Specific structure of convection currents in the system layered intrusion–feeding conduit–parental magma chamber

2007 ◽  
Vol 48 (12) ◽  
pp. 1037-1045 ◽  
Author(s):  
L.Sh. Bazarov ◽  
V.I. Gordeeva ◽  
E.I. Petrushin
Keyword(s):  
Magma Chamber ◽  
Parental Magma ◽  
Layered Intrusion ◽  
Specific Structure

scholarly journals GEOLOGIA, ESTRATIGRAFIA E PETROGRAFIA DO COMPLEXO DE BREJO SECO, FAIXA RIACHO DO PONTAL, SUDESTE DO PIAUÍ

2014 ◽  
Author(s):  
Silas Santos Salgado ◽  
Cesar Fonseca Ferreira Filho ◽  
Alexandre Uhlein ◽  
Fabrício de Andrade Caxito
Keyword(s):  
Magma Chamber ◽  
Parental Magma ◽  
Layered Intrusion ◽  
Transitional Zone ◽  
Oceanic Lithosphere ◽  
Fold Belt ◽  
Geological Evolution ◽  
Geological Map ◽  
Brasiliano Orogeny ◽  
Host Rocks

O Complexo máfico-ultramáfico de Brejo Seco ocorre no extremo oeste do cinturão de dobramentos e empurrões neoproterozóico Riacho do Pontal, limite norte do Cráton São Francisco, Estado do Piauí, Nordeste do Brasil. Neste trabalho, novos dados geológicos sobre o complexo são apresentados, incluindo um mapa geológico e uma detalhada caracterização estratigráfica e petrográfica. A estratigrafia do Complexo de Brejo Seco foi dividida em quatro zonas principais: Zona Máfica Inferior (ZMI), Zona Ultramáfica (ZU), Zona Máfica Transicional (ZMT) e Zona Máfica Superior (ZMS). As ZMI e ZMS são interpretadas como a base e o topo da câmara magmática, respectivamente. Estas unidades foram tectonicamente invertidas durante a Orogênese Brasiliana. A sequência de cristalização definida para o Complexo de Brejo Seco indica um padrão de enriquecimento em Fe-Ti em direção ao topo da câmara magmática, sugerindo uma afinidade toleítica para o magma parental. O Complexo de Brejo Seco é uma intrusão acamadada, de porte médio, inserido tectonicamente na unidade metavulcanossedimentar Morro Branco. Duas possibilidades podem ser sugeridas para sua evolução geológica: i) o complexo representa a câmara magmática exumada de suas rochas vulcânicas encaixantes (Complexo Morro Branco), possuindo provavelmente uma idade Mesoproterozóica; ii) o Complexo de Brejo Seco teria intrudido o Complexo Morro Branco, possuindo assim uma idade Neoproterozóica e estaria relacionado ao magmatismo máfico-ultramáfico responsável pela constituição da litosfera oceânica da Faixa Riacho do Pontal. Trabalhos continuam sendo realizados para elucidar a evolução geológica do Complexo de Brejo Seco.Palavras-Chave: COMPLEXO DE BREJO SECO, INTRUSÃO ACAMADADA MÁFICO-ULTRAMÁFICA, FAIXA RIACHO DOPONTAL ABSTRACTGEOLOGY, STRATIGRAPHY AND PETROGRAPHY OF BREJO SECO COMPLEX, RIACHO DO PONTAL FOLD BELT, SOUTHEAST OF PIAUÍ. The Mafic-Ultramafic Brejo Seco Complex occurs on the western end of the Neoproterozoic Riacho do Pontal fold belt, the northern limit of the São Francisco Craton, State of Piaui, Northeast of Brazil. In this paper, new geological data on the complex are presented, including a geological map and detailed characterization of the stratigraphy and petrography. The stratigraphy of the complex can be divided into four major zones: Lower Mafic Zone (LMZ), Ultramafic Zone (UZ), Mafic Transitional Zone (MTZ) and Upper Mafic Zone (UMZ). The LMZ and UMZ are correlated to the base and the top of the magma chamber, respectively. These units were tectonically inverted during the Brasiliano Orogeny. The sequence of magmatic crystallization set for the parental magma Brejo Seco Complex indicates a pattern of Fe-Ti enrichment towards the top of the magma chamber, suggesting a tholeiitic affinity for parental magma. The Brejo Seco Complex is a layered intrusion, medium-sized, inserted tectonically in a unit metavulcanosedimentary Morro Branco. Two possibilities may be suggested for its geological evolution: i ) the complex represent the magma chamber exhumed volcanic host rocks (Morro Branco Complex) and own a probable Mesoproterozoic age; ii ) the Brejo Seco Complex would have intruded the Morro Branco Complex, would Neoproterozoic in age and it is related to mafic - ultramafic magmatism of the oceanic lithosphere of the Riacho do Pontal fold belt. Works still running should help to clarify the geological evolution of the Brejo Seco Complex.Keywords: BREJO SECO COMPLEX, MAFIC-ULTRAMAFIC LAYERED INTRUSION, RIACHO DO PONTAL FOLD BELT

