Informatics Publishing Limited

Jyotiranjan S. Ray ¹, R. Ramesh ¹

Affiliations
1 Physical Research Laboratory, Ahmedabad 380 009, IN

Abstract

A fluid-rock interaction model for treating the stable carbon and oxygen isotopic variations in altered carbonatites is presented and illustrated with an example using data from the ferrocarbonatites of Amba Dongar, Gujarat. The Amba Dongar ferrocarbonatites appear to have been altered by a fluid of magmatic origin at 100 to 200°C contrary to an earlier suggestion of meteoric groundwater alteration at ∼50°C.

Keywords

Isotope Geology, Ferrocarbonatite, Fluorite, Fluid-Rock Interaction Model, Carbon and Oxygen Isotopes, Amba Dongar, Gujarat.

Full Text

     

Neeraj Awasthi ¹, Jyotiranjan S. Ray ¹, Kanchan Pande ²

Affiliations
1 Physical Research Laboratory, Navrangpura, Ahmedabad 380 009, IN
2 Department of Earth Sciences, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, IN

Abstract

The Mile Tilek Tuff is one of several consolidated volcanic ash deposits in the Andaman and Nicobar Islands that has preserved evidence of a large-scale volcanic eruption in Southeast Asia. Assumed to be of Mio-Pliocene age (~25-2 Ma), the tuff was thought to have been generated by the Andaman-Indonesia volcanic arc. Little was known about its source volcano because of absence of critical isotope data. To provide accurate age information and determine its source, we dated the tuff by ⁴⁰Ar-³⁹Ar method and measured its trace element contents and Sr-Nd isotopic ratios. The ⁴⁰Ar-³⁹Ar plateau age for the whole rock is 0.73 ± 0.16 (2σ) Ma, which suggests that the tuff got deposited much later than previously believed. Chemically, the tuff possesses typical characteristics of subduction zone magmatism. Its Sr-Nd isotopic compositions (⁸⁷Sr/⁸⁶Sr = 0.7073 and ε_Nd ≤ 0.9) suggest substantial continental crustal contamination of its source magma, which points to a source volcano in Sumatra. Based on available age information on large-scale volcanic eruptions in Indonesia, we speculate that the Ranau volcano in south Sumatra could have been the source of the Mile Tilek Tuff.

Keywords

⁴⁰Ar–³⁹Ar Dating, Geochemical Fingerprinting, Mile Tilek Tuff, Sumatra.

Full Text

   

Jyotiranjan S. Ray ¹, R. Ramesh ¹

Affiliations
1 Physical Research Laboratory, Navrangpura, Ahmedabad 380009, IN

Abstract

Accurate analysis of coexisting calcite and dolomite for δ¹³C and δ¹⁸O is generally hindered by the difficulty in the physical separation of these minerals. The difference in the reaction rates of calcite and dolomite with phosphoric acid, has been used to chemically separate these carbonates. Previously established procedures are only suitable for samples containing 1:1 calcite-dolomite pairs. However, these are sometimes tedious and time-consuming. Using mixtures of calcite and dolomite, two different selective acid extraction procedures (for reactions at 25°C), one for calcite-rich and the other for dolomite-rich carbonates, have been developed. Reduction of grain size (to 37μm - 45μm) increased the reaction rate and hence decreased the total reaction time to a reasonable interval (≤72 hours for dolomite). Applying these procedures, δ¹³C and δ¹⁸O of calcite and dolomite/ankerite of carbonatites from Amba Dongar and Sung Valley carbonatite complexes of India were measured and their temperatures of crystallization determined. Accurate isotopic compositions of individual carbonates of calcite-dolomite mixtures can be determined for geological interpretations by these procedures.

Keywords

Stable Isotopes, Carbonate Mixtures, CO₂ Extraction Technique, Calcite, Dolomite, Ankerite, Carbonatite, Amba Dongar, Sung Valley.

Full Text

     

Dwijesh Ray ¹, Anil D. Shukla ¹, Jyotiranjan S. Ray ¹

Affiliations
1 Physical Research Laboratory, Ahmedabad 380 009, IN

Abstract

Barren Island is the northernmost active stratovolcano of the Sunda Volcanic Arc system in the northeastern Indian Ocean. It is the only active volcano in the Indian territory. The arc is a result of subduction of the Indian plate beneath the Burma plate, a sliver of the Eurasian plate. This subduction zone is a southward extension of the Himalayan convergent boundary that takes a turn at the Eastern Syntaxial Bend. Located ~135 km northeast of Port Blair (12°70'N/93°51'E), the Barren Island volcano covers a subaerial area of ~8 km.

Full Text

   

Jyotiranjan S. Ray ¹

Affiliations
1 Physical Research Laboratory, Navrangpura, Ahmedabad 380 009, IN

Abstract

Even after more than 100 years of the initial discovery of isotopes, we are yet to fully utilize their potential in science and technology. The unique properties of isotopes of elements covering the entire periodic table have wide-ranging applications. The modern earth and planetary sciences owe a lot to such exploits for understanding of the fundamental aspects of evolution of the solar system and planetary interiors. Isotopes have remained the most advanced tools in determining the timescales of various events that shaped the solar system and understanding the nature of processes that occur in it. Isotopes are either stable or radioactive. Stable isotopes are powerful tracers of geochemical processes, whereas radioactive isotopes and their products (radiogenic isotopes) are the basis of geochronology or radiometric dating.

Full Text

   

Jyotiranjan S. Ray ¹

Affiliations
1 Physical Research Laboratory, Navrangpura, Ahmedabad 380 009, IN

Abstract

Rengaswamy Ramesh was a man of extraordinary scientific latitude with countless important contributions to stable isotope geochemistry, palaeoclimatology, oceanography, biogeochemistry and solid earth studies. He was mentor to a long list of Master’s and Ph D students, postdoctoral fellows and university teachers, and had inspired many young minds to take up science as a career. He was instrumental in shaping stable isotope research activities in numerous universities and institutions in India. He was extremely intelligent and a scholar in the true sense.

Full Text

   

Neeraj Awasthi ¹, Jyotiranjan S. Ray ²

Affiliations
1 Department of Earth and Planetary Sciences, Prof. Rajendra Singh (Rajju Bhaiya) Institute of Physical Sciences for Study and Research, VBS Purvanchal University, Jaunpur 222 003, IN
2 Physical Research Laboratory, Navrangpura, Ahmedabad 380 009, IN

Abstract

Terrestrial and marine sediments preserved on the Indian sub-continent and in seas/oceans around it are excellent archives for studying and reconstructing past variations in monsoonal climate. Based on the multiproxy studies on the sediment cores, a coherent relationship between the intensities of the monsoon and glacial–interglacial conditions and a strong atmospheric teleconnection between the Asian and North Atlantic climates has been suggested. Terrestrial sediment cores clearly established that the variations in the monsoonal climate and/or change in glacial extant played an important role in varying weathering/erosion in source regions and relative supply of sediments. Marine sediment studies presented a more complicated picture because their depositions were influenced by changes in sea-levels, movement of shorelines, river mouths, deltas and sea surface-circulations. A composite climate record suggested that the intensity of Indian SW monsoon has weakened and NE monsoon strengthened during glacial periods and vice-versa during the interglacial periods.

Keywords

Climate, Himalaya, Indian Monsoon, Sediment Cores, Sr–Nd Isotopes, Weathering-Erosion.

Full Text