scholarly journals Origin of alkali-rich volcanic and alkali-poor intrusive carbonatites from a common parental magma

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Ivan F. Chayka ◽  
Vadim S. Kamenetsky ◽  
Nikolay V. Vladykin ◽  
Alkiviadis Kontonikas-Charos ◽  
Ilya R. Prokopyev ◽  
...  
Keyword(s):  
Empirical Evidence ◽  
Fractional Crystallization ◽  
Melt Inclusions ◽  
Parental Magma ◽  
Progressive Increase ◽  
Topical Problem ◽  
Oldoinyo Lengai ◽  
Southern Siberia ◽  
Magmatic Stage ◽  
Common Parent

AbstractThe discrepancy between Na-rich compositions of modern carbonatitic lavas (Oldoinyo Lengai volcano) and alkali-poor ancient carbonatites remains a topical problem in petrology. Although both are supposedly considered to originate via fractional crystallization of a “common parent” alkali-bearing Ca-carbonatitic magma, there is a significant compositional gap between the Oldoinyo Lengai carbonatites and all other natural compositions reported (including melt inclusions in carbonatitic minerals). In an attempt to resolve this, we investigate the petrogenesis of Ca-carbonatites from two occurrences (Guli, Northern Siberia and Tagna, Southern Siberia), focusing on mineral textures and alkali-rich multiphase primary inclusions hosted within apatite and magnetite. Apatite-hosted inclusions are interpreted as trapped melts at an early magmatic stage, whereas inclusions in magnetite represent proxies for the intercumulus environment. Melts obtained by heating and quenching the inclusions, show a progressive increase in alkali concentrations transitioning from moderately alkaline Ca-carbonatites through to the “calcite CaCO3 + melt = nyerereite (Na,K)2Ca2(CO3)3” peritectic, and finally towards Oldoinyo Lengai lava compositions. These results give novel empirical evidence supporting the view that Na-carbonatitic melts, similar to those of the Oldoinyo Lengai, may form via fractionation of a moderately alkaline Ca-carbonatitic melt, and therefore provide the “missing piece” in the puzzle of the Na-carbonatite’s origin. In addition, we conclude that the compositions of the Guli and Tagna carbonatites had alkali-rich primary magmatic compositions, but were subsequently altered by replacement of alkaline assemblages by calcite and dolomite.

scholarly journals Parental magma of the Skaergaard intrusion: constraints from melt inclusions in primitive troctolite blocks and FG-1 dykes

2009 ◽  
Vol 159 (1) ◽  
pp. 61-79 ◽  
Author(s):  
Jakob K. Jakobsen ◽  
Christian Tegner ◽  
C. Kent Brooks ◽  
Adam J. R. Kent ◽  
Charles E. Lesher ◽  
...  
Keyword(s):  
Melt Inclusions ◽  
Parental Magma ◽  
Skaergaard Intrusion

scholarly journals Petrogenesis of Ultramafic Lamprophyres from the Terina Complex (Chadobets Upland, Russia): Mineralogy and Melt Inclusion Composition

Minerals ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 419 ◽  
Author(s):  
Ilya Prokopyev ◽  
Anastasiya Starikova ◽  
Anna Doroshkevich ◽  
Yazgul Nugumanova ◽  
Vladislav Potapov
Keyword(s):  
Mineral Composition ◽  
Fractional Crystallization ◽  
Fluid Inclusions ◽  
Siberian Craton ◽  
Melt Inclusions ◽  
Melt Inclusion ◽  
Inclusion Composition ◽  
Accessory Minerals ◽  
Secondary Minerals ◽  
Peridotite Mantle

The mineral composition and melt inclusions of ultramafic lamprophyres of the Terina complex were investigated. The rocks identified were aillikites, mela-aillikites, and damtjernites, and they were originally composed of olivine macrocrysts and phenocrysts, as well as phlogopite phenocrysts in carbonate groundmass, containing phlogopite, clinopyroxene and feldspars. Minor and accessory minerals were fluorapatite, ilmenite, rutile, titanite, and sulphides. Secondary minerals identified were quartz, calcite, dolomite, serpentine, chlorite, rutile, barite, synchysite-(Ce), and monazite-(Ce). Phlogopite, calcite, clinopyroxene, Ca-amphibole, fluorapatite, magnetite, and ilmenite occurred as daughter-phases in melt inclusions. The melt inclusions also contained Fe–Ni sulphides, synchysite-(Ce) and, probably, anhydrite. The olivine macrocrysts included orthopyroxene and ilmenite, and the olivine phenocrysts included Cr-spinel and Ti-magnetite inclusions. Crystal-fluid inclusions in fluorapatite from damtjernites contain calcite, clinopyroxene, dolomite, and barite. The data that were obtained confirm that the ultramafic lamprophyres of the Terina complex crystallized from peridotite mantle-derived carbonated melts and they have not undergone significant fractional crystallization. The investigated rocks are considered to be representative of melts that are derived from carbonate-rich mantle beneath the Siberian craton.

