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Rao C.V.D.,National Disaster Management Authority | Santosh M.,Kochi University | Santosh M.,China University of Geosciences | Kim S.W.,Korea Institute of Geoscience and Mineral Resources
Gondwana Research | Year: 2012

The NW domain of the Indian lithosphere witnessed multiple cycles of the birth and demise of ocean basins associated with the history of Proterozoic supercontinents. Here we present field, petrological and geochemical evidence for imbricated ocean plate stratigraphy from the Sindreth Group in Rajasthan characterized by pillow basalt, bedded chert, rhyolite, sandstone and conglomerate suggesting the accretion of oceanic sediments together with continental detritus. The petrographic and geochemical characteristics of basalts and associated rhyolites indicate a volcanic arc setting for the Sindreth Group. The SHRIMP U-Pb analyses of zircons from a siliceous tuff and a rhyolitic tuff intercalated with chert yield well-defined 206Pb/ 238U concordia ages of 765.1±7.2 (MSWD=0.76) and 768.2±6.9 (MSWD=2.3), constraining the timing of arc volcanism associated with mid Neoproterozoic subduction. A younger population of zircons in the rhyolitic tuff yield ages in the range of 666 to 644Ma, suggesting that the arc magmatism continued to late Cryogenian. Our results correlate the Sindreth Group with the Malani volcanics and we interpret the tuff beds to have been derived from ash flows from a volcanic arc associated with mid Neoproterozoic subduction realm. The data from this study together with those from the recent works in other regions including the Syechelles, Madagascar, southern India and Sri Lanka suggest that Cryogenian magmatic arcs were widely distributed along the margins of the East African Orogen associated with the subduction history of the Mozambique Ocean lithosphere, prior to the final amalgamation of the Gondwana supercontinent in the latest Neoproterozoic-Cambrian. © 2011 International Association for Gondwana Research.


News Article | December 2, 2015
Site: www.reuters.com

The national weather office predicted three more days of torrential downpours in the southern state of nearly 70 million people. "There will be no respite," Laxman Singh Rathore of the India Meteorological Department told reporters on Wednesday. No deaths were reported in the latest floods, but since heavy rain set in on Nov. 12 there have been 150 deaths in Tamil Nadu. More than 200 people were critically injured over the past 24 hours in Chennai, a senior home ministry official said. Prime Minister Narendra Modi has blamed climate change for the deluge, injecting urgency into the debate at global climate talks in Paris and highlighting the vulnerability of tropical nations like India to extreme weather. Physician Rupam Choudhury said he and a friend had to wade through neck-deep water to reach high ground from where an army truck brought him to his hospital in the heart of Chennai. Dr. A. Ramachandran's Diabetes Hospital was running out of oxygen for patients and diesel for power generators, he said by telephone. Most mobile networks were down in the city and food supplies running low. Chennai, India's fourth most populous city, is a major auto manufacturing and IT outsourcing hub. Ford Motor, Daimler, Hyundai and Nissan told workers to stay at home, while U.S. listed outsourcing firm Cognizant shut its 11 local offices. Airlines suspended flights into Chennai's flooded international airport, causing wider disruption to air travel. Authorities later decided to close the airport until Dec. 6. "The biggest challenge is to find a way to clear the inundated airport and main roads," said Anurag Gupta at the National Disaster Management Authority (NDMA) in New Delhi. Passengers stranded at the airport said they did not know when they would be able to fly, or where to stay if they could not. "All of us here are getting agitated because none of the hotels nearby are vacant. Where do we go?" traveller Vinit Jain told Reuters Television. In a limited initial relief effort, four helicopters dropped food, water and medicines, while fishing boats commandeered by the military were collecting stranded residents. A major relief effort by 5,000 soldiers was promised within 24 hours. "The entire state machinery has collapsed. Most officials are forced to sit at home. It's a very frustrating situation," said a home ministry official, who requested anonymity because he was not authorised to speak on the record. Weather experts say the seasonal northeast monsoon was responsible for the flooding in the city of six million, but was amplified this year by El Nino, a warming of the eastern Pacific Ocean that can have far-reaching climate effects. Tamil Nadu is a major rice and sugar cane producing region, and a senior member of a local farmers' association said floods had washed out up to four agricultural districts. Modi has ordered rescue teams and paramilitary forces to launch an extensive relief and rescue operation in Chennai. He had blamed climate change for the heavy rains that hit the southern state last month, tweeting before attending the UN climate summit in Paris this week: "We are feeling the impact of fast-paced climate change." Hundreds of divers and army rescue teams entered inundated homes, taking the injured to hospital. Authorities said more than a million people were affected by the flooding, with some residents bemoaning the slow response of the relief teams. Social media networks carried many appeals for help, while others offered assistance. Siddarth, a popular Tamil film actor who goes by one name, was coordinating a relief effort on Twitter. "The police want to help but there are no boats. We are trying not to panic," said Ramana Goda, who took refuge at a police station after fleeing his home with his family overnight.


