Sub‑arc mantle enrichment in the Sunda rear‑arc inferred from HFSE systematics in high‑K lavas from Java
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Springer
Materia
Rear-arc volcanism Superchondritic Nb/Ta Muria Sunda arc
Fecha
2021-12-21Referencia bibliográfica
Kirchenbaur, M... [et al.]. Sub-arc mantle enrichment in the Sunda rear-arc inferred from HFSE systematics in high-K lavas from Java. Contrib Mineral Petrol 177, 8 (2022). [https://doi.org/10.1007/s00410-021-01871-9]
Patrocinador
German Research Foundation (DFG) KI 1802/1-1 German Research Foundation (DFG); European Commission 1406/9; DAAD academic exchange program; ERC STG project O2RIGIN 636808Resumen
Many terrestrial silicate reservoirs display a characteristic depletion in Nb, which has been explained in some studies by the
presence of reservoirs on Earth with superchondritic Nb/Ta. As one classical example, K-rich lavas from the Sunda rear-arc,
Indonesia, have been invoked to tap such a high-Nb/Ta reservoir. To elucidate the petrogenetic processes active beneath the
Java rear-arc and the causes for the superchondritic Nb/Ta in some of these lavas, we studied samples from the somewhat
enigmatic Javanese rear-arc volcano Muria, which allow conclusions regarding the across-arc variations in volcanic output,
source mineralogy and subduction components. We additionally report some data for an along-arc sequence of lavas from
the Indonesian part of the Sunda arc, extending from Krakatoa in the west to the islands of Bali and Lombok in the east.
We present major and trace element concentrations, Sr–Nd–Hf–Pb isotope compositions, and high-field-strength element
(HFSE: Nb, Ta, Zr, Hf, W) concentrations obtained via isotope dilution and MC-ICP-MS analyses. The geochemical data are
complemented by melting models covering different source compositions with slab melts formed at variable P–T conditions.
The radiogenic isotope compositions of the frontal arc lavas in combination with their trace element systematics confirm
previously established regional variations of subduction components along the arc. Melting models show a clear contribution
of a sediment-derived component to the HFSE budget of the frontal arc lavas, particularly affecting Zr–Hf and W. In
contrast, the K-rich rear-arc lavas tap more hybrid and enriched mantle sources. The HFSE budget of the rear-arc lavas is in
particular characterized by superchondritic Nb/Ta (up to 25) that are attributed to deep melting involving overprint by slab
melts formed from an enriched garnet–rutile-bearing eclogitic residue. Sub-arc slab melting was potentially triggered along
a slab tear beneath the Sunda arc, which is the result of the forced subduction of an oceanic basement relief ~ 8 Myr ago as
confirmed by geophysical studies. The purported age of the slab tear coincides with a paucity in arc volcanism, widespread
thrusting of the Javanese basement crust as well as the short-lived nature of the K-rich rear-arc volcanism at that time.