu University |
Lehmann B.,Clausthal University of Technology |
Mainkar D.,Directorate of Geology and Mining |
Panwar B.K.,Banaras Hindu University
Mineralogy and Petrology | Year: 2012
Widespread and abundant spinel is the only primary mineral of petrogenetic significance preserved in the hydrothermally altered, crater-facies, Neoproterozoic (≥620 Ma) Tokapal kimberlite pipe that intruded the Indrāvati basin, Bastar craton, Central India. Two distinct spinel populations occur: (i) finer-grained (<50 μm) microcrysts which are zoned from titaniferous magnesiochromite-chromite to magnetite; and (ii) larger macrocrysts (>400 μm) with cores having distinctly chromium-rich (Cr 2O 3 up to 63. 67 wt%), and TiO 2-poor (<0.68 wt%) compositions. Based on their morphology and chemical composition the macrocrysts are inferred to be disaggregated mantle xenocrysts and their compositional range extends well into the diamond stability field. However, the reported absence of diamond and other indicator minerals (such as pyrope garnet, chrome diopside and magnesian ilmenite) in the Tokapal pipe is intriguing since diamondiferous cratonic roots are indeed preserved in the Bastar craton, and also the kimberlite itself was derived from a similar source region(s) as that of the well-known diamondiferous Mesoproterozoic (ca. 1,100 Ma) kimberlites from Wajrakarur, Dharwar craton, southern India. Given the large areal extent (>550 ha) of kimberlite, there is a possibility that it contains diamonds but they were not recovered during the sampling. Alternately, highly oxidising conditions imparted by the metasomatic fluids/melts derived from (i) asthenosphere-lithosphere interaction, or (ii) the kimberlite itself might have played an important role in the destruction of diamond, and other indicator minerals. © 2012 Springer-Verlag.
Lehmann B.,Clausthal University of Technology |
Burgess R.,University of Manchester |
Frei D.,Geological Survey of Denmark |
Belyatsky B.,Russian Academy of Sciences |
And 4 more authors.
Earth and Planetary Science Letters | Year: 2010
Recently discovered diamondiferous kimberlite (Group-II) pipes in central India have surprisingly young 40Ar/39Ar whole rock and U-Pb perovskite ages around 65 million years. These ages overlap with the main phase of the Deccan flood basalt magmatism, and suggest a common tectonomagmatic control for both flood basalts and kimberlites. The occurrence of macrodiamonds in the pipes implies the presence of a thick subcratonic lithosphere at the Cretaceous/Tertiary boundary, significantly different from the present-day thickness of the Indian lithosphere. About one third of the Indian lithosphere was lost during or after the Deccan flood basalt event. The superfast northward motion of the Indian plate prior to the collision with Eurasia cannot be related to lithospheric thinning during the Gondwana break-up at 130 Ma, as previously thought. © 2009 Elsevier B.V. All rights reserved.