• Kanchan Pande

      Articles written in Journal of Earth System Science

    • Emplacement of Amba Dongar carbonatite-alkaline complex at Cretaceous/Tertiary boundary: Evidence from40Ar-39Ar chronology

      Jyotiranjan S Ray Kanchan Pande T R Venkatesan

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    • Stable isotope systematics of surface water bodies in the Himalayan and Trans-Himalayan (Kashmir) region

      Kanchan Pande J T Padia R Ramesh K K Sharma

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      Stable hydrogen (δD) and oxygen (δ18O) isotope ratios of the headwaters of the Indus and its tributaries, surface ice in glaciers, saline and fresh water lakes and thermal springs in the Himalayan and Trans-Himalayan (Kashmir) region are reported. The δ5D-δ18 relationship for the river samples shows a slope of 9.12 +-0.29 which agrees well with the estimate of 8.99 ±0.33 based on a simple Rayleigh fractionation model. The unique signature of a higher deuterium excess (d) of the ‘Western Disturbance’ is preserved in these samples. An altitude effect of -0.9 per mil/km is observed in the δ18O of Indus waters. At a lower altitude (Beas) the altitude effect is almost double, indicating that the altitude effect decreases with elevation in this region.

    • 40Ar-39Ar age of carbonatite-alkaline magmatism in Sung valley, Meghalaya, India

      Jyotiranjan S Ray Kanchan Pande

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      40Ar-39Ar analyses of one alkali pyroxenite whole rock and two phlogopite separates of calcite carbonatites from the Sung Valley carbonatite-alkaline complex, which is believed to be a part of the Rajmahal-Bengal-Sylhet (RBS) flood basalt province, yielded indistinguishable plateau ages of 108.8 ± 2.0Ma, 106.4 ± 1.3Ma and 107.5 ± 1.4Ma, respectively. The weighted mean of these ages, 107.2 ± 0.8 Ma, is the time of emplacement of this complex. This implies that Sung Valley complex and probably other such complexes in the Assam-Meghalaya Plateau postdate the main flood basalt event (i.e., the eruption of tholeiites) in the RBS province by ∼10Ma.

    • Age and duration of the Deccan Traps, India: A review of radiometric and paleomagnetic constraints

      Kanchan Pande

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      A review of the available radiometric and paleomagnetic data from the Deccan Flood Basalt Province (DFBP) suggests that the volcanism was episodic in nature and probably continued over an extended duration from 69Ma to 63Ma between 31R and 28N. It is likely that the most intense pulse of volcanism at 66.9 ± 0.2Ma preceded the Cretaceous Tertiary Boundary (KTB, 65.2 ± 0.2Ma) events by ∼1.7Ma. The magnetostratigraphic record in the Deccan lava pile is incomplete and it is therefore possible that the lava ows constituting the reverse polarity sequence were erupted in more than one reversed magnetic chron.

    • Preface

      Hetu Sheth Kanchan Pande

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    • Tectono-thermal evolution of the India-Asia collision zone based on40Ar-39Ar thermochronology in Ladakh, India

      Rajneesh Bhutani Kanchan Pande T R Venkatesan

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      New40Ar-39Ar thermochronological results from the Ladakh region in the India-Asia collision zone provide a tectono-thermal evolutionary scenario. The characteristic granodiorite of the Ladakh batholith near Leh yielded a plateau age of 46.3 ± 0.6 Ma (2σ). Biotite from the same rock yielded a plateau age of 44.6 ± 0.3 Ma (2σ). The youngest phase of the Ladakh batholith, the leucogranite near Himya, yielded a cooling pattern with a plateau-like age of ∼ 36 Ma. The plateau age of muscovite from the same rock is 29.8 ±0.2 Ma (2σ). These ages indicate post-collision tectono-thermal activity, which may have been responsible for partial melting within the Ladakh batholith. Two basalt samples from Sumdo Nala have also recorded the post-collision tectono-thermal event, which lasted at least for 8 MY in the suture zone since the collision, whereas in the western part of the Indus Suture, pillow lava of Chiktan showed no effect of this event and yielded an age of emplacement of 128.2 ±2.6 Ma (2σ). The available data indicate that post-collision deformation led to the crustal thickening causing an increase in temperature, which may have caused partial melting at the base of the thickened crust. The high thermal regime propagated away from the suture with time.

