The Role of Water in Basaltic Magma I.

The Xingdi No.2 intrusion in the Kuluktag Block of northeastern Tarim Craton, which intrudes into the Palaeoproterozoic basement with an exposed area of ca. 12 km2, is an orthopyroxene-rich mafic-ultramafic intrusion in a continental rift setting. It consists of gabbros, pyroxenites, and peridotites, and exhibits a crystallization sequence of the principal rock-forming minerals from olivine, orthopyroxene, clinopyroxene, to plagioclase. The gabbros show a concordant SHRIMP U-Pb zircon age of 752 ± 5.4 Ma. In addition, the olivine grains have forsterite content values of 78–85 mole% and mostly contain low NiO, MnO, CaO, and Cr2O3. The rocks are relatively enriched in large ion lithophile elements and LREE, and depleted in HSFE, have non-radiogenic Pb, low εNd (t) values (−2.8 to −23), initial 87Sr/86Sr ratios (0.7059–0.7130). It could be concluded that the rocks represent an analogue of siliceous high magnesium basaltic magma originated by the partial melting of a hydrous and enriched subcontinental lithospheric mantle and contaminated by the continental crust.

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Role of oxygen pressure in the crystallization and differentiation of basaltic magma

American Journal of Science ◽

10.2475/ajs.257.9.609 ◽

1959 ◽

Vol 257 (9) ◽

pp. 609-647 ◽

Cited By ~ 350

Author(s):

E. F. Osborn

Keyword(s):

Oxygen Pressure ◽

Basaltic Magma

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ROLE OF PYROXENITE MANTLE IN MAGMA GENESIS OF THE OLIGOCENE BASALTS FROM THE NORTHERN PART OF EAST SIKHOTE ALIN

Tikhookeanskaya Geologiya ◽

10.30911/0207-4028-2020-39-6-82-97 ◽

2020 ◽

Vol 39 (6) ◽

pp. 82-97

Author(s):

A.Yu. Martynov ◽

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Yu.A. Martynov ◽

A.I. Malinovskii ◽

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...

Keyword(s):

Basaltic Magma ◽

Volcanic Belt ◽

Sikhote Alin ◽

Late Cenozoic ◽

Magma Genesis ◽

First Order ◽

Geodynamic Environment ◽

Magma Sources ◽

Magma Compositions

Identification of magma sources as well as its role in creating the diversity of magma compositions still remains one of the fundamental petrological problems. In our work, on the basis of new comprehensive isotope-geochemical and mineralogical data, we made an attempt to reconstruct the contribution of pyroxenite mantle source in the Oligocene basaltic magma genesis of the northern part of East Sikhote Alin volcanic belt. The most important indicators of this source are significant variations the first order transit elements ratios (Zn/Fe = 11–17, Zn/Mn = 6–10, Cr/Ni (1.8–6) and concentration of Ni (2000–3600 г/т) in olivine. LIL elements behavior suggests the presence of amphibole in pyroxenite substrate. The data obtained can be useful for the correct reconstruction of the magma generation and the geodynamic environment of this territory at the Late Cenozoic.

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Silicate melt inclusions in the cumulate minerals of gabbroic nodules from Stromboli Volcano (Aeolian Islands, Italy): main components of the fluid phase and crystallization temperatures

Mineralogical Magazine ◽

10.1180/0026461026660071 ◽

2002 ◽

Vol 66 (6) ◽

pp. 969-984 ◽

Cited By ~ 11

Author(s):

E. Salvioli-Mariani ◽

M. Mattioli ◽

A. Renzulli ◽

G. Serri

Keyword(s):

