Other
Scientific paper
Dec 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990e%26psl.101..323j&link_type=abstract
Earth and Planetary Science Letters, Volume 101, Issue 2-4, p. 323-331.
Other
37
Scientific paper
Analyses of water in MORB glasses have been performed using mass spectrometry techniques on speciments selected from worldwide localities (Mid Atlantic Ridge, East Pacific Rise, Red Sea, Lau Basin). Specimens belong to both normal and enriched types. Some OIB glasses have also been analyzed. The amounts of water found, comparable to those previously reported, are within the 1700-6000 ppm range. Positive correlations are observed with other trace elements, particularly K2O. Samples may be divided into two groups: (1) N-MORB (La/Sm < 1) with a constant K2O/H2O ratio of0.2 +/- 0.05; (2) enriched glasses (La/Sm > 1) with K2O/H2O varying from 0.4 up to 1. The correlation found for N-MORB may be explained by variable degrees of partial melting (possibly complicated by fractional crystallization), water and potassium behaving as incompatible elements. The worldwide validity of the correlation demonstrates that K2O/H2O is constant in the source even though that source may have been depleted to a variable extent. The enriched samples though cannot be derived from the same source as the N-MORB through simple processes such as partial melting and fractional crystallization.
The respective importance of source composition and degree of partial melting may be assessed using additional data available in the literature. For sources with H2O contents between 70 and 550 ppm a 5-15% partial melting may be proposed. The positive correlation between (La/Sm)n and K2O/H2O requires the existence of (at least) two mantle components that may be variously depleted or enriched. One is the depleted MORB source with low La/Sm and K2O/H2O, while the other displays both high La/Sm and K2O/H2O ratios. The enriched source cannot be a primitive one because addition of an external composition (crust + ocean) with a K2O/H2O of 0.14 to a depleted MORB source (K2O/H2O = 0.25) cannot produce a source with an overall ratio close to 1. If a model of oceanic crust recycling is considered, then the recycled crust must be significantly dehydrated before mixing with the mantle source. This serves to explain why water is more abundant than K2O in the external reservoir, even though its incompatible behaviour is undistinguishable from that of K upon melting. An estimate of bulk earth water abundance is poorly constrained and strongly model dependent, and the proposed 1300 ppm is speculative. A value in the 550-1900 ppm range is however very plausible.
Jambon Albert
Zimmermann Jean Louis
No associations
LandOfFree
Water in oceanic basalts: evidence for dehydration of recycled crust does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Water in oceanic basalts: evidence for dehydration of recycled crust, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Water in oceanic basalts: evidence for dehydration of recycled crust will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1630268