Mid-Miocene (post 12 Ma) displacement along the central Karakoram fault zone in the Nubra Valley,Ladakh, India from spot LA-ICPMS U/Pb zircon ages of granites

The Karakoram fault zone is a prominent right lateral fault that connects the frontal thrust of the North Pamir with the Indus suture zone near Mount Kailas. Its nature and age of initiation is controversial. In the Nubra valley, Ladakh, India, a Karakoram range granite is thrust over Cretaceous magmatic arc rocks and this thrust is cut by a western strand of the Karakoram fault zone. Three different lithologies from this granite gave weighted mean zircon U/Pb ages of 12.92±0.77 Ma, 12.41±0.43 Ma, and 11.72±0.31 Ma. The ages indicate a relatively short intrusive history of about 1 Ma for the phases: the geochemistry is practically identical to the Pangong leucogranites in the same tectonic block. The Karakoram fault zone in this area is thus less than ~12 Ma old which supports a post middle Miocene (Serravallian) age of Karakoram fault initiation in this area.     

Sedimentary record of the northward flight of India and its collision with Eurasia (Ladakh Himalaya,India)

Abstract

— Stratigraphic and petrographic analysis of the Cretaceous to Eocene Tibetan sedimentary succession has allowed us to reinterpret in detail the sequence of events which led to closure of Neotethys and continental collision in the NW Himalaya.

During the Early Cretaceous, the Indian passive margin recorded basaltic magmaüc activity. Albian volcanic arenites, probably related to a major extensional tectonic event, are unconformably overlain by an Upper Cretaceous to Paleocene carbonate sequence, with a major quartzarenite episode triggered by the global eustatic sea-level fall at the Cretaceous/Tertiary boundary. At the same time, Neotethyan oceanic crust was being subducted beneath Asia, as testified by calc-alkalic volcanism and forearc basin sedimentation in the Transhimalayan belt.

Onset of collision and obduction of the Asian accretionary wedge onto the Indian continental rise was recorded by shoaling of the outer shelf at the Paleocene/Eocene boundary, related to flexural uplift of the passive margin. A few My later, foreland basin volcanic arenites derived from the uplifted Asian subduction complex onlapped onto the Indian continental terrace. All along the Himalaya, marine facies were rapidly replaced by continental redbeds in collisional basins on both sides of the ophiolitic suture. Next, foreland basin sedimentation was interrupted by fold-thrust deformation and final ophiolite emplacement.

The observed sequence of events compares favourably with theoretical models of rifted margin to overthrust belt transition and shows that initial phases of continental collision and obduction were completed within 10 to 15 My, with formation of a proto-Himalayan chain by the end of the middle Eocene.     

New age constraints on the cooling and unroofing history of the Trans-Himalayan Ladakh Batholith (Kargil area), N. W. India

Thermotectonic history of the Trans-Himalayan Ladakh Batholith in the Kargil area, N. W. India, is inferred from new age data obtained here in conjunction with previously published ages. Fission-track (FT) ages on apatite fall around 20±2 Ma recording cooling through temperatures of ∼100°C and indicating an unroofing of 4 km of the Ladakh Range since the Early Miocene. Coexisting apatite and zircon FT ages from two samples in Kargil show the rocks to have cooled at an average rate of 5–6°C/Ma in the past 40 Ma. Zircon FT ages together with mica K−Ar cooling ages from the Ladakh Batholith cluster around 40–50 Ma, probably indicating an Eocene phase of uplift and erosion that affected the bulk of the batholith after the continental collision of India with the Ladakh arc at 55 Ma. Components of the granitoids in Upper Eocene-Lower Oligocene sediments of the Indus Molasse in Ladakh supports this idea. Three hornblende K−Ar ages of 90 Ma, 55 Ma, and 35 Ma are also reported; these distinctly different ages probably reflect cooling through 500–550°C of three phases of I-type plutonism in Ladakh also evidenced by other available radiometric data: 102 Ma (mid-Cretaceous), 60 Ma (Palaeocene), and 40 Ma (Late Eocene); the last phase being localised sheet injections. The geodynamic implications of the age data for the India-Asia collision are discussed.     

