Significance of compositional zoning in cumulate chromites of the Kabanga chonoliths, Tanzania

2018 ◽  
Vol 82 (3) ◽  
pp. 675-696 ◽  
Author(s):  
David M. Evans
Keyword(s):  
Divalent Cations ◽  
Chrome Spinel ◽  
Compositional Zoning ◽  
Sulfide Deposits ◽  
Nickel Copper ◽  
History Of ◽  
Trivalent Cations ◽  
Indicator Mineral ◽  
Normal Zoning ◽  
North Western

ABSTRACTCompositional zoning is observed rarely in chrome-spinel grains from slowly-cooled layered intrusions because diffusion of cations continues within the spinel to low temperatures. However, in certain circumstances, such gradational zoning of both divalent and trivalent cations is observed and may be useful in deciphering the thermal history of the host intrusions. The accessory chrome-spinels of the Kabanga mafic-ultramafic chonolith intrusions of the Kibaran igneous event in north western Tanzania are notable because they have preserved gradational compositional zoning. This zoning is demonstrated to predate and be independent of later hydrous alteration of the silicate assemblage. At Kabanga, most chrome-spinel grains within olivine-rich cumulate rocks are gradationally and cryptically zoned from Fe2+-Cr3+ rich cores to more Mg2+-Al3+ rich rims (normal zoning). A few grains are zoned from Mg2+-Al3+ rich cores to more Fe2+-Cr3+ rich rims (reverse zoned). The zoning of divalent cations is proportional to that of trivalent cations with Mg2+ following Al3+ and Fe2+ following Cr3+ from core to rim. The zoning of trivalent and tetravalent cations is interpreted to be caused by either new growth from an evolving melt or peritectic reactions between evolved or contaminated melt and adjacent Al-Cr-bearing ferromagnesian minerals, which is preserved by relatively rapid initial cooling in the small chonolith intrusions. Divalent cation zoning is controlled by sub-solidus exchange of Fe2+ and Mg with adjacent ferromagnesian minerals and continues to lower temperatures, indicated to be 580 to 630°C by the spinel-olivine geothermometer. Preservation of such zoning is more likely in the smaller chonolith intrusions that typically host magmatic nickel-copper sulfide deposits and can be used as an exploration indicator when interpreting chromite compositions in regional heavy indicator mineral surveys.

Distribution, systematics and nomenclature of the three taxa of Common Stonechats (Aves, Passeriformes, Muscicapidae, Saxicola) that breed in the Caucasian region

2020 ◽  
Vol 29 (1) ◽  
pp. 33-57
Author(s):  
V.M. Loskot ◽  
G.B. Bakhtadze
Keyword(s):  
Geographic Distribution ◽  
Habitat Preferences ◽  
Junior Synonym ◽  
Type Locality ◽  
Diagnostic Features ◽  
Western Turkey ◽  
Geographical Variations ◽  
History Of ◽  
The Individual ◽  
North Western

Geographic distribution and habitat preferences of Saxicola rubicola rubicola (Linnaeus, 1766), S. maurus variegatus (S.G. Gmelin, 1774), and S. m. armenicus (Stegman, 1935) inhabiting the Caucasian Isthmus and adjacent areas are described in detail. We examined the individual, sexual, age, seasonal and geographical variations of seven main diagnostic features of both plumage and morphometrics (exactly, the length of wing and tail) using 381 skin specimens. Substantially improved diagnoses of S. m. variegatus and S. m. armenicus are provided. After a thorough examination of the materials and history of the expedition of Samuel Gmelin in 1768–1774, and his description of Parus variegatus, it was concluded that the type locality of this taxon was the vicinity of Shamakhi in Azerbaijan not Enzeli in North-Western Turkey. It is also shown the fallacy of the recently proposed attribution of the holotype of the northern subspecies S. m. variegatus to the southern taxon S. m. armenicus and synonymisation of these names, as well as the replacement of the name S. m. variegatus by its junior synonym S. m. hemrichii Ehrenberg, 1833 for the northern subspecies.

