Magma Genesis and Mantle Heterogeneity in the Manus Back-Arc Basin, Papua New Guinea (original) (raw)
Related papers
Proceedings of the Ocean Drilling Program, 135 Scientific Results, 1994
New major, trace element, and isotope data (Pb, Sr, and Nd) reveal an impressive compositional variation in the basalts recovered from Site 834. Major element compositions span almost the entire range observed in basalts from the modern axial systems of the Lau Basin, and variations are consistent with low-pressure fractionation of a mid-ocean-ridge-basalt (MORB)-like parent, in which Plagioclase crystallization has been somewhat suppressed. Trace element compositions deviate from MORB in all but one unit (Unit 7) and show enrichments in large-ion-lithophile elements (LILEs) relative to high-field-strength elements (HFSEs) more typically associated with island-arc magmas. The Pb-isotope ratios define linear trends that extend from the field of Pacific MORB to highly radiogenic values similar to those observed in rocks from the northernmost islands of the Tofua Arc. The Sr-isotope compositions also show significant variation, and these too project from radiogenic values back into the field for Pacific MORB. The variations in key trace element and isotopic features are consistent with magma mixing between two relatively mafic melts: one represented by Pacific MORB, and the other by a magma similar to those erupted on 'Eua when it was part of the original Tongan arc, or perhaps members of the Lau Volcanic Group (LVG). Based on our model, the most radiogenic compositions (Units 2 and 8) represent approximately 50:50 mixtures of these MORB and arc end-members. Magma mixing requires that both components are simultaneously available, and implies that melts have not shown a compositional progression from arc-like to MORB-like with extension at this locality. Rather, it is apparent that essentially pristine MORB can erupt as one of the earliest products of backarc initiation. Indeed, repetition of isotopic and trace element signatures with depth suggests that eruptions have been triggered by periodic injections of fresh MORB melts into the source regions of these magmas. The slow and almost amagmatic extension of the original arc complex envisaged to explain the observed chemistry is also consistent with the horst-and-graben topography of the western side of the Lau Basin. Given the similarities between basalts erupted at the modern Lau Basin spreading centers and MORB from the Indian Ocean, the overwhelming evidence for involvement of mantle similar to Pacific MORB in the petrogenesis of basalts from Site 834 is a new and important observation. It indicates that the original arc was underlain by asthenospheric material derived from the Pacific mantle convection cell, and that this has somehow been replaced by Indian Ocean MORB during the last-5.5 Ma.
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.
Chemical characteristics of island-arc basalts: Implications for mantle sources
Chemical Geology, 1980
Perfit, M.R., Gust, D.A., Bence, A.E., Arculus, R.J. and Taylor, S.R., 1980. Chemical characteristics of island-arc basalts: implications for mantle sources. In: R.W. Le Maitre and A. Cundari (Guest-Editors), Chemical Characterization of Tectonic Provinces. Chem. Geol., 30: 227--256.
Contributions To Mineralogy and Petrology, 2008
The Tabar–Lihir–Tanga–Feni (TLTF) islands of Papua New Guinea mainly comprise high-K calc-alkaline and silica undersaturated alkaline rocks that have geochemical features typical for subduction-related magmatism. Numerous sedimentary, mafic, and ultramafic xenoliths recovered from Tubaf seamount, located on the flank of Lihir Island, provide a unique opportunity to study the elemental and isotopic composition of the crust and mantle wedge beneath the arc and to evaluate their relationships to the arc magmatism in the region. The sedimentary and mafic xenoliths show that the crust under the islands is composed of sedimentary sequences and oceanic crust with Pacific affinity. A majority of the ultramafic xenoliths contain features indicating wide spread metasomatism in the mantle wedge under the TLTF arc. Leaching experiments reveal that the metasomatized ultramafic xenoliths contain discrete labile phases that can account for up to 50% or more of elements such as Cu, Zn, Rb, U, Pb, and light REE (rare-earth elements), most likely introduced in the xenoliths via hydrous fluids released from a subducted slab. The leaching experiments demonstrated that the light REE enrichment pattern can be more or less removed from the metasomatized xenoliths and the residual phases exhibit REE patterns that range from flat to light REE depleted. Sr–Nd isotopic data for the ultramafic residues show a coupled behavior of increasing 87Sr/86Sr with decreasing 143Nd/144Nd ratios. The labile phases in the ultramafic xenoliths, represented by the leachates, show decoupling between Sr and Nd with distinctly more radiogenic 87Sr/86Sr than the residues. Both leachates and residues exhibit very wide range in their Pb isotopic compositions, indicating the involvement of three components in the mantle wedge under the TLTF islands. Two of the components can be identified as Pacific Oceanic mantle and Pacific sediments. Some of the ultramafic samples and clinopyroxene separates, however, exhibit relatively low 206Pb/204Pb at elevated 207Pb/204Pb suggesting that the third component is either Indian Ocean-type mantle or Australian subcontinental lithospheric mantle. Geochemical data from the ultramafic xenoliths indicate that although the mantle wedge in the area was extensively metasomatized, it did not significantly contribute to the isotopic and incompatible trace element compositions of TLTF lavas. Compared to the mantle samples, the TLTF lavas have very restricted Pb isotopic compositions that lie within the Pacific MORB range, indicating that magma compositions were dominated by melts released from a stalled subducted slab with Pacific MORB affinity. Interaction of slab melts with depleted peridotitic component in the mantle wedge, followed by crystal fractionation most likely generated the geochemical characteristics of the lavas in the area.
