The Idea of Contrasted Differentiation

1936 ◽  
Vol 73 (5) ◽  
pp. 228-238 ◽  
Author(s):  
Arthur Holmes
Keyword(s):  
Basaltic Magma ◽  
Necessary Condition ◽  
Residual Liquid ◽  
Continuous Separation ◽  
Intermediate Composition ◽  
Rock Types ◽  
Crystallization Differentiation ◽  
Intermediate Layers ◽  
Intermediate Rock ◽  
Basic Rocks

As early as 1915, it was made clear by Bowen that, given continuous separation of crystals from the successive residual liquids of a consolidating magma which was initially basaltic in composition, the inevitable result would be a gabbroic rock in depth, a granitic one above, and “various intermediate types in the intermediate layers”. As a necessary condition to the evolution of a magmatic residuum of granitic composition, this process of progressive crystallization differentiation involves the generation of intermediate rock-types from residual liquids of intermediate composition. Certain investigators, however, led by the authors of the Mull memoir (1924), have entirely overlooked the necessity of this condition. Faced with the association of contrasted acid and basic rocks, which is a conspicuous characteristic of many continental central complexes, they have attempted to account for the facts by introducing a modified conception of crystallization differentiation for which Nockolds has recently proposed the name contrasted differentiation. According to this conception, the residual liquid of consolidating basaltic magma is of granitic composition and can be separated in bulk from a crystalline gabbroic phase.

scholarly journals REE Minerals as Geochemical Proxies of Late-Tertiary Alkalic Silicate ± Carbonatite Intrusions Beneath Carpathian Back-Arc Basin

Minerals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 369
Author(s):  
Vratislav Hurai ◽  
Monika Huraiová ◽  
Patrik Konečný
Keyword(s):  
Basaltic Magma ◽  
Accessory Mineral ◽  
Rock Fragments ◽  
Rock Types ◽  
Volcanic Reservoir ◽  
Late Tertiary ◽  
Volcanic Ejecta ◽  
Intermediate Rock ◽  
Magmatic Reservoir ◽  
Back Arc

The accessory mineral assemblage (AMA) of igneous cumulate xenoliths in volcanoclastic deposits and lava flows in the Carpathian back-arc basin testifies to the composition of intrusive complexes sampled by Upper Miocene-Pliocene basalt volcanoes. The magmatic reservoir beneath Pinciná maar is composed of gabbro, moderately alkalic to alkali-calcic syenite, and calcic orthopyroxene granite (pincinite). The intrusive complex beneath the wider area around Fiľakovo and Hajnáčka maars contains mafic cumulates, alkalic syenite, carbonatite, and calc-alkalic granite. Both reservoirs originated during the basaltic magma underplating, differentiation, and interaction with the surrounding mantle and crust. The AMA of syenites is characterized by yttrialite-Y, britholite-Y, britholite-Ce, chevkinite-Ce, monazite-Ce, and rhabdophane(?). Baddeleyite and REE-zirconolite are typical of alkalic syenite associated with carbonatite. Pyrochlore, columbite-Mn, and Ca-niobates occur in calc-alkalic granites with strong peralkalic affinity. Nb-rutile, niobian ilmenite, and fergusonite-Y are crystallized from mildly alkalic syenite and calc-alkalic granite. Zircons with increased Hf/Zr and Th/U ratios occur in all felsic-to-intermediate rock-types. If rock fragments are absent in the volcanic ejecta, the composition of the sub-volcanic reservoir can be reconstructed from the specific AMA and zircon xenocrysts–xenolith relics disintegrated during the basaltic magma fragmentation and explosion.

scholarly journals Evidence of mingling between contrasting magmas in a deep plutonic environment: the example of Várzea Alegre, in the Ribeira Mobile Belt, Espírito Santo, Brazil

2001 ◽  
Vol 73 (1) ◽  
pp. 99-119 ◽  
Author(s):  
SILVIA R. MEDEIROS ◽  
CRISTINA M. WIEDEMANN-LEONARDOS ◽  
SIMON VRIEND
Keyword(s):  
Partial Melting ◽  
Granitic Magma ◽  
Geochemical Data ◽  
Mobile Belt ◽  
Tholeiitic Magma ◽  
Rock Types ◽  
Upper Proterozoic ◽  
Incompatible Elements ◽  
Wide Range ◽  
Intermediate Rock

At the end of the geotectonic cycle that shaped the northern segment of the Ribeira Mobile Belt (Upper Proterozoic to Paleozoic age), a late to post-collisional set of plutonic complexes, consisting of a wide range of lithotypes, intruded all metamorphic units. The Várzea Alegre Intrusive Complex is a post-collisional complex. The younger intrusion consists of an inversely zoned multistage structure envolved by a large early emplaced ring of megaporphyritic charnoenderbitic rocks. The combination of field, petrographic and geochemical data reveals the presence of at least two different series of igneous rocks. The first originated from the partial melting of the mantle. This was previously enriched in incompatible elements, low and intermediate REE and some HFS-elements. A second enrichment in LREE and incompatible elements in this series was due to the mingling with a crustal granitic magma. This mingling process changed the composition of the original tholeiitic magma towards a medium-K calc-alkalic magma to produce a suite of basic to intermediate rock types. The granitic magma from the second high-K, calc-alkalic suite originated from the partial melting of the continental crust, but with strong influence of mantle-derived melts.

