N. C. Pant

Chapter 5 Controls on sedimentation in Indian Palaeoproterozoic basins: clues from the Gwalior and Bijawar basins, central India

Abstract Overlying Archaean Bundelkhand Granite Gneiss Complex, the Gwalior and Bijawar Groups of rocks represent two Palaeoproterozoic basin successions which, despite their common sediment provenance and analogous rift-related tectonic setup, record more dissimilarity in their sedimentation pattern than similarity. Whereas early sedimentation in the Gwalior Basin is clastic, the early Bijawar sedimentation is dominantly chemogenic (limestone and chert) except for an early, restricted volcano-clastic record. Although both of the basins record syn-depositional volcanic/volcaniclastic event(s) in the form of occurrence of basaltic and basaltic–andesite sills encased within their respective basin fills, the occurrence of iron formation in the later part of Gwalior sedimentation history and its absence in the Bijawar succession is related to variable oxidation conditions in the water columns of the two basins. Rising sea-level and upwelling on the continental margins of these two rift-related basins possibly generated different water chemistries; these allowed the deposition of iron formation in the Gwalior Basin and phosphorite in the Bijawar Basin. Effects of post-depositional digenetic re-crystallization are noticed within both iron formation and phosphorite deposits present in the basin successions.

Provenance of Pleistocene sediments from Site U1359 of the Wilkes Land IODP Leg 318 – evidence for multiple sourcing from the East Antarctic Craton and Ross Orogen

Abstract Site U1359 is located on the eastern levée of the Jussieau submarine channel on the Wilkes Land margin, East Antarctica. The upper approximately 60 m of the sediment core records more than 2.5 Ma of the depositional history. Present work focuses on inferring provenance from the heavy mineral fraction from the Pleistocene sediments. Clay and non-clay fractions were characterized using X-ray diffraction and micro-beam techniques. Metamorphic minerals including orthopyroxene, high-Ca garnet and high-Ti biotite indicate a source in a high-grade metamorphic terrain. Mixing from a low- to medium-grade metamorphic component is also indicated. Several basaltic rock fragments, showing mineralogical affinities to the Ferrar volcanic province in the Ross Sea sector, are present. The metamorphic component is correlatable with the Proterozoic East Antarctic cratonic shield component. Ordovician–Silurian ages for the euhedral xenotime and monazite, coupled with the Ferrar equivalent basalts, indicate an additional sediment source from the Ross Orogen along with that from the craton.

Inferring a Neoproterozoic orogeny preceding the Rodinia break-up in the Sirohi Group, NW India

Abstract Recent studies indicate the Delhi Orogeny to be a Grenvillian-age collision event in the NW Indian Shield. West of the southern part of the South Delhi Fold Belt, aeromagnetic anomalies show a high-angle relationship with the Delhi Fold Belt trend. We examined an argillaceous–calcareous metamorphosed sequence exposed within and adjacent to this aeromagnetic anomaly. This sequence, deposited over a granitic basement, is reported as the Sirohi Group. The basement granite is dated to be 892±10 Ma (Erinpura age) and this was partially reset at 815±43 Ma. The metapelites preserve a low- to medium-grade metamorphic assemblage (peak temperature of c. 460°C) and the metamorphism took place at 822±29 Ma, which was partially reset at 723±65 Ma. The partial resetting can be ascribed to the Malani eruption. Control of accessory minerals on the garnet trace element chemistry is evident in the Y distribution of the two analysed garnets. It is contended that the Rodinia break-up, marked by Malani Igneous Suite, was preceded by an orogenic event (the Sirohi Orogeny) which marked the culminating mountain-building event in the cratonization of the NW Indian Shield.

