Extended defects in natural diamonds: Atomic Force Microscopy investigation

Surfaces of natural diamonds etched in high-pressure experiments in H2O, CO2 and H2O-NaCl fluids were investigated using Atomic Force Microscopy. Partial dissolution of the crystals produced several types of surface features including the well-known trigons and hillocks and revealed several new types of defects. Besides well-known trigons and dissolution hillocks several new types of defects are observed. The most remarkable ones are assigned to anelastic twins of several types. The observation of abundant microtwins, ordering of hillocks and presence of defects presumably related to knots of branched dislocations suggests importance of post-growth deformation events on formation of diamond microstructure. This work confirms previous reports of ordering of extended defects in some deformed diamonds. In addition, the current work shows that natural diamonds deform not only by dislocation mechanism and slip, but also but mechanical twinning. The dominant mechanism should depend on pressure-temperature-stress conditions during diamond transport from the formation domain to the Earth surface.Comment: Submitted to special issue (1st European Mineralogical congress, Frankfurt, Germany, September 2012) of European Journal of Mineralogy. 21 page, 9 figure

Multistep evolution of harzburgitic mantle underneath pipe 200 kimberlite, northern Lesotho: a study on xenoliths and their implication on diamond-barren nature of pipe 200 kimberlite

The Pipe 200 kimberlite in northern Lesotho on the southeast margin of the Kaapvaal Craton is a diamond-poor deposit despite its proximity to economically viable kimberlites like the Liqhobong kimberlite. We study harzburgite xenoliths' mineral composition, geochemistry, and pressure–temperature evolution to understand factors influencing diamond destruction. The xenoliths are classified into five types based on their petrography and geochemistry. The diversity in the mineral assemblage correlates with a sampling depth of ~ 100 to 175 km (~ 2.8 to < 5.0 GPa). The signatures of metasomatism are evident in type 3 and 4 xenoliths, where garnet breaks down to form a cluster (henceforth assemblage) of phlogopite, chromite, and diopside. Fine-grained melts associated with an uplift in the mantle to shallower depths of < 90 km (< 2.3 GPa) encompass the minerals in the assemblage, which display resorption at the boundaries. Water contents (structural hydroxyl) of olivine and possibly orthopyroxene are lower in the xenoliths with metasomatism-induced breakdown of garnet. The structural hydroxyl distribution in the nominally anhydrous minerals shows flat distribution profiles of re-equilibration due to residence in the kimberlite magma. It is supported by the disruption of the inter-mineral water partition coefficient due to olivine water diffusion during residence in the kimberlite magma. The barren nature of the Pipe 200 kimberlite is attributed to the signatures of mantle metasomatism and residence in kimberlite magma, which led to the diamond destruction

Experimental study of dissolution style of diamonds from volcaniclastic vs. hypabyssal kimberlite facies: the effect of melt composition on kimberlite eruption and geology

&amp;lt;p&amp;gt;Kimberlites are the deepest and the most enigmatic magmas that reach the surface of the Earth. Their source, origin and even composition are a subject of debates. Kimberlites form hypabyssal sills and dykes but most often occur as explosion pipes, which comprise various volcaniclastic and magmatic units. Differences in the geological composition, shape and size of kimberlite pipes worldwide arise from the differences in the eruption processes and are the base for distinguishing three kimberlite classes. However, it is not clear if these differences result from the properties of the country rocks or from variable magma composition especially H2O : CO2 ratio.&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;During the ascent, kimberlites transport mantle fragments including diamonds to the surface and partially dissolve them. Previous studies have shown that dissolution features on diamond reflect the conditions in the host magma and especially presence and composition of fluid. Diamonds from volcaniclastic facies of different kimberlite classes all show very similar low-relief surface features indicating presence of fluid. Geometry of the trigonal etch pits on diamonds helps to deduce H2O:CO2 ratio of kimberlitic fluid. On the contrary, &amp;amp;#8220;corrosive&amp;amp;#8221; resorption styles of diamonds from hypabyssal kimberlite (HK) units are different between the three kimberlite classes allowing to examine differences in their crystallization conditions. This study aims to reproduce corrosive resorption of diamonds in controlled experiments in order to examine the composition of kimberlite magma in different kimberlite classes and its effects on magma emplacement.&amp;lt;/p&amp;gt; &amp;lt;p&amp;gt;Experiments were conducted in piston-cylinder apparatus at pressure 0.5 &amp;amp;#8211; 1 GPa and temperatures 1000 &amp;amp;#8211; 1200&amp;lt;sup&amp;gt;o&amp;lt;/sup&amp;gt;C using a range of volatile-undersaturated silicate and silico-carbonate melts. Experiments produced three specific resorption styles previously reported on natural diamonds from HK: (i) sharp pointy features common for diamonds from HK in class 3 kimberlites; (ii) corrosion sculptures common for diamonds from HK in class 1 kimberlite; (iii) deep channels &amp;amp;#8211; rare but prominent feature of natural diamonds. We compare our experimental results to the features of natural diamonds from HK units of class 1 kimberlites (Orapa kimberlite cluster, Botswana) and class 3 (Ekati Mine kimberlites, Canada) to compare magma composition and emplacement conditions of different kimberlite classes.&amp;lt;/p&amp;gt;</jats:p

