scholarly journals Petrogeochemical features of the Neogene collision volcanism of the Lesser Caucasus (Azerbaijan)

2020 ◽  
Vol 29 (2) ◽  
pp. 289-303
Author(s):  
Nazim A. Imamverdiyev ◽  
Minakhanym Y. Gasanguliyeva ◽  
Vagif M. Kerimov ◽  
Ulker I. Kerimli
Keyword(s):  
Fractional Crystallization ◽  
Water Pressure ◽  
Basaltic Magma ◽  
Volcanic Rocks ◽  
Fluid Pressure ◽  
Material Balance ◽  
Parental Magma ◽  
High Alumina ◽  
Fractionation Process ◽  
Lesser Caucasus

The article is devoted to the petrogeochemical features of Neogene collision volcanism in the central part of the Lesser Caucasus within Azerbaijan. The main goal of the study is to determine the thermodynamic conditions for the formation of Neogene volcanism in the central part of the Lesser Caucasus using the available petrogeochemical material. Using factor analysis, as well as the “IGPET”, “MINPET”, “Petrolog-3” programs, material balance calculations were performed that simulate the phenocryst fractionation process, the crystallization temperature, pressure, and figurative nature of the rock-forming minerals of the formation rocks were calculated. It was determined that at the early and middle stages of crystallization of the rocks of the andesite-dacite-rhyolite formation, the fractionation of amphibole played an important role in the formation of subsequent differentiates. Based on computer simulation, it was revealed that rocks of the andesite-dacite-rhyolite formation were formed by fractional crystallization of the initial high-alumina basaltic magma of high alkalinity in the intermediate magma foci. The calculations of the balance of the substance, simulating the process of fractionation of phenocrysts, as well as magnetite, confirmed the possibility of obtaining rock compositions from andesites to rhyolites as a result of this process. In this case, the process of crystallization differentiation was accompanied by processes of contamination, hybridism and mixing. Based on the geochemical features of rare and rare-earth elements, changes in their ratios, the nature of the mantle source and the type of fractionation process are determined. It was revealed that the enrichment of formation rocks by light rare earths, as well as by many incoherent elements, is associated with the evolution of enriched mantle material. Under high water pressure, as a result of the fractionation of olivine and pyroxene, high-alumina basalts are formed from primary high-magnesian magma, which can be considered parental magma. It was established that, in contrast to the elevated Transcaucasian zone in the more lowered East Caucasus, under conditions of increased fluid pressure and reduced temperature, the melt underwent fractional crystallization in the intermediate centers, being enriched with alkaline, large-ion lithophilic elements, light REEs, etc. This is evidenced by the presence of large crystals of feldspars, the contamination of these minerals by numerous crystals of biotite, magnetite, several generations of these minerals, zonality, as well as the presence of related “water” inclusions, such as hornblendites, hornblende gabbro, etc. The physicochemical conditions for the formation of Neogene volcanic rocks of the Lesser Caucasus are determined.

The Border Ranges ultramafic and mafic complex, south-central Alaska: cumulate fractionates of island-arc volcanics

1985 ◽  
Vol 22 (7) ◽  
pp. 1020-1038 ◽  
Author(s):  
Laurel E. Burns
Keyword(s):  
Fractional Crystallization ◽  
Compositional Data ◽  
Basaltic Magma ◽  
Volcanic Rocks ◽  
Island Arc ◽  
Minor Amount ◽  
The North ◽  
South Central ◽  
Mafic Complex ◽  
Wide Range