Field, geochemical, and isotopic evidence for magma mixing and assimilation and fractional crystallization processes in the Quottoon Igneous Complex, northwestern British Columbia and southeastern Alaska

1999 ◽  
Vol 36 (5) ◽  
pp. 819-831 ◽  
Author(s):  
J B Thomas ◽  
A K Sinha
Keyword(s):  
British Columbia ◽  
Fractional Crystallization ◽  
Magma Mixing ◽  
Parental Magma ◽  
Geochemical Data ◽  
Igneous Complex ◽  
Source Regions ◽  
Magmatic Body ◽  
Color Indices ◽  
Lower Crustal

The quartz dioritic Quottoon Igneous Complex (QIC) is a major Paleogene (65-56 Ma) magmatic body in northwestern British Columbia and southeastern Alaska that was emplaced along the Coast shear zone. The QIC contains two different igneous suites that provide information about source regions and magmatic processes. Heterogeneous suite I rocks (e.g., along Steamer Passage) have a pervasive solid-state fabric, abundant mafic enclaves and late-stage dikes, metasedimentary screens, and variable color indices (25-50). The homogeneous suite II rocks (e.g., along Quottoon Inlet) have a weak fabric developed in the magmatic state (aligned feldspars, melt-filled shears) and more uniform color indices (24-34) than in suite I. Suite I rocks have Sr concentrations <750 ppm, average LaN/YbN = 10.4, and initial 87Sr/86Sr ratios that range from 0.70513 to 0.70717. The suite II rocks have Sr concentrations >750 ppm, average LaN/YbN = 23, and initial 87Sr/86Sr ratios that range from 0.70617 to 0.70686. This study suggests that the parental QIC magma (initial 87Sr/86Sr approximately 0.706) can be derived by partial melting of an amphibolitic source reservoir at lower crustal conditions. Geochemical data (Rb, Sr, Ba, and LaN/YbN) and initial 87Sr/86Sr ratios preclude linkages between the two suites by fractional crystallization or assimilation and fractional crystallization processes. The suite I rocks are interpreted to be the result of magma mixing between the QIC parental magma and a mantle-derived magma. The suite II rocks are a result of assimilation and fractional crystallization processes.

Dolerites Associated with the Karroo System, South Africa

1930 ◽  
Vol 67 (3) ◽  
pp. 97-110 ◽  
Author(s):  
Reginald A. Daly ◽  
Tom F. W. Barth
Keyword(s):  
South Africa ◽  
Great Britain ◽  
Fractional Crystallization ◽  
Parental Magma ◽  
Magmatic Differentiation ◽  
Plateau Basalt ◽  
Homogeneous Crystal ◽  
High Degree ◽  
Vast Area ◽  
Basaltic Liquid

Summary—The field impression of a high degree of uniformity in the composition of the intrusive Karroo dolerites over a vast area is confirmed by new chemical and microscopical studies. The pyroxene characteristic of the dolerites is a typical pigeonite, which, however, does not display any twinning on (100). The plagioclase is potash-free, usually a labradorite, but it has been observed that a homogeneous crystal of plagioclase may be in twin position to another homogeneous crystal of a very differently composed plagioclase. The close resemblance of the doleritic liquid to the artificial liquid taken by Bowen to represent basaltic liquid is noted, and his conclusion that pyroxene and feldspar should crystallize simultaneously in natural basaltic liquid is confirmed.Conceivably the doleritic liquid was quite original and not a differentiate of any earlier liquid. However, analogies like those with the tholeiites and similar hypabyssal rocks of Great Britain suggest that in South Africa, as in Great Britain, the liquids of these hypabyssal rocks were derived from the slightly more femic plateau-basalt.On that assumption the question of the mode of differentiation arises. The fractional crystallization of plateau-basalt, as now described by Bowen and other leaders, does not appear competent to explain the abnormally low soda of one of the analyzed dolerites, nor the excess of soda and total alkalies in plateau-basalt respectively over the soda and total alkalies of the Karroo dolerite. Further, the settling-out of early olivine does not explain the excess of (total) FeO in plateau-basalt over the (total) FeO in the Karroo dolerite. The actual relations indicate the need of renewed examination of the theory of magmatic differentiation by crystal-fractionation. In any case many more data are required before it is possible to decide upon the precise relation of the Karroo dolerite to a parental magma. Possibly such additions to knowledge may annul present difficulties in the way of accounting for the composition of the dolerite.

