Major Element, Trace Element, and Isotope (Pb, Sr, and Nd) Geochemistry of Site 839 Basalts and Basaltic Andesites: Implications for Arc Volcanism (original) (raw)
Related papers
Journal of Geophysical Research, 2009
1] We report major, trace, and volatile element data on basaltic glasses from the northernmost segment of the Eastern Lau Spreading Center (ELSC1) in the Lau back-arc basin to further test and constrain models of back-arc volcanism. The zero-age samples come from 47 precisely collected stations from an 85 km length spreading center. The chemical data covary similarly to other back-arc systems but with tighter correlations and welldeveloped spatial systematics. We confirm a correlation between volatile content and apparent extent of melting of the mantle source but also show that the data cannot be reproduced by the model of isobaric addition of water that has been broadly applied to back-arc basins.
Journal of Petrology, 1998
Basin, whereas the subduction signature and volatile (CO 2 and F) of Niua fo'ou in the back-arc Lau Basin, and Pacific Ocean contents increase eastwards towards the modern arc. These obsediments from DSDP Sites 204 and 275, and ODP Site 596, servations suggest that depletion is due to melt extraction during are integrated with existing geochemical data for lavas from the Lau back-arc extension and volcanism, together with a long 'residence Basin, Samoa, the Louisville Ridge Seamount Chain (LR-SMC) time' of mantle material within the mantle wedge. The upper mantle and the extinct Lau Ridge arc, giving new insights into the beneath the northernmost end of the Tonga arc and Lau Basin petrogenesis of lavas in an active arc-back-arc system. Geochemical contains an ocean-island basalt (OIB) component derived from the variations in Tonga-Kermadec arc lavas are the result of (1) Samoa plume to the north. This is reflected in high concentrations differences in the amount and composition of the material being of Nb relative to other HFSE in lavas from Niua fo'ou, and Tafahi subducted along the arc, and (2) pre-existing heterogeneities in the and Niuatoputapu islands at the northern end of the Tonga arc. upper mantle. Differences in the material being subducted beneath Pb isotopes also suggest an LR-SMC contribution into Tafahi and the arc have an important influence on the chemistry of the arc Niuataputapu. Trace element and isotope modelling is used to lavas. At the Kermadec Trench,~1 km thick layer of sediment is investigate the combined effects of varying mantle source depletion being subducted beneath the arc, compared with~200 m at the and subduction on the geochemistry of the arc lavas. The results Tonga Trench. This results in the high Th/U and more radiogenic suggest that the arc lava geochemistry can be explained largely by Pb isotope compositions of Kermadec lavas compared with Tonga the balance between a relatively constant subduction input of Pb, lavas. The latter have Pb isotope compositions intermediate between Th, U, Cs, Ba, Sr, Rb, K and Sc [corresponding to 0•001-0•005 those of Pacific sediments and Pacific mid-ocean ridge basalt weight fraction of the Stolper & Newman (1994, Earth (MORB), suggesting that much of the Pb in these lavas is derived and Planetary Science Letters, 121, 293-325] 'H 2 O-rich from subducting Pacific Ocean crust. This is supported by the Pb component' composition), into the overlying, but variably depleted isotope signatures of the subducting LR-SMC, which are also mantle wedge. observed in lavas from the northern Tongan islands of Tafahi and Niuatoputapu. High field strength element (HFSE) and heavy rare earth element (HREE) concentrations are generally lower in Tongan lavas (particularly those from northern Tongan islands) than in Kermadec lavas. The Tonga Ridge basement, the proto-Tonga arc lavas (ODP Site 839) and the older Lau Ridge arc lavas are KEY WORDS: Tonga-Kermadec arc lavas; trace elements; isotopes; petrogenesis; mantle plumes generally less depleted than the modern arc lavas. In the back-arc
Journal of Volcanology and Geothermal Research, 1987
Jenner, G.A., Cawood, P.A., Rautenschlein, M. and White, W.M., 1987. Composition of back-arc basin volcanics, Valu Fa Ridge, Lau Basin: evidence for a slab-derived component in their mantle source.