Origin and evolution of Suru Valley ophiolite peridotite slice along Indus suture zone,Ladakh Himalaya,India: Implications on melt-rock interaction in a subduction-zone environment

In this paper, we present whole-rock and mineral geochemistry of serpentinized peridotites from the Suru Valley ophiolite slice Ladakh Himalaya, in an attempt to put constraints on their petrogenesis and tectonic evolution in the context of Mesozoic Neo-Tethys Ocean. On the basis of petrographic study, Suru Valley serpentinized peridotites can be identified as serpentinized harzburgites. Relative to primitive mantle these rocks have depleted major and rare earth element (REE) geochemical characteristics comparable to ocean floor mantle rocks reflecting their mantle residual nature. However, higher abundance of highly incompatible large ion lithophile elements (e.g., Rb, Ba, Th, U, Pb and Sr), reflect metasomatism in a subduction zone environment. The presence of silicate assemblage includes Mg-rich olivine (Fo_90-92) and orthopyroxene (En_91-93 Fs_6.4-8.7) of supra-subduction zone affinity. Evaluation of mineral and whole-rock geochemistry suggests that the Suru Valley ophiolitic peridotites represent residues left after moderate degrees of partial melting thereby underwent metasomatism in a supra-subduction zone environment related to north dipping intra-oceanic island arc during Cretaceous in the context of Mesozoic Neo-Tethys ocean.     

Signatures of rift environment in the production of garnet-amphibolites and eclogites from Tso-Morari region, Ladakh, India: A geochemical study

The geochemistry of eclogites and garnet-amphibolites from Tso-Morari region, Ladakh, India has been investigated to characterize their protoliths on the basis of immobile elements, especially trace elements including REE. The eclogites and garnet-amphibolites have coherent compositions, except for the UHP metamorphic minerals being preserved in eclogites. Compositionally, the metabasites range from ‘depleted’ to ‘enriched’, and span from within-plate basalts (WPB) to MORB fields, and match with various enriched or ‘transitional’ MORB types (e.g., on Ti–Zr–Y and Nb–Zr–Y ternary plots). Isotopically they have Sr_i ratio 0.706 which is similar to some of the Ocean Island Basalt (OIB). The rocks under study suggest that the enriched components are probably derived by melting of a mantle source with an enriched OIB-type component rather than due to the crustal contamination. We propose a rift environment for their protoliths and relate to advanced intra-continental rift situation. Furthermore, our geochemical studies envisage an initial phase of plume activity (Cambrian or earlier) resulting in basaltic magma in the eclogitic layers at sub-lithospheric levels, wherein they were subjected to crystallization under ultra-high pressure conditions. At a later stage the reactivation of faults (probably during Permo-Triassic times) acted as channels for the emplacement of the high pressure rocks in the continental crust. Subsequently, the ultra-high pressure rocks got re-equilibrated as amphibolites, with some remaining as relict eclogites, which later got exposed to the surface during various phases of the Himalayan uplift.     

Correlation of the tertiary geosynclinal sediments of the Surma Valley,Assam, and Tripura State (India)

The Tertiary geosynclinal sediments of the Surma Valley and Tripura State range in age from Eocene to Mio-Pliocene. They are classified into those of the Disang, Barail, Surma and Tipam groups which respectively represent sediments belonging to geosynclinal, flysch, early molasse and late molasse stages. These sediments are devoid of diagnostic and persistent faunal and palynological assemblages. Frequent lithofacial variations render lithologic criteria unsuitable for regional correlation. Heavy-mineral suites, however, appear diagnostic and they, along with lithologic criteria, can be utilised for local and regional correlations.The mode of evolution of the heavy-mineral suites is discussed. Appearance of marker heavy minerals in successively younger sequences is concluded to be a reflection of successive cycles of positive tectonism in the provenance. The study brings out that the bulk of the sediments were derived from the Shillong Plateau. Contributions from older sedimentaries are also concluded.     

