Compositions of dikes and lavas from the Pito Deep Rift: Implications for crustal accretion at superfast spreading centers

• Published in: Journal of Geophysical Research. B. Solid Earth 2009-03, Vol.114 (B3), p.n/a
• Main Authors: Pollock, Meagen A., Klein, Emily M., Karson, Jeffrey A., Coleman, Drew S.
• Format: Article
• Language: English
• Subjects: dikes and lavas; Earth sciences; Earth, ocean, space; Exact sciences and technology; Marine; MORB geochemistry; tectonic window
• ISSN: 0148-0227; 2156-2202
• DOI: 10.1029/2007JB005436

The northwest trending walls of the Pito Deep Rift (PDR), a tectonic window in the southeast Pacific, expose in situ oceanic crust generated ∼3 Ma at the superfast spreading southern East Pacific Rise (SEPR). Whole rock analyses were performed on over 200 samples of dikes and lavas recovered from two ∼8 km2 study areas. Most of the PDR samples are incompatible‐element‐depleted normal mid‐ocean ridge basalts (NMORB; (La/Sm)N < 1.0) that show typical tholeiitic fractionation trends. Correlated variations in Pb isotope ratios, rare earth element patterns, and ratios of incompatible elements (e.g., (Ce/Yb)N) are best explained by mixing curves between two enriched and one depleted mantle sources. Pb isotope compositions of most PDR NMORB are offset from SEPR data toward higher values of 207Pb/204Pb, suggesting that an enriched component of the mantle was present in this region in the past ∼3 Ma but is not evident today. Overall, the PDR crust is highly variable in composition over long and short spatial scales, demonstrating that chemically distinct lavas and dikes can be emplaced within the same segment over short timescales. However, the limited spatial distribution of high 206Pb/204Pb samples and the occurrence of relatively homogeneous MgO compositions (ranging