The remnant rear-arc segment of the early Izu-Bonin arc, known as the Kyushu-Palau Ridge (KPR), is a key location where magmatic outputs can be constrained during the lifetime of an island arc. We present new geochemical data for coarse-grained basaltic to andesitic volcaniclastic sandstones derived from the KPR and deposited in the Amami Sankaku Basin (IODP Site U1438, Unit III rocks) in the time period 40-30 Ma. Bulk disaggregated and cleaned volcaniclastic sand-stones of Unit III at Site U1438 retain primary magmatic signatures and can be used to infer the evolution of magmatic sources of the juvenile Izu-Bonin island arc through time. A sharp increase of slab-derived components to the source of KPR magmatism developed at about 35 Ma, indicated by increasing Th/La and decreasing Sm/La, Yb/Hf and Nb/Nd. Systematic variations in trace element ratios and increasing trace element abundances in younger samples through the 40-30 Ma time window are decoupled from Hf-Nd isotope ratios, which are measurably more depleted (e Hf = 16.5-15, e Nd = 9.6-8.2) than boninites produced during the preceding magmatic phase and sampled in the modern Izu-Bonin forearc. Hafnium isotopic compositions in the Unit III sandstones remain little-changed and similar to the subducting Pacific Plate after 40 Ma and do not revert to highly radiogenic compositions of the Indian-type MORB mantle wedge which is reflected in highly-depleted basalts produced at Site U1438 and in the forearc (commonly e Hf ! 18.0). The overall pattern recorded in Unit III sandstones indicates that the Pacific-type MORB slab-melt component, which was present in the preceding boninite phase of magmatism, persisted after 40 Ma, while the subducted sediment component in the boninite source was lost or significantly reduced. Variations in trace element ratios (at constant e Nd and near-constant and radiogenic e Hf) and in high field strength element abundances of the early Izu Bonin arc are controlled by the addition of a subducted Pacific MORB melt or super-critical fluid to the mantle wedge. A subducted MORB (slab melt) component is thus sampled throughout the early life of the Izu-Bonin arc and in the currently active Izu-Bonin arc-backarc system.
Mineralogy and Petrology, 1992
Fresh back-arc basin lavas were recovered during five dives of the submersible 'Mir' during the 1990 cruise of the research vessel 'Akademik Mstislav Keldysh' to the Lau Basin. Three dives were conducted on the central spreading center of the 'King's Triple Junction' (KTJ) in the northeastern part of the Lau Basin east of Niuafo'ou Island at approximately 15°S. The lavas from the KTJ can be divided into types I and II based on their similarities to N-MORB and the BABB magma type of Sinton and Fryer (1987) respectively. One dive each was made on the Central Lau Spreading Center (CLSC) at 18°S and the Eastern Lau Spreading Center (ELSC) at 19°S. Lavas sampled on the CLSC werc associated with active hydrothermal sulphide chimneys occurring at the base of a collapsed caldera structure on the central volcanic axial high. Sampled lavas from both the CLSC and ELSC are all of type I geochemistry.
Evolution of the basalts from three back-arc basins of southwest Pacific
Geo-marine Letters, 1999
Petrography, petrochemistry, and mineral chemistry of basalts from the Woodlark, Manus, and Lau basins from the southwest Pacific, have been studied to understand their magmatic evolution. Basalt from the western Woodlark Basin (Dobu Seamount) indicates mixing of a near-primitive magma with fractionated basaltic melt in shallow magma chambers. Basalts from Manus Basin and Central Lau Spreading Center (Lau Basin) are typical N-MORBs, and they exhibit olivine fractionation under high oxidizing conditions while basalts from Mangatolu Triple Junction (Lau Basin) are enriched in Al2O3, K2O, and Zr indicative of a contribution from a subducting plate.
Geochimica et Cosmochimica Acta
The remnant rear-arc segment of the early Izu-Bonin arc, known as the Kyushu-Palau Ridge (KPR), is a key location where magmatic outputs can be constrained during the lifetime of an island arc. We present new geochemical data for coarse-grained basaltic to andesitic volcaniclastic sandstones derived from the KPR and deposited in the Amami Sankaku Basin (IODP Site U1438, Unit III rocks) in the time period 40-30 Ma. Bulk disaggregated and cleaned volcaniclastic sandstones of Unit III at Site U1438 retain primary magmatic signatures and can be used to infer the evolution of magmatic sources of the juvenile Izu-Bonin island arc through time. A sharp increase of slab-derived components to the source of KPR magmatism developed at about 35 Ma, indicated by increasing Th/La and decreasing Sm/La, Yb/Hf and Nb/Nd. Systematic variations in trace element ratios and increasing trace element abundances in younger samples through the 40-30 Ma time window are decoupled from Hf-Nd isotope ratios, which are measurably more depleted (e Hf = 16.5-15, e Nd = 9.6-8.2) than boninites produced during the preceding magmatic phase and sampled in the modern Izu-Bonin forearc. Hafnium isotopic compositions in the Unit III sandstones remain little-changed and similar to the subducting Pacific Plate after 40 Ma and do not revert to highly radiogenic compositions of the Indian-type MORB mantle wedge which is reflected in highlydepleted basalts produced at Site U1438 and in the forearc (commonly e Hf ! 18.0). The overall pattern recorded in Unit III sandstones indicates that the Pacific-type MORB slab-melt component, which was present in the preceding boninite phase of magmatism, persisted after 40 Ma, while the subducted sediment component in the boninite source was lost or significantly reduced. Variations in trace element ratios (at constant e Nd and near-constant and radiogenic e Hf) and in high field strength element abundances of the early Izu Bonin arc are controlled by the addition of a subducted Pacific MORB melt or supercritical fluid to the mantle wedge. A subducted MORB (slab melt) component is thus sampled throughout the early life of the Izu-Bonin arc and in the currently active Izu-Bonin arc-backarc system.