ALBERT

Description: The pre-Himalayan evolution of Tethys is fundamental in interpreting the significance of India’s Paleogene deceleration and the timing of the India-Eurasia collision—the archetype continental collision that governs our understanding of collisional processes. Here we date zircons from plagiogranite sheeted dikes in the Muslim Bagh ophiolite that yield a U-Pb age of 80.2 ± 1.5 Ma. This age is interpreted as dating the crystallization of plagiogranites that occur at the top of gabbro plutons as well as within sheeted dikes. These represent highly fractionated magma chamber differentiates. The plagiogranite’s trace element abundances are typical of subduction petrogenesis and can be explained by the addition of slab-derived components to a depleted mantle wedge. Muslim Bagh ophiolite formation was coeval with the Spongtang Arc in a similar tectonic environment. We interpret the chain of ophiolites within western Pakistan as corollaries of the Spongtang Arc that formed ~15 Ma before they were obducted on the Indian passive margin. These form an extensive arc system that developed as oceanic crust in Tethys foundered during India’s migration north. Latest Maastrichtian ophiolite-sole formation and subsequent Paleocene obduction of the arc onto India was the first arc-India collision—a herald of the collisions to come later.

Description: Reclamation of saline lands seems difficult for climatic and economic reasons, but cultivation of salt-tolerant plants is an approach to increasing productivity and improvement of salt-affected wastelands. A five-year field study was conducted to evaluate the effects of growing a salt-tolerant species Leptochloa fusca (L.) Kunth (kallar grass) on chemical properties of a saline sodic soil irrigated with poor quality groundwater. Soil salinity, sodicity and pH decreased exponentially by growing kallar grass as a result of leaching of salts from surface (0–20 cm) to lower depths (〉100 cm). Concentrations of soluble cations (Na+, K+, Ca2+ and Mg2+) and anions (Cl−, SO42− and HCO3−) were reduced through to greater soil depths. A significant decline in soil pH was attributed to release of CO2 by grass roots and solublization of CaCO3. Both soil salinity and soil pH were significantly correlated with Na+, Ca2+, Mg2+, K+, Cl−, HCO3− and sodium adsorption ratio (SAR). Significant correlations were found between soluble cations (Na+, Ca2+ and K+), soluble anions (Cl−, SO42− and HCO3−) and the SAR. In contrast, there were negative correlations between soil organic matter content and all chemical properties. The ameliorative effects on the soil chemical environment were pronounced after three years of growing kallar grass. Cultivation of kallar grass enhanced leaching and interactions among soil chemical properties and thus restored soil fertility. The soil maintained the improved characteristics with further growth of the grass up to five years suggesting that growing salt-tolerant plants is a sustainable approach to biological amelioration of saline wastelands.