Genetic interpretation of CSD for olivine through the dunite section of the Dovyren layered intrusion: linking with geochemistry and probable dynamics of the cumulate mush.

2020 ◽  
Author(s):  
Sergei Sobolev ◽  
Alexey Ariskin ◽  
Simone Tarquini ◽  
Ivan Pshenitsyn ◽  
Georgy Nikolaev ◽  
...  
Keyword(s):  
Parental Magma ◽  
Layered Intrusion ◽  
Coarse Grained ◽  
Main Body ◽  
Russian Science ◽  
Narrow Zone ◽  
Genetic Interpretation ◽  
Modal Layering ◽  
Lower Temperature ◽  
Log Linear

<p>The Yoko-Dovyren ultramafic-mafic intrusion (the northern Baikal region, Russia) has excellent outcropping as well as layering falls vertically. It`s age is 728 Ma. Length of the main body is 26 km. The modal layering of its central part (~3 km thick) includes a basal reversal (from chilled rocks to plagiolherzolites) followed with Pl-bearing to adcumulate dunite, troctolite and gabbroic sequence.</p><p>Over the past 20 years, several sections of the massif have been studied in detail. (Ariskin et al 2018) have determined two major types of parental magmas recorded in the FeO vs MgO trends for the Ol cumulates through the first 500 m of the cross-section. These two geochemically similar magmas are consistent with equilibrium olivine Fo88 and Fo86 in the range of temperatures from 1290°C to ~1200°C.</p><p>We present the results of quantification of CSD of olivine from the dunite succession, which argue for two types of olivine grain populations differing for the more primitive and relatively evolved magma.</p><p>The slope of the log-linear CSD function in the lower-temperature magmas has a less steep as compared to the higher temperature ones.  Both populations can be considered to represent intratelluric olivine crystallized at a pre-emplacement stage. At a stratigraphic level of 200 m from the lower contact, in some of the samples we observed changes in the CSD patterns, which evidence a coarsening of the populations within the Dovyren chamber. Starting from 350-400 m coarsening is noticeable everywhere, so that the CSD cease to be log-linear. In addition, in a narrow zone of 500-550 m dunite are found to display a pronounced bimodal (kinked) distribution of olivine. In a larger population, olivine has highest aspect ratio (up to 3-3.5) compared to other dunite samples. The origin of such dunite can be explained by the intrusion of hot portions of magma into the colder cumulus. In this case such elongated crystals may be due to the increased growth rate of the original olivine grains. The smaller population may be due to a new nucleation event after emplacement. CSD in cumulates above the «kinked dunites» demonstrate coarsening of olivine, with the most coarse-grained populations typical of highly contaminated dunite.</p><p>Thus, a rather narrow zone is distinguished in dunite, where we can observe primary intratelluric CSD, which is not substantially altered nither by peritectic reactions in the loose cumulus of the reversal sequence, where the temperature drops rapidly, nor by coarsening during long history of temperature oscillations close to the primary magmas condition above this zone.</p><p>This work support from the Russian Science Foundation (RSF, grant No. 16-17-10129)</p><p>Ariskin Alexey, Danyushevsky Leonid, Nikolaev Georgy, Kislov Evgeny, Fiorentini Marco, McNeill Andrew, Kostitsyn Yuri, Goemann Karsten, Feig Sandrin, and Malyshev Alexey. The dovyren intrusive complex (southern siberia, russia): Insights into dynamics of an open magma chamber with implications for parental magma origin, composition, and cu-ni-pge fertility. Lithos, 302:242–262, 2018.</p>

