Tectonic Significance of Fissure Veins Associated with Pseudotachylites of the Kui-Chitraseni Shear Zone, Aravalli Mountain, NW India

Kui-Chitraseni Shear Zone of the Precambrian Aravalli Mountain, NW India is marked by a nearly 400 m-wide NE-SW trending belt of cataclasites developed on the granites and metasediments of the Delhi Supergroup. The cataclasites are criss crossed by pseudotachylite and fissure-veins. While the pseudotachylites are aphanitic to microlitic, the fissure veins are characterized by syntaxial-bitaxial as well as unitaxial growth of elongate quartz grains. Textural study of the fissure veins suggests crystallization of quartz grains in a dilational environment in hydrous condition. Contrarily the pseudotachylites bear the evidence of frictional melting of rocks under anhydrous conditions. Since in many instances it is observed that the fissure veins have replaced the pseudotachylites following the crack seal mechanism, the formation of fissure veins is considered to be latekinematic to pseudotachylites. Hence it is interpreted that the pseudotachylites and fissure veins were formed in two distinct tectonic events. While pseudotachylites were formed in a compressional setting resulted from thrusting along the shear zone, the fissure veins have been formed in an extensional setting during a late stage normal faulting. In light of this tectonic rejuvenation along the Kui-Chitraseni Shear Zone, various lineaments present within the Aravalli Mountains need further study for understanding the evolution of the region.     

Distribution of polycyclic aromatic hydrocarbons in recent sediments of Sundarban mangrove wetland of India and Bangladesh: a comparative approach

The present work is the first attempt to compare the data of a comprehensive study of the origin and distribution of 16 priority pollutant polycyclic aromatic hydrocarbons (PAHs) in surface sediments (<63 μm) from 18 sampling stations, 9 from Sundarban of Bangladesh and 9 from Indian counterpart. Σ19PAHs concentration in sediments showed wide variations from 208.3 to 12,993.1 ng g^?1 dry weight in Indian Sundarban, whereas 208.4 to 4,687.9 ng g^?1 in the case of Bangladesh. Fluoranthene, pyrene, benzo(b)fluoranthene, benzo(a)pyrene and dibenzo(a,h)anthracene were predominant species for both the countries. The PAH diagnostic ratios indicated that the PAHs in sediments from both the countries were of mixed source of hydrocarbons of both petrogenic and pyrolytic origin. According to the numerical effect-based sediment quality guidelines, the levels of PAHs in the Sundarban wetland of Bangladesh and India should not exert adverse biological effects. The TEQ values calculated for samples from the Bangladesh and Indian Sundarban varied from 13.68 to 1,014.75 and 1.31 to 2,451 ng g^?1 d.w. with an average of 221.02 and 358.63 ng g^?1, respectively. The overall contamination status of PAH was higher in India than Bangladesh.