Pétrologie du granite peralcalin du lac Brisson, Labrador central, Nouveau-Québec. 1. Mode de mise en place et évolution chimique

1992 ◽  
Vol 29 (2) ◽  
pp. 353-372 ◽  
Author(s):  
D. Pillet ◽  
M. Chenevoy ◽  
M. Bélanger
Keyword(s):  
Fractional Crystallization ◽  
Fluid Phase ◽  
Major Elements ◽  
Magmatic Stage ◽  
Recent Phase ◽  
Element Enrichment ◽  
Magmatic Suite ◽  
End Members ◽  
Trace Element Enrichment ◽  
Middle Proterozoic

The Lake Brisson peralkaline granite in Labrador, which by way of its age of 1189 Ma is the most recent phase of the Gardar magmatic stage, was intruded in the Middle Proterozoic at the margin of a granulitic complex, retrograded to an amphibolite facies during Aphebian, and of an Elsonian adamellite pluton. It shows a petrographie zonation ("feldspathic" facies at the center, "quartzose" facies including early quartz at the edge) suggestive of a permissive multiphase intrusion, and is characterized by deuteritic alteration via metalliferous fluids (Zr, Y, Nb, Be; rare earths). All facies are Na-peralkaline, well evolved, and represent end-members of a differentiated magmatic suite of the designated A type. The relative behavior of the major elements indicates that the facies differentiation was controlled by fractional crystallization and was also greatly influenced by alkaline feldspath and by increase of f(O2) in the final stage of evolution. The trace elements contents, significantly higher than those reported for other peralkaline complexes, are a confirmation of the influence of fractional crystallization. The unsual trace element enrichment in an altered quartzose facies is the result of the effects of a final oxidizing fluid phase, rich in F; the relative depletion of Na and the enrichment in Sr and Ca of the fluid are explained by its having been contaminated by the wall rocks. [Journal Translation]

scholarly journals MINERALOGY AND PETROLOGY OF THE BRNJICA GRANITOIDS (EASTERN SERBIA)

2004 ◽  
Vol 36 (1) ◽  
pp. 615 ◽  
Author(s):  
N. Vaskovic ◽  
A. Kuroneos ◽  
G. Christofides ◽  
D. Sreckovic-Batocanin ◽  
D. Milovanovic
Keyword(s):  
Fractional Crystallization ◽  
Mineral Assemblage ◽  
Parental Magma ◽  
Acid Magma ◽  
Tectonic Environment ◽  
Discrimination Diagram

The Variscan Brnjica granitoids in East Serbia, occurring in the Kucaj Terrane of the Carpatho-Balkanides, are composed of hornblende - biotite tonalité (TON), biotite granodiorite (GRD), twomica granite (TMG) and leucogranite (LG). The rocks analyzed are slightly peraluminous. A preplate collision tectonic environment is supported based on the R1-R2 discrimination diagram. A two-step mixing plus fractional crystallization (MFC) process is considered responsible for the evolution of the Brnjica granitoids. In the 1st step, the parental magma (having the composition of the more basic TON) is forming the mineral assemblage Pl596Biio.3Hbio.7Mto.7Titi.oQzi7.7 by 44% crystallization, and at the same time is mixed (r=0.1) with a magma similar to TMG to give a melt similar to the composition of the less evolved GRD. In the 2nd step, 60% crystallization (Pl39oKfi oBÌ25oZr06Api aMti 4Titi 0QZ303) of the less evolved GRD and a simultaneous mixing with the same acid magma (TMG) but with higher r (0.6) is needed for the genesis of GRD group. The TON could originate in the crust by melting of amphibolites and basalts under various P-T conditions while the granites could be crustal melts produced by melting of amphibolites, gneisses, graywackes and pelites. Pressure of 2.3 to 4.1 kb and temperatures from 626 to 813 °C were calculated for TON, using hornblende and co-existing hornblende and plagioclase compositions respectively.

scholarly journals New Constraints on the Main Mineralization Event Inferred from the Latest Discoveries in the Bor Metallogenetic Zone (BMZ, East Serbia)

Minerals ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 672
Author(s):  
Banješević ◽  
Cvetković ◽  
von Quadt ◽  
Ljubović Obradović ◽  
Vasić ◽  
...  
Keyword(s):  
Gold Deposit ◽  
Fractional Crystallization ◽  
Parental Magma ◽  
Simplified Model ◽  
The South ◽  
Epithermal Mineralization ◽  
The World ◽  
Phase 1B ◽  
World Class

