Danyushevsky, LV and Falloon, TJ and Sobolev, AV and Crawford, AJ and Carroll, M and Price, RC, The H2O content of basalt glasses from Southwest Pacific back-arc basins, Earth and Planetary Science Letters, 117, (3-4) pp. 347-362. ISSN 0012-821X (1993) [Refereed Article]
Copyright 1993 Elsevier
The H2O content of 35 glasses from Southwest Pacific back-arc basins (Lau, North Fiji, Woodlark and Manus) have been determined by infrared spectroscopy. On a plot of K2O vs. H2O the glass data define two distinct trends characterized by different slopes. Trend I, with a slope (K2O/H2O) of 0.25, can be explained by addition of a subduction-related component with K2O/H2O = 0.25 to a depleted mid-ocean ridge basalt mantle source (N- or D-MORB-like). Trend II, which coincides with the N- to E-MORB compositional spectrum, can be produced by addition of a non-subduction component, possibly an alkaline magma with K2O/H2O∼ 1.5, to the same depleted mantle source. The K2O/TiO2 and K/Nb values of E-MORB and back-arc basin basalts (BABB) of Trend II suggest that the enriched component involved in their genesis is not derived from a typical ocean island basalt (OIB, e.g. Hawaiian) mantle source. Our data show that the entire spectrum of BABB compositions can be explained by different degrees of mixing of a mantle source of either D-, N- or E-MORB composition with the subduction-related component, characterized by a K2O/H2O value of 0.25.
Different BABB types correlate with tectonic setting. Samples from the Trend II are associated with relatively stable spreading ridges, whereas those affected by the subduction-related component are always associated with more complex tectonic settings, or come from young or incipient back-arc basins. Pronounced E-MORB affinities of mantle sources are demonstrated only for samples from the Lau, North Fiji and Scotia Sea basins.
The most H2O enriched BABB of Trend I partly overlap in terms of H2O and K2O content and H2O/TiO2 and K2O/TiO2 values with island arc tholeiites. This suggests involvement of similar subduction-related components in the genesis of these two magma types. Because a larger database is now available, the K2O/H2O vs. TiO2 tectonic discriminan diagram of Muenow et al.  appears to be less useful than when originally proposed.
The very low K2O/H2O value ( < 0.05) of the H2O-bearing phase involved in boninite genesis implies that it maybe a fluid derived from the subducted slab. The significantly higher K2O/H2O value (0.25) of the subduction-related component involved in petrogenesis of BABB and some arc tholeiites indicates that it was a melt, rather than a fluid. This K2O/H2>O value (0.25) is also of some interest, as the same value occurs in depleted MORB.
|Item Type:||Refereed Article|
|Keywords:||MORB, BABB, SW Pacific, H2O content natural glasses, subduction, Lau Basin, back arc basins|
|Research Division:||Earth Sciences|
|Research Field:||Igneous and metamorphic petrology|
|Objective Division:||Expanding Knowledge|
|Objective Group:||Expanding knowledge|
|Objective Field:||Expanding knowledge in the earth sciences|
|UTAS Author:||Danyushevsky, LV (Professor Leonid Danyushevsky)|
|UTAS Author:||Falloon, TJ (Dr Trevor Falloon)|
|UTAS Author:||Crawford, AJ (Professor Anthony Crawford)|
|Web of Science® Times Cited:||134|
|Deposited By:||Earth Sciences|
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