The Petrology of the Tarosero Volcanic Complex: Constraints on the formation of extrusive agpaitic rocks

2021 ◽  
Author(s):  
S Braunger ◽  
M A W Marks ◽  
T Wenzel ◽  
A N Zaitsev ◽  
G Markl
Keyword(s):  
Trace Element ◽  
Water Activity ◽  
Fractional Crystallization ◽  
Genetic Relationships ◽  
Alkali Feldspar ◽  
High Water ◽  
Low Pressure ◽  
Water Soluble ◽  
Volcanic Complex ◽  
Rock Types

Abstract The Quaternary Tarosero volcano is situated in the East African Rift of northern Tanzania and mainly consists of trachyte lavas and some trachytic tuffs. In addition, there are minor occurrences of extrusive basalts, andesites, latites, as well as peralkaline trachytes, olivine trachytes and phonolites. Some of the peralkaline phonolites contain interstitial eudialyte, making Tarosero one of the few known occurrences for extrusive agpaitic rocks. This study investigates the genetic relationships between the various rock types and focuses on the peculiar formation conditions of the extrusive agpaitic rocks using a combination of whole-rock geochemistry, mineral chemistry, petrography, thermodynamic calculations, as well as major and trace element modelling. The Tarosero rocks formed at redox conditions around or below the fayalite-magnetite-quartz buffer (FMQ). During multi-level magmatic fractionation at depths between ∼40 km and the shallow crust, temperature decreased from > 1100 °C at near-liquidus conditions in the basalts to ∼ 700 °C in the peralkaline residue. Fractional crystallization models and trace element characteristics do not indicate a simple genetic relationship between the trachytes and the other rock types at Tarosero. However, the genetic relationships between the primitive basalts and the intermediate latites can be explained by high pressure fractional crystallization of olivine + clinopyroxene + magnetite + plagioclase + apatite. Further fractionation of these mineral phases in addition to amphibole and minor ilmenite led to the evolution towards the peralkaline trachytes and phonolites. The eudialyte-bearing varieties of the peralkaline phonolites required additional low-pressure fractionation of alkali feldspar and minor magnetite, amphibole and apatite. In contrast to the peralkaline trachytes and phonolites, the peralkaline olivine trachytes contain olivine instead of amphibole, thus indicating a magma evolution at even lower pressure conditions. They can be modelled as a derivation from the latites by fractional crystallization of plagioclase, clinopyroxene, magnetite and olivine. In general, agpaitic magmas evolve under closed system conditions which impedes the escape of volatile phases. In case of the extrusive agpaitic rocks at Tarosero, the early exsolution of fluids and halogens was prevented by a low water activity. This resulted in high concentrations of Rare Earth Elements (REE) and other High Field Strength Elements (HFSE) and the formation of eudialyte in the most evolved peralkaline phonolites. Within the peralkaline rock suite, the peralkaline olivine trachytes contain the lowest HFSE and REE concentrations, consistent with mineralogical evidence for a formation at a relatively high water activity. The lack of amphibole fractionation, which can act as a water buffer of the melt, as well as the evolution at relatively low pressure conditions caused the early exsolution of fluids and loss of water-soluble elements. This prevented a strong enrichment of HFSE and REE before the magma finally extruded.

Petrology and geochemistry of the Kamloops Group volcanics, British Columbia

1981 ◽  
Vol 18 (9) ◽  
pp. 1478-1491 ◽  
Author(s):  
Thomas E. Ewing
Keyword(s):  
British Columbia ◽  
Fractional Crystallization ◽  
Middle Eocene ◽  
Volcanic Rocks ◽  
Primary Source ◽  
Low Pressure ◽  
Rock Types ◽  
South Central ◽  
High K ◽  
Petrology And Geochemistry