    • 40Ar-39Ar age of a lava flow from the Bhimashankar Formation, Giravali Ghat, Deccan Traps

      Kanchan Pande S K Pattanayak K V Subbarao P Navaneethakrishnan T R Venkatesan

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      We report here a40Ar-39Ar age of 66.0 ± 0.9 Ma (2σ) for a reversely magnetised tholeiitic lava flow from the Bhimashankar Formation (Fm.), Giravali Ghat, western Deccan province, India. This age is consistent with the view that the 1.8–2 km thick bottom part of the exposed basalt flow sequence in the Western Ghats was extruded very close to 67.4 Ma.

    • Cones and craters on Mount Pavagadh, Deccan Traps: Rootless cones?

      Hetu C Sheth George Mathew Kanchan Pande Soumen Mallick Balaram Jena

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      Rootless cones, also (erroneously) called pseudocraters, form due to explosions that ensue when a lava flow enters a surface water body, ice, or wet ground. They do not represent primary vents connected by vertical conduits to a subsurface magma source. Rootless cones in Iceland are well studied. Cones on Mars, morphologically very similar to Icelandic rootless cones, have also been suggested to be rootless cones formed by explosive interaction between surface lava flows and ground ice. We report here a group of gentle cones containing nearly circular craters from Mount Pavagadh, Deccan volcanic province, and suggest that they are rootless cones. They are very similar morphologically to the rootless cones of the type locality of Mývatn in northeastern Iceland. A group of three phreatomagmatic craters was reported in 1998 from near Jabalpur in the northeastern Deccan, and these were suggested to be eroded cinder cones. A recent geophysical study of the Jabalpur craters does not support the possibility that they are located over volcanic vents. They could also be rootless cones. Many more probably exist in the Deccan, and volcanological studies of the Deccan are clearly of value in understanding planetary basaltic volcanism.

    • Laboratory technique for quantitative thermal emissivity measurements of geological samples

      George Mathew Archana Nair T K Gundu Rao Kanchan Pande

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      Thermal infrared spectroscopy is a powerful technique for the compositional analysis of geological materials. The spectral feature in the mid-IR region is diagnostic of the mineralogy and spectral signatures of mixtures of minerals that add linearly, and therefore, can be used as an important tool to determine the mineralogy of rocks in the laboratory and remotely for planetary exploration. The greatest challenge in the emission measurement lies in the measurement of the weak thermal photons emitted from geological materials in a laboratory setup, and accurately records the temperature of the rock sample. The present work pertains to the details of a new Thermal Emission Spectrometer (TES) laboratory that has been developed under the ISRO Planetary Science and Exploration (PLANEX) programme, for emission related mineralogical investigations of planetary surfaces. The focus of the paper is on the acquisition and calibration technique for obtaining emissivity, and the deconvolution procedure to obtain the modal abundances of the thermal emission spectra in the range of 6–25 𝜇 m using Fourier Transform Infrared (FTIR) spectroscopy. The basic technique is adopted from the work of Ruff et al (1997). This laboratory at the Department of Earth Sciences, IIT-Bombay is currently developing pure end mineral library of mineral particulates (> 65 𝜇m), and adding new end members to the existing ASU spectral library. The paper argues the need for considering Lunar Orbiter Thermal Emission Spectrometer (LOTES) for future Indian Moon mission programme (Chandrayan-II) to determine evidences of varied lithologies on the lunar surface.

