scholarly journals Boron isotope evidence for devolatilized and rehydrated recycled materials in the Icelandic mantle source

2021 ◽  
Author(s):  
Edward Marshall ◽  
Eemu Ranta ◽  
Sæmundur Halldórsson ◽  
Alberto Caracciolo ◽  
Eniko Bali ◽  
...  
Keyword(s):  
Oceanic Crust ◽  
Mantle Source ◽  
Melt Inclusions ◽  
Melt Inclusion ◽  
Isotope Ratios ◽  
Boron Isotope ◽  
Source Control ◽  
Mantle Heterogeneity ◽  
Recycled Materials ◽  
Mantle Heterogeneities

Enriched mantle heterogeneities are widely considered to be generated through subduction, but the connections between specific subducted materials and the chemical signatures of mantle heterogeneities are not clearly defined. Boron is strongly isotopically fractionated at the surface and traces slab devolatilization, making it a potent tracer of previously subducted and recycled materials. Here, we present high-precision SIMS boron concentrations and isotope ratios on a comprehensive suite of quenched basaltic glasses from all neovolcanic zones in Iceland, two rhyolite glasses, and a set of primitive melt inclusions from central Iceland. Boron isotope ratios (δ11B) in Icelandic basalts and melt inclusions range from -11.6‰ to -1.0‰, averaging -4.9‰, which is higher than mid-ocean ridge basalt (MORB; δ11B = -7.1‰). Because the δ11B value of the Icelandic crust is low, the high δ11B compositions of the Icelandic lavas are not easily explained through crustal assimilation processes. Icelandic basalt glass and melt inclusion B/Ce and δ11B values correlate with trace element ratio indicators of the degree of mantle partial melting and mantle heterogeneity (e.g. Nb/Zr, La/Yb, Sm/Yb), which indicate that the boron systematics of basalts are controlled by mantle heterogeneity. Additionally, basalts with low B/Ce have high 206Pb/204Pb, further indicating mantle source control. These correlations can be used to deduce the boron systematics of the individual Icelandic mantle components. The enriched endmember within the Iceland mantle source has a high δ11B value and low B/Ce, consistent with the composition of “rehydrated” recycled oceanic crust. The depleted endmember comprises multiple distinct components with variable B/Ce, likely consisting of depleted MORB mantle and/or high 3He/4He mantle and two more minor depleted components that are consistent with recycled metasomatized mantle wedge and recycled slab gabbro.The compositions of these components place constraints on the devolatilization history of recycled oceanic crust. The high δ11B value and low B/Ce composition of the enriched component within the Iceland mantle source is inconsistent with a simple devolatilization process and suggests that the recycled oceanic crust component may have been isotopically overprinted by B-rich fluids derived from the underlying hydrated slab lithospheric mantle (i.e. “rehydration”). Further, the B/Ce and δ11B systematics of other OIBs can be used to constrain the devolatilization histories of recycled components on a global scale. Globally, most OIB B/Ce compositions suggest that recycled components have lost >99% of their boron, and their δ11B values suggest that rehydration may be a sporadic process, and not ubiquitous.

scholarly journals Constraining Mantle Heterogeneity beneath the South China Sea: A New Perspective on Magma Water Content

Minerals ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 410 ◽  
Author(s):  
Wei Wang ◽  
Fengyou Chu ◽  
Xichang Wu ◽  
Zhenggang Li ◽  
Ling Chen ◽  
...  
Keyword(s):  
South China Sea ◽  
Water Content ◽  
South China ◽  
Mantle Source ◽  
Melt Inclusions ◽  
The South China Sea ◽  
Spreading Ridge ◽  
Mantle Heterogeneity ◽  
The South ◽  
China Sea

The nature of upper mantle is important to understand the evolution of the South China Sea (SCS); thus, we need better constrains on its mantle heterogeneity. Magma water concentration is a good indicator, but few data have been reported. However, the rarity of glass and melt inclusions and the special genesis for phenocrysts in SCS basalts present challenges to analyzing magmatic water content. Therefore, it is possible to estimate the water variations through the characteristics of partial melting and magma crystallization. We evaluated variations in Fe depletion, degree of melt fractions, and mantle source composition along the fossil spreading ridge (FSR) using SCS basalt data from published papers. We found that lava from the FSR 116.2° E, FSR 117.7° E, and non-FSR regions can be considered normal lava with normal water content; in contrast, lava from the FSR 117° E-carbonatite and 114.9–115.0° E basalts have higher water content and show evidence of strong Fe depletion during the fractional crystallization after elimination of the effects of plagioclase oversaturation. The enriched water in the 117° E-carbonatite basalts is contained in carbonated silicate melts, and that in the 114.9–115.0° E basalts results from mantle contamination with the lower continental crust. The lava from the 117° E-normal basalt has much lower water content because of the lesser influence of the Hainan plume. Therefore, there must be a mantle source compositional transition area between the southwestern and eastern sub-basins of the SCS, which have different mantle evolution histories. The mantle in the west is more affected by contamination with continental materials, while that in the east is more affected by the Hainan mantle plume.

