Mélange versus fluid and melt enrichment of subarc mantle: A novel test using barium isotopes in the Tonga-Kermadec arc

Geology ◽  
2020 ◽  
Vol 48 (11) ◽  
pp. 1053-1057 ◽  
Author(s):  
Fei Wu ◽  
Simon Turner ◽  
Bruce F. Schaefer
Keyword(s):  
Pacific Ocean ◽  
Partial Melting ◽  
Oceanic Crust ◽  
Pb Isotope ◽  
Southwest Pacific ◽  
The Past ◽  
Isotope Study ◽  
Subducting Plate ◽  
Model Components

Abstract In the past few years, the so-called mélange model has been offered as an alternative to the long-standing model of enrichment of the subarc mantle by separate additions of fluid and sediment components from the subducting plate. In the mélange model, components from the subducting plate become physically mixed at the slab-mantle interface. Partial melting of the peridotite subsequently occurs after being hybridized by the mélange material that diapirically rises into hotter portions of the wedge. Here, we present the first Ba isotope study of lavas from the Tonga-Kermadec arc (southwest Pacific Ocean) and show that Ba isotopes distinguish between fluid and melt derived from different subducted components. This provides fresh constraints on the debate. Remarkable along-strike Ba isotope variations were observed and are best explained by contributions from variable proportions of sediment and altered oceanic crust (AOC) fluid from the subducting plate. Combined Ba-Sr-Pb isotope relationships indicate that sediment melt and AOC fluid were added to the source of the arc lavas separately at different times. This is inconsistent with the mélange model, at least in this arc.

Glacial/interglacial sea surface temperature changes in the Southwest Pacific ocean over the past 360ka

2009 ◽  
Vol 28 (13-14) ◽  
pp. 1160-1170 ◽  
Author(s):  
Kazuyo Tachikawa ◽  
Laurence Vidal ◽  
Corinne Sonzogni ◽  
Edouard Bard
Keyword(s):  
Pacific Ocean ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Sea Surface ◽  
Temperature Changes ◽  
Southwest Pacific ◽  
The Past

scholarly journals Petrogenesis of a late-stage calc-alkaline granite in a giant S-type batholith: geochronology and Sr–Nd–Pb isotopes from the Nomatsaus granite (Donkerhoek batholith), Namibia

2021 ◽  
Author(s):  
S. Aspiotis ◽  
S. Jung ◽  
F. Hauff ◽  
R. L. Romer
Keyword(s):  
Partial Melting ◽  
Mineral Assemblage ◽  
Central Zone ◽  
Calc Alkaline ◽  
Pb Isotope ◽  
Alkaline Granite ◽  
Ti Oxides ◽  
Eu Anomaly ◽  
Environment Characteristic ◽  
Southern Central

AbstractThe late-tectonic 511.4 ± 0.6 Ma-old Nomatsaus intrusion (Donkerhoek batholith, Damara orogen, Namibia) consists of moderately peraluminous, magnesian, calc-alkalic to calcic granites similar to I-type granites worldwide. Major and trace-element variations and LREE and HREE concentrations in evolved rocks imply that the fractionated mineral assemblage includes biotite, Fe–Ti oxides, zircon, plagioclase and monazite. Increasing K2O abundance with increasing SiO2 suggests accumulation of K-feldspar; compatible with a small positive Eu anomaly in the most evolved rocks. In comparison with experimental data, the Nomatsaus granite was likely generated from meta-igneous sources of possibly dacitic composition that melted under water-undersaturated conditions (X H2O: 0.25–0.50) and at temperatures between 800 and 850 °C, compatible with the zircon and monazite saturation temperatures of 812 and 852 °C, respectively. The Nomatsaus granite has moderately radiogenic initial 87Sr/86Sr ratios (0.7067–0.7082), relatively radiogenic initial εNd values (− 2.9 to − 4.8) and moderately evolved Pb isotope ratios. Although initial Sr and Nd isotopic compositions of the granite do not vary with SiO2 or MgO contents, fSm/Nd and initial εNd values are negatively correlated indicating limited assimilation of crustal components during monazite-dominated fractional crystallization. The preferred petrogenetic model for the generation of the Nomatsaus granite involves a continent–continent collisional setting with stacking of crustal slices that in combination with high radioactive heat production rates heated the thickened crust, leading to the medium-P/high-T environment characteristic of the southern Central Zone of the Damara orogen. Such a setting promoted partial melting of metasedimentary sources during the initial stages of crustal heating, followed by the partial melting of meta-igneous rocks at mid-crustal levels at higher P–T conditions and relatively late in the orogenic evolution.