The Kamloops Group is an alkali-rich calc-alkaline volcanic suite of Early to Middle Eocene age, widespread in south-central British Columbia. Rock types in the suite range from high-K basalt through andesite to rhyolite. The suite is characterized by relatively high K2O, Sr, and Ba, but low Zr, Ti, and Ni concentrations, only moderate Ce enrichment, and little or no Fe enrichment. Initial ratios 87Sr/86Sr are about 0.7040 in the western half, and about 0.7060 in the eastern half of the study area. No difference in chemistry or mineralogy marks this sharp transition. Chemically similar suites include the Absaroka–Gallatin suite in Wyoming and the lower San Juan (Summer Coon) suite in Colorado. The content of K2O at 60% SiO2 increases regularly eastward across southern British Columbia. The chemical data support the subduction-related continental arc origin of the Kamloops Group volcanics.The volcanic rocks consist in the main of augite–pigeonite andesites ranging from 52 to 62% silica, with subordinate quantities of olivine–augite–pigeonite basalt and biotite rhyodacite and rhyolite. The andesites and basalts were derived by a combination of low-pressure fractional crystallization, higher pressure fractional crystallization, and variable parental magmas, whereas low-pressure fractional crystallization of plagioclase, biotite, and apatite from parental basalt and andesite produced the rhyolites. The parental magmas were basalts and basaltic andesites with high K, Sr, and Ba. The primary source of these magmas is inferred to have been an alkali-enriched hydrous peridotite with neither plagioclase nor garnet present in the residuum.

Magmatic and Tectonic Setting of Archean Granitoids in the Southeastern Singhbhum Craton, India: Developing constraints with major and trace element geochemistry and geochronology

2020 ◽  
Vol 22 ◽  
Author(s):  
Claudia Banks
Keyword(s):  
Trace Element ◽  
Genetic Relationships ◽  
Tectonic Setting ◽  
Trace Element Geochemistry ◽  
Element Geochemistry ◽  
Peninsular India ◽  
Singhbhum Craton ◽  
Rock Types ◽  
Granite Emplacement ◽  
Singhbhum Granite

The Singhbhum craton is one of five Archean nuclei comprising Peninsular India. It is a composite Archean block that includes the Older Metamorphic Group, the Older Metamorphic Tonalite Gneisses, the Singhbhum Granite, and the Iron Ore Group as its major units. The ages of these components range from ~3.5 to ~3.1 Ga, although overlapping ages and similar rock types confound their genetic relationships. Plutonic felsic rocks from the southeastern Singhbhum craton (BK1: a foliated tonalite, KP1: a non-foliated granite, and SG14: a non-foliated granite) yield U-Pb (zircon) ages of 3321 ± 2 Ma (BK1), 3301 ± 1 Ma (KP1), and  3261 ± 1 Ma (SG14) that coincide with a pulse of Singhbhum Granite emplacement at 3.27 to 3.33 Ga. REE patterns and tectonic discrimination diagrams based on major and trace element ratios suggest a subduction zone setting for these rocks. We report major and trace element data for and compare them to previous works in order to characterize the Archean felsic plutonic history of the craton.

Geochemical constraints on the differentiation processes that were active in the Sept Iles complex

1986 ◽  
Vol 23 (5) ◽  
pp. 670-681 ◽  
Author(s):  
Michael D. Higgins ◽  
R. Doig
Keyword(s):  
Mass Balance ◽  
Trace Element ◽  
Fractional Crystallization ◽  
Major Element ◽  
Alkali Feldspar ◽  
Granitic Magma ◽  
Trace Element Distribution ◽  
Accessory Mineral ◽  
Quartz Syenite ◽  
Element Abundances

Major- and trace-element abundances in the major units (gabbro, anorthosite, monzonite, syenite, and granite) of the unmetamorphosed Sept Iles complex have been evaluated to determine if these rocks can be related by simple magmatic processes or if it is necessary to invoke separately derived magmas. Major-element mass-balance and trace-element distribution calculations indicate that the diorite and quartz syenite were produced by fractional crystallization of plagioclase and augite, together with minor hypersthene and ilmenite, from a parental gabbroic magma. The Sr depletion of the granite, as compared with the quartz syenite, cannot be developed readily by partial melting and is better explained by fractional crystallization models. Major-element mass-balance solutions indicate that the granite was formed by removal of alkali feldspar, plagioclase, amphibole, and ilmenite from a quartz syenitic magma. Depletion of REE in the granite was probably the result of amphibole or REE-rich accessory mineral fractionation. It is unlikely that an unrelated, independently generated granitic magma could have a composition so related to the remainder of the complex. Therefore, fractional crystallization of a parental gabbroic magma is the dominant process that controlled the diversity of magma in the complex.

scholarly journals Chemical Evolution of Calc-alkaline Magmas during the Ascent through Continental Crust: Constraints from Methana, Aegean Arc

