Cenomanian Basalts on the Brazilian Equatorial Margin: Insights into Trigger Mechanisms of OIB-like Volcanism in Continental Environments

Antomat A. Macêdo Filho¹, Alisson L. Oliveira¹, Marthe Klöcking², Valdecir A. Janasi¹, Carlos J. Archanjo¹, Lucas M. Lino¹

• Affiliations:  ¹Universidade de São Paulo, Brazil; ²University of Münster, Germany 

• Presentation type: Poster

• Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

• Poster Board Number: 11

• Programme No: 3.7.18

• Theme 3 > Session 7

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Abstract

Olivine basalts from the Serra do Cuó magmatism in the onshore Potiguar basin exhibit SiO₂ = 46-53 wt.%, MgO = 9-12 wt.%, and total alkalis = 3.5-6 wt.%, combined to elevated concentrations of large ion lithophile elements (Rb, Ba, Th, U, K), positive anomalies of Nb and Ta, and fractionated heavy rare earth elements. These lavas constitute a single volcanic event with evidence of fractional crystallization primarily involving olivine and pyroxene. Whole rock ⁴⁰Ar/³⁹Ar geochronology provided a minimum crystallization age of 99 ± 1 Ma, which is chronologically compatible with other Albian/Cenomanian igneous activity in NE Brazil. Clinopyroxene geothermobarometry indicates a range of crystallization depths from 23 km to 6 km, supporting crystal growth in a magma plumbing system before the emplacement. Radiogenic isotopes reveal enriched mantle-type, akin to Paleogene/Neogene alkali basalts elsewhere in NE Borborema Province. Rare earth element inverse modeling hints that Serra do Cuó melts originated at a mantle potential temperature of 1350°C, approximately 60 km depth. The long-lived alkali basaltic volcanism across the NE Borborema Province likely resulted from decompression melting of the mantle due to a combination of geodynamic factors, including episodes of hotspot influence and changes in South America's drift pattern.