Petrology of continental tholeiitic magmas forming a 350-km-long Mesozoic dyke swarm in NE Brazil: constraints of geochemical and isotopic data

Ngonge, Emmanuel Donald, de Hollanda, Maria Helena Bezerra Maia, Archanjo, Carlos Jose, de Oliveira, Diogenes Custodio, Vasconcelos, Paulo Marcosde Paula and Munoz, Patricio Rodrigo Montecinos (2016) Petrology of continental tholeiitic magmas forming a 350-km-long Mesozoic dyke swarm in NE Brazil: constraints of geochemical and isotopic data. Lithos, 258-259 228-252. doi:10.1016/j.lithos.2016.04.008


Author Ngonge, Emmanuel Donald
de Hollanda, Maria Helena Bezerra Maia
Archanjo, Carlos Jose
de Oliveira, Diogenes Custodio
Vasconcelos, Paulo Marcosde Paula
Munoz, Patricio Rodrigo Montecinos
Title Petrology of continental tholeiitic magmas forming a 350-km-long Mesozoic dyke swarm in NE Brazil: constraints of geochemical and isotopic data
Journal name Lithos   Check publisher's open access policy
ISSN 0024-4937
1872-6143
Publication date 2016-08
Year available 2016
Sub-type Article (original research)
DOI 10.1016/j.lithos.2016.04.008
Open Access Status Not Open Access
Volume 258-259
Start page 228
End page 252
Total pages 25
Place of publication Amsterdam, Netherlands
Publisher Elsevier BV
Collection year 2017
Language eng
Formatted abstract
The Ceará Mirim dyke swarm (northeastern Brazil) is composed of Cretaceous tholeiites with plagioclase, clinopyroxene (±olivine), Fe-Ti oxides and pigeonite in their groundmass. These tholeiites have been subdivided into three groups: high-Ti olivine tholeiites, evolved high-Ti tholeiites (TiO2 ≥ 1.5 wt.%; Ti/Y > 360), and low-Ti tholeiites (TiO2 ≤ 1.5 wt%; Ti/Y ≤ 360), with all exhibiting distinct degrees of enrichment in incompatible elements relative to Primitive Mantle. Negative Pb anomalies are found in all three groups, while Nb-Ta abundances similar to those of OIB-type magmas are found in the olivine tholeiites, with moderate to high depletions being observed, respectively, in the evolved high-Ti and low-Ti tholeiites. The low-Ti tholeiites exhibit some contamination with crustal (felsic) materials during ascent. The initial isotopic compositions of the olivine tholeiites show uniform and unradiogenic 87Sr/86Sr (~0.7035-0.7039) combined with (in part) radiogenic 143Nd/144Nd and 206Pb/204Pb (>19.1) ratios, which together reveal a likely contribution of FOZO (FOcalZOne) component in their genesis. The other tholeiite groups show variable Sr-Nd ratios with relatively consistent 206Pb/204Pb ratios clustering towards an isotopically enriched mantle (EM1) component. Taken in conjunction with the Nb, this enriched signature reflects the involvement of a subduction-modified lithospheric mantle in the source of the evolved high-Ti and low-Ti tholeiites. Thus, we propose that FOZO and EMI components coexisted (including minor mixing with E-MORB magmas) and contributed in varying extents to the generation of the Ceará-Mirim dyke swarm primary melts, which segregated at 75 to 60 km in depth around the garnet-spinel facies transition zone. The mechanism that promoted melting was most likely non-plume related. We suggest that plate-boundary forces linked to the opening of the Atlantic Ocean promoted passive rifting and that the resulting asthenospheric upwelling was responsible for the melting that generated the tholeiitic magmas.
Keyword Ceara-Mirim dyke swarm
Mesozoic continental tholeiitic basalts
Enriched sub-continental lithospheric mantle
FOZO mantle component
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Earth Sciences Publications
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