2020 ◽  
Vol 61 (3) ◽  
Author(s):  
Milena V Schoenhofen ◽  
Karsten M Haase ◽  
Christoph Beier ◽  
Dominic Woelki ◽  
Marcel Regelous
Keyword(s):  
Trace Element ◽  
Continental Crust ◽  
Fractional Crystallization ◽  
Magma Mixing ◽  
Basaltic Magma ◽  
High Water ◽  
Calc Alkaline ◽  
Mafic Enclaves ◽  
Aegean Arc ◽  
Mineral Compositions

Abstract Quaternary calc-alkaline andesitic to dacitic lavas effusively erupted on top of about 30 km thick accreted continental crust at Methana peninsula in the western Aegean arc. We present new data of major and trace element concentrations as well as of Sr–Nd–Pb isotope ratios along with mineral compositions of Methana lavas and their mafic enclaves. The enclaves imply a parental basaltic magma and fractional crystallization processes with relatively little crustal assimilation in the deep part of the Methana magma system. The composition of amphibole in some mafic enclaves and lavas indicates deeper crystallization at ∼25 km depth close to the Moho compared with the evolved lavas that formed at <15 km depth. The presence of amphibole and low Ca contents in olivine suggest high water contents of ∼4 wt% in the primitive magmas at Methana. The compositions of andesitic and dacitic lavas reflect fractional crystallization, assimilation of sedimentary material, and magma mixing in the upper 15 km of the crust. The Methana magmas have fO2 of FMQ + 1 to FMQ + 2 (where FMQ is the fayalite–magnetite–quartz buffer) at temperatures of 1200 to 750 °C and the fO2 does not vary systematically from mafic to felsic compositions, suggesting that the mantle wedge was oxidized by sediment subduction. Amphibole is an important fractionating phase in the more evolved Methana magmas and causes significant changes in incompatible element ratios. Although xenocrysts and mineral compositions indicate magma mixing, the major and trace element variation implies only limited mixing between dacitic and basaltic melts.

Moisture migration in a cereal composite food at high water activity: Effects of initial porosity and fat content

2006 ◽  
Vol 43 (2) ◽  
pp. 144-151 ◽  
Author(s):  
Elisabeth Roca ◽  
Valérie Guillard ◽  
Stéphane Guilbert ◽  
Nathalie Gontard
Keyword(s):  
Water Activity ◽  
High Water ◽  
Fat Content ◽  
Initial Porosity ◽  
Moisture Migration

Major- and trace-element composition of REE-rich turkestanite from peralkaline granites of the Morro Redondo Complex, Graciosa Province, south Brazil

2010 ◽  
Vol 74 (4) ◽  
pp. 645-658 ◽  
Author(s):  
F. C. J. Vilalva ◽  
S. R. F. Vlach
Keyword(s):  
Trace Element ◽  
Inductively Coupled Plasma ◽  
Alkali Feldspar ◽  
Trace Element Composition ◽  
Inductively Coupled ◽  
Coupled Substitution ◽  
Plasma Mass Spectrometry ◽  
Compositional Variations ◽  
End Members ◽  
South Brazil

AbstractTurkestanite, a rare Th- and REE-bearing cyclosilicate in the ekanite–steacyite group was found in evolved peralkaline granitesfrom the Morro Redondo Complex, south Brazil. It occurswith quartz, alkali feldspar and an unnamed Y-bearing silicate. Electron microprobe analysis indicates relatively homogeneous compositions with maximum ThO2, Na2O and K2O contentsof 22.4%, 2.93% and 3.15 wt.%, respectively, and significant REE2O3 abundances(5.21 to 11.04 wt.%). The REE patterns show enrichment of LREE over HREE, a strong negative Eu anomaly and positive Ce anomaly, the latter in the most transformed crystals. Laser ablation inductively coupled plasma mass spectrometry trace element patterns display considerable depletions in Nb, Zr, Hf, Ti and Li relative to whole-rock sample compositions. Observed compositional variations suggest the influence of coupled substitution mechanisms involving steacyite, a Na-dominant analogue of turkestanite, iraqite, a REE-bearing end-member in the ekanite–steacyite group, ekanite and some theoretical end-members. Turkestanite crystals were interpreted as having precipitated during post-magmatic stages in the presence of residual HFSE-rich fluidscarrying Ca, the circulation of which wasenhanced by deformational events.

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