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 Petrology, 1998
a wide range in chemical compositions. The source of the lavas The New Britain region of Papua New Guinea represents shares isotopic characteristics with Indian Ocean type mid-ocean an outstanding opportunity to reach an understanding ridge basalt (MORB). In contrast, the high field strength elements of the processes of magma genesis in an oceanic island (HFSE) are extremely depleted in the volcanic front rocks compared arc. The Quaternary volcanoes found there define the with MORB. We propose that this results from a previous melteastern part of the Bismarck volcanic arc, and have extraction event-hypotheses invoking residual phases in either the formed in response to northward subduction of the small mantle wedge or subducting slab cannot account for the depletion Solomon plate beneath the Bismarck plate ( . The relative to MORB. In addition, elements other than the HFSE are New Britain arc is outstanding for two main reasons: also affected. Chemical signatures in parts of the New Britain arc
Chemical Geology, 1980
Nicholls, I.A., Whitford, D.J., Harris, K.L. and Taylor, S.R., 1980. Variation in the geochemistry of mantle sources for tholeiitic and ealc-alkaline mafic magmas, Western Sunda volcanic arc, Indonesia. In: R.W. Le Maitre and A. Cundari (Guest-Editors), Chemical Characterization of Tectonic Provinces. Chem. Geol., 30: 177--199.
An assessment of the mantle and slab components in the magmas of 1 an oceanic arc volcano
2009
Raoul Volcano occupies a simple oceanic subduction setting in the northern part of the Kermadec Arc on the Pacific-Australian convergent plate boundary. The primary inputs to the magmatic system that feeds the volcano are a subduction component derived from the subducting old Pacific oceanic lithosphere and its veneer of pelagic sediment, and the overlying peridotitic mantle wedge. Conservative trace elements that are very incompatible during mantle melting are relatively depleted in Raoul lavas indicating a source that has been depleted during an earlier melting event. Major element co-variations indicate magma genesis by 25% near fractional melting of a mantle source that is weakly depleted (2% melt extraction) relative to a fertile MORB source. An important influence on the composition of the mantle component is progressive melt extraction coupled with minimal advection of fresh material into the sub-arc zone followed by melt extraction from a melting column beneath the spreading centre of an adjacent back arc basin. High field strength element and rare earth element systematics indicate involvement of a subduction-related component of constant composition. Two fluid components can be distinguished, one enriched in large ion lithophile elements inferred to be an aqueous fluid that is continuously added to the ascending melt column and the other a less mobile fluid that transfers Th. A homogeneous subduction-related component of constant composition and magnitude * Manuscript Click here to view linked References arises if the slab-derived flux migrates from the slab-mantle interface to the sub-arc melting column by repeated episodes of amphibole formation and decomposition its composition is then governed by the distribution coefficients of pyroxene and its magnitude by the degree of amphibole saturation of mantle peridotite. The results from Raoul Volcano are comparable to those from other oceanic subduction-related arcs such as South Sandwich and Marianas suggesting that this is a general model for oceanic arcs.
Proceedings of the Ocean Drilling Program, 1994
A suite of volcanic and volcaniclastic rocks selected from Ocean Drilling Program Leg 134 Sites 832 and 833 in the North Aoba Basin (Central New Hebrides Island Arc) has been analyzed for Sr, Nd, and Pb isotopes to investigate the temporal evolution of the arc magmatism. This arc shows two unusual features with respect to other western Pacific arcs: 1) subduction is eastdirected; and 2) a major submarine ridge, the d'Entrecasteaux Zone, has been colliding almost perpendicularly with the central part of the arc since about 3 Ma. Volcanic rocks from the upper parts of both holes, generated during the last 2 m.y., show higher δ7 Sr/ 86 Sr and significantly lower 206 Pb/ 204 Pb and 143 Nd/ Nd values compared to those volcanics erupted before the collision of this ridge, as represented by samples from the lower section of both holes, or remote from the collisional region, in the southern part of the arc. These isotopic differences in the respective mantle sources cannot be interpreted in terms of geochemical input into the mantle wedge induced by the collision itself. Rather, they require long term (>500 m.y.) enrichment processes. The enriched mantle source could be, on a regional scale, a DUPAL-type reservoir with strong similarities to the source of Indian Ocean basalts. Isotopic analyses of drilled rocks from the DEZ show that the anomalous, enriched mantle component is not derived from this feature. We currently cannot identify a source for this enriched component, but note that it also exists in Lau Basin backarc volcanics, lavas from the West Philippine Sea, and also some lavas from the Mariana-Izu-Bonin arc.