Publication Date:
2017-10-11
Description:
Trace elements and Sr–Nd–Pb isotopes have been analyzed on sedimentary and igneous (metabasalt, metadiorite and metagabbro) samples from the Jurassic oceanic crust beneath Gran Canaria (Canary Islands). The igneous crust exhibits extreme heterogeneity in 87Sr/86Sr (0.7029–0.7052), 206Pb/204Pb (18.2–20.8) and 208Pb/204Pb (38.1–41.3). Leaching experiments indicate that seawater alteration has elevated the 87Sr/86Sr ratio but has not appreciably affected 143Nd/144Nd (0.51295–0.51306). An Sm–Nd isochron gives an age of 178 ± 17 Ma, which agrees with the age predicted from paleomagnetic data. Hydrothermal alteration near the ridge axis has increased 207Pb/204Pb (15.59−15.73), 208Pb/204Pb (as well as Δ7/4Pb and Δ8/4Pb), 238U/204Pb (μ) and Ce/Pb but has not appreciably changed 206Pb/204Pb. The large range in 206Pb/204Pb and 208Pb/204Pb reflects radiogenic ingrowth with μ being as high as 107. Portions of the Jurassic ocean crust have trace element and isotope characteristics within the range found at St Helena, the Atlantic type locality for the HIMU (high μ) mantle end-member. Evaluation of the published isotopic data for Gran Canaria volcanic rocks indicates that the isotopic composition of these melts primarily represents the composition of their mantle sources rather than crustal assimilation.
Type:
Article
,
PeerReviewed
Format:
text
DOI:
10.1093/petroj/39.5.859