Melt Inclusions ◽

Basaltic Magma ◽

Fluid Phase ◽

Silicate Melt ◽

High Alumina ◽

Variable Degree ◽

Fe Content ◽

Interstitial Material ◽

Main Components

Abstract The studied gabbroic nodules occurring in the Petrazza pyroclastic rocks consist mainly of plagioclase (An95–87), olivine (Fo83-73) and clinopyroxene (Mg# 90–77), with subordinate opaques (Ti-magnetite) and amphibole (Mg-hastingsite), which constitute the cumulate minerals. Interstitial material has a relatively high, but variable, degree of vesicularity and consists of variable amounts of glass and quenched crystals of plagioclase (An71–55), amphibole, clinopyroxene and rare biotite, olivine and opaques. Silicate melt inclusions are abundant in the cumulate minerals, but complete homogenization to melt has been observed only in the inclusions occurring in clinopyroxene, where the temperatures of homogenization vary from 1134 to 1190°C. Microthermometric investigations of fluid inclusions and of the shrinkage bubble of the melt inclusions suggest that the magma contained CO2. The apparent scarcity of H2O indicates that this component was strongly partitioned into the magma at the time of crystallization of the investigated minerals; this is further supported by the occurrence of (1) daughter biotite- and amphibole-bearing inclusions which show that the H2O activity in the magma was sufficiently high to allow their crystallization, and (2) calcic plagioclase (An95–87) which can be crystallized from a high-alumina basaltic magma at pressure ≤2 kbar, temperatures in the range 1050–1100°C and in the presence of 3–4 wt.% of water (MELTS software simulations). The composition of the melt inclusions suggests that the hosting plagioclase, olivine and clinopyroxene crystallized from slightly different batches of magma. The S content in the melt inclusions of clinopyroxene and olivine is high (up to 0.41 wt.%). The presence of Fe-Cu(-Ni)-rich blebs of sulphide in plagioclase, olivine, amphibole, and locally in the melt inclusions too, further supports the important role of sulphur in the primitive magmas of the investigated gabbros. Small differences in redox conditions or in the Fe content of the melts favoured S mobilization as sulphide.

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The role of water in basaltic magma II.

Zeitschrift für Kristallographie Mineralogie und Petrographie ◽

10.1007/bf02943369 ◽

1934 ◽

Vol 45 (2-3) ◽

pp. 99-132

Author(s):

T. C. Phemister

Keyword(s):

Basaltic Magma

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Thermodynamic limits for assimilation of silicate crust in primitive magmas

Geology ◽

10.1130/g49139.1 ◽

2021 ◽

Author(s):

Jussi S. Heinonen ◽

Frank J. Spera ◽

Wendy A. Bohrson

Keyword(s):

Basaltic Magma ◽

Wall Rock ◽

Weight Percent ◽

Upper Crust ◽

Basaltic Composition ◽

Primitive Magma ◽

Partial Melts ◽

Geochemical Models ◽

Thermodynamic Limits

Some geochemical models for basaltic and more primitive rocks suggest that their parental magmas have assimilated tens of weight percent of crustal silicate wall rock. But what are the thermodynamic limits for assimilation in primitive magmas? We pursue this question quantitatively using a freely available thermodynamic tool for phase equilibria modeling of open magmatic systems—the Magma Chamber Simulator (https://mcs.geol.ucsb.edu)—and focus on modeling assimilation of wall-rock partial melts, which is thermodynamically more efficient compared to bulk assimilation of stoped wall-rock blocks in primitive igneous systems. In the simulations, diverse komatiitic, picritic, and basaltic parental magmas assimilate progressive partial melts of preheated average lower, middle, and upper crust in amounts allowed by thermodynamics. Our results indicate that it is difficult for any subalkaline primitive magma to assimilate more than 20–30 wt% of upper or middle crust before evolving to compositions with higher SiO2 than a basaltic magma (52 wt%). On the other hand, typical komatiitic magmas have thermodynamic potential to assimilate as much as their own mass (59–102 wt%) of lower crust and retain a basaltic composition. The compositions of the parental melt and the assimilant heavily influence both how much assimilation is energetically possible in primitive magmas and the final magma composition given typical temperatures. These findings have important implications for the role of assimilation in the generation and evolution of, e.g., ultramafic to mafic trans-Moho magmatic systems, siliceous high-Mg basalts, and massif-type anorthosites.

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