The antecryst compositional influence on Cretaceous alkaline lamprophyre dykes, SE Brazil

Author(s)

Menezes, Saulo Gobbo ^[1] ; Azzone, Rogerio Guitarrari ^[1] ; Enrich Rojas, Gaston Eduardo ^[1] ; Ruberti, Excelso ^[1] ; Cagliarani, Renata ^[1] ; Gomes, Celso de Barros ^[1] ; Chmyz, Luanna ^[2]

Affiliation

^[1] Univ Sao Paulo, Geosci Inst, Sao Paulo, SP - Brazil

^[2] Univ Fed Parana UFPR, Postgrad Program Geol, Curitiba, PR - Brazil

• Document type: Journal article
• Source: BRAZILIAN JOURNAL OF GEOLOGY; v. 45, n. 1, p. 79-93, MAR 2015.
• Web of Science Citations: 7

Abstract

The question of whether the antecryst assemblage affects the bulk composition of lamprophyre dykes, and could be responsible for the compositional zonation between their centers and borders is addressed through a detailed study involving four monchiquite and camptonite dykes (basanites and tephrites) representative of the Arco de Ponta Grossa and Serra do Mar alkaline provinces. In them, antecrysts are interpreted as early-crystallized minerals that are no longer in equilibrium with their hostliq-uid, albeit still linked to the same magmatic system. They represent recycled crystals of earlier stages of the magmatic system at depth. The antecryst microtextures, such as zoned clinopyroxene megacrysts (augite cores and titanaugite rims) with partly corroded cores, olivine crystals with corroded rims surrounded by biotite coronas, chrome-spinel inclusions in clinopyroxene and olivine megacryst cores, and titanomagnetite crystals surrounded by biotite coronas, suggest chemical re-equilibrium with the matrix. The greatest antecryst cargo in these dykes is found in their centers. After subtracting the antecryst volume from the center analyses of each body, the calculated compositions are very similar to the border analyses. The mafic antecryst cargo of each occurrence proportionally leads to enrichment of MgO, FeO, TiO2, CaO, compatible trace elements (Cr, Ni and Co), and depletion of SiO2, K2O, Na2O, Al2O3 and incompatible trace elements (Ba, Sr and REE). The whole-rock geochemical analyses of each dyke represent the combination of accumulated crystals and melt. The compositional zonation of the studied dykes is associated with the antecryst cargo rather than different magmatic pulses. (AU)

• FAPESP's process: 12/06082-6 - The Paraná-Etendeka magmatic province in Brazil: temporal and petrologic relationships between the tholeiitic and alkaline magmatism and geodynamic implications
• Grantee: Excelso Ruberti
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 10/20425-8 - Petrology of Meso-Cenozoic alkaline mafic magmatism of the southeastern part of the Brazilian Platform (SP): lamprophyre dikes and cumulitic stocks
• Grantee: Rogério Guitarrari Azzone
• Support Opportunities: Regular Research Grants
• FAPESP's process: 13/18073-4 - Alkaline magmatism of the Brazilian Platform: petrology and geochemistry
• Grantee: Celso de Barros Gomes
• Support Opportunities: Regular Research Grants