Dharma Rao C.V.,National Disaster Management Authority | Santosh M.,Kochi University | Wu Y.-B.,Wuhan University
Gondwana Research | Year: 2011

The Kanigiri mélange within the Proterozoic Nellore-Khammam schist belt in southern Peninsular India includes ophiolitic fragments that represent the remnants of an oceanic plate. The ophiolitic units were accreted along a NE-trending suture that juxtaposes the Proterozoic Eastern Ghats Granulite Belt (EGGB) against the Archean Nellore Schist Belt of the Dharwar craton. The ophiolite components in the Kanigiri mélange include plagiogranites and gabbros which show mutually intrusive relations indicating their coeval nature. We report laser ablation-ICP-MS age data and REE geochemistry of zircons from the gabbro and granite. The zircons from both gabbro and granite show high REE contents, prominent HREE enrichment and a conspicuous negative Eu anomaly, suggesting a common melt source. Zircon REE abundances and normalized patterns show little intersample and intrasample variations. U-Pb dating of the zircons reveals prominent Mesoproterozoic ages for the plagiogranite, with the ca.1.33. Ga age of the Kanigiri ophiolitic mélange offering important clues for arc-continent collision during the final stages of amalgamation of the Columbia-derived fragments within the Neoproterozoic supercontinent assembly. © 2010.


Dharma Rao C.V.,National Disaster Management Authority | Santosh M.,Kochi University | Chmielowski R.M.,University of Milan
Geoscience Frontiers | Year: 2012

We report equilibrium sapphirine + quartz assemblage in biotite-orthopyroxene-garnet granulites from a new locality in Panasapattu of Paderu region in the Eastern Ghats granulite belt, which provide new evidence for ultrahigh-temperature (UHT) metamorphism at 1030-1050°C and 10 kbar in this region. The development of migmatitic texture, stabilization of the garnet-orthopyroxene-plagioclase-K-feldspar association, prograde biotite inclusions within garnet and sapphirine as well as sapphirine and cordierite inclusions within garnet in these granulites indicate that the observed peak assemblages probably formed during prograde dehydration melting of a Bt-Sill-Qtz assemblage, and constrain the prograde stage of the P-T path. The core domains of orthopyroxene porphyroblasts have up to wt(Al 2O 3) 9.6%, which suggest that the temperatures reached up to 1150°C suggesting extreme crustal metamorphism. These conditions were also confirmed by the garnet-orthopyroxene thermobarometery, which yields a P-T range of 1012-960°C and 9.4 kbar. The P-T phase topologies computed using isochemical sections calculated in the model system Na 2O-CaO-K 2O-FeO-MgO-Al 2O 3-SiO 2-H 2O (NCKFMASH) for metapelites, garnet-free sapphirine granulites and garnet-bearing sapphirine granulites match the melt-bearing assemblages observed in these rocks. Isochemical sections constructed in the NCKFMASH system for an average sub-aluminous metapelite bulk composition, and contoured for modal proportions of melt and garnet, as well as for the compositional isopleths of garnet, predict phase and reaction relations that are consistent with those observed in the rocks. Garnet and orthopyroxene contain Ti-rich phlogopite inclusions, suggesting formation by prograde melting reactions at the expense of phlogopite during ultrahigh-temperature conditions. These P-T results underestimate 'peak' conditions, in part as a result of the modification of garnet compositions in the domains where some melt was retained. The post-peak evolution is constrained by a succession of melt-present reactions that occur at P < 10 kbar, inferred from micro-structural relations among various minerals. After high-temperature decompression from the metamorphic peak, the P-T path followed a near isobaric cooling stage to T < 900°C. The UHT rocks investigated in this study occur within a continental collision suture which witnessed prolonged subduction-accretion history prior to the final collision. We correlate the extreme metamorphism and the stabilization of UHT mineral assemblages to heat and volatile input from an upwelled asthenosphere during subduction-collision tectonics in a Proterozoic convergent plate margin. © 2011, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. All rights reserved.