Cryptic variation in the Rhum layered intrusion

1978 ◽  
Vol 42 (323) ◽  
pp. 347-356 ◽  
Author(s):  
A. C. Dunham ◽  
W. J. Wadsworth
Keyword(s):  
Magma Chamber ◽  
Fractional Crystallization ◽  
Electron Microprobe ◽  
Magma Mixing ◽  
Layered Intrusion ◽  
The Other ◽  
Layered Series ◽  
Cryptic Variation ◽  
High Calcium

SummaryElectron-microprobe analyses of cumulus olivine, chromite, pyroxene, and plagioclase from layered peridotites and allivalites of the Eastern and Western Layered Series of Rhum demonstrate the presence of cryptic variation. Olivine varies from Fo88-78 within individual units, and there are corresponding changes in the Mg/(Mg+Fe2+) ratios in the pyroxenes and chromites. Plagioclase changes are not so dramatic, but the An-content broadly follows the Mg/(Mg+Fe2+) ratio in the other minerals. The most Fe-(and Na-) rich phases do not occur at the top of lithological units, but some way below. The composition trend above them is reversed. The data are interpreted as the result of periodic infilling of a magma chamber, the new magma mixing with the remains of the previous pulse. Each pulse was followed by a period when fractional crystallization produced the layered rocks. New data on Ni in the olivines suggests that the ratio of the volume of initial magma to volume of layered rocks was about four to one, the initial magma being allied to the high-calcium low-alkali tholeiitic basalts of Skye.

Nonlinear nature of the unavoidable long-lived isotopic, trace and major element contamination of a developing magma chamber

1980 ◽  
Vol 297 (1431) ◽  
pp. 215-227 ◽  
Keyword(s):  
Magma Chamber ◽  
Alternative Explanation ◽  
Incompatible Element ◽  
Sea Water ◽  
Parental Magma ◽  
Final States ◽  
Short Term ◽  
Crustal Rocks ◽  
Pressure Phase ◽  
Nonlinear Nature

Contamination of magmas by crustal materials is a possible alternative explanation of many of the trace element and isotopic features of basalts which have been advanced as evidence of mantle heterogeneity. The space problems associated with the emplacement of large masses of plutonic cumulates in most central volcanoes, and with the formation of the gabbro-dunite portion of the oceanic crust, indicates that at least some digestion of pre-existing crustal rocks has occurred. Contamination is therefore unavoidable. In the ocean basins, contamination is not due directly to incorporation of sea water, but to the digestion of previously erupted basalts which may have been hydrothermally altered by circulating sea water, plus some sediment. In a magma chamber that is periodically replenished with parental magma and periodically tapped to provide lava flows during fractional crystallization, contamination produces changes in the composition of the erupted product which are not, in general, linear between the initial and final states of the system. Moreover, the change in composition produced need not lead towards the composition of the contaminant. Provided that the periodic additions and subtractions of magma are small relative to the size of the magma chamber, the effects of short-term variations in the amount of contamination are smoothed out, while the effects on incompatible element concentrations are persistent long after active contamination has ceased. The effects on major components that enter the crystallizing phases are constrained by the need for the remaining liquid to conform to the relevant low-pressure phase equilibria.

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