Gondwana biostratigraphy of the Purnea Basin (eastern Bihar,India), and its correlation with Rajmahal and Bengal Gondwana basins

Integrated biostratigraphic studies are undertaken on the newly discovered Gondwana successions of Purnea Basin which have been recognized in the subsurface below the Neogene Siwalik sediments. The four exploratory wells, so far drilled in Purnea Basin, indicated the presence of thick Gondwana sussession (± 2450m) with varied lithological features. However, precise age of different Gondwanic lithounits of this basin and their correlation with standard Gondwana lithounits is poorly understood due to inadequate biostratigraphic data.Present biostratigraphic studies on the Gondwana successions in the exploratory wells of PRN-A, RSG-A, LHL-A and KRD-A enable recognition of fifteen Gondwanic palynological zones ranging in age from Early Permian (Asselian-Sakmarian) to Late Triassic (Carnian-Norian). Precise age for the Gondwanic palynological zones, recognized in the Purnea Basin and already established in other Indian Gondwana basins, are provided in the milieu of additional palynological data obtained from the Gondwana successions of this basin.The Lower Gondwana (Permian) palynofloras of Purnea Basin recorded from the Karandighi, Salmari, Katihar and Dinajpur formations resemble the palynological assemblages earlier recorded from the Talchir, Karharbari, Barakar and Raniganj formations respectively, and suggests the full development of lower Gondwana succession in this basin. The Upper Gondwana (Triassic) succession of this basin is marked by the Early and Middle to Late Triassic palynofloras that resemble Panchet and Supra-Panchet (Dubrajpur/Maleri Formation) palynological assemblages, and indicates the occurrence of complete Upper Gondwana succession also in the Purnea Basin.The lithological and biostratigraphic attributes of Gondwana sediments from Purnea, Rajmahal and western parts of Bengal Basin (Galsi Basin) are almost similar and provides strong evidences about the existence of a distinct N-S trending Gondwana Graben, referred as the Purnea-Rajmahal-Galsi Gondwana Graben. Newly acquired biostratigraphic data from the Gondwana sediments of CHK-A, MNG-A and PLS-A wells from central part of Bengal Basin and Bouguer anomaly data suggest that these wells fall in a separate NE-SW trending graben of “Chandkuri-Palasi-Bogra Gondwana Graben”. Although, the post-Gondwana latest Jurassic-Early Cretaceous Rajmahal Traps and and intertrappean beds succeed the Upper Gondwana successions in Rajmahal, Galsi and Chandkuri-Palasi Gondwana basins, but not recorded in the drilled wells of Purnea Basin, instead succeeded by the Neogene Siwalik sediments.     

Petrography and metamorphism of the lower Gondwana (Permian) coal of Rangit Valley, eastern Himalays, India

A triangular outlier of coal-bearing lower Gondwana rocks comprises a tectonic window within the Precambrian metamorphic terrain of the Rangit Valley, in the eastern Himalays of India. Due to a series of tectonic events which took place during the Mesozoic and Tertiary the succession has become reversed and the coal has undergone severe physical, chemical, microstructural and optical changes. Studies reveal that (1) the rank of the coal prior to tectonism was low, (2) the coal underwent oxidation in the peat forming stage and during subsequent orogenic stages but effect of oxidation on the properties of coal was insignificant, (3) the coal reached its present abnormally high rank mainly due to heating under tectonic pressure and (4) the heat which was generated due to tectonic pressure, affected all the coal seams of this belt.     

Geochemical and isotopic constraints on the age and origin of the Nidar Ophiolitic Complex, Ladakh, India: Implications for the Neo-Tethyan subduction along the Indus suture zone

The Nidar ophiolite complex is exposed within the Indus suture zone in eastern Ladakh, India. The suture zone is considered to represent remnant Neo-Tethyan Ocean that closed via subduction as the Indian plate moved northward with respect to the Asian plate. The two plates ultimately collided during the Middle Eocene. The Nidar ophiolite complex comprises a sequence of ultra-mafic rocks at the base, gabbroic rocks in the middle and volcano-sedimentary assemblage on the top. Earlier studies considered the Nidar ophiolite complex to represent an oceanic floor sequence based on lithological assemblage. However, present study, based on new mineral and whole rock geochemical and isotopic data (on bulk rocks and mineral separates) indicate their generation and emplacement in an intra-oceanic subduction environment. The plutonic and volcanic rocks have nearly flat to slightly depleted rare earth element (REE) patterns. The gabbroic rocks, in particular, show strong positive Sr and Eu anomalies in their REE and spidergram patterns, probably indicating plagioclase accumulation. Depletion in high field strength elements (HFSE) in the spidergram patterns may be related to stabilization of phases retaining the HFSE in the subducting slab and / or fractional crystallization of titano-magnetite phases. The high radiogenic Nd- and low radiogenic Sr-isotopic ratios for these rocks exclude any influence of continental material in their genesis, implying an intra-oceanic environment.

