High-Ti basalt from the Abrolhos platform, offshore Brazil 18/sup 0/S: implications for mantle metasomatism and heterogeneity, South Atlantic region

Conference · Tue Jan 01 00:00:00 EST 1985 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:6873913

Fodor, R V; Ragland, J P

Surface and core samples of the Abrolhos islands and platform (30,000 km/sup 2/), offshore Brazil 18/sup 0/S, yields 35-65 Ma mafic flows and hypabyssal and cumulate rocks. (a) Basalt has very high TiO/sub 2/ attended by high FeO* but not proportionate amounts of incompatible elements; extreme Ti is shown by TiO/sub 2/ 5% at FeO*/MgOapprox. 2.5; LREE enrichment, La/sub (n)/ 80-110, La/Yb/sub (n)/approx. 8.5, Zr/Nbapprox. 6, Zr/Y approx. 7 are those of P-type MORB. (b) Cpx is transitional, Fs/sub 14-23/Wo/sub 42-36/, TiO/sub 2/ 1-2%, Al/sub 2/O/sub 3/ 2-5%. (c) Cumulates are clinopyroxenite and wehrlite, with cpx compositions like those of the basalts. The unusually high Ti, several trace elements, and mineral compositions correspond to certain high-TiO/sub 2/ flows and dikes in neighboring Serra Geral CFB province. Age differences and approx. 2 x higher P, Ba, and Sr in Serra Geral point to Abrolhos representing (re-)melting of an enriched CFB source-area similar to that for Serra Geral CFB but differing in metasomatic phases such as ap, amph, and mica. Extensive fractionation of enriched tholeiites with major-element compositions of certain S. Atlantic basin basalts accounts for Abrolhos compositions except for extreme Ti. Cumulates attest to the chamber environment necessary for fractionation, but high Ti must reflect the mantle source. Because Abrolhos rocks have compositional links to both continental and oceanic magmatism that occurred since Gondwanaland rifting, source-regions for each may have been similar throughout South Atlantic history, but with notable anomalies, due in part to localized Fe-Ti metasomatism.

• Research Organization: North Carolina State Univ., Raleigh (USA)
• OSTI ID: 6873913
• Report Number(s): CONF-8510489-
• Journal Information: Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
BASALT
CHEMICAL COMPOSITION
PETROGENESIS
BRAZIL
ATLANTIC OCEAN
CATAGENESIS
GEOLOGIC HISTORY
MAGMATISM
METAMORPHISM
OFFSHORE SITES
TITANIUM COMPOUNDS
DEVELOPING COUNTRIES
IGNEOUS ROCKS
LATIN AMERICA
ROCKS
SEAS
SOUTH AMERICA
SURFACE WATERS
TRANSITION ELEMENT COMPOUNDS
VOLCANIC ROCKS
580400* - Geochemistry- (-1989)