scholarly journals Plagioclase archives of depleted melts in the oceanic crust

2021 ◽  
Author(s):  
David Neave ◽  
Olivier Namur
Keyword(s):  
Oceanic Crust ◽  
Upper Mantle ◽  
Incompatible Element ◽  
Melt Inclusions ◽  
Melt Inclusion ◽  
Ocean Island Basalts ◽  
Depleted Mantle ◽  
Ocean Ridge ◽  
High Degree ◽  
Lower Crustal

Mid-ocean ridge and ocean island basalts provide vital but incomplete insights into the chemical structure of Earth’s mantle. For example, high-anorthite plagioclase carried by these basalts is generally too primitive and incompatible-element depleted to have crystallized from them. Moreover, erupted basalts rarely preserve the strong isotopic and incompatible-element depletions found in some melt inclusions and mantle residua represented by abyssal peridotites. By integrating experimental observations with published analyses of natural crystals and glasses, we demonstrate that high-anorthite plagioclase is in equilibrium with melts generated by high-degree melting of depleted mantle sources. Although such melts seldom erupt, their imprints on crystal and melt inclusion records nonetheless suggest that high-anorthite plagioclase grows from endmember but essentially unexotic magmas. The widespread occurrence of high-anorthite plagioclase in both oceanic basalts and the oceanic crust hence indicates that depleted melts are pervasive in the upper mantle and lower crust despite rarely reaching the surface. Plagioclase archives therefore imply that depleted melts play much a greater role in lower crustal accretion than typically recognized and that the upper mantle may also be more depleted than previously thought.

Generation of Late Cretaceous Ji’an basalts through asthenosphere-slab interaction in South China

2020 ◽  
Vol 132 (5-6) ◽  
pp. 1316-1332 ◽  
Author(s):  
Yangming Wu ◽  
Feng Guo ◽  
Xuan-Ce Wang ◽  
Bo Zhang ◽  
Xiaobing Zhang ◽  
...  
Keyword(s):  
Numerical Modeling ◽  
Oceanic Crust ◽  
Late Cretaceous ◽  
South China ◽  
Melt Inclusions ◽  
Melt Inclusion ◽  
Geochemical Data ◽  
Oceanic Plate ◽  
Asthenospheric Mantle ◽  
Geochemical Analyses

Abstract Recycled crustal components have been widely identified in the source of continental basalts with geochemical features similar to oceanic island basalts (OIBs). However, the mechanism of how these recycled materials are involved remains highly debatable. Here we conduct comprehensive geochemical analyses (including whole-rock, olivine, and melt inclusion) and numerical modeling on Late Cretaceous Ji’an basalts from South China interior, aiming to investigate the possible role of recycled crustal components in basalt petrogenesis driven by the subducted paleo-Pacific oceanic plate. The Ji’an basalts show geochemical characteristics akin to OIBs and have depleted asthenospheric mantle-like Sr-Nd-Pb-Hf isotopic compositions with moderately radiogenic Os. Their olivine-hosted melt inclusions have low H2O and highly negative δD values and olivine phenocrysts are mainly characterized by depletion of 18O with δ18O values lowering to 3.9‰. These features are consistent with positive Sr and Eu anomalies in some whole-rock samples. The combined geochemical data suggest that the primary magmas were derived from an asthenospheric mantle enriched by melts from an altered gabbroic oceanic crust, which had experienced intensive dehydration. Further numerical modeling shows that melting of the dehydrated oceanic crust can occur along the torn flank of the subducting lithosphere, in the case that the slab is strongly thinned and fractured. The low δ18O preserved in olivine and the estimated slab age (<300 Ma) from the radiogenic whole-rock Os and Pb compositions also require the involvement of a recently recycled slab, probably represented by the subducted paleo-Pacific oceanic plate. Rollback of the subducting paleo-Pacific slab might create a slab window, in which melt from the torn/fractured slab reacted with the upwelling asthenosphere to form an enriched mantle source for the Ji’an basalts and similar counterparts.