A discontinuous, elongate zone of mafic and ultramafic plutonic rock crops out in south-central Alaska for a distance of more than 1000 km. Intermediate- and detailed-scale geologic mapping, petrographic study, and compositional data suggest that the plutonic rocks are compositionally, petrologically, and mineralogically distinct from rocks in mid-ocean ridge and back-arc basin ophiolites. The mafic and ultramafic rocks instead represent part of the plutonic core of an intraoceanic island arc.The mafic–ultramafic zone, referred to as the Border Ranges ultramafic and mafic complex (BRUMC), is composed of ultramafic cumulates, gabbronorite cumulates, and massive gabbronorites. A very minor amount of tectonized ultramafic rock of mantle origin is present in the southern part of the BRUMC. A thick sequence of andesitic volcanic rocks, the Talkeetna Formation of Early Jurassic age, lies to the north of and structurally above the mafic–ultramafic zone. Voluminous calcalkaline plutons composed of quartz diorite, tonalite, and minor granodiorite intrude both the mafic plutonic complexes and the andesitic volcanic rocks.The cumulate ultramafic sections are largely composed of dunite ± chromite, wehrlite, clinopyroxenite, and websterite and are characterized by a wide range of Mg–Fe silicate compositions (Fo90–81; En45–50, Fs1–7, Wo45–49; En88–82, Fs11–17), chrome-rich spinels, and a lack of plagioclase. The gabbroic sections are composed of gabbronorites with up to 10–15% magnetite ± ilmenite. Hornblende, if present, is a very minor phase in most gabbroic rocks. The coexisting mineral compositions seen in the gabbroic rocks of the BRUMC (relatively iron-rich pyroxene—Fs6–13, En45–40; En81–63 —and calcic plagioclase An75–100) and their association with magnetite are common in plutonic xenoliths in island-arc rocks.The mineralogy and composition of the gabbroic rocks in the BRUMC are consistent with the fractional crystallization products predicted to be associated with the formation of andesite from a basaltic magma. Consideration of additional data, including detailed and regional field mapping of the plutonic and volcanic rocks and geochronology of the BRUMC and the nearby Talkeetna arc volcanic rocks, strongly suggests that the BRUMC represents relatively deep fractional crystallization products of magmas that produced the Talkeetna Formation volcanic rocks. Field relationships also indicate that intrusion of quartz diorites, tonalites, and granodiorites of batholithic proportions occurred slightly later than formation of the BRUMC.

Andean andesites and crustal growth

1981 ◽  
Vol 301 (1461) ◽  
pp. 305-320 ◽  
Keyword(s):  
Fractional Crystallization ◽  
Volcanic Rocks ◽  
Parental Magma ◽  
Alkaline Magmatism ◽  
Chemical Compositions ◽  
Crustal Growth ◽  
Calc Alkaline ◽  
Asthenospheric Mantle ◽  
The Andes ◽  
Variable Extent

Over the last 200 Ma, the ensialic Andean plate margin has been characterized by calc-alkaline magmatism. The early (Mesozoic), activity was dominantly of basaltic volcanism while the Cainozoic volcanism was of intermediate, calc-alkaline character. The restriction of Recent volcanism to parts of the Andes underlain by thick wedges of asthenospheric mantle, and the Sr and Nd isotopic relations, indicate that the calc-alkaline parental magmas are derived from the asthenospheric mantle. There is no unequivocal geochemical and geophysical evidence that continental crust or sediment has contributed to the mantle source for Andean magmatism. The chemical compositions of the calc-alkaline volcanic rocks of the active volcanic zones are controlled by fractional crystallization, whereas O-Sr isotopic relations reflect crustal interaction of mantle-derived parental magma with the sialic basement of the Andes. The variable extent of fractional crystallization, partial melting, and mixing of crustal contaminant are related to the variable thickness and age of crust in the different volcanic provinces. Calc-alkaline magmatism was largely responsible for post-Mesozoic crustal growth in the Andes and would have depleted the underlying mantle unless balanced by circulation within the asthenospheric mantle wedge. In terms of net growth of the South American continent, it is not certain where the balance lies between growth by magmatic addition and shrinking by erosion.

Stratigraphy and eruptive history of the Late Devonian Mount Pleasant Caldera Complex, Canadian Appalachians

1997 ◽  
Vol 134 (1) ◽  
pp. 17-36 ◽  
Author(s):  
S. R. McCUTCHEON ◽  
H. E. ANDERSON ◽  
P. T. ROBINSON
Keyword(s):  
Fractional Crystallization ◽  
Basaltic Magma ◽  
Late Devonian ◽  
Crustal Material ◽  
Basaltic Rocks ◽  
Stratigraphic Subdivision ◽  
Mount Pleasant ◽  
History Of ◽  
High Level ◽  
Mafic Lavas

