91 research outputs found
The transpressional connection between Dom Feliciano and Kaoko Belts at 580–550 Ma
No full textA new U–Pb SHRIMP age of 551 ± 4 Ma on a mylonitic porphyry that intruded into the Sierra Ballena Shear Zone (Southernmost Dom Feliciano Belt, Uruguay) and a review of relevant published data make possible a more refined correlation and reconstruction of Brasiliano/Pan-African transpressional events. Paleogeographic reconstruction, kinematics and timing of events indicate a connection between the shear systems of the Dom Feliciano and Kaoko Belts at 580–550 Ma. Sinistral transpression recorded in shear zones accommodates deformation subsequent to collision between the Congo and Río de la Plata Cratons. The correlation is strengthened by the similarity of magmatic and metamorphic ages in the Coastal Terrane of the Kaoko Belt and the Punta del Este Terrane of the Dom Feliciano Belt. This post-collisional sinistral transpression brought these units near to their final position in Gondwana and explains the different evolution at 550–530 Ma. While in the Kaoko Belt, an extensional episode resulted in exhumation as a consequence of collision in the Damara Belt, in the Dom Feliciano Belt, sinistral transpression occurred associated with the closure of the southern Adamastor Ocean due to Kalahari-Río de la Plata collision
Geoconservation and scientific rock sampling: Call for geoethical education strategies
No full textSome geological outcrops have a special scientific or educational value, represent a geological type locality and/or
have a considerable aesthetical/photographic value. Such important outcrops require appropriate management
to safeguard them from potentially damaging and destructive activities. Damage done to such rock exposures
can include drill sampling by geologist undertaken in the name of scientific advancement. In order to illustrate
the serious damage scientific sampling can do, we give some examples of outcrops from Western Europe, North
America and South Africa, important to structural geology and petrology, where sampling was undertaken by
means of drilling methods without any protective measures. After the rock coring, the aesthetic and photographic
value of these delicate outcrops has decreased considerably. Unfortunately, regulation and protection mechanisms
and codes of conduct can be ineffective. The many resources of geological information available to the geoscientist
community (e.g. via Internet, such as outcrops stored in websites like “Outcropedia”) promote access to sites
of geological interest, but can also have a negative effect on their conservation. Geoethical education on rock
sampling is therefore critical for conservation of the geological heritage. Geoethical principles and educational
actions are aimed to be promoted at different levels to improve geological sciences development and to enhance
conservation of important geological sites. Ethical protocols and codes of conduct should include geoconservation
issues, being explicit about responsible sampling. Guided and inspired by the UK Geologists’s Association “Code
of Conduct for Rock Coring” (MacFadyen, 2010), we present a tentative outline requesting responsible behaviour:
» Drill sampling is particularly threatening because it has a negative visual impact, whilst it is often unnecessary.
Before sampling, geologists should think about the question “is drill sampling necessary for the study being
carried on?”
» Do not take samples from the centre of a geological type locality or a site of especial scientific, didactic interest
or aesthetical/photographic value. If an outcrop is spectacular enough to be photographed, then you should not
core or sample the rock face that has been recorded. The same applies to outstanding outcrops stored in websites.
» Sample other parts of the same or a neighbouring outcrop where there is less impact. Core samples must be
discrete in location; take cores from the least exposed, least spectacular part of an outcrop and try to plug the holes
using the outer end of the core, if possible.
» Before sampling ask experts and authorities (e.g. Natural Reserve or National Park managers if the area is
protected) for advise and permission.
References:
MacFadyen, C.C.J., 2010. The vandalizing effects of irresponsible core sampling: a call for a new code of conduct:
Geology Today 26, 146-151.
Outcropedia: http://www.outcropedia.org
Fluid inclusions associated with the generation of pseudotachylyte and ultramylonite in the French Pyrénées
No full textIn the Saint-Barthélemy Massif, French Pyrenees, narrow ultramylonite and pseudotachylyte bands were generated in a major ductile shear zone at the end of a retrogressive mylonitic event. Ultramylonite bands formed partly by grain size reduction and recrystallization mechanisms and partly by ductile deformation of pseudotachylyte. Microthermometry shows that fluid inclusions in the major shear zone contain pure CO2, and are never aqueous. The low water content of the rock probably hampered hydrolitic weakening during mylonitic deformation. As a result, ultramylonite and pseudotachylyte bands were formed at 2-3.5 kbar an 450-550 °C The relatively high temperature of the host rock is probably the main cause for ductile deformation of pseudotachylyte. Fluid inclusion study can be an important method to detect depth of pseudotachylyte generation.Dans le Massif du Saint-Barthélémy, des rubans d'ultramylonite et de pseudotachylite se sont développés dans une zone de cisaillement importante à la fin d'une phase de mylonitisation à caractère rétromorphique. Certains rubans ultramylonitiques ont été partiellement formés par des mécanismes de recristallisation et de décroissance de la taille des grains, d'autres par une déformation ductile de la pseudotachylite. Des mesures microthermométriques indiquent que les inclusions fluides dans la zone de cisaillement contiennent du CO2 pur.