Rao C.V.D.,National Disaster Management Authority | Chmielowski R.M.,University of Milan
Geological Journal | Year: 2011

The sapphirine granulites from Gangaraju Madugula, Eastern Ghats Belt (EGB), India preserve a rich variety of mineral assemblages and unique isolated and composite mineral inclusions within garnet that provide robust evidence for extreme crustal metamorphism at ultrahigh temperature (UHT) conditions (>900°C). Diagnostic UHT assemblages in these rocks include sapphirine+quartz, spinel+quartz and high alumina orthopyroxene+sillimanite+quartz. The stability of spinel+quartz, sapphirine+quartz and orthopyroxene+sillimanite+quartz assemblages provides evidence for temperatures exceeding 960°C at moderate pressures. The mineral association of garnet-orthopyroxene is indicative of a subsequent high P-UHT metamorphic event as indicated by the high alumina contents of orthopyroxene (>10wt% Al2O3) coexisting with garnet. Peak P-T conditions of ∼970°C and 9.5kbars are calculated from conventional garnet-orthopyroxene geothermobarometry. Calculated isochemical sections constructed in the model system Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2-Fe2O3 (NCKFMASHTO) for the sapphirine granulites and garnet-orthopyroxene granulites adequately predict phase relationships that are consistent with those observed in the rocks. An evaluation of the assemblages and textures and P-T estimates indicate a three-stage evolution of the sapphirine granulites and associated garnet-orthopyroxene granulites: (1) inclusion assemblages with sapphirine, spinel and quartz on the low-pressure prograde path (M1 stage); (2) a peak UHT assemblage of porphyroblastic garnet-orthopyroxene (M2 stage) and (3) a retrogression that resulted in orthopyroxene-cordierite intergrowths and biotite rims on Grt (M3 stage). The sapphirine granulites and associated garnet-orthopyroxene granulites indicate that they grew during the prograde and retrograde stage. The thermo-barometric estimates from mineral compositions and the complimentary isochemical sections approached from bulk rock compositions allow tighter constraints to be placed on the P-T evolution of this sector of the EGB. © 2010 John Wiley & Sons, Ltd..


Gupta H.,National Disaster Management Authority | Gupta H.,CSIR - Central Electrochemical Research Institute | Gahalaut V.K.,CSIR - Central Electrochemical Research Institute
Gondwana Research | Year: 2014