Stratigraphic, petrographic and geochemical evidence indicate that the volcano-sedimentary rocks of the Late Devonian Piskahegan Group, located in the northern Appalachians of southwestern New Brunswick, represent the eroded remnants of a large epicontinental caldera complex. This complex – the Mount Pleasant Caldera – is one of few recognizable pre-Cenozoic calderas and is divisible into Exocaldera, Intracaldera and Late Caldera-Fill sequences. The Intracaldera Sequence comprises four formations that crop out in a triangular-shaped area and includes: thick ash flow tuffs, thick sedimentary breccias that dip inward, and stocks of intermediate to felsic composition that intrude the volcanic pile or are localized along caldera-margin faults. The Exocaldera Sequence contains ash flow tuffs, mafic lavas, alluvial redbeds and porphyritic felsic lavas that comprise five formations. The Late Caldera-Fill Sequence contains rocks that are similar to those of the outflow facies and comprises two formations and two minor intrusive units. Geochemical and mineralogical data support the stratigraphic subdivision and indicate that the basaltic rocks are mantle-derived and have intraplate chemical affinities. The andesites were probably derived from basaltic magma by fractional crystallization and assimilation of crustal material. The various felsic units are related by episodes of fractional crystallization in a high-level, zoned magma chamber. Fractionation was repeatedly interrupted by eruption of material from the roof zone such that seven stages of caldera development have been identified. The genesis of the caldera is related to a period of lithospheric thinning that followed the Acadian Orogeny in the northern Appalachians.

Relative roles of source composition, fractional crystallization and crustal contamination in the petrogenesis of Andean volcanic rocks

1984 ◽  
Vol 310 (1514) ◽  
pp. 675-692 ◽  
Keyword(s):  
Subduction Zone ◽  
Continental Crust ◽  
Fractional Crystallization ◽  
Magma Mixing ◽  
Volcanic Rocks ◽  
Crustal Contamination ◽  
Oceanic Lithosphere ◽  
Alkaline Basalt ◽  
Complex Process ◽  
Heterogeneous Mantle

There are well established differences in the chemical and isotopic characteristics of the calc-alkaline basalt—andesite-dacite-rhyolite association of the northern (n.v.z.), central (c.v.z.) and southern volcanic zones (s.v.z.) of the South American Andes. Volcanic rocks of the alkaline basalt-trachyte association occur within and to the east of these active volcanic zones. The chemical and isotopic characteristics of the n.v.z. basaltic andesites and andesites and the s.v.z. basalts, basaltic andesites and andesites are consistent with derivation by fractional crystallization of basaltic parent magmas formed by partial melting of the asthenospheric mantle wedge containing components from subducted oceanic lithosphere. Conversely, the alkaline lavas are derived from basaltic parent magmas formed from mantle of ‘within-plate’ character. Recent basaltic andesites from the Cerro Galan volcanic centre to the SE of the c.v.z. are derived from mantle containing both subduction zone and within-plate components, and have experienced assimilation and fractional crystallization (a.f.c.) during uprise through the continental crust. The c.v.z. basaltic andesites are derived from mantle containing subduction-zone components, probably accompanied by a.f.c. within the continental crust. Some c.v.z. lavas and pyroclastic rocks show petrological and geochemical evidence for magma mixing. The petrogenesis of the c.v.z. lavas is therefore a complex process in which magmas derived from heterogeneous mantle experience assimilation, fractional crystallization, and magma mixing during uprise through the continental crust.

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.

Origin of the Tulameen ultramafic-gabbro complex, southern British Columbia

1969 ◽  
Vol 6 (3) ◽  
pp. 399-425 ◽  
Author(s):  
D. C. Findlay
Keyword(s):  
British Columbia ◽  
Internal Structure ◽  
Fractional Crystallization ◽  
Volcanic Rocks ◽  
Age Determination ◽  
Upper Triassic ◽  
Ultramafic Rocks ◽  
Metasedimentary Rocks ◽  
Gabbroic Intrusion

The Tulameen Complex is a composite ultramafic-gabbroic intrusion that outcrops over 22 sq. mi. (57 km2) in the Southern Cordillera of British Columbia. The complex intruded Upper Triassic metavolcanic and metasedimentary rocks of the Nicola Group, and on the basis of geologic relations and a K–Ar age determination (186 m.y.) is tentatively dated as Late Triassic.The principal ultramafic units — dunite, olivine clinopyroxenite, and hornblende clinopyroxenite — form an elongate, non-stratiform body whose irregular internal structure is best explained by deformation contemporaneous with crystallization of the rocks. The derivation of the ultramafic rocks is attributed to fractional crystallization of an ultrabasic magma. The gabbroic mass, which consists of syenogabbro and syenodiorite, partly borders and partly overlies the ultramafic body and was apparently intruded by it.The ultramafic and gabbroic parts of the complex probably formed from separate intrusions of different magmas, but the two suites have sufficient mineralogical and chemical features in common to indicate an ultimate petrogenic affinity of the magmas. Comparison of the Tulameen rocks with nearby intrusions of the same general age, in particular the Copper Mountain stock, suggests that they are members of a regional suite of alkalic intrusions. The possibility is also raised that these intrusions may be comagmatic with the Nicola volcanic rocks.

