|
|||||
|
|
Ti-rich Eocene Basaltic Rocks, Abrolhos Platform, Offshore Brazil, 18?S: Petrology with Respect to South Atlantic Magmatism |
|
| Authors: | FODAR R V; MUKASA S B; GOMES C B; CORDANI U G |
| Institution: | 1Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University Raleigh, NC 27695 2Department of Geology, University of Florida Gainesville, FL 32611 3Instituto de Geociencias, Universidade de S?o Paulo S?o Paulo, SP, Brazil |
| Abstract: | Eocene igneous rocks from the Abrolhos Islands and surroundingsedimentary platform, offshore Brazil, 18?S, are largely Ti-richbasalt and diabase (4–6 wt.% TiO2), and cumulate rockssuch as wehrlite. Despite high Ti, incompatible-element abundancesare relatively low (e.g., K2O {small tilde} 1 wt.%; P2O5 0.5%; Zr 225 ppm; Rb 23 ppm; Ba 275 ppm); LREE enrichment yieldsLa/YbN {small tilde}8. Compared to other mafic rocks of theSouth Atlantic region, such as Mesozoic high-Ti dikes ({smalltilde}5 wt.% TiO2) and basalts (3–4 wt.% TiO2) of theSerra Geral (Paran?, southern Brazil) province, and high-Tibasalts ({small tilde}4 wt% TiO2) of some South Atlantic features(Walvis, southwest Indian ridge), Abrolhos basalts differ bylower incompatible-element concentrations and/or by isotopiccompositions that emphasize depleted characteristics ( Sr–12;Nd 3) relative to bulk earth. Abrolhos isotopic compositionsdo, however, match those of some S. Atlantic islands (e.g.,Pb like those of nearby Trindade), and conform generally toDupal anomaly contours. Abrolhos high-Ti basalts can be modeled as liquids from about90% crystallization of parent picritic liquid emplaced nearthe base of the Brazilian crustal margin; no mantle geochemicalanomaly or special metasomatism are needed to account for theTi contents. Isotopic and trace-clement compositions (e.g.,Zr, Nb, Y) of the Abrolhos province suggest parentage in a mantlerepresenting a plume of bulk earth or ‘enriched’composition that interacted with overlying depleted mantle. |
| Keywords: | |
| 本文献已被 Oxford 等数据库收录！ | |