Le manque d'eau dans la phase fluide a probablement entraîné le durcissement de la roche pendant la déformation mylonitique. L'ultramylonite et la pseudotachylite ont été formées à 2-3,5 kbar et 450-550 °C. La température relativement élevée de la roche-hôte est probablement la cause principale de la déformation ductile de la pseudotachylite. Des recherches sur les inclusions fluides autour des rubans de pseudotachylite peuvent être importantes pour déterminer les conditions de formation de tels rubans.Passchier Cees W. Fluid inclusions associated with the generation of pseudotachylyte and ultramylonite in the French Pyrénées. In: Bulletin de Minéralogie, volume 107, 2, 1984. Inclusions fluides
Historical and Technical Notes on Aqueducts from Prehistoric to Medieval Times
No full textThe aim of this paper is to present the evolution of aqueduct technologies through the millennia, from prehistoric to medieval times. These hydraulic works were used by several civilizations to collect water from springs and to transport it to settlements, sanctuaries and other targets. Several civilizations, in China and the Americas, developed water transport systems independently, and brought these to high levels of sophistication. For the Mediterranean civilizations, one of the salient characteristics of cultural development, since the Minoan Era (ca. 3200–1100 BC), is the architectural and hydraulic function of aqueducts used for the water supply in palaces and other settlements. The Minoan hydrologists and engineers were aware of some of the basic principles of water sciences and the construction and operation of aqueducts. These technologies were further developed by subsequent civilizations. Advanced aqueducts were constructed by the Hellenes and, especially, by the Romans, who dramatically increased the application scale of these structures, in order to provide the extended quantities of water necessary for the Roman lifestyle of frequent bathing. The ancient practices and techniques were not improved but survived through Byzantine and early medieval times. Later, the Ottomans adapted older techniques, reintroducing large-scale aqueducts to supply their emerging towns with adequate water for religious and social needs. The scientific approach to engineering matters during the Renaissance further improved aqueduct technology. Some of these improvements were apparently also implemented in Ottoman waterworks. Finally the industrial revolution established mechanized techniques in water acquisition. Water is a common need of mankind, and several ancient civilizations developed simple but practical techniques from which we can still learn. Their experience and knowledge could still play an important role for sustainable water supply, presently and in future, both in developed and developing countries
Boudinage classification: end-member boudin types and modified boudin structures
No full textCopyright © 2003 Elsevier Ltd. All rights reserved.In monoclinic shear zones, there are only three ways a layer can be boudinaged, leading to three kinematic classes of boudinage. These are (1) symmetrically without slip on the inter-boudin surface (no-slip boudinage), and two classes with asymmetrical slip on the inter-boudin surface: slip being either (2) synthetic (S-slip boudinage) or (3) antithetic (A-slip boudinage) with respect to bulk shear sense. In S-slip boudinage, the boudins rotate antithetically, and in antithetic slip boudinage they rotate synthetically with respect to shear sense. We have investigated the geometry of 2100 natural boudins from a wide variety of geological contexts worldwide. Five end-member boudin block geometries that are easily distinguished in the field encompass the entire range of natural boudins. These five end-member boudin block geometries are characterized and named drawn, torn, domino, gash and shearband boudins. Groups of these are shown to operate almost exclusively by only one kinematic class; drawn and torn boudins extend by no-slip, domino and gash boudins form by A-slip and shearband boudins develop by S-slip boudinage. In addition to boudin block geometry, full classification must also consider boudin train obliquity with respect to the fabric attractor and material layeredness of the boudinaged rock mass. Modified or complex boudin structures fall into two categories: sequential boudins experienced a sequence of different boudin block geometry components during progressive boudinage (i.e. continued stretch), whereas reworked boudins were modified by subsequent deformational episodes (folded, sheared and shortened types). Correct classification of boudins and recognition of their modification are the crucial first stages of interpretation of natural boudin structures, necessary to employing them as indicators of shear sense, flow regime and/or extension axes in terranes otherwise devoid of stretching lineations. © 2003 Elsevier Ltd. All rights reserved.Ben D. Goscombe, Cees W. Passchier and Martin Handhttp://www.elsevier.com/wps/find/journaldescription.cws_home/539/description#descriptio
Evolution of Tunneling Hydro-Technology: From Ancient Times to Present and Future
