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The geologic story of North America is a fascinating one. It’s also more than 4 billion years long—much more than we could ever hope to cover here. However, if you’re curious about the world around you, enjoy the big-picture perspective, and are interested in some of the processes that are constantly reshaping our planet, here’s a crash course on the basics. It’s a good place to start on your aerial tour of the continent’s most breathtaking landforms.
From the point of view of geomagnetism, the earth may be considered as made up of three parts: core, mantle and crust (Figure 1.1). Convection processes in the liquid part of the iron core give rise to a dipolar geomagnetic field that resembles that of a large bar-magnet aligned approximately along the earth's axis of rotation (Figure 1.2). The mantle plays little part in the earth's magnetism, while interaction of the (past and present) geomagnetic field with the rocks of the Earth's crust produces the magnetic anomalies recorded in detailed (e.g. aeromagnetic) surveys carried out close to the earth's surface.
African Mineral and Energy Resources Classification and Management System (AMREC) is a continental system for management of Africa’s mineral and energy resources.
The AMREC is based on United Nations Framework Classification for Resources (UNFC) Principles, Generic Specifications and Guidelines and is aligned to Africa Mining Vision (AMV) and the Sustainable Development Goals (SDGs). Adapting to national or local needs, the AMREC provides the specifications and guidelines required for sustainable development of Africa’s mineral and energy resources.
For many centuries Africa’s rich mineral endowment has shaped the fortunes of its peoples and the environment. Beginning in the early twenty-first century, the commodities price boom and concerns about human impacts on the environment have seen increasing value placed on the continent’s renewable and non-renewable natural resources. Operators explored and extracted mineral and energy resources at an unprecedented pace during the boom, with regulators scrambling to keep up. The limitations of the so-called commodities super cycle soon became apparent to Africa’s policymakers and investors alike, however, prompting a need for revised approaches to resource governance in the past five years.1 At the same time, competing land and water uses, deforestation, and loss of biodiversity remain key concerns for climate change mitigation and environmental conservation. This raises an enduring question: How does Africa develop its mineral fortune sustainably, both in environmental and in socio-economic terms? The concentration of low-income, resource-dependent countries in Africa places it at the center of global debates about sustainable development and the extractive industries. <...>
Fossil hunting is by far the most fascinating of all sports. It has some danger, enough to give it zest and probably about as much as in the average modern engineered big-game hunt, and the danger is wholly to the hunter. It has uncertainty and excitement and all the thrills of gambling with none of its vicious features. The hunter never knows what his bag may be, perhaps nothing, perhaps a creature never before seen by human eyes. It requires knowledge, skill, and some degree of hardihood. And its results are so much more important, more worthwhile, and more enduring that those of any other sport! The fossil hunter does not kill, he resurrects. And the result of this sport is to add to the sum of human pleasure and to the treasure of human knowledge.
ТЬе Zhamanshin impact ci'ater is the only impact crater оп the Earth where impactites, various tektites and microtektites coexist. Тhus the Crater becomes the best object to solve the old tektite puzzle. Published before and new data оп the radiogenic ages and chemistry of the Zhamanshin tektites and Australasian tektites summarized to demonstrate their close genetic relations. ТЬе tektite age-paradox serves as the base evidence in favor of the exstraterrestrial origin of tektites. Тhe petrographical and petrochemical features of tektites demonstrate their most рсоЬаЫе volcanic origin.
Carlin-type gold deposits are difficult to date and a wide range of ages has been reported for individual deposits. Therefore, several methods were employed to constrain the age of the gold deposits in the Jerritt Canyon district. Dated igneous rocks with well-documented crosscutting relationships to ore provided the most reliable constraints. K/Ar and 40Ar/39Ar dates on igneous rocks are as follows: andesite dikes 324 Ma, sericitic alteration in andesite dikes 118 Ma, basalt dikes 40.8 Ma, quartz monzonite dikes 39.2 Ma, and calc-alkaline ignimbrites 43.1 to 40.1 Ma. Of these, only the andesite and basalt dikes are clearly altered and mineralized. The gold deposits are, therefore, younger than the 40.8 Ma basalt dikes. The sericitic alteration in the andesite dikes is unrelated to the gold deposits. A number of dating techniques did not work. K/Ar and 40Ar/39Ar dates on mica from mineralized Ordovician to Devonian sedimentary rocks gave misleading results. The youngest date of 149 Ma from the smallest <0.1-)U,m-size fraction shows that the temperature (120°-260°C) and duration (?) of hydrothermal activity was insufficient to reset preexisting fine-grained micas in the host rocks. The temperature and duration was also insufficient to anneal fission tracks in zircon from Ordovician quartzites as they yield Middle Proterozoic dates in both mineralized and barren samples. Apatites were too small for fission track dating. Hydrothermal sulfides have pronounced crustal osmium isotope signatures (18'Os/188Osinitiai = 0.9-3.6) but did not yield a meaningful isochron due to very low Re and Os concentrations and large analytical uncertainties. Paleomagnetic dating techniques failed because the hydrothermal fluids sulfidized nearly all of the iron in the host rocks leaving no remnant magnetism.
Aggregates are defined here as particles of rock which, when brought together in a bound or unbound condition, form part or the whole of an engineering or building structure.
Mencl, V.: Plastizitätslehre und das wirkliche Verhalten von Gebirgsmassen. Mit 9 Textabbildungen Veder, Ch.: Bodenstabilisierung durch Ausschaltung von Grenzflächenerscheinungen. Mit 15 Textabbildungen Magar, K.: Zur Klassifizierung überwiegend bindiger Halbfestgesteine Haefeli, R.: Gedanken zum Problem der glazialen Erosion. Mit 16 Textabbildungen Wittke, W. und Cl. Louis: Modellversuche zur Durchströmung klüftiger Medien. Mit 24 Textabbildungen Wittke, W.: Zur Reichweite von Injektionen in klüftigem Fels. Mit 7 Textabbildungen Link, H.: Zum Verhältnis seismisch und statisch ermittelter Elastizitätsmoduln von Fels. Mit 9 Textabbildungen und 1 Tabelle