Bounded by the western and eastern syntaxes, the Himalayan region has experienced at least five M. ~. 8 earthquakes during a seismically very active phase from 1897 through 1952. However, there has been a paucity of M. ~. 8 earthquakes since 1952. Examining of various catalogues and seismograms from the Gottingen Observatory, it is established that this quiescence of M. ~. 8 earthquakes is real. While it has not been possible to forecast earthquakes, there has been a success in making a medium term forecast of an M. 7.3 earthquake in the adjoining Indo-Burmese arc. Similarly we find that in the central Himalayan region, earthquakes of M. >. 6.5 have been preceded by seismic swarms and quiescences. In the recent past, based on GPS data, estimates have been made of the accumulated strains and it is postulated that a number of M. ~. 8 earthquakes are imminent in the Himalayan region. We examine these estimates and find that while earthquakes of M. ~. 8 may occur in the region, however, the available GPS data and their interpretation do not necessarily suggest their size and time of occurrence and whether an earthquake in a particular segment will occur sooner in comparison to that in the neighboring segment. We also comment on the inference of occurrence of M. ~. 8 earthquakes based on M8 algorithm for the region. We conclude that while an M. ~. 8 earthquake could occur any time anywhere in the Himalayan region, there is no indication as of now as to where and when it would occur. We impress on the need for preparedness to mitigate the pending earthquake disaster in the region. © 2012 International Association for Gondwana Research.


Dharma Rao C.V.,National Disaster Management Authority | Santosh M.,Kochi University | Dong Y.,Northwest University, China
Journal of Asian Earth Sciences | Year: 2012

The Pangidi-Kondapalle layered intrusion is emplaced within high-grade supracrustal rocks in the southern sector of the Eastern Ghats Granulite Belt proximal to the south-eastern periphery of the Indian plate. This layered complex consists mainly of anorthosites and gabbronorites with pyroxenite cumulates containing orthopyroxenites and chromitites in a regressive intrusive sequence. Here we report laser ablation ICP-MS data and REE geochemistry of zircons from three co-spatial anorthositic bodies in this complex. Our results show mean 207Pb/ 206Pb ages of 1634±18Ma (MSWD=0.55) for the anorthosite from Pangidi. Two anorthosite samples from Kondapalle yield mean 207Pb/ 206Pb ages of 1628±36Ma (MSWD=0.54) and 1693±110Ma (MSWD=5.5). The zircons from all the anorthosite samples show high REE contents, prominent HREE enrichment and a conspicuous positive Eu anomaly, suggesting a common melt source. The prominent Mesoproterozoic ages revealed from our U-Pb dating of zircons from these layered complexes suggest subduction-related magmatic underplating in a convergent margin setting associated with the amalgamation of the Columbia-derived fragments within the Neoproterozoic supercontinent. © 2011 Elsevier Ltd.


The magmatic suite at Kondapalle represents a Mesoproterozoic (~ca. 1634Ma) magmatic arc emplaced in the southern sector of the Eastern Ghats Belt (EGB). Here we present new geological, mineralogical and geochemical data on the various lithological units in this complex including anorthosites, gabbronorites and pyroxenites. The major mineral constituents in these rocks are plagioclase (An98-57), amphibole (XMg 0.93-0.52), orthopyroxene (XMg 0.94-0.51), clinopyroxene (XMg 0.93-0.63) and chromite (XMg 0.20-50). The near-absence of plagioclase in the orthopyroxenites, early and abundant crystallization of orthopyroxene, and formation of gabbronorites rather than gabbro or olivine gabbro in the Kondapalle suite are correlated with the features of arc cumulates. The chemistry of chromian spinel and clinopyroxene also displays the trend for arc cumulates. The variations in the anorthite content of plagioclase vs. the Mg# of olivine attest to an arc-related magma source. The rocks display low abundance of incompatible trace elements (Ba, Rb, K and Zr) comparable to the values typically observed in subduction-related magmatic arcs. In trace element N-MORB normalized diagrams, all the rock units show Nb-Ta-Ti-Zr troughs reflecting the features characteristic of arc magmas. We interpret the Kondapalle rocks to represent the root zone of a deeply eroded magmatic arc built during the Mesoproterozoic associated with the subduction of an oceanic lithosphere in a long-lived convergent margin. We identify that the Mesoproterozoic subduction along the eastern margin of the Indian plate generated a wide arc-accretionary complex with an extruded high P-T metamorphic orogen during the final stage of collision. The subduction-accretion process is also supported by recent findings of Mesoproterozoic ophiolite mélanges from this zone, marking the history from the break-up of the Paleoproterozoic Columbia supercontinent to the assembly of the Neoproterozoic Rodinia supercontinent. © 2011 Elsevier B.V.


