C. K. Singh

Active deformations extracted from drainage geomorphology: A case study from southern Sonbhadra district, Central India

Since the Precambrian time the Narmada-Son Lineament (NSL) is a zone of weakness and both the northern and southern portions of Narmada-Son Lineament experienced vertical block movements. It is established by the earlier workers that NSL is a sub-crustal feature which is responsible for the deposition and folding of the Vindhyans (Meso- Neoproterozoic) and Gondwanas (Permo-Carboniferous-lower Cretaceous). Recent tectonic activity in the Narmada- Son region is evidenced by high heat flow thermal activity, sulphur springs and seismically the Narmada-Son Lineament region is known to be a significantly disturbed zone. The present study area is the part of Narmada-Son Lineament zone. The drainage geomorphology of the area between Kanahar and Rihand rivers (tributaries of the tectonically controlled Son river) around Renukoot area have been studied aiming to understand active tectonics of the region, integrating detailed analysis of landforms and drainages. Various geomorphic features present in the study area such as incision of valley, aligned drainage, aligned valleys, linear valleys, offset channels, offset ridges and fault scarps demonstrate that the area is undergoing active deformation.

Reaction textures and metamorphic evolution of sapphirine–spinel-bearing and associated granulites from Diguva Sonaba, Eastern Ghats Mobile Belt, India

The Diguva Sonaba area (Vishakhapatnam district, Andhra Pradesh, South India) represents part of the granulite-facies terrain of the Eastern Ghats Mobile Belt. The Precambrian metamorphic rocks of the area predominantly consist of mafic granulite (±garnet), khondalite, leptynite (±garnet, biotite), charnockite, enderbite, calc-granulite, migmatic gneisses and sapphirine–spinel-bearing granulite. The latter rock type occurs as lenticular bodies in khondalite, leptynite and calc-granulite. Textural relations, such as corroded inclusions of biotite within garnet and orthopyroxene, resorbed hornblende within pyroxenes, and coarse-grained laths of sillimanite, presumably pseudomorphs after kyanite, provide evidence of either an earlier episode of upper-amphibolite-facies metamorphism or they represent relics of the prograde path that led to granulite-facies metamorphism. In the sapphirine–spinel-bearing granulite, osumilite was stable in addition to sapphirine, spinel and quartz during the thermal peak of granulite-facies metamorphism but the assemblage was later replaced by Crd–Opx–Qtz–Kfs-symplectite and a variety of reaction coronas during retrograde overprint. Variable amounts of biotite or biotite+quartz symplectite replaced orthopyroxene, cordierite and Opx–Crd–Kfs–Qtz-symplectite at an even later retrograde stage. Peak metamorphic conditions of c . 1000°C and c . 12 kbar were computed by isopleths of X Mg in garnet and X Al in orthopyroxene. The sequence of reactions as deduced from the corona and symplectite assemblages, together with petrogenetic grid and pseudosection modelling, records a clockwise P–T evolution. The P–T path is characteristically T -convex suggesting an isothermal decompression path and reflects rapid uplift followed by cooling of a tectonically thickened crust.

Node inoculation: A quick and easy technique to screen pigeonpea for resistance to Phytophthora blight

The petiole on pigeonpea was removed for easy, precise inoculation of node with Phytophthora drechsleri f. sp. cajani. After node inoculation, 96.0% plants were infected compared with 89.0% after stem-cut inoculation. Among various nodes inoculated on 30-day-old plants, the 5th node had the greatest relative susceptibility (90.0%), followed by the 3rd node (78.0%). This technique was validated on different cultivars (ICP 7119, Bahar, MA 6 and MAL 13), and 586 lines were successfully screened in the field, confirming the rapidity and effectiveness of the technique for resistance screening.