Petrogenesis of Mesozoic giant dike swarms and geodynamical insights about EMI-Gough flavors in the Equatorial Atlantic Magmatic Province

Author(s)

Macedo Filho, Antomat A. ; Hollanda, Maria Helena B. M.

• Document type: Journal article
• Source: LITHOS; v. 412-413, p. 18-pg., 2022-02-01.

Abstract

The Rio Ceara-Mirim magmatism produced Mesozoic giant arcuate dike swarms during the initial stage of the West Gondwana breakup near the Equatorial Atlantic Ocean (NE Brazil), where they assemble tholeiites and subordinate intermediate rocks (SiO2 > 57 wt%). A multidata approach based on petrography, mineral chemistry, whole-rock geochemistry, and Sr-Nd-Pb isotopes enables the discrimination of four geochemical groups (two high-Ti and two low-Ti). High-Ti groups are composed of (1) basalts and basaltic andesites with TiO2 generally higher than 2.0 wt%, MgO > similar to 3 wt% (named the HT group) and rich in incompatible elements and (2) (trachy)andesites and trachytes with lower TiO2 (<2.5 wt%; Mg < 3 wt%) interpreted as fractionated magmas from the HT group, therefore named evolved HT. Both these groups have similar Sr-87/Sr-86(()127) (similar to 0.706) and epsilon Nd-(127) (-2.90 to -2.56) and moderately radiogenic Pb-206/Pb-204((m)) ratios between 18.66 and 18.21. Conversely, low-Ti tholeiites (TiO2 < 2 wt%) are (3) LT1 composed of evolved basaltic andesites, with similar to Ti/Zr < 70, MgO <6 wt%, and Al2O3 > 15 wt%; and (4) LT2 composed of subalkaline (to transitional) basalts and basaltic andesites but similar to Ti/Zr >70, and MgO > 6 wt%. These two low-Ti groups are, respectively, less radiogenic (LT1 epsilon Nd-(127)-4.65 to -4.40) and slightly more radiogenic (LT2 epsilon Nd-(127)-1.44 to -1.08) in Nd relative to the broad HT group. The geochemical groups present different degrees of enrichment in large ion lithophile and light rare-earth elements coupled with depletion in high-field-strength elements (Nb-Ta) combined with isotopic (Sr-Nd-Pb) signatures compatible with enriched mantle sources. We showed that the EMI (Gough-like) isotope compositions of Rio Ceara-Mirim magmatism may be explained by mixing DMM with enriched SCLM-derived melts plus minor crustal assimilation or by the involvement of OIBs derived from mantle plumes of the South Atlantic area mixed with lithospheric sources. In a geodynamical perspective, given the narrow similarity of HT Rio Ceara-Mirim isotope compositions with EMI-Gough type and high-Ti magmas of Transminas swarm, a genetic connection between Equatorial Atlantic and Parana-Etendeka provinces must be considered. (AU)

• FAPESP's process: 17/13130-0 - An integrated geochemical and isotope study to characterize the Equatorial Atlantic Magmatic Province (EQUAMP)
• Grantee: Antomat Avelino de Macêdo Filho
• Support Opportunities: Scholarships in Brazil - Doctorate