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

Journal article
(Original article)

Publication Details

Author(s): Caulfield JT, Turner SP, Dosseto A, Pearson NJ, Beier C
Journal: Earth and Planetary Science Letters
Publisher: Elsevier
Publication year: 2008
Journal issue: 273
Pages range: 279-288
ISSN: 0012-821X
Language: English


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 Authors / FAU Editors

Beier, Christoph PD Dr.
Lehrstuhl für Endogene Geodynamik

External institutions
Macquarie University
University of Wollongong (UOW)

How to cite

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.


Last updated on 2018-03-07 at 00:23