Critical Evaluation and Assessment of Average Annual Precipitation in The Indus, The Ganges and The Brahmaputra Basins, Northern India

Three major river basins of India which include the Indus , the Ganges and the Brahmaputra contribute more than 50 % of the river discharge of the country. Widely varying average annual precipitations have been reported for these basins. The average annual precipitation is a basic input data for any developmental planning. Low density of rain gauge stations especially in mountainous area, extreme variation in altitudes and large size of these basins forces adaption of remote sensed data for estimation of average annual precipitation. In the present study, 11-years (2000–2010) Tropical Rain Measurement Mission (TRMM) generated radar precipitation raw data has been used for estimating the annual precipitation. The results indicate 434, 1,094 and 2,143 mm annual precipitation for the Indus, the Ganges and the Brahmaputra basins respectively. The contoured distribution of precipitation indicates the orographic control as the primary factor on the summer monsoon precipitation in the Ganges and the Brahmaputra basins. Indus basin behaves independent of the Indian summer monsoon.

Low Grade Metamorphism in the Lalsot-Bayana Sub-Basin of the North Delhi Fold Belt and its Tectonic Implication

From west to east, the North Delhi Fold Belt (NDFB) is composed of the Khetri sub-basin, the Alwar subbasin and the Lalsot-Bayana sub-basin. The metamorphic history of the easternmost Lalsot-Bayana sub-basin is considerably different from the other two as it has been reported to be nearly unmetamorphosed, while the other two subbasins display medium grade metamorphic assemblages. Textural, mineralogical and geothermometric data obtained for metabasic lithology, indicate metamorphism in the sub-greenschist facies conditions (~300°C temperature). This is corroborated by the development of chemically distinct authigenic phengitic muscovite in metasiltstone. The Alwar and the Khetri sub-basins preserve evidence of ~1000 Ma orogeny signifying closure of the Delhi basin in the form of amphibolites facies metamorphism which is lacking in the Lalsot-Bayana sub-basin. The lithopackage and metamorphism of this sub-basin suggests it to be a pre-Delhi intracratonic rift related volcanosedimentary sequence.

Current Status of Himalayan Cryosphere and Adjacent Mountains

Hindu Kush-Karakoram-Himalaya (HKKH) region represents one of the major non-polar cryosphere domains on the Earth. This region feeds three major rivers namely: the Indus, the Ganga and the Brahmaputra and supports a huge population of more than 1 billion people. There is wide variability and uncertainty in data on most aspects of this cryospheric domain. The behaviour of glacial melting in HKH region is highly heterogeneous with the highest negative mass balance in the eastern Himalaya, relatively less negative mass balance in the western Himalaya with positive mass balance in the Karakoram. The hydrological budget of the higher Himalayan rivers depends on the precipitation (snowfall and rainfall) but the available estimates on snow cover and rainfall are highly variable and in few cases appear to be unacceptable. Reported precipitation variability for the Indus basin is more than 250%, for the Ganga basin it is 100% and for the Brahmaputra basin the variability is more than 240%. The estimate on glacial cover and its volume in the Himalayan-Karakoram regions shows variability of more than 130 and 250% respectively. The available estimates on the glacial melt fraction also show high variability, for example for the Indus basin the variability is ~170%, for the Ganga basin it is ~300% and for the Brahmaputra basin the variability is more than 100%. The number of glaciers in the Himalaya and the adjacent mountains differ in the different glacier inventories. Similarly, published data on basin wise glaciated area varies from 300% for Indus basin, 200% for the Ganga basin and it is more than 450% for the Brahmaputra basin. The present work reviews current status of the Himalayan cryosphere.

Microanalytical Characterization and Application in Magmatic Rocks

Chemical characterization of magmatic rocks is a primary requirement in interpreting their evolutionary history. Magmatic rocks are nearly always heterogeneous and thus require micro-scale chemical characterization. Two of the main micro-characterization techniques are Scanning Electron Microscopy (SEM) and Electron Probe Micro Analysis (EPMA). Both are near surface characterization techniques and utilize the effects of interaction of an electron beam with the targeted sample. Back Scattered Electrons (BSE) represent an atomic number dependent elastic scattering effect which provides high resolution petrographic information of heterogeneities while generation of characteristic X-rays from inner shell energy-level transitions of different atoms, a type of inelastic scattering effect, provides quantitative chemical characterization at micron scale. Both are highly useful for describing magmatic rocks as well as inferring the operative magmatic processes.