Search

The Beas valley section in Himachal Pradesh is characterized by the presence of kyanite as the alumino-silicate phase and a small extent of Neogene quartzo-feldspathic intrusives. The present paper explores the reasons for the lack of extensive granite occurrences through a detailed petrologic study on samples of a drill core (200 m, inclined 60° due ESE) close to Manali, the expected highest point in P–T space in this section. The highest assemblage encountered is quartz+muscovite+biotite+garnet+plagioclase+kyanite±apatite±zircon±tourmaline±ilmenite±rutile. The chemical analyses of mineral grains were carried out on a CAMECA SX51 EPMA. The following two reactions that constrain the P–T regime of the area have been established. St + Qtz → Alm + Ky + H 2 O Bio + Plg + Qtz + Ksp → Gar + Ky + Liq . Our result, P=8.25±1 kbar, T=638±4 °C, falls in a region between curves representing a H 2 O = 1.0 and a H 2 O = 0.7 of the fluid in Thompson [Trans. Royal Soc. Edinb. 87 (1996) 1] diagram. The P–T estimate falls in the kyanite field and is very close to the mica dehydration-melting curve. The studies indicate that the core samples are a part of progressive metamorphic sequence. It implies that the absence of sillimanite and large scale melting is perhaps chance brought about by thrusting and erosion. The present section experienced single stage dehydration melting.

An asymmetric binary Margules formulation for excess Gibbs energy, enthalpy, and entropy is adequate to describe the 1 bar halite-sylvite solvus in NaCl-KCl (Thompson and Waldbaum 1969). However, a binary Margules formulation is not adequate to describe excess volumes of single-phase chlorides in P-V-T-X from ambient P-T to ~20 kbar and 700 °C. Excess volumes across NaCl-KCl increase with temperature, decrease with pressure, and show systematic deficits in the consolute region. These patterns can be explained by the importance of a third component—vacancy defects that relieve the lattice stresses of K-Na size mismatch. New, two-phase observations in P-V-T-X allow delineation of the excess Gibbs energies to high pressures where the excess enthalpies and entropies do not depend on T at each P , but show significant variation between 1 bar and ~20 kbar. The volume, entropy, and enthalpy of K-Na mixing become more ideal at high pressure. But the solvus expands with pressure because entropy approaches ideality faster than enthalpy and, therefore, Gibbs energy of K-Na mixing becomes less ideal with pressure. The consolute temperature rises about 80 °C in 17 kbar, with little change in consolute composition. The binary Margules equation of state provides a prediction of the rise of the solvus that is impressively convergent with the new observations. This convergence is especially impressive given the clear inadequacies of the binary excess volume formulation on which the prediction is based.

Unit-cell volumes of four single-phase intermediate halite-sylvite solid solutions have been measured to pressures and temperatures of ~28 kbar and ~700 °C. Equation-of-state fitting of the data yields thermal expansion and compressibility as a function of composition across the chloride series. The variation of the product α 0 · K 0 is linear (ideal) in composition between the accepted values for halite and sylvite. Taken separately, the individual values of α 0 and K 0 are not linear in composition. α 0 shows a maximum near the consolute composition ( X NaCl = 0.64) that exceeds the value for either end-member. There is a corresponding minimum in K 0 . The fact that the α 0 · K 0 product is variable (and incidentally so well behaved as to be linear across the composition series) reinforces the significance of the complementary maxima and minima in α 0 and K 0 (significantly, near the consolute composition). These extrema in α 0 and K 0 provide an example of intermediate properties that do not follow simply from values for the end-members. Cell volumes across this series show small, well-behaved positive excesses, consistent with K-Na substitution causing defects through lattice mismatches. Barrett and Wallace (1954) showed maximum defect concentrations in the consolute region. Defect-riddled, weakened structures in the consolute region are more easily compressed or more easily thermally expanded, providing an explanation for our observed α 0 and K 0 variations. These compliant, loosened lattices should resist diffusive transfer less than non-defective crystals and, hence, might be expected to show higher diffusivities. Tracer diffusion rates are predicted to peak across the consolute region as exchange diffusion rates drop to zero.