scholarly journals Multi-stage arc magma evolution recorded by apatite in volcanic rocks

Geology ◽  
2020 ◽  
Vol 48 (4) ◽  
pp. 323-327 ◽  
Author(s):  
Chetan L. Nathwani ◽  
Matthew A. Loader ◽  
Jamie J. Wilkinson ◽  
Yannick Buret ◽  
Robert H. Sievwright ◽  
...  
Keyword(s):  
Fractional Crystallization ◽  
Volcanic Rocks ◽  
Explosive Volcanism ◽  
Ore Deposits ◽  
Magma Evolution ◽  
Arc Magmas ◽  
Deep Crust ◽  
Multi Stage ◽  
Novel Approach ◽  
Arc Magma

Abstract Protracted magma storage in the deep crust is a key stage in the formation of evolved, hydrous arc magmas that can result in explosive volcanism and the formation of economically valuable magmatic-hydrothermal ore deposits. High magmatic water content in the deep crust results in extensive amphibole ± garnet fractionation and the suppression of plagioclase crystallization as recorded by elevated Sr/Y ratios and high Eu (high Eu/Eu*) in the melt. Here, we use a novel approach to track the petrogenesis of arc magmas using apatite trace element chemistry in volcanic formations from the Cenozoic arc of central Chile. These rocks formed in a magmatic cycle that culminated in high-Sr/Y magmatism and porphyry ore deposit formation in the Miocene. We use Sr/Y, Eu/Eu*, and Mg in apatite to track discrete stages of arc magma evolution. We apply fractional crystallization modeling to show that early-crystallizing apatite can inherit a high-Sr/Y and high-Eu/Eu* melt chemistry signature that is predetermined by amphibole-dominated fractional crystallization in the lower crust. Our modeling shows that crystallization of the in situ host-rock mineral assemblage in the shallow crust causes competition for trace elements in the melt that leads to apatite compositions diverging from bulk-magma chemistry. Understanding this decoupling behavior is important for the use of apatite as an indicator of metallogenic fertility in arcs and for interpretation of provenance in detrital studies.

Origin of non-cotectic cumulates: A novel approach

Geology ◽  
2020 ◽  
Vol 48 (6) ◽  
pp. 604-608 ◽  
Author(s):  
R.M. Latypov ◽  
S.Yu. Chistyakova
Keyword(s):  
Phase Equilibria ◽  
Basaltic Magma ◽  
Parental Magma ◽  
Magma Chambers ◽  
Mechanical Mixing ◽  
Novel Approach ◽  
In Situ Crystallization ◽  
Mechanical Separation ◽  
Novel Concept

Abstract Plutonic mafic complexes are composed of cumulates in which minerals mostly occur in cotectic proportions. This is consistent with a concept that basaltic magma chambers predominantly crystallize in situ from margins inward. However, cumulates with two (or more) minerals in proportions that are at odds with those expected from liquidus phase equilibria also locally occur in these complexes. Such non-cotectic cumulates are commonly attributed to either mechanical separation of minerals crystallizing from the same parental magma or mechanical mixing of minerals originating from different parental magmas. Here we introduce a novel concept that does not require any of these processes to produce non-cotectic cumulates. The model involves melts that start crystallizing upon their cooling, while ascending along feeder conduits from deep staging reservoirs toward the Earth’s surface. Depending on the degree of cooling, the melts become successively saturated in one, two, and more liquidus phases. Given that most crystals are kept in suspension, the resulting magmas would contain a cargo of equilibrium phenocrysts in notably non-cotectic proportions. The replenishment of basaltic chambers developing through in situ crystallization by such magmas is likely responsible for the occasional formation of non-cotectic cumulates in plutonic mafic complexes.

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