Source depletion and extent of melting in the Tongan sub-arc mantle.

Beitrag in einer Fachzeitschrift

Details zur Publikation

Autorinnen und Autoren: Caulfield JT, Turner SP, Dosseto A, Pearson NJ, Beier C
Zeitschrift: Earth and Planetary Science Letters
Verlag: Elsevier
Jahr der Veröffentlichung: 2008
Heftnummer: 273
Seitenbereich: 279-288
ISSN: 0012-821X
Sprache: Englisch


The fluid immobile High Field Strength Elements (HFSE) Nb and Ta can be used to distinguish between the effects of variable extents of melting and prior source depletion of the Tongan sub-arc mantle. Melting of spinel lherzolite beneath the Lau Basin back-arc spreading centres has the ability to fractionate Nb from Ta due to the greater compatibility of the latter in clinopyroxene. The identified spatial variation in plate velocities and separation of melt extraction zones, combined with extremely depleted lavas make Tonga an ideal setting in which to test models for arc melt generation and the role of back-arc magmatism. We present new data acquired by laser ablation-ICPMS of fused sample glasses produced without the use of a melt fluxing agent. The results show an arc trend towards strongly sub-chondritic Nb/Ta (< 17) with values as low as 7.2. Melting models show that large degree melts of depleted MORB mantle fail to reproduce the observed Nb/Ta. Alternatively, incorporation of residual back-arc mantle that has undergone less than 1% melting into the sub-arc melting regime reproduces arc values. However, the extent of partial melting required to produce the composition of the Lau Basin back-arc basalts averages 7%. This apparent discrepancy can be explained if only the lowermost 4 km of the residua from the mantle melt column beneath the back-arc is added to the source of arc magmas. We have identified that the degree of arc/back-arc coupling displayed in the rock record provides an index of the depth of hydrous melting beneath the arc. In this case, this would imply a depth of ~ 75 km for generation of arc magmas, indicating that hydrous melting in the mantle wedge is triggered by the breakdown of hydrous phases in the subducting slab. 

FAU-Autorinnen und Autoren / FAU-Herausgeberinnen und Herausgeber

Beier, Christoph PD Dr.
Lehrstuhl für Endogene Geodynamik

Einrichtungen weiterer Autorinnen und Autoren

Macquarie University
University of Wollongong (UOW)


Caulfield, J.T., Turner, S.P., Dosseto, A., Pearson, N.J., & Beier, C. (2008). Source depletion and extent of melting in the Tongan sub-arc mantle. Earth and Planetary Science Letters, 273, 279-288.

Caulfield, John T., et al. "Source depletion and extent of melting in the Tongan sub-arc mantle." Earth and Planetary Science Letters 273 (2008): 279-288.


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