Compressibility of solids generally drops as compression proceeds. Bonds shorten and stiffen with density increase in the same structure. However for the B1-B2 phase transition in many measured alkali halides, bond lengths increase in going to the denser phase. And IR mode frequencies decrease (Hofmeister 1997), leading to the counter-intuitive expectation that compressibility should increase in going to the denser B2 phase. Past volume measurements have been equivocal at best in recognizing any such compressibility increase. New thermal equations of state for B1 and B2 KCl from in-situ X-ray diffraction measurements of phase volumes on Station 16.4 of the CLRC Daresbury Laboratory are no less equivocal about the issue of whether compressibility increases or decreases across the transition. In contrast, the new volume measurements show an easily resolved thermal expansion increase in going from B1 to B2 KCl. The product α·K, which is better known than either α or K, increases from 0.0195 ± 0.0005 kbar/∞C in B1 to 0.0275 ± 0.0009 kbar/∞C in B2 KCl. Yagi (1978) demonstrated a similar increase for KF, also supported mainly by increases in α. This increase can also be seen in RbCl (Walker et al. 2001). Bond weakening indicated by the thermal expansion increase is consistent with the elusive compressibility increase that is expected across the B1-B2 transition but which is not resolved from volume measurements. The thermal effects are more visible than the compressional effects on α·K across the transition. Bond tightening upon decompression reduces α, increases solid viscosity, and hence decreases the Rayleigh number. An upwelling of material undergoing a decompression phase change with decrease of coordination number may have its convective friskiness damped at such a transition.

The prevalence of congenital heart disease (CHD) is not known in our country. The aim of present study was to find out the prevalence of CHD in school children of eastern Uttar Pradesh.A team consisting of a cardiologist, physicians and junior residents visited schools in the area. All the children were examined for presence of cardiac murmur or history of heart disease or any intervention. Those with murmurs or previous history of heart disease were called to the Medical College Hospital for evaluation by ECG, chest X-ray and echocardiography for confirmation of the lesion.Out of 118,212 children examined, 142 were found to have CHD. The prevalence was 1.3 per 1000 children and the commonest lesions were ventricular and atrial septal defects, aortic stenosis with or without regurgitation, and pulmonary stenosis.CHD prevalence is 1.3 per 1000 school children that is nearly two and a half times more than that of RHD. Knowing it is important for development of facilities for CHD care in our setup.

The present study is on the Ultra High Pressure Metamorphic rocks of the Tso Morari Crystalline Complex of the northwestern Himalayas. Five different mineral associations representative of five stages of P–T (pressure–temperature) evolution of these rocks have been established based on metamorphic textures and mineral chemistry. The pre-UHP metamorphic association 1 of Na-Ca-amphibole + epidote ± paragonite ± rutile ± magnetite with T–P of ~ 500°C and 10 kbar. This is followed by UHP metamorphic regime marked by association 2 and association 3. Association 2 (Fe>Mg>Ca-garnet + omphacite + coesite + phengite + rutile ± ilmenite) marks the peak metamorphic conditions of atleast 33 kbar and ~ 750°C. Association 3 (Fe>Mg>Ca-garnet + Na-Ca amphibole + phengite ± paragonite ± calcite ± ilmenite ± titanite) yields a P–T condition of ~28 kbar and 700°C. The post-UHP metamorphic regime is defined by associations 4 and 5. Association 4 (Fe>Ca>Mg-garnet + Ca-amphibole + plagioclase (An05) + biotite + epidote ± phengite yields a P–T estimate of ~14 kbar and 800°C) and association 5 (Chlorite + plagioclase (An05) + quartz + phengite + Ca-amphibole ± epidote ± biotite ± rutile ± titanite ± ilmenite) yields a P–T value of ~7 kbar and 350°C.