The oxygen isotope composition of the surface crystalline rocks of the Canadian Shield

1978 ◽  
Vol 15 (11) ◽  
pp. 1773-1782 ◽  
Author(s):  
Yuch-Ning Shieh ◽  
Henry P. Schwarcz
Keyword(s):  
Isotope Composition ◽  
Crystalline Rocks ◽  
Canadian Shield ◽  
Granitic Rocks ◽  
Baffin Island ◽  
Grenville Province ◽  
Metasedimentary Rocks ◽  
Rock Types ◽  
Northern District ◽  
Basic Rocks

The average 18O/16O ratios of the major rock types of the surface crystalline rocks in different parts of the Canadian Precambrian Shield have been determined, using 47 composite samples prepared from 2221 individual rock specimens. The sampling areas include Baffin Island, northern and southwestern Quebec, Battle Harbour – Cartwright, northern District of Keewatin, Fort Enterprise, Snowbird Lake, Kasmere Lake, and Saskatchewan, covering approximately 1 400 000 km2. The granitic rocks from the Superior, Slave, and Churchill Provinces vary only slightly from region to region (δ18O = 6.9–8.4‰) and are significantly lower in 18O than similar rock types from the younger Grenville Province (δ = 9.2–10.0‰). The sedimentary and metasedimentary rocks have δ18O = 9.0–11.7‰ and hence are considerably lower than their Phanerozoic equivalents, possibly reflecting the presence of a high percentage of little-altered igneous rock detritus in the original sediments. The basic rocks in most regions fall within a δ18O range of 6.8–7.6‰, except in northern and southwestern Quebec where the δ-values are abnormally high (8.5–8.9‰). The overall average 18O/16O ratio of the surface crystalline rocks of the Canadian Shield is estimated to be 8.0‰, which represents an enrichment with respect to probable mantle derived starting materials by about 2‰.

Caracteres petrographiques de l'ophite de Vebre (Ariege)

1965 ◽  
Vol S7-VII (1) ◽  
pp. 168-171
Author(s):  
Ch Riotte ◽  
Jean Thiebaut
Keyword(s):  
Basaltic Magma ◽  
Petrographic Analysis ◽  
Chemical Analyses ◽  
Rock Types ◽  
The Right ◽  
Potassium Enrichment ◽  
Later Phase

Abstract Petrographic analysis of the ophite outcrop on the right bank of the Ariege river, below Vebre, France, shows that the rock is rich in epidote and exhibits pegmatoid differentiation. Three rock types are distinguished--common ophite with variable amounts of epidote; ophite with phlogopite; and pegmatoid rocks with orthoclase. The results of four chemical analyses indicate that the Vebre ophites were affected by pneumatolysis during crystallization from a saturated basaltic magma. The pneumatolysis caused the crystallization of hornblende and, in a later phase of potassium enrichment, the superimposition of orthoclase in the pegmatoid plagioclases and the phlogopite in the hornblende crystals of the ophite.

A Grenville-age layered intrusion in the subsurface of west Texas: petrology, petrography, and possible tectonic setting

1995 ◽  
Vol 32 (12) ◽  
pp. 2159-2166 ◽  
Author(s):  
Hulusi Kargi ◽  
Calvin G. Barnes
Keyword(s):  
Tectonic Setting ◽  
Basaltic Magma ◽  
Layered Intrusion ◽  
Mafic Magma ◽  
Magma Source ◽  
Rock Types ◽  
Hornblende Gabbro ◽  
Tectonic Environment ◽  
Extensional Tectonic ◽  
General Order