Nine point mineral–whole rock Sm–Nd isochron corresponds to an age of 140 ± 32 Ma with an initial ¹⁴³Nd/¹⁴⁴Nd of 0.513835 ± 0.000053 (E_Nd t = + 7.4). This age is consistent with the precise Early Cretaceous age of Hauterivian (132 ± 2 to 127 ± 1.6 Ma) to Aptian (121 ± 1.4 to 112 ±1.1 Ma) for the overlying volcano-sedimentary (radiolarian bearing chert) sequences based on well-preserved radiolarian fossils (Kojima, S., Ahmad, T., Tanaka, T., Bagati, T.N., Mishra, M., Kumar, R. Islam, R., Khanna, P.P., 2001. Early Cretaceous radiolarians from the Indus suture zone, Ladakh, northern India. In: News of Osaka Micropaleontologists (NOM), Spec. Vol., 12, 257–270.) and cooling ages of 110–130 Ma based on ³⁹Ar/⁴⁰Ar for Nidar–Spontang ophiolitic rocks (Mahéo, G., Berttrand, H., Guillot, S., Villa, I. M., Keller, F., Capiez, P., 2004. The South Ladakh Ophiolites (NW Himalaya, India): an intra-oceanic tholeiitic arc origin with implications for the closure of the Neo-Tethys. Chem. Geol., 203, 273–303.). As these gabbroic and volcanic rocks are interpreted to be arc related, the new Sm–Nd age data may indicate that intra-ocean subduction in the Neo-Tethyan ocean may have started much before  140 ± 32 Ma as this date is interpreted as the age of crystallization of the arc magma. Present and published age data on the arc magmatic rocks from the Indus suture zone may collectively indicate episodic magmatism with increasing maturity of the arc from more basic (during ~ 140 ± 32 Ma) when the arc was immature through intermediate (andesitic/granodioritic) at ~ 100 Ma to more felsic (rhyolitic/dioritic) magmatism at ~ 50–45 Ma, when the Indian and the Asian plates collided.     

Relicts of an intra-oceanic arc in the Sapi-Shergol mélange zone (Ladakh, NW Himalaya, India): implications for the closure of the Neo-Tethys Ocean

In the Ladakh–Zanskar area, relicts of both ophiolites and paleo-accretionary prism have been preserved in the Sapi-Shergol mélange zone. The paleo-accretionary prism, related to the northward subduction of the northern Neo-Tethys beneath the Ladakh Asian margin, mainly consists of tectonic intercalations of sedimentary and blueschist facies rocks. Whole rock chemical composition data provide new constraints on the origin of both the ophiolitic and the blueschist facies rocks. The ophiolitic rocks are interpreted as relicts of the south Ladakh intra-oceanic arc that were incorporated in the accretionary prism during imbrication of the arc. The blueschist facies rocks were previously interpreted as oceanic island basalts (OIB), but our new data suggest that the protolith of some of the blueschists is a calc-alkaline igneous rock that formed in an arc environment. These blueschists most likely originated from the south Ladakh intra-oceanic arc. This arc was accreted to the southern margin of Asia during the Late Cretaceous and the buried portion was metamorphosed under blueschist facies conditions. Following oceanic subduction, the external part of the arc was obducted to form the south Ladakh ophiolites or was incorporated into the Sapi-Shergol mélange zone. The incorporation of the south Ladakh arc into the accretionary prism implies that the complete closure of the Neo-Tethys likely occurred by Eocene time.     

