Petrogenesis of the Sukadana Basalt based on petrology and whole rock geochemistry, Lampung, Indonesia: Geodynamic significances

The petrogenesis of Sukadana Basalt remains an enigma till present. Major and trace element data are analyzed from Sukadana Basalt lava, located at East Lampung, Sumatra, to study the processes involved in the petrogenesis of the erupted magmas and the origin of mantle source compositions. The Sukadana Basalt display SiO2 (48.1-52.5 wt%), MgO (5.3-9.3 wt%), TiO2 (1.3-2.6 wt%), P2O5 (0.2-0.6 wt%), and Fe2O3T (8.9-11.3 wt%) contents. The Sukadana Basalt enriched in light rare earth elements with weak negative Eu anomalies (Eu/Eu* = 0.8-1) and show Ocean Island Basalt (OIB)-like characteristics. There are two different petrogenesis groups, namely group A and group B. Group A samples show enrichment of Hf, Pb, K, and Sr and depletion of Nb. Group B samples show enrichment of K, Sr, and depletion of Pb. These differences are closely related to the mechanism of slab roll-back and normal fault activity. This study shows that Sukadana Basalt has Nb = 7.4-29.8 ppm, Nb/U = 18-060.3, and Nb/La = 0.8-1.6. These characteristics were similar to those found in typical Nb-enriched basalts. Geochemical analyses suggest that the Sukadana Basalt have experienced minimal crustal contamination and Olivine plagioclase, clinopyroxene, and magnetite fractional crystallization. The chemical features, together with high incompatible-element ratios, are consistent with low degrees of partial melting of a dominantly a partial melting of garnet-peridotite mantle source. The trace-element patterns suggest a mantle source influenced by an enriched component. The occurrence of OIB-like basalt suggests significant upwelling of the asthenosphere in response to slab roll-back. These processes occured in the above of a Paleo Indo-Australia subducting N-S beneath the southern part of Sumatra.