No full textWater tunnels are one of the oldest hydro-technologies for extracting water resources and/or transmitting them through water distribution systems. In the past, human societies have used tunneling for various purposes, including development, as a measure to enable underground resource extraction and the construction of transportation networks in challenging landscapes and topographies. The development of hydro-technology potentially involves the construction of tunnels to feed aqueducts, irrigation and waste water systems. Thus, the ability to make and maintain tunnels became an important component in creating lasting and sustainable water systems, which increased water supply and security, minimized construction costs, and reduced environmental impact. Thus, this review asks how, when and why human societies of the past included tunneling for the development of lasting water supply systems. This review presents a comprehensive overview across time and space, covering the history of tunneling in hydro technology from antiquity to the present, and it ponders how past experiences could impact on future hydro-technological projects involving tunneling. A historical review of tunnel systems enhances our understanding of the potential, performance, challenges, and prospects associated with the use of hydro-techniques. In the past, as the different examples in time and space demonstrate, tunneling was often dedicated to solving local problems of supply and disposal. However, across the world, some features were repeated, including the need for carving through the living rock or digging to create tunnels covered with stone slabs. Also, the world-wide use of extensive and costly tunnel systems indicates the high level of investment which human societies are willing to make for securing control over and with its water resources. This study helps us to gather inspiration from proven technologies of the past and more recent knowledge of water tunnel design and construction. As we face global warming and its derivate problems, including problems of water scarcity and flooding, the ability to create and maintain tunnels remains an important technology for the future
Polymetamorphism and ductile deformation of staurolite-cordierite schist of the Bossost Dome: indication for Variscan extension in the Axial Zone of the central Pyrenees
No full textAbstract – The Bossòst dome is an E–W-trending elongated structural and metamorphic dome developed in Cambro-Ordovician metasedimentary rocks in the Variscan Axial Zone of the central Pyrenees. A steep fault separates a northern half-dome, cored by massif granite, from an E–W-trending doubly plunging antiform with granitic sills and dykes in the core to the south. The main foliation is a flat-lying S1/2 schistosity that grades into a steeper-dipping slaty cleavage at the dome margins. Three major deformational and two metamorphic phases can be differentiated. S1/2 schistosity is an axial planar cleavage to W-vergent recumbent folding that probably occurred in mid-Westphalian time. Peak regional metamorphism M1 is characterized by static growth of staurolite and garnet following thermal relaxation of the previously thickened crust. Strong non-coaxial deformation recording uniform top-to-the-SE extension during D2a is preserved in staurolite–garnet schists in a 1.5 km thick, shallowly SE-dipping zone in the southeastern dome. A 500 m thick contact aureole (M2) was imprinted on the regionally metamorphosed rocks following the intrusion the Bossòst granite during D2b. More coaxial deformation prevailed during synkinematic growth of M2 phases in the inner part of the contact aureole around the northern part of the dome, where it obliterated D2a fabrics. Progressive non-coaxial deformation continued in the southeastern antiform and is recorded by late-synkinemati
Sustainability of Water, Sanitation, and Hygiene: From Prehistoric Times to the Present Times and the Future
No full textContaminated water and poor sanitation are associated with disease transmission. Absent, inadequate, or improperly managed water resources and sanitation systems expose individuals to preventable health risks. Billions of people lack access to these basic services today and will remain in this condition for decades to come. As we are usually thinking and talking about water, sanitation and hygiene services have changed. Looking back at the history of water, sanitation, and hygiene can help us understand the challenges and opportunities of these issues and draw lessons to achieve sustainable development in the future. Throughout history, civilizations have successfully experimented with treating water and using it for drinking, sanitation, and agriculture. For example, the Minoan civilizations originally focused on water treatment and cleaning to improve the aesthetic properties of drinking water. During prehistoric times, Minoan and Indus Valley civilizations, dating back to about 2000 BC, were the first to focus on the treatment of water supplies. From the early Minoan period, they relied on rainwater collection. During historic times, Hippocrates was the first to invent and used a water filter in the form of a cloth bag, at about 400 BC, known today as the Hippocrates Sleeve. The Romans perfected existing water technologies on a larger scale and initiated their spread throughout the Empire. Hygiene in ancient Rome was promoted by the famous public baths and toilets, which were supplied with water through widely branched aqueducts that had a high standard of cleanliness for the time and were regularly maintained
Fluid inclusions associated with the generation of pseudotachylyte and ultramylonite in the French Pyrénées
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