Dharma Rao C.V.,National Disaster Management Authority | Santosh M.,Kochi University | Sajeev K.,Indian Institute of Science | Windley B.F.,University of Leicester
Precambrian Research | Year: 2013

The Neoarchean layered anorthositic complex at Sittampundi in southern India is known for its chromitite layers that are mostly associated with anorthosite (An90-100). The chromitites contain FeAl-rich chromites concentrated in layers between amphibole-rich layers with a dominant mineralogy of amphibole-spinel-plagiocase±sapphirine. The chromite-rich layers contain only amphibole and plagioclase. Mineral compositions illustrated by X-ray composition maps and profiles show subtle chemical differences. The chrome spinels are of refractory grade with Cr2O3 and Al2O3 contents varying between 34-40wt.% and 23-28wt.%. The chromite compositions are noticeably different from those in layered igneous intrusions of the Bushveld-Stillwater type. The existence of original highly calcic plagioclase, FeAl-rich chromite, and magmatic amphibole is consistent with derivation from a parental magma of hydrous tholeiitic composition that was most likely generated in a supra-subduction zone arc setting. In terms of mineralogy and field relations, the Sittampundi chromitites are remarkably similar to anorthosite-hosted chromitites in the Neoarchean Fiskenæsset anorthositic complex, Greenland. We propose that the Sittampundi chromitites formed by partial melting of unusually aluminous harzburgite in a hydrated mantle wedge above a subduction zone. This melting process produced hydrous, aluminous basalt, which fractionated at depth to give rise to a variety of high-alumina basalt compositions from which the anorthositic complex with its cumulate chromite-rich and amphibole-rich layers formed within the magma chamber of a supra-subduction zone arc. © 2011 Elsevier B.V.


Dharma Rao C.V.,National Disaster Management Authority | Windley B.F.,University of Leicester | Choudhary A.K.,Indian Institute of Technology Roorkee
Journal of Asian Earth Sciences | Year: 2011

New major and trace element data on the Proterozoic Chimalpahad layered anorthositic Complex and associated basaltic amphibolites of the Nellore Schist Belt of South India provide new constraints on their petrogenesis and geodynamic setting. The Complex consists of layered anorthosites, leucogabbros, gabbros, ultramafic rocks and is spatially associated with basaltic amphibolites. Despite deformation and metamorphism, primary cumulate textures and igneous layering are locally well preserved throughout the Complex. Whereas the amphibolites display diverse REE systematics, the Chimalpahad anorthositic-gabbroic rocks are characterized by moderately depleted to strongly enriched LREE patterns and by flat to depleted HREE patterns. The field relations, major and trace element compositions of the basaltic amphibolites suggest that they are petrogenetically related to the anorthositic-gabbroic rocks by fractional crystallization. The anorthositic rocks and the basaltic amphibolites share the depletion of Nb relative to Th and La on primitive mantle-normalized diagrams. They exhibit signatures of arc magmatic rocks, such as high LILE and LREE relative to the HFSE and HREE, as well as high Ba/Nb, Ba/Zr, Sr/Y, La/Yb ratios that mimic chondrite-normalized REE and primitive mantle-normalized trace element patterns of arc magmas. Similarly, on log-transformed tectonic discrimination diagrams, the Chimalpahad rocks plot within the field of Phanerozoic magmatic arcs, consistent with a subduction zone origin. On the basis of field relations and geochemical characteristics, the Chimalpahad Complex is interpreted as a fragment of a magma chamber of an island arc, which is tectonically juxtaposed against its original volcanic cover. A new preliminary Sm-Nd date of anorthosite from the Chimalpahad Complex indicates a model age of 1170. Ma. © 2010 Elsevier Ltd.

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