The Nellie intrusion is a thick (more than 4420 m) mafic to ultramafic layered intrusion with a radiometric age of ~1163 Ma. Rock types change abruptly with stratigraphic height and include norite, pyroxenite, gabbronorite, hornblende gabbro, gabbro, anorthosite, harzburgite, and lherzolite. Norite is most abundant, but gabbro and hornblende gabbro are locally abundant. Rare olivine-rich layers are also present. The general order of crystallization was olivine, orthopyroxene, plagioclase + clinopyroxene, and hornblende. Mg#'s, expressed as 100 Mg/(Mg + Fe), range from 76.3 to 85.8 for olivine, 56.7 to 84.9 for orthopyroxene, 62.5 to 90.3 for clinopyroxene, and 52.4 to 82.8 for amphibole. Mg#'s vary with height and display abrupt reversals, which indicate open-system addition of new mafic magma. Eleven cyclic units were identified on the basis of evidence for injection of basaltic magma; these can be grouped into three megacyclic units. The abundance of orthopyroxene, and mineral compositional evidence for Fe enrichment within cyclic units, indicates that parental magmas were subalkaline and tholeiitic. Plagioclase in equilibrium with olivine ranges from An65 to An46, which precludes an arc-related magma source. Although the intrusion is approximately coeval with Keweenawan magmatism and with emplacement of diabasic dikes in western North America, it is dissimilar in detail to both suites of rocks. Nevertheless, its composition and geophysical setting are consistent with emplacement in an extensional tectonic environment.

scholarly journals GAMMA-RAY SPECTROMETRY FOR DISTINGUISHING ACID AND BASIC ROCKS OF THE SERRA GERAL FORMATION, IN THE SERRA GAÚCHA WINE REGION, BRAZIL

2016 ◽  
Vol 34 (4) ◽  
Author(s):  
Rudi Cesar Comiotto Modena ◽  
Rosemary Hoff ◽  
André Rodrigo Farias ◽  
Jorge Antônio Viel ◽  
Osmar Gustavo Wohl Coelho
Keyword(s):  
Volcanic Rock ◽  
Gamma Ray ◽  
Rio Grande ◽  
Gamma Ray Spectrometry ◽  
Rio Grande Do Sul ◽  
Geophysical Method ◽  
Radioactive Elements ◽  
Rock Types ◽  
Wine Region ◽  
Basic Rocks

ABSTRACT. The gamma-ray spectrometric research has allowed for observation of the distribution of radioactive elements such as K, U and Th for recognizing the radioactive signatures of different rock types. The objective of this study was to evaluate the possibility to distinguish between acid and basic rocks of the Serra Geral Formation, in the Serra Gaúcha wine region in the state of Rio Grande do Sul (Brazil) through gamma-ray spectrometry techniques. This study contributed to geologically...Keywords: geophysical method, wine terroir, volcanic rock. RESUMO. A pesquisa por gamaespectrometria tem permitido observar a distribuição de elementos radioativos, tais como K, U e Th reconhecendo as assinaturas radioativas de diferentes tipos de rocha. O objetivo deste estudo foi avaliar a possibilidade de distinguir entre as rochas ácidas e básicas da Formação Serra Geral, na região vitivinícola Serra Gaúcha, no estado do Rio Grande do Sul (Brasil) por meio de técnicas de gamaespectrometriaPalavras-chave: m´étodos geofísicos, terroir vitivinícola, rocha vulcânica.

An Evaluation of the Permittivity of Two Different Rock Types Using Microwave Resonator and Waveguide Cutoff Principles

Frequenz ◽  
2014 ◽  
Vol 69 (1-2) ◽  
pp. 75-82
Author(s):  
Martta-Kaisa Olkkonen ◽  
Pekka Eskelinen ◽  
Eeva Huuskonen-Snicker ◽  
Terhi Pellinen ◽  
Pablo Olmos Martinez
Keyword(s):  
Rock Type ◽  
Cutoff Frequency ◽  
Metavolcanic Rock ◽  
Frequency Range ◽  
Frequency Method ◽  
Cylindrical Resonator ◽  
Intermediate Composition ◽  
Reference Measurement ◽  
Rock Types ◽  
Resonator Method

Abstract Methods of measuring the complex permittivity of different rock types are demonstrated in the frequency range from 6 GHz to 17 GHz. The used methods are based on the cylindrical resonator and waveguide cutoff frequency principles. This study is part of a larger research project that aims to characterize the electrical properties of asphalt for road surveying purposes. The studied rock types are metavolcanic rock with intermediate composition and pegmatite. The permittivity values gained with the resonator method are 6.2 for the metavolcanic rock and 4.5 for the pegmatite rock type, whereas the imaginary parts are 0.04 and 0.02. The permittivity values gained with the cutoff frequency method are 6.17 and 4.76 respectively. A reference measurement was made only for the metavolcanic rock in a transmission configuration with two antennas and the permittivity result was 6.21. The three different methods provide consistent permittivity values and are suitable for reliable permittivity evaluation.

