Imprints of Archean to Neoproterozoic crustal processes in the Madurai Block, Southern India

Madurai Block, the largest crustal block in the Southern Granulite Terrane (SGT) of Peninsular India, preserves the imprints of multistage tectonic evolution. Here, we present U-Pb and Hf isotope data on zircons from a charnockite-granite suite in the north-western part of this block. The oscillatory zoning, and the LREE to HREE enriched patterns of the zircons with positive Ce and negative Eu anomalies suggest that the zircon cores are of magmatic origin, with ages in the range of 2634-2435 Ma implying Neoarchean-Paleoproterozoic magmatism followed by subsequent metamorphism and protocontinent formation in the north-western part of the Madurai Block. A regional 550-500 Ma metamorphic overprint is also preserved in the zircons coinciding with the final amalgamation of the Gondwana supercontinent. The Hf isotopic data suggest that the granite and charnockite were derived from isotopically heterogeneous juvenile crustal domains and the charnockites show a significant contribution of mantle-derived components. Therefore, the Hf isotopic data reflect mixing of crustal and mantle-derived sources for the generation of Neoarchean crust in the north-western Madurai Block, possibly in a suprasubduction zone setting during continent building processes. (c) 2014 Elsevier Ltd. All rights reserved.

Plate-shaped transformation products in zirconium-base alloys

Plate-shaped products resulting from martensitic, diffusional, and mixed mode transformations in zirconium-base alloys are compared. in the present study. These alloys are particularly suitable for the comparison in view of the fact that the lattice correspondence between the parent beta (bcc) and the product alpha (hcp) or gamma-hydride (fct) phases are remarkably similar for different types of transformations. Crystallographic features such as orientation relations, habit planes, and interface structures associated with these transformations have been compared:, with a view toward examining whether the transformation mechanisms have characteristic imprints on these experimental observables. Martensites exhibiting dislocated lath, internally twinned plate, and self-accommodating three-plate cluster morphologies have been encountered in Zr-2.5Nb alloy. Habit planes corresponding to all these morphologies have been found to be consistent with the predictions based on the invariant plane strain (IFS) criterion. Different morphologies have been found to reflect the manner in which the neighboring martensite variants are assembled. Lattice-invariant shears (LISs) for all these cases have been identified to be either {10 (1) over bar 1}(alpha) ((1) over bar 123)(alpha) slip or twinning on (10 (1) over bar 1)(alpha) planes. Widmanstatten alpha precipitates, forming in a step-quenching treatment, have been shown to have a lath morphology, the alpha/beta interface being decorated with a periodic array of (c + a) dislocations at a spacing of 8 to 10 nm. The line vectors of these dislocations are nearly parallel to the invariant lines. The alpha precipitates, forming in the retained beta phase on aging, exhibit an internally twinned structure with a zigzag habit plane. Average habit planes for the morphologies have been found to lie near the {103}(beta) - {113}(beta) poles, which are close to the specific variant of the {112}(beta) plane, which transforms into a prismatic plane of the type {1 (1) over bar 00}(alpha). The crystallography of the formation of the gamma-hydride phase (fct) from both the alpha and beta phases is seen to match the IFS predictions. While the beta-gamma transformation can be treated approximately as a simple shear on the basal plane involving a change in the stacking sequence, the alpha-gamma transformation call be conceptually broken into a alpha --> beta transformation following the Burgers correspondence and the simple beta-gamma shear process. The active eutectoid decomposition in the Zr-Cu system, beta --> alpha + beta', has been described in terms of cooperative growth of the alpha phase from the beta phase through the Burgers correspondence and of the partially ordered beta' (structurally similar to the equilibrium Zr2Cu phase) through an ordering process. Similarities and differences in crystallographic features of these transformations have been discussed. and the importance of the invariant line vector in deciding the geometry of the corresponding habit planes has been pointed out.

Contractive Hilbert modules and their dilations

In this note, we show that a quasi-free Hilbert module R defined over the polydisk algebra with kernel function k(z,w) admits a unique minimal dilation (actually an isometric co-extension) to the Hardy module over the polydisk if and only if S (-1)(z, w)k(z, w) is a positive kernel function, where S(z,w) is the Szego kernel for the polydisk. Moreover, we establish the equivalence of such a factorization of the kernel function and a positivity condition, defined using the hereditary functional calculus, which was introduced earlier by Athavale [8] and Ambrozie, Englis and Muller [2]. An explicit realization of the dilation space is given along with the isometric embedding of the module R in it. The proof works for a wider class of Hilbert modules in which the Hardy module is replaced by more general quasi-free Hilbert modules such as the classical spaces on the polydisk or the unit ball in a'', (m) . Some consequences of this more general result are then explored in the case of several natural function algebras.

Fingerprinting environmental conditions and related stress using stable isotopic composition of rice (Oryza sativa L.) grain organic matter

Sea level rise (SLR) is a primary factor responsible for inundation of low-lying coastal regions across the world, which in turn governs the agricultural productivity. In this study, rice (Oryza sativa L.) cultivated seasonally in the Kuttanad Wetland, a SLR prone region on the southwest coast of India, were analysed for oxygen, hydrogen and carbon isotopic ratios (delta O-18, delta H-2 and delta C-13) to distinguish the seasonal environmental conditions prevalent during rice cultivation. The region receives high rainfall during the wet season which promotes large supply of fresh water to the local water bodies via the rivers. In contrast, during the dry season reduced river discharge favours sea water incursion which adversely affects the rice cultivation. The water for rice cultivation is derived from regional water bodies that are characterised by seasonal salinity variation which co-varies with the delta O-18 and delta H-2 values. Rice cultivated during the wet and the dry season bears the isotopic imprints of this water. We explored the utility of a mechanistic model to quantify the contribution of two prominent factors, namely relative humidity and source water composition in governing the seasonal variation in oxygen isotopic composition of rice grain OM. delta C-13 values of rice grain OM were used to deduce the stress level by estimating the intrinsic water use efficiency (WUEi) of the crop during the two seasons. 1.3 times higher WUE, was exhibited by the same genotype during the dry season. The approach can be extended to other low lying coastal agro-ecosystems to infer the growth conditions of cultivated crops and can further be utilised for retrieving paleo-environmental information from well preserved archaeological plant remains. (c) 2015 Elsevier Ltd. All rights reserved.