Crystallochemical classifications of phyllosilicates based on the unified system of projection of chemical composition: I. The mica group

Clay Minerals ◽  
1990 ◽  
Vol 25 (1) ◽  
pp. 73-81 ◽  
Author(s):  
A. Wiewióra
Keyword(s):  
Chemical Composition ◽  
Divalent Cations ◽  
Layer Charge ◽  
Vector Representation ◽  
Similar Formula ◽  
Crystallochemical Formula ◽  
Trivalent Cations ◽  
Image Position ◽  
Composition I ◽  
Unit Vectors

AbstractA unified system of vector representation of chemical composition is proposed for the phyllosilicates based on projection of the composition, as given by crystallochemical formula, onto a field with orthogonal axes chosen for octahedral divalent cations, R2+, and Si (X, Y, respectively), and oblique axes for octahedral trivalent cations, R3+, and vacancies, □, (V, Z, respectively). Point coordinates for each set of axes were used to define the direction and length of the unit vectors for phyllosilicates belonging to different groups. Parallel to these fundamental directions the composition isolines were drawn in the projection fields. Applied to micas, this system enables control of the chemical composition by the general crystallochemical formula covering all varieties of Li-free dioctahedral and trioctahedral micas:where z (number of vacancies) = (y-x+ m)/2; m (layer charge) =1; u+y+z = 3. There is a similar formula for vacancy-free lithian micas:where w = m — x+y;m=1; u+y+w = 3, and for Li-free brittle micas:where z = (y — x+m)/2; m = 2; u+y+z = 3. Projection fields were used to classify micas.

Myth and History in Celtic and Scandinavian Traditions

2021 ◽  
Keyword(s):  
Western Europe ◽  
Archaeological Evidence ◽  
History Of ◽  
North Western

Myth and History in Celtic and Scandinavian Traditions explores the traditions of two fascinating and contiguous cultures in north-western Europe. History regularly brought these two peoples into contact, most prominently with the viking invasion of Ireland. In the famous Second Battle of Mag Tuired, gods such as Lug, Balor, and the Dagda participated in the conflict that distinguished this invasion. Pseudohistory, which consists of both secular and ecclesiastical fictions, arose in this nexus of peoples and myth and spilled over into other contexts such as chronological annals. Scandinavian gods such as Odin, Balder, Thor, and Loki feature in the Edda of Snorri Sturluson and the history of the Danes by Saxo Grammaticus. This volume explores such written works alongside archaeological evidence from earlier periods through fresh approaches that challenge entrenched views.

scholarly journals Techno-morphological features of items made of antler from the site near the village of Michnievičy (north-western Belarus)

2019 ◽  
Vol 8 (4) ◽  
pp. 116-122
Author(s):  
Anna Andreevna Malyutina ◽  
Aleksandr Nikolaevich Vashanov ◽  
Mariya Ivanovna Tkacheva ◽  
Evgenia Sergeevna Tkach
Keyword(s):  
Morphological Analysis ◽  
Raw Materials ◽  
Morphological Features ◽  
National Academy Of Sciences ◽  
History Of ◽  
The 1960S ◽  
Academy Of Sciences ◽  
The Village ◽  
North Western ◽  
Selection Of

The paper presents the results of a techno-morphological analysis of items made of antler obtained as a result of the collections from the 1960s-1990s from the site near the village of Michnievičy Smorgon District of the Grodno Region (north-western Belarus). Currently, more than 100 artifacts are known from this site, as well as a large number of fauna residues with no visible traces of processing. Radiocarbon dating was obtained for some categories of products, which link them to 9-2 thousand BC. The largest part of the collection refers to the period of the Mesolithic - Neolithic. At the first stage of work, the most expressive and numerous group of artifacts made of horn (24 exemplars), stored in the fonds of the Institute of History of the National Academy of Sciences of Belarus, was selected for a techno-morphological analysis. The degree of preservation of the external surface of objects is relatively good, which made it possible to analyze macro-traces related to the technology of manufacturing various categories of products, on the basis of which a process flow was proposed - from the selection of raw materials to the finished product. The analysis of the technological traces recorded on the products allowed us to highlight the differences in the manufacturing processes of the oldest tools. In addition, on the basis of the macro signs of utilitarian wear, preliminary observations on the functional using of objects were obtained. According to technological and morphological features, the whole of the analyzed material was divided into conditional categories of instruments with a selected heel and without it. The presence or absence of this element, apparently, influenced the method of using objects in various household situations.

scholarly journals Between the past and the present: the Ixil Maya and the discovery of rare mural paintings in Guatemala

2014 ◽  
Vol 34 ◽  
pp. 169-185
Author(s):  
Jarosław Źrałka ◽  
Katarzyna Radnicka
Keyword(s):  
Colonial Period ◽  
Cultural Continuity ◽  
Wall Paintings ◽  
The Past ◽  
The North ◽  
Mural Paintings ◽  
History Of ◽  
Maya Area ◽  
Distinct Features ◽  
North Western

