A rare composite xenolith from Salt Lake Crater,Oahu: high-pressure fractionation and implications for kimberlitic melts in the Hawaiian mantle

A composite xenolith of olivine-bearing garnet clinopyroxenite wall rock intruded by two spinels + garnet veins is described. Vein minerals exhibit textural evidence of a reaction relationship with the mineral phases in the wall rock. Wall rock clinopyroxene contains exsolved blebby garnet and very fine lamellar exsolution of orthopyroxene, indicating that this xenolith had undergone considerable subsolidus cooling. Garnet-clinopyroxene thermometry suggests that the xenolith last equilibrated in the mantle at a temperature of about 1,060 (ᆭ °C). The spinels in the veins are of two kinds: pleonaste (that occurs with vein garnet) and a high-Mg, high-Al titanomagnetite (MAT spinels). Intriguingly, the MAT spinels are chemically very similar to the spinels found as groundmass in kimberlites, are moderately subhedral to euhedral, have a weakly developed cumulate texture, and, at places, show a reaction relation with the pleonaste + garnet (cumulate?) assemblage in the vein. Based on petrographic, chemical, and phase equilibrium considerations, we propose the following evolutionary history of this composite xenolith. (1) In the first stage the olivine-bearing garnet clinopyroxenite formed as crystal extracts (cumulates) as a result of high pressure fractionation of an alkaline melt in the deepest levels of Hawaiian lithosphere/uppermost asthenosphere (100-110 km). (2) In the second stage, igneous veining (the melt composition of this vein is not precisely known but could be kimberlitic) occurs in the already existing wall rock resulting in the precipitation of pleonaste + garnet. A reaction relation between the igneous veins and the wall rock also characterizes this stage. (3) The last igneous episode in this xenolith is recorded by MAT spinels in the wall rock and their precipitation close to the previous pleonaste + garnet veins. The last igneous stage could well be due again to high pressure fractionation of a kimberlitic melt (the residual melt after precipitation of pleonaste + garnet). The time relationship between exsolution and the later igneous veining stages is not known. The MAT spinels are not a result of sub-solidus solvus processes as partial reaction (melt present) between the pleonaste + garnet (from the second igneous stage) and MAT spinel exists, pointing to the igneous nature of the MAT spinel. Based on striking similarity between the MAT spinels in our xenolith and those found as groundmass in kimberlites, we propose that the veining stages could well have been kimberlitic. Thus, even though kimberlitic melts are not seen on the Koolau shield, this particular xenolith clearly shows the existence of such melts at great depths beneath Hawaii. We also propose that the initial wall rock, which represents crystal extracts (even though it does not exhibit definitive cumulate texture) as a result of high-pressure fractionation of an alkaline melt and subsequent veining episodes, are of pre-Koolau age. This implies that the Koolau shield volcano may have had a pre-shield alkalic stage.     

Modeling of particle breakage in a smooth double roll crusher

A model has been developed to describe the breakage behavior of particle breakage in a smooth double roll crusher. In addition to this, an empirical relationship has been obtained between Hardgrove Grindability Index (HGI) of material and breakage parameters. The model uses matrix method of breakage process analysis. Experiments were carried out in a laboratory scale smooth double roll crusher using different materials. The model has been verified experimentally and gives product size distribution after breakage which matches with the experimental distribution well within the satisfactory range.     

Analysis of Y-component of Geomagnetic Field and SYM-H Index Using Wavelet Multiresolution Analysis

Geomagnetism and Aeronomy - Electrodynamical coupling between the solar wind’s plasma and the Earth’s magnetosphere creates geomagnetic disturbances recorded on the ground. This work...     

The role of mechanical stratigraphy in the lateral variations of thrust development along the central Alberta Foothills,Canada

Fold-thrust belts generally exhibit significant variations in structural styles such as differences in thrust geometries and frequencies in imbrication. A natural laboratory of this pattern is preserved in the central Alberta Foothills of the Canadian Rockies, where differences in thrust geometries are represented by the existence vs. non-existence of triangle zones. To seek the factors that make this difference in these regions in terms of structural geometry, stratigraphic thickness variations and mechanical stratigraphy of the sedimentary layers, structural interpretation is conducted based on admissible cross-sections and well log interpretations. In northern region, a backthrust is detached from an incompetent layer(viz.Nomad Unit of the Wapiabi Formation), which gets thinner from the Foothills to the Plains, indicating that it is developed where the shale layers are pinched out where triangle zone is developed. Backthrust is also developed in the southern region, where mechanical strengths of strata(viz. Bearpaw Formation)increase toward the foreland. In the central region, however, only forethrusts are developed along the weak continuous decollement layers(viz. Turner Valley and Brazeau formations), forming an imbricate fan without development of the triangle zone. Incompetent layers such as the top Wapiabi(Nomad),Brazeau(Bearpaw), Coalspur and Paskapoo formations are also pinched out laterally, forming fault glide horizons in different stratigraphic levels in each region. These results indicate that, along the transport direction, triangle zone is developed in relation to the stratigraphic pinch out of the Nomad Unit in the northern region, and is formed associated with the variations in strengths of the layers constituting the Bearpaw Formation in the southern region. It is notable that all the glide horizons are developed along incompetent layers. However, triangle zones are not developed in the areas of continuous stratigraphy of the Nomad Unit, which does not serve as a glide horizon in the central region. This suggests that factors such as stratigraphic thickness changes of incompetent layers and mechanical stratigraphy of the sedimentary layers play an important role in the development of lateral variations in thrust system evolution in terms of triangle zone vs. imbricate fan in the central Alberta Foothills.     