scholarly journals Partial Melting of Lower Oceanic Crust Gabbro: Constraints From Poikilitic Clinopyroxene Primocrysts

2018 ◽  
Vol 6 ◽  
Author(s):  
Julien Leuthold ◽  
C. Johan Lissenberg ◽  
Brian O'Driscoll ◽  
Ozge Karakas ◽  
Trevor Falloon ◽  
...  
Keyword(s):  
Partial Melting ◽  
Oceanic Crust ◽  
Lower Oceanic Crust

Variability of tropical cyclones over the southwest Pacific Ocean using a high-resolution climate model

2007 ◽  
Vol 97 (1-4) ◽  
pp. 171-180 ◽  
Author(s):  
L. M. Leslie ◽  
D. J. Karoly ◽  
M. Leplastrier ◽  
B. W. Buckley
Keyword(s):  
High Resolution ◽  
Pacific Ocean ◽  
Tropical Cyclones ◽  
Climate Model ◽  
Southwest Pacific

Has Nitrogen Supply to Coral Reefs in the South Pacific Ocean Changed Over the Past 50 Thousand Years?

2019 ◽  
Vol 34 (4) ◽  
pp. 567-579
Author(s):  
Dirk V. Erler ◽  
Benjamin O. Shepherd ◽  
Braddock K. Linsley ◽  
Luke D. Nothdurft ◽  
Quan Hua ◽  
...  
Keyword(s):  
Pacific Ocean ◽  
Coral Reefs ◽  
South Pacific ◽  
Nitrogen Supply ◽  
The South ◽  
The Past ◽  
South Pacific Ocean

scholarly journals New isotope constraints on the Mg oceanic budget point to cryptic modern dolomite formation

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Netta Shalev ◽  
Tomaso R. R. Bontognali ◽  
C. Geoffrey Wheat ◽  
Derek Vance
Keyword(s):  
Low Temperature ◽  
Carbon Cycle ◽  
Oceanic Crust ◽  
Isotope Fractionation ◽  
Hydrothermal Fluids ◽  
Carbonate Precipitation ◽  
Magnesium Isotopes ◽  
Conventional View ◽  
The Past ◽  
Dolomite Formation

AbstractThe oceanic magnesium budget is important to our understanding of Earth’s carbon cycle, because similar processes control both (e.g., weathering, volcanism, and carbonate precipitation). However, dolomite sedimentation and low-temperature hydrothermal circulation remain enigmatic oceanic Mg sinks. In recent years, magnesium isotopes (δ26Mg) have provided new constraints on the Mg cycle, but the lack of data for the low-temperature hydrothermal isotope fractionation has hindered this approach. Here we present new δ26Mg data for low-temperature hydrothermal fluids, demonstrating preferential 26Mg incorporation into the oceanic crust, on average by εsolid-fluid ≈ 1.6‰. These new data, along with the constant seawater δ26Mg over the past ~20 Myr, require a significant dolomitic sink (estimated to be 1.5–2.9 Tmol yr−1; 40–60% of the oceanic Mg outputs). This estimate argues strongly against the conventional view that dolomite formation has been negligible in the Neogene and points to the existence of significant hidden dolomite formation.

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