Risk Assessment,Emergency Preparedness and Response to Hazards: The Case of the 1997 Red River Valley Flood,Canada

The prevention and/or mitigation offlood disasters requires continual research, numerouscapital investment decisions, and high-qualitymaintenance and modifications of flood-controlstructures. In addition, institutional and privatepreparedness is needed. The experience offlood-control in North America has shown mixedoutcomes: while flood frequency has declined duringthe last few decades, the economic losses havecontinued to rise. Recent catastrophic floods havealso been linked to major structural interventions inthe region. The flood diversions may cause harmfuleffects upon the floodplain inhabitants by influencingflood levels in areas which are not normallyflood-prone. The increasing vulnerability of thefloodplain inhabitants poses new challenges and raisesquestions concerning the existing risk assessmentmethods, institutional preparedness and responses todisaster-related public emergencies, and local-levelpublic involvement in flood mitigation efforts.In the context of the catastrophic 1997 floods of theRed River Valley, Manitoba, Canada, this researchfocuses on two aspects of flood-related emergencygovernance and management: (i) the functions andeffectiveness of control structures, and (ii) theroles, responsibilities and effectiveness oflegislative and other operational measures. The studyconcludes that the flood-loss mitigation measures,both in terms of effects of control structures andinstitutional interventions for emergency evacuation,were not fully effective for ensuring the well-beingand satisfaction of floodplain inhabitants. Althoughorganizational preparedness and mobilization to copewith the 1997 flood emergency was considerable, theirsuccess during the onset of the flood event waslimited. Lack of communication and understandingbetween institutions, a reluctance to implementup-to-date regulations, and minimal publicparticipation in the emergency decision-making processall contributed to the difficulties experienced byfloodplain inhabitants.     

Comparative analysis of two rainfall retrieval algorithms during extreme rainfall event: a case study on cloudburst, 2010 over Ladakh (Leh), Jammu and Kashmir

Natural Hazards - Intense rainfall events lead to floods and landslides in the Western Himalayas (WH). These rainfall amounts are considered comparatively moderate over the plains. These events,...     

Dextral transpression and late Eocene magmatism in the trans-Himalayan Ladakh Batholith (North India): implications for tectono-magmatic evolution of the Indo-Eurasian collisional arc

The trans-Himalayan Ladakh batholith is a result of arc magmatism caused by the northward subduction of the Tethyan oceanic lithosphere below the edge of the Eurasian plate. The batholith dominantly consists of calc-alkaline I-type granitoids which are ferromagnetic in nature with the presence of magnetite as the principal carrier of magnetic susceptibility. The mesoscopic and magnetic fabric are concordant and generally vary from WNW–ESE to ENE–WSW for different intrusions of ferromagnetic granites in different parts of the batholith. Strike of magnetic fabric is roughly parallel with the regional trend of the Ladakh batholith in the present study area and is orthogonal to the direction of India-Eurasia collision. In Khardungla and Changla section, the magnetic fabric is distributed in a sigmoidal manner. It is inferred that this sigmoidal pattern is caused by shearing due to transpression induced by oblique convergence between the two plates. U–Pb zircon geochronology of a rhyolite from the southern parts of the batholith gives a crystallization age of 71.7 ± 0.6 Ma, coeval with ~68 Ma magmatism in the northern parts of the batholith. The central part of the batholith is characterized by S-type two-mica granites, which gives much younger age of magmatism at 35.5 ± 0.5 Ma. The magnetic fabric of these two-mica granites is at a high angle to the regional trend of the batholith. It is proposed that these two-mica granites were emplaced well after the cessation of subduction and arc magmatism, along fractures that developed perpendicular to the regional strike of the batholith due to shearing.     

An unusual diagenetic structure in the Precambrian banded iron formation (BIF) of Orissa,India, and its interpretation

An unusual type of late diagenetic tectonic and compaction structure simulating boudinage phenomena is described and documented from the Precambrian banded iron formation (BIF) of Orissa, India. The structure was seemingly initiated by the development of tension cracks in the hydroplastic stage followed by rotation and imbrication of the segments of the iron (magnetite) bands. The tension cracks were subsequently filled up by finely crystalline diagenetic quartz veins.