The Ixil Maya area is located in Quiche Department of the north-western part of the Guatemalan Highlands. It has witnessed a continuous occupation since the 1st millennium BC till today. This archaeologically interesting region has provided many important discoveries of rare cultural mixture, with distinct features typical for both Maya Highlands and more distant Lowlands. Recently, the scholarly interest has focused on Chajul where a few years ago, in one of the local houses, well preserved wall paintings dated to the Colonial period were exposed by the house owner during the process of its renovation. With this extraordinary finding a question emerged - are we able to confirm the cultural continuity between the pre-Columbian settlers and modem Ixil who claim «to be always here»? This paper presents a brief outline of the history of the Ixil Maya. It also presents results of some recent and preliminary studies conducted by Polish scholars in this region.

scholarly journals Bluetongue virus in Europe: the current epidemiological situation

2022 ◽  
Vol 78 (02) ◽  
pp. 6619-2022
Author(s):  
WIESŁAW NIEDBALSKI
Keyword(s):  
Western Europe ◽  
Climatic Changes ◽  
Host Factors ◽  
Entire Country ◽  
History Of ◽  
Sporadic Cases ◽  
Vaccination Campaigns ◽  
First Time ◽  
North Western ◽  
The Mediterranean Basin

The article reviews the history of BT occurrence in Europe and its present status. It describes the distribution of BT in Europe before 1998, the emergence of BTV in southern and eastern Europe in 1998-2006 and the epidemiology of BT in north-western Europe after 2006. Up to 1998, sporadic cases of BT were noted in Cyprus, on the Iberian Peninsula and on several Greek islands. However, since 1998, probably due to climatic changes, BTV has spread northwards into the Mediterranean Basin, where five BTV serotypes (1, 2, 4, 9 and 16) have been identified. In August 2006, BTV passed for the first time latitude 50°N, and BT outbreaks caused by BTV serotype 8 occurred in the Netherlands, Belgium, Germany, France and Luxembourg. Mass vaccination campaigns implemented in Europe in the spring of 2008 quickly limited the spread of disease caused by BTV-8, and it was eradicated by 2011. However, after a 3-year break, in September 2015, BTV-8 re-emerged in Europe, in central France, and subsequently spread throughout the entire country. In the following years, BTV-8 outbreaks were found in Switzerland, Germany, Belgium and Spain. In addition to BTV-8 outbreaks, BTV serotypes 1, 2, 4, 9 and 16 have recently circulated in Europe. As revealed by phylogeographic inference, the recent spread of BTV in Europe is a consequence of climatic, landscape and vertebrate host factors

scholarly journals The ethnic composition of the population of Prinevye area and the Southern Ladoga area at the end of the XV century

2020 ◽  
Vol 12 (1) ◽  
pp. 62-72
Author(s):  
Boris I. Chibisov
Keyword(s):  
Economic History ◽  
Ethnic Composition ◽  
Rural Settlements ◽  
North West ◽  
Introduction History ◽  
The North ◽  
History Of ◽  
The Baltic ◽  
North Western ◽  
Descriptive Method

Introduction. History of the North-West area of Novgorod land at the end of the XV century attracted the attention of researchers mainly in the socio-economic aspect. This is due to the fact that Novgorod scribal books are dated by the end of the XV century. From the standpoint of socio-economic history their value is not in doubt, but from an ethno-historical point their onomastic content is underestimated. Materials and methods. The main source of research was the scribe book of the Vodskaya Pyatina 1499/1500. The descriptive method of research is to identify and record the Baltic-Finnish oikonyms (names of rural settlements) and anthroponyms mentioned in the scribe books. Baltic-Finnish anthroponyms are identified on the basis of an analysis of formal indicators of borrowing the anthroponyms. Results and Discussion. There are several areas where the Baltic-Finnish oikonymy and anthroponymy were concentrated, namely Korboselsky graveyard in the northern Prinevye, Lopsky and Terebuzhsky graveyards in the southern Ladoga, as well as Dudorovsky and Izhora graveyards south of the Neva. Archaeological sources record a significant presence of the Izhora antiquities. The presence of Karelians is noted in the northern Prievye and southern Ladoga. Slavic onomastic materials are recorded throughout Orekhovsky and Ladoga counties, but to mostly in the cities of Oreshka, Ladoga and their nearest areas. Conclusion. By the end of the XV century the north-western graveyards of Novgorod land were inhabited by representatives of various ethnic groups: Slavs, Vodians, Izhora and Karelians, as evidenced by the data of anthroponyms and toponyms of the scribe’s books and confirmed by archaeological sources.

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