    • Arc parallel extension in Higher and Lesser Himalayas, evidence from western Arunachal Himalaya, India

      Sharmistha De Sarkar George Mathew Kanchan Pande

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      The existence of E–W extensional features from northeast (NE) Himalaya is poorly documented. Our investigation in the western part of Arunachal Himalaya provides evidences of active Quaternary E–W arc-parallel extensional features in the Higher and Lesser Himalayas. They are represented by arcperpendicular normal faults and arc-parallel sinistral strike-slip faults. We discuss the occurrences of these arc-parallel extensional features in terms of oblique convergence and radial expansion models. The partitioning of stress due to oblique convergence is argued based on evidences of left-lateral slip in NEHimalaya, right-lateral slip in NW-Himalaya and absence of translation in the central part. The amount of arc-parallel extension in the hinterland regions is correlated to the amount of radial shortening in the foreland. The computation of arc-parallel extension in the NE Himalayan arc is carried out by defining a small-circle centered at 88° 39′ \pm 0.7′E longitude and 33° 40′ \pm 0.6′N latitude having a radius of 770.7 ± 15.1 km, for the segment between 92° 01′ and 95° 16′E longitudes. The amount of arc-parallel extension estimated is ∼110 km for the NE Himalayan segment. Our result agrees closely with the 104 km extension determined based on geodetically computed extension rate and age of initiation of rifting in southern Tibet.

    • An Ediacaran–Cambrian thermal imprint in Rajasthan, western India: Evidence from 40Ar-39Ar geochronology of the Sindreth volcanics

      Archisman Sen Kanchan Pande Hetu C Sheth Kamal Kant Sharma Shraboni Sarkar A M Dayal Harish Mistry

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      The Sindreth Group exposed near Sirohi in southern Rajasthan, western India, is a volcanosedimentary sequence. Zircons from Sindreth rhyolite lavas and tuffs have yielded U–Pb crystallization ages of ∼768–761 Ma, suggesting that the Sindreth Group is a part of the Malani magmatic event. Earlier 40Ar-39Ar studies of other Malani volcanic and plutonic rocks yielded disturbed argon release spectra, ascribed to a ∼550 Ma thermal event possibly related to the Pan-African orogeny. To test and confirm this possibility, we dated two whole-rock and three feldspar separate samples of the Sindreth volcanics by the 40Ar-39Ar method. All samples yield disturbed argon release spectra suggesting radiogenic argon loss and with plateau segments at 550 Ma or 490 Ma. We interpret these as events of argon loss at 550–490 Ma related to an Ediacaran–Cambrian thermal event, possibly related to the Malagasy orogeny. The combined older and new 40Ar-39Ar results are significant in showing that whereas Ediacaran–Cambrian magmatic and metamorphic events are well known from many parts of India, they left thermal imprints in much of Trans-Aravalli Rajasthan as well. The overall evidence is consistent with a model of multiphase assembly of Gondwanaland from separate continental landmasses.

    • Implications of new ⁴⁰Ar / ³⁸Ar age of Mallapur Intrusives on the chronology and evolution of the Kaladgi Basin, Dharwar Craton, India

      Shilpa Patil Pillai Kanchan Pande Vivek S Kale

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      The Kaladgi Basin on the northern edge of the Dharwar craton has characters diverse from the other epicratonic Purana basins of Peninsular India. Sedimentological studies in the basin have established the presence of three cycles of flooding separated by an event of intra-basinal deformation accompaniedby low grade incipient metamorphism. The overall structural configuration of the basin indicates its development by supracrustal extension accompanied by shearing in a trans-tensional regime during the Mesoproterozoic. This was followed by sagging that yielded Neoproterozoic sedimentation in a successornested basin. ⁴⁰Ar / ³⁸Ar dating

      of an intrusive mafic dyke along the axial plane of a fold has yielded a plateau age of 1154±4Ma. This helps constraint the age of the various events during the evolution of this basin.

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