The origin of the Daly gap by fractional crystallization in a transcrustal plumbing system in the Passa Quatro alkaline complex (SE Brazil)

The surface gap of tephriphonolite compositions in the Passa Quatro alkaline complex, in SE Brazil, is attributed to non-buoyancy of these high viscosity intermediate compositions during magmatic fractional crystallization at different depths. Thermodynamic and Rayleigh models for three alkaline sui...

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Bibliographic Details
Published in:International geology review 2024-06, Vol.66 (11), p.2031-2054
Main Authors: da Silva, Júlio César Lopes, de Castro Valente, Sérgio, Neysi Almeida, Cícera, Medeiros Marins, Gabriel
Format: Article
Language:English
Subjects:
Basalt
Buoyancy
Chambers
Composition
Continental crust
Cretaceous
Crystallization
Depth
Feldspars
Fractional crystallization
Fractional crystallization modelling
Lava
Liquids
Magma
Magma chambers
Mineralogy
Olivine
Palaeogene
Paleogene
Plumbing
Potassium aluminum silicates
Silica
Syenite
thermodynamic model, Rayleigh model
Viscosity
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Summary:The surface gap of tephriphonolite compositions in the Passa Quatro alkaline complex, in SE Brazil, is attributed to non-buoyancy of these high viscosity intermediate compositions during magmatic fractional crystallization at different depths. Thermodynamic and Rayleigh models for three alkaline suites of a strongly silica-undersaturated series were integrated to demonstrate that parental (basanite, nephelinite and alkaline basalt) and residual (phonolites) magmas are cogenetic by fractional crystallization at pressures of 10 kbar and 5 kbar, i.e. at magma chambers located above and below the Conrad discontinuity within the Upper Cretaceous-Palaeogene 40 km-thick continental crust in SE Brazil. The fractional crystallization of the parental magmas produced an ultramafic residual solid (wehrlite, olivine-bearing clinopyroxenite and clinopyroxenite) and residual liquids (evolved basanite and alkaline basalt, and phonotephrite). The latter moved up and built magma chambers at lower depths in the continental crust where those magmas initially crystallized clinopyroxenite extracts and high viscosity residual liquid that was entrapped and prevented to ascent towards the surface. Then, an abrupt change in the extract mineralogy produced a feldspathic-rich extract (leucocratic leucite monzosyenite, mesocratic syenite or leucocratic monzodiorite) and a residual phonolitic liquid with low viscosity. Following the feldspar crystallization, the magma viscosity decreased, acquiring adequate buoyancy that resulted in shallow-crust magma chambers in which phonolite diversification took place. These processes occurred due to the existence of a transcrustal, plumbing architecture where the high viscosity intermediate tephriphonolites were prevented to reach shallower depths, resulting in the Daly gap observed in the Passa Quatro Alkaline Complex.
ISSN:0020-6814
1938-2839
DOI:10.1080/00206814.2023.2269441