This study aims at better constraining the link between magmatism and metallogeny in the south-easternmost sector of the Bor Metallogenetic Zone (BMZ), where the world-class copper and gold deposit of Čukaru Peki was recently discovered. The obtained U/Pb zircon ages confirm the earlier knowledge that the major Cu–Au porphyry and epithermal mineralization in the BMZ is genetically related to the first volcanic phase (‘Timok andesite’; 85–90 Ma). However, the data also suggest that during this phase, two subgroups of andesite porphyry were formed; they are named volcanic phase 1A (V1A) and volcanic phase 1B (V1B). The V1A andesite (89–90 Ma) is plagioclase-hornblende phyric, holocrystalline and ubiquitously hydrothermally altered and/or mineralized, whereas the V1B (85–86 Ma) is hornblende-plagioclase phyric, holo- to hypocrystalline, fresh, and non-mineralized. According to our simplified model, the contrasting productivity of the V1A and V1B is explained by fluctuations during AFC (assimilation-fractional crystallization) processes of water-rich parental magma, which have controlled the order of crystallization of hornblende and plagioclase in the V1A and V1B andesite.

The effects of source mixing and fractional crystallization on the composition of Eocene granites in the Himalayan orogen

2021 ◽  
Author(s):  
Peng Gao ◽  
Yong-Fei Zheng ◽  
Chris Yakymchuk ◽  
Zi-Fu Zhao ◽  
Zi-Yue Meng
Keyword(s):  
Trace Element ◽  
Partial Melting ◽  
Fractional Crystallization ◽  
Melt Inclusions ◽  
Thermal Anomaly ◽  
Continental Collision ◽  
Plate Boundaries ◽  
Crustal Anatexis ◽  
Himalayan Orogen ◽  
Heavy Rare Earth Elements

Abstract Granites are generally the final products of crustal anatexis. The composition of the initial melts may be changed by fractional crystallization during magma evolution. Thus, it is crucial to retrieve the temperatures and pressures conditions of crustal anatexis on the basis of the composition of the initial melts rather than the evolved melts. Here we use a suite of ∼46–41 Ma granites from the Himalayan orogen to address this issue. These rocks can be divided into two groups in terms of their petrological and geochemical features. One group has high maficity (MgO + FeOt = 2–4 wt%) and mainly consists of two-mica granites, and is characterized by apparent adakite geochemical signatures, including high Sr concentrations, Sr/Y and La/Yb ratios; and low concentrations of HREE (heavy rare earth elements) and Y. The other group has low maficity (MgO + FeOt &lt;1 wt%) and consists of subvolcanic porphyritic granites and garnet/tourmaline-bearing leucogranites. This group does not possess apparent adakite signatures. The low maficity group (LMG) has lower MgO + FeOt contents and the high maficity group (HMG) has higher Mg# compared with initial anatectic melts determined by experiment petrology and melt inclusions study. Petrological observations indicate that the HMG and the LMG can be explained as a crystal-rich cumulate and its fractionated melt, respectively, such that the initial anatectic melt is best represented by an intermediate composition. Such a cogenetic relationship is supported by the comparable Sr–Nd isotopic compositions of the two coeval groups. However, these compositions are also highly variable, pointing to a mixed source that was composed of amphibolite and metapelite with contrasting isotope compositions. We model the major and trace element compositions of anatectic melts generated by partial melting of the mixed source at four apparent thermobaric ratios of 600, 800, 1000 and 1200 °C/GPa. Modeling results indicate that melt produced at 1000 °C/GPa best matches the major and trace element compositions of the inferred initial melt compositions. In particular, a binary mixture generated from 10 vol% partial melting of amphibolite and 30 vol% melting of metapelite at 850 ± 50 °C and 8.5 ± 0.5 kbar gives the best match. Therefore, this study highlights that high thermobaric ratios and subsequent fractional crystallization are responsible for the generation of the apparent adakitic geochemical signatures, rather than melting at the base of the thickened crust as previously proposed. The thermal anomaly responsible for the Eocene magmatism in the Himalayan orogen was probably related to asthenosphere upwelling in response to rollback of the subducting Neo-Tethyan oceanic slab at the terminal stage of continental collision between India and Asia. As such, a transition in dynamic regime from compression to extension is necessary for the generation of high thermobaric ratios in the continental collision zone. Therefore, on the basis of evaluating the potential role of fractional crystallization in altering the composition of the initial melt, granite geochemistry coupled with thermodynamic modeling can better elucidate the petrogenesis of granites and the geodynamic mechanisms associated with anatexis at convergent plate boundaries.

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