Low-cost inundation modelling at the reach scale with sparse data in the Lower Damodar River basin,India

Abstract

Data unavailability is the main reason for limited applications of hydrodynamic models for predicting inundation in the developing world. This paper aims to generate moderately high-resolution hybrid terrain data by merging height information from low-cost Indian Remote Sensing satellite (IRS) Cartosat-1 stereo satellite images, freely-available Shuttle Radar Topograph Mission (SRTM) digital elevation model (DEM) data, and limited surveyed channel cross-sections. The study reach is characterized by anabranching channels that are associated with channel bifurcation, loops and river islands. We compared the performance of a simple 1D–2D coupled LISFLOOD-FP model and a complex fully 2D finite element TELEMAC-2D model with the hybrid terrain data. The results show that TELEMAC-2D produced significantly improved simulated inundation with the hybrid terrain data, as compared to the SRTM DEM. LISFLOOD-FP was found unsuitable to work with the hybrid DEM in a complicated fluvial environment, as it failed to efficiently divert water in the branches from the main channel.

Editor D. Koutsoyiannis; Associate editor A. Viglione     

Hazardous Waste Pollution Prevention Using Clay with Admixtures

Landfill is the most commonly used method for disposal of waste materials since it is one of the least expensive methods. In order to dispose of any hazardous material to a landfill, a liner is used, which protects the underlying land and groundwater since it acts as a barrier to fluid movement. Of the various methods available for providing improved and more effective properties of landfills, methods involving the use of bentonite, cement, lime, gypsum, etc., have been explored in the laboratory. The aim is to overcome the problem and deficiencies of the existing liners. It is observed from the experimental results that the metal concentrations of the input waste solution can be reduced to 80–98% using a soil‐cement admixture, 60–95% using a soil‐gypsum mixture, 45–95% using a soil‐bentonite mixture, 50–90% for soil, 35–80% using a soil‐lime mixture, as liner materials. The permeation rate of different metals through the different soil‐admixture media depends on various factors. A simple mathematical treatment of the phenomenon related to the permeation of liquid through the admixture of the clay and other components has been developed. The experimental results show satisfactory agreement with the predictions.     

Possible role of warming on Indian summer monsoon precipitation over the north-central Indian subcontinent

ABSTRACT

Broad disagreement between modelled and observed trends of Indian summer monsoon (ISM) over the north-central part of the Indian subcontinent (NCI) implies a gap in understanding of the relationship between the forcing factors and monsoonal precipitation. Although the strength of the land–sea thermal gradient (LSG) is believed to dictate monsoon intensity, its state and fate under continuous warming over the Bay of Bengal (BoB) and part of the NCI (23–28°N, 80–95°E) are less explored. Precipitation (1901–2017) and temperature data (1948–2017) at different vertical heights are used to understand the impact of warming in the ISM. In NCI, surface air temperature increased by 0.1–0.2°C decade^?1, comparable to the global warming rate. The ISM precipitation prominently weakened and seasonality reduced after 1950, which is caused by a decrease in the LSG at the depth of the troposphere. Warming-induced increase in local convection over the BoB further reduced ISM precipitation over NCI.     

Deccan plume,lithosphere rifting,and volcanism in Kutch,India

Kutch (northwest India) experienced lithospheric thinning due to rifting and tholeiitic and alkalic volcanism related to the Deccan Traps K/T boundary event. Alkalic lavas, containing mantle xenoliths, form plug-like bodies that are aligned along broadly east–west rift faults. The mantle xenoliths are dominantly spinel wehrlite with fewer spinel lherzolite. Wehrlites are inferred to have formed by reaction between transient carbonatite melts and lherzolite forming the lithosphere. The alkalic lavas are primitive (Mg# = 64–72) relative to the tholeiites (Mg# = 38–54), and are enriched in incompatible trace elements. Isotope and trace element compositions of the tholeiites are similar to what are believed to be the crustally contaminated Deccan tholeiites from elsewhere in India. In terms of Hf, Nd, Sr, and Pb isotope ratios, all except two alkalic basalts plot in a tight cluster that largely overlap the Indian Ridge basalts and only slightly overlap the field of Reunion lavas. This suggests that the alkalic magmas came largely from the asthenosphere mixed with Reunion-like source that welled up beneath the rifted lithosphere. The two alkalic outliers have an affinity toward Group I kimberlites and may have come from an old enriched (metasomatized) asthenosphere. We present a new model for the metasomatism and rifting of the Kutch lithosphere, and magma generation from a CO₂-rich lherzolite mantle. In this model the earliest melts are carbonatite, which locally metasomatized the lithosphere. Further partial melting of CO₂-rich lherzolite at about 2–2.5 GPa from a mixed source of asthenosphere and Reunion-like plume material produced the alkalic melts. Such melts ascended along deep lithospheric rift faults, while devolatilizing and exploding their way up through the lithosphere. Tholeiites may have been generated from the main plume head further south of Kutch.     

Surface-level moisture transport over the Indian Ocean during southwest monsoon months using NOAA/HIRS data

Surface-level moisture transport over the Indian Ocean has been computed using NOAA/HIRS data for the years 1980, 1981 and 1984. The global relation between monthly mean surface-level humidity and precipitable water (Liu, 1986) has been applied for the computation of surface-level humidity using monthly mean satellite-derived water vapour. The monthly mean surface wind fields over the Indian ocean provided by Florida State University have been used for the surface-level moisture flux computations. Our analysis indicates net positive surface-level moisture flux divergence over the Arabian Sea and negative moisture flux divergence over the Bay of Bengal. It has also been found that evaporation over the Arabian Sea is a variable quantity and forms a significant part of the net moisture budget over the Arabian Sea. The relative contribution of cross-equatorial flux and evaporation from the Arabian Sea has been studied for all three years.