Development Lendplatz-Lendkai:"Urban Villages" as a Method for Inner-City Densification

Deutsche Version:Die Entwicklung österreichischer Städte war in den letzten Jahren stark von einer zunehmenden Bodenversiegelung geprägt. Neue, großflächige Stadtviertel entstehen verstärkt in den Randbe-zirken und bieten zahlreiche Wohnmöglichkeiten. Um diese Gebiete lebenswert zu gestalten, sind umfangreiche Infrastrukturerweiterungen erforderlich, was häufig zu Großprojekten mit hohem Flächenverbrauch führt. Eine Möglichkeit, diesen Verbrauch zu reduzieren, besteht da-rin, ungenutzte Flächen innerhalb bereits bestehender Infrastrukturen zu nutzen. Insbesondere innerstädtische Brachflächen verfügen oft über eine gute Anbindung an bestehende Versor-gungseinrichtungen. Diese Arbeit stellt einen städtebaulichen Entwurf vor, welcher das Ziel verfolgt, die bisherige dynamischen Stadtteilentwicklung im Bezirk Lend an einer der letzten zentralen Stellen fortzu-setzen und die Lebensqualität zu steigern. Die im gültigen Stadtentwickungskonzept 4.08. der Stadt Graz formulierten städtebaulichen Prinzipien sowie der historische und soziale Kontext bilden neben dem Konzept des Urban Village - als Modell für eine qualitative Stadtentwicklung - die Grundlagen für den städtebaulichen Entwurf am gewählten Gebiet: Keplerstraße-Lendkai-Fellingergasse-Lenplatz-Neubaugasse.Englische Version:Urban development in Austrian cities has been characterised by an increased amount of land sealing. New, large urban districts primarily emerge in the suburbs, offering a wide range of res-idential opportunities. To raise there liveability, infrastructure expansions are necessary, often resulting in large-scale projects with significant land consumption. One way to mitigate this con-sumption is by re-using spaces within existing infrastructures. Many inner-city unused are often well-connected to existing facilities. This thesis presents a development plan and urban design with the goal to continue recent de-velopments within the thriving district of Lend and create a place of high liveability. The design is based on principles of the official Urban Development Concept (STEK 4.08.), as well as the Urban Village model the historical and social context of the chosen area: Keplerstraße-Lendkai-Fellingergasse-Lenplatz-Neubaugasse.Abweichender Titel laut Übersetzung von der:dem Verfasser:inBachelorarbeit FH JOANNEUM 202

Emplacement conditions of some Lac de Gras kimberlites and their effect on the resorption of diamonds

Crystallization temperatures (T) and oxygen fugacities (fO2) of kimberlite magma estimated from oxides included in olivine phenocrysts from eight kimberlite pipes in the central Slave Province, Canada, are compared to the degree and character of resorption observed in diamonds recovered from these kimberlites. The mechanism of diamond oxidation in kimberlite melts and the rate-controlling parameters for this reaction are explored in oxidation experiments. The T and maximum fO2 recorded by olivine - chromite pairs at an assumed pressure of 1 GPa are 970° -- 1070°C and 2.2 - 3.1 log units below the nickel - nickel oxide (NNO) buffer. This mineral assemblage crystallized from a magma with 1 1 to 28 mol% of liquid, 10 mol% of earlier-precipitated olivine phenocrysts and 62 to 79 molc7o of mantle xenocryst olivine. The T - fO2 values vary between kimberlites from Northwest and Southeast clusters within 150°C and one log unit, respectively, and form a trend of decreasing fO2 and increasing crystallization T in the southeast direction. This trend corresponds to substantial differences in the diamond populations. A detail description of morphological forms and surface resorption features for five diamond parcels (> 7000 stones) show an increase in diamond resorption with increase in kimberlite crystallization T and more extensive surface etching in more oxidized kimberlites. The surface etch features on diamonds are determined by the conditions in the kimberlite melt, whereas some of the volume resorption occurs in the mantle and its relationship with the melt conditions is obscure. The diamond grade is higher in kimberlites with lower fO2 confirming the effect of the melt conditions on diamond preservation. Diamond oxidation experiments at 1350°C to 1500°C and 1 GPa produced only surface graphitisation, and no diamond resorption in volatile undersaturated melts. In contrast, volatile oversaturated conditions produce resorption features seen in diamonds recovered from kimberlites, suggesting that the process of diamond resorption is its reaction with the fluid and not with the melt. Both CO2 and H2O oxidize diamonds at a similar rate, but produce very different surface features. Therefore, the surface features of natural diamonds may provide information on the H2O/CO2 ratio in the kimberlitic fluid. The morphologies of diamonds from this study imply high H2O/CO2. The scarcity of surface graphitisation and presence of highly resorbed diamonds in kimberlites suggest presence of free fluid phase in kimberlite magmas for the most of their history. The diamond oxidation is not affected by the physical properties of diamonds