Geochemistry of High-silica Peralkaline Rhyolites, Naivasha, Kenya Rift Valley

Macdonald, Ray; Davies, Gareth R.; Bliss, C. M.; Leat, P. T.; Bailey, D. K.; Smith, Robert L.

doi:10.1093/petrology/28.6.979

Cited by 158 publications

(62 citation statements)

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“…Their high Ce/Nb ratios are like those found in post-orogenic magmatic associations, such as Snowdon Rhyolites (Leat et al 1986). The lower Ce and Sm and, higher Rb and Ta contents, together with the lower Ce/Nb ratios of high-Nb rhyolites suggest that this magmatism is related to sources with less influence of subduction-related metasomatism, like the Naivasha Rhyolites, Kenya (MacDonald et al 1987).…”

Section: The Shoshonitic Magmatismmentioning

confidence: 98%

The evolution of Neoproterozoic magmatism in Southernmost Brazil: shoshonitic, high-K tholeiitic and silica-saturated, sodic alkaline volcanism in post-collisional basins

Sommer

Lima

Nardi

et al. 2006

An. Acad. Bras. Ciênc.

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The Neoproterozoic shoshonitic and mildly alkaline bimodal volcanism of Southernmost Brazil is represented by rock assemblages associated to sedimentary successions, deposited in strike-slip basins formed at the post-collisional stages of the Brasilian/Pan-African orogenic cycle. The best-preserved volcanosedimentary associations occur in the Camaquã and Campo Alegre Basins, respectively in the Sul-riograndense and Catarinense Shields and are outside the main shear belts or overlying the unaffected basement areas. These basins are characterized by alternation of volcanic cycles and siliciclastic sedimentation developed dominantly on a continental setting under subaerial conditions. This volcanism and the coeval plutonism evolved from high-K tholeiitic and calc-alkaline to shoshonitic and ended with a silica-saturated sodic alkaline magmatism, and its evolution were developed during at least 60 Ma. The compositional variation and evolution of post-collisional magmatism in southern Brazil are interpreted as the result mainly of melting of a heterogeneous mantle source, which includes garnet-phlogopite-bearing peridotites, veined-peridotites with abundant hydrated phases, such as amphibole, apatite and phlogopite, and eventually with the addition of an asthenospheric component. The subduction-related metasomatic character of post-collisional magmatism mantle sources in southern Brazil is put in evidence by Nb-negative anomalies and isotope features typical of EM1 sources.

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Section: The Shoshonitic Magmatismmentioning

confidence: 98%

The evolution of Neoproterozoic magmatism in Southernmost Brazil: shoshonitic, high-K tholeiitic and silica-saturated, sodic alkaline volcanism in post-collisional basins

Sommer

Lima

Nardi

et al. 2006

An. Acad. Bras. Ciênc.

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“…basalts to form peralkaline trachyte, followed by fractional crystallisation of the trachyte to form peralkaline rhyolites (Lowenstern and Mahood 1991;Bohrson and Reid 1997;Trua et al 1999;Avanzinelli et al 2004). In the third type of model, the formation of the peralkaline melts is by partial melting of continental crust; basalt does not directly contribute to melt production but may be the heat source promoting the melting (Bailey and Macdonald 1970;Macdonald et al 1987; White et al 2006). Other processes, such as magma mixing and crustal contamination, may be involved in all three types of petrogenesis.…”

Section: Introductionmentioning

confidence: 99%

Peralkaline felsic magmatism at the Nemrut volcano, Turkey: impact of volcanism on the evolution of Lake Van (Anatolia) IV

Macdonald

Sumita

Schmincke

et al. 2015

Contrib Mineral Petrol

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“…Little is known on the behavior of volatiles at pressures and temperatures of the volcanic environment (Burnham 1979;Caroff et al 1997;De Hoogh and Van Bergen 2000;Greenough et al 1999) and, moreover, on the effects that fluids can exert on magmatic melts and on their "differentiation" (meaning in more general terms the diversification of magmas). Some authors have suggested the possible role of volatiles in the evolution particularly of peralkaline acid products (e.g., comendites; Bohrson and Reid 1997;Davies and MacDonald 1987;MacDonald et al 1987;Taylor et al 1981). However, only modest attention has been so far paid to the investigation of "volatile-induced differentiation" in the evolution of Etnean magmas.…”

Section: Introductionmentioning

confidence: 99%

Volatile-induced magma differentiation in the plumbing system of Mt. Etna volcano (Italy): evidence from glass in tephra of the 2001 eruption

2007

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Mount Etna volcano was shaken during the summer 2001 by one of the most singular eruptive episodes of the last centuries. For about 3 weeks, several eruptive fractures developed, emitting lava flows and tephra that significantly modified the landscape of the southern flank of the volcano. This event stimulated the attention of the scientific community especially for the simultaneous emission of petrologically distinct magmas, recognized as coming from different segments of the plumbing system. A stratigraphically controlled sampling of tephra layers was performed at the most active vents of the eruption, in particular at the 2,100 m (CAL) and at the 2,550 m (LAG) scoria cones. Detailed scanning electron microscope and energy dispersive x-ray spectrometer (SEM-EDS) analyses performed on glasses found in tephra and comparison with lava whole rock compositions indicate an anomalous increase in Ti, Fe, P, and particularly of K and Cl in the upper layers of the LAG sequence. Mass balance and thermodynamic calculations have shown that this enrichment cannot be accounted for by "classical" differentiation processes, such as crystal fractionation and magma mixing. The analysis of petrological features of the magmas involved in the event, integrated with the volcanological evolution, has evidenced the role played by volatiles in controlling the magmatic evolution within the crustal portion of the plumbing system. Volatiles, constituted of H 2 O, CO 2 , and Cl-complexes, originated from a deeply seated magma body (DBM). Their upward migration occurred through a fracture network possibly developed by the seismic swarms during the period preceding the event. In the upper portion of the plumbing system, a shallower residing magma body (ABT) had chemical and physical conditions to receive migrating volatiles, which hence dissolved the mobilized elements producing the observed selective enrichment. This volatile-induced differentiation involved exclusively the lowest erupted portion of the ABT magma due to the low velocity of volatiles diffusion within a crystallizing magma body and/or to the short time between volatiles migration and the onset of the eruption. Furthermore, the increased amount of volatiles in this level of the chamber strongly affected the eruptive behavior. In fact, the emission of these products at the LAG vent, towards the end of the eruption, modified the eruptive style from classical strombolian to strongly explosive.

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Geochemistry of High-silica Peralkaline Rhyolites, Naivasha, Kenya Rift Valley

Cited by 158 publications

References 0 publications

The evolution of Neoproterozoic magmatism in Southernmost Brazil: shoshonitic, high-K tholeiitic and silica-saturated, sodic alkaline volcanism in post-collisional basins

The evolution of Neoproterozoic magmatism in Southernmost Brazil: shoshonitic, high-K tholeiitic and silica-saturated, sodic alkaline volcanism in post-collisional basins

Peralkaline felsic magmatism at the Nemrut volcano, Turkey: impact of volcanism on the evolution of Lake Van (Anatolia) IV

Volatile-induced magma differentiation in the plumbing system of Mt. Etna volcano (Italy): evidence from glass in tephra of the 2001 eruption

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