Experimental study of aqueous fluid infiltration into quartzite: implications for the kinetics of fluid redistribution and grain growth driven by interfacial energy reduction

To investigate the kinetics of interfacial energy‐driven fluid infiltration, experiments were carried out in a quartzite–water system at 621–925°C and 0.8 GPa. Infiltration couples were made by juxtaposing presynthesized dry quartzite cylinders and fluid reservoirs. The infiltration process was confirmed by the presence of pores at the quartzite grain edges. As predicted from theoretical considerations and previous experiments, wetting fluids such as pure water and NaCl aqueous solution infiltrated into quartzite, whereas nonwetting CO₂‐rich fluids did not. Newly precipitated quartz layers at the surfaces of the infiltrated sample proved that infiltration took place by a dissolution–precipitation mechanism. The enhancement of grain growth by fluid infiltration was observed over the entire range of experimental temperatures. The fluid fraction, gauged by the porosity of the run products, increases at the infiltration front and then decreases towards the fluid reservoir to form a high‐porosity zone with a maximum porosity of 2.3–2.9%. As infiltration proceeds, the high‐porosity zone advances like a travelling wave. This porosity wave is probably caused by a grain curvature gradient resulting from preferential grain growth in the infiltrated part of the quartzite, perhaps combined with other factors. The infiltration kinetics were modelled with a steady‐state diffusion model over the high‐porosity zone. The solubility difference between dissolving and precipitating grains was deduced to be 2 × 10^?2?3 × 10^?1 wt %. The experimentally obtained infiltration rate of aqueous fluid in the steady‐state diffusion regime (2 ± 0.5 × 10^?8 m sec^?1 at 823°C) is much faster than the estimated metamorphic fluid flux rates, so that interfacial energy‐driven fluid redistribution in quartz‐rich layers could significantly contribute to the fluid flux in high‐grade metamorphism, at least over a short distance. Cathodoluminescence observations of the run products revealed that the grain growth of quartzite in the presence of fluid proceeds extensively, which would promote the chemical equilibration between fluid and rock more effectively than would volume diffusion in quartz crystals.     

Paul Touvier et L'église: rapport de la commission historique institutée par le cardinal decourtray

Burke's view of history is an aspect of his thought that has been largely neglected by scholars, despite the wide recognition of its importance. In Burke's view, history, led by providence and by a human nature designed by God, is necessarily progressive. It is, nevertheless, human beings who are largely responsible for building their nations. A variety of civilisations could be generated if people governed a nation in harmony with its peculiar manners and circumstances. Nations can, however, be unstable, because their fortunes fluctuate. Although Burke was very familiar with—and influenced by—several different traditions of historiography, his ideas on history should also be seen as the product of his own reflections.     

Stratigraphy and geochronology of La Playa archaeological site,Sonora, Mexico

La Playa archaeological site in northern Sonora, Mexico contains a long record of human activity that includes the Paleoindian period (terminal Pleistocene) and much of the Holocene. The size and complexity of La Playa has discouraged a systematic characterization of its stratigraphy and geochronology, a deficiency we redress in the study. We distinguished seven stratigraphic units ranging in age from >44,570 to 400 cal yr B.P. using ¹⁴C dates from charcoal and terrestrial gastropods found mostly in archaeological features. All of the buried (in situ) cultural remains are contained in Units B (4690–1580 cal yr B.P.) and C (1010–400 cal yr B.P.) and represent overbank deposition from the nearby Rio Boquillas. Occupation at the site peaks in Units B₄ and B₅, corresponding to the Cienega phase (2800–1800 cal yr B.P.) of the Early Agricultural period. This period coincides with the growth of early agricultural villages in the region and is marked at La Playa by thousands of archaeological features including roasting pits, human burials, and extensive canal irrigation systems. The presence of semi-aquatic and aquatic snails demonstrates that water was present year round in the canal systems constructed during this period. Stable and radiometric isotopic evidence suggests that early agriculturalists diverted ground water over several kilometers from the nearby Rio Boquillas. The extensive Cienega phase occupation ended after about 1700 cal yr B.P. with deep erosion of the site, an event also visible in alluvial records in southern Arizona that marked the end of the Early Agricultural period and significant changes in settlement organization in the region.     

Khaki Girls,VADs, and Tommy's Sisters: Gender and Class in First World War Britain

Abstract

Since the end of the cold war, and with particular urgency since the invasions of Afghanistan and Iraq, historians and pundits have searched for parallel cases that make sense of the United States' military and economic predominance in the current international order. Many have chosen the British empire in the nineteenth and early twentieth centuries as the most telling. As Dane Kennedy argues in an article recently published in The International History Review: ‘The United States' immediate predecessor was the British empire, and it should be the first case to which we turn for meaningful historical comparisons.’¹ For Kennedy, the United States, despite coming into existence by breaking away from the British empire, retained many of its institutions and doctrinal traditions. Having marshalled them to new purposes while expanding across the continent, the United States turned its attention abroad. Kennedy shows that, despite the different worlds of the nineteenth and twentieth centuries, both Britain and the United States built their global power in comparable fashion through the techniques of indirect rule, military strategies geared towards protecting imperial and commercial networks, and ideological claims to universally applicable civilizing missions.     

Mesolithic plant exploitation at the Roc del Migdia, Catalonia

Charred plant remains from the mesolithic site of Roc del Migdia have been analysed in detail. Hazel shell and endocarp fragments of sloe (Prunus spinosa L.) have been identified by incident light microscopy and an attempt has been made at the identification of quantities of parenchymatous plant remains through the use of the scanning electron microscope. A number of different classes of tissue are described and the implications of the results discussed.     

Urbanity, Sociability, and Commercial Exchange in the Barbados Sugar Trade: A Comparative Colonial Archaeological Perspective on Bridgetown, Barbados in the Seventeenth Century

In one of the most notable studies on the political economy of the modern Atlantic world, Sidney W. Mintz (Mintz, Sweetness and power: the place of sugar in modern history. Penguin, London, 1985) explored the rise of sugar production in the Caribbean and emphasized Barbados’ role in shaping the trajectory of the sugar industry in the seventeenth century. Yet, while sugar was certainly the defining commodity of the Barbadian economy, not all of the island’s citizens were directly involved in the sugar production process. Residents of the island’s main urban center, Bridgetown, lived at the interface between producers of sugar on rural estates in Barbados and consumers of sugar in metropolitan Europe. They were the glue that held the emerging Atlantic sugar business together and their efforts to develop a functioning urban infrastructure in Barbados helped fuel the trade in this valuable commodity.