Mixing of basaltic and andesitic magmas in the Bazman volcanic field of southeastern Iran as inferred from plagioclase zoning

2017 ◽  
Vol 81 (4) ◽  
pp. 975-985 ◽  
Author(s):  
Zahra Firouzkouhi ◽  
Ali Ahmadi ◽  
David Richard Lentz ◽  
Ali-Asghar Moridi-Farimani
Keyword(s):  
Basaltic Magma ◽  
Volcanic Field ◽  
Common Type ◽  
Oscillatory Zoning ◽  
Plagioclase Feldspar ◽  
The Core ◽  
Rock Types ◽  
Anorthite Content ◽  
Plagioclase Zoning ◽  
Compositional Zonation

AbstractLate Cenozoic basalts of the Bazman volcanic field, Makran volcanic arc of southern Iran, contain two types of plagioclase feldspar phenocrysts with significant textural and compositional differences. The most common type is rather homogeneous with only weak zoning and maximum An content of 83 mol.%. The less common type of phenocryst exhibits complex zoning and, other than rims, is close in composition and similar in texture to those of associated andesites. This type of plagioclase phenocryst is characterized by an engulfed core with oscillatory zoning, which is overgrown by sieve-textured, moderately zoned mantle, and a relatively narrow rim. In both rock types, the An content of the core is between 40 and 63 mol.% with abrupt fluctuations. No significant correlation between An content and MgO, FeO, SrO and BaO is apparent in the core of phenocrysts in basalts. Anorthite content of the core of phenocrysts in andesites inversely correlates with SrO and BaO. The mantle of plagioclase phenocrysts in both rock types is characterized by sharp increases of An (up to 41 mol.%), MgO, and FeO, in the contact with the core. Anorthite correlates positively with MgO and FeO in the mantle, but correlation between An and SrO and BaO is not evident. It is assumed that plagioclase phenocrysts originally crystallizing from the host andesitic magma were interrupted by mixing with a hotter, juvenile basaltic magma. The resulting changes in temperature, composition, and H2O content of the surrounding melt caused compositional zonation, and the development of resorption in the cores and sieve texture in the mantles. As the An contents of the rims of the phenocrysts resemble the average An content of the groundmass plagioclases in both rock types, it is thought that the two involved magmas gained their independent physical identity before the formation of compositionally-distinct rims of plagioclase phenocrysts.

The Problem of the Association of Acid and Basic Rocks in Central Complexes

1931 ◽  
Vol 68 (6) ◽  
pp. 241-255 ◽  
Author(s):  
Arthur Holmes
Keyword(s):  
North America ◽  
Igneous Rocks ◽  
Iron Ores ◽  
Residual Magma ◽  
Crystallization Differentiation ◽  
Igneous Complexes ◽  
Basaltic Magmas ◽  
Parent Stock ◽  
Mechanical Separation ◽  
Basic Rocks

One of the outstanding problems of petrogenesis at the present time is that offered by the remarkable association of sharply contrasted acid and basic rocks (e.g. granite-gabbro; granophyredolerite; pitchstone-tholeiite; and rhyolite-basalt) in igneous complexes such as those of the British Tertiary Province and those of the great lopoliths of Duluth and Sudbury in North America and the Bushveld in South Africa. The contrast was first recognized in the lavas of Iceland by Bunsen (1) and it led him to the conception that two fundamental magmas, respectively acid and basic, were concerned in the genesis of the igneous rocks of Iceland and similar provinces elsewhere. Bunsen's view, however, has had little influence in the development of petrological philosophy. The petrologists of the Geological Survey in this country, and Bowen and others in North America, have assembled a very weighty and reasonable mass of field and laboratory evidence supporting the hypothesis that the acid rocks are residual products arising from the crystallization-differentiation of basaltic magmas. In the recently published Ardnamurchan Memoir (2), for example, it is claimed that as a result of the early extraction from the Plateau Magma of olivine, pyroxenes, basic plagioclase, and iron ores, the residual magma would reach a composition “which would find expression as quartz-doleritic rocks with an acid mesostasis capable of mechanical separation and a separate existence as acid lavas or intrusions” (p. 95). Bunsen's two magmas are thus regarded as successive products from a single parent stock.

A mechanism forming silicic segregations from basaltic magma discovered in igneous rocks of Western Sicily

1983 ◽  
Vol 120 (4) ◽  
pp. 321-329 ◽  
Author(s):  
G. Lucido
Keyword(s):  
Basaltic Magma ◽  
Liquid Immiscibility ◽  
Igneous Rocks ◽  
Silicate Liquid ◽  
Basaltic Magmas ◽  
Western Sicily ◽  
Basic Rocks ◽  
Silicate Liquid Immiscibility ◽  
Textural Evidence

Summary. Mechanisms forming silicic segregations from basaltic magmas are considered of primary importance when dealing with magmatic problems. However, the processes which give rise to silicic segregations from basaltic magmas are so far obscure. Fortunately, the discovery of spheroidal felsic masses in some basic rocks of Western Sicily throws light on this subject. To clarify the relationships between felsic and basic fractions particular attention has been paid to the interactions which occurred at their contact. Textural evidence indicates that the accretion mechanism of the Sicilian felsic segregations tends to obliterate the silicate liquid immiscibility effects and suggests that the formation of silicic segregations is a consequence of liquid unmixing phenomena.

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