Mantle source of tephritic porphyry in the Tarim Large Igneous Province constrained from Mg, Zn, Sr, and Nd isotope systematics: Implications for deep carbon cycling

2021 ◽  
Author(s):  
Weiliang Kong ◽  
Zhaochong Zhang ◽  
Zhiguo Cheng ◽  
Bingxiang Liu ◽  
M. Santosh ◽  
...  
Keyword(s):  
Oceanic Crust ◽  
Mantle Source ◽  
Large Igneous Province ◽  
Mantle Heterogeneity ◽  
Nd Isotopes ◽  
Igneous Province ◽  
Rock Suite ◽  
Sedimentary Carbonates ◽  
Tarim Large Igneous Province

The nature and source of magmatism associated with large igneous provinces (LIPs) remain disputed. Here we investigate the role of recycled materials that contributed to mantle heterogeneity in the Tarim Large Igneous Province (TLIP) in China through integrated Zn−Mg−Sr−Nd isotopes of a rare tephritic rock suite. The Sr−Nd isotopes [(87Sr/86Sr)i = 0.70368−0.70629; εNd(t) = −0.25−4.64] and δ26Mg values (−0.23‰ to −0.34‰) of the tephritic porphyries are consistent with a normal mantle origin. In contrast, the whole rock and pyroxene phenocrysts yield δ66Zn values of +0.28‰ to +0.46‰ and +0.30‰ to +0.39‰, which are slightly heavier than those of the terrestrial mantle (+0.16 ± 0.06‰) and mid-oceanic-ridge basalts (MORBs) (+0.27 ± 0.05‰). We exclude the possibility that the heavy Zn isotopes of the Wajilitag tephritic porphyries are caused by magmatic processes such as fractional crystallization and partial melting and correlate the isotopic features to the role of altered oceanic crust along with magnesite in the mantle source. The Wajilitag tephritic porphyry displays trace-element patterns similar to those of the melts from natural hornblendite, especially those of hornblendite + peridotite. Additionally, the geochemical characteristics such as enrichment in Nb and Ta, depletion in K, high TiO2, and constant Na2O/K2O ratios also suggest that the tephritic porphyries were derived from an amphibole-bearing source contributed by altered oceanic crust along with sedimentary carbonates. Our study provides insight into the contribution of subducted materials to the mantle heterogeneity beneath the TLIP and highlights the role of subduction in the deep carbon cycle and subducted slab-lithosphere-plume interaction in the generation of LIPs.

scholarly journals Extreme isotopic heterogeneity in Samoan clinopyroxenes constrains sediment recycling

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Jenna V. Adams ◽  
Matthew G. Jackson ◽  
Frank J. Spera ◽  
Allison A. Price ◽  
Benjamin L. Byerly ◽  
...  
Keyword(s):  
Mantle Source ◽  
Magma Mixing ◽  
Major And Trace Elements ◽  
Mantle Heterogeneity ◽  
Isotopic Data ◽  
Nd Isotopes ◽  
Isotopic Heterogeneity ◽  
Total Variability ◽  
High Silica ◽  
Insight Into

AbstractLavas erupted at hotspot volcanoes provide evidence of mantle heterogeneity. Samoan Island lavas with high 87Sr/86Sr (>0.706) typify a mantle source incorporating ancient subducted sediments. To further characterize this source, we target a single high 87Sr/86Sr lava from Savai’i Island, Samoa for detailed analyses of 87Sr/86Sr and 143Nd/144Nd isotopes and major and trace elements on individual magmatic clinopyroxenes. We show the clinopyroxenes exhibit a remarkable range of 87Sr/86Sr—including the highest observed in an oceanic hotspot lava—encompassing ~30% of the oceanic mantle’s total variability. These new isotopic data, data from other Samoan lavas, and magma mixing calculations are consistent with clinopyroxene 87Sr/86Sr variability resulting from magma mixing between a high silica, high 87Sr/86Sr (up to 0.7316) magma, and a low silica, low 87Sr/86Sr magma. Results provide insight into the composition of magmas derived from a sediment-infiltrated mantle source and document the fate of sediment recycled into Earth’s mantle.

scholarly journals Mantle Source Heterogeneity Inferred from Olivine-Hosted Melt Inclusions

2020 ◽  
Author(s):  
Mischa Böhnke ◽  
Felix Genske ◽  
Andreas Stracke
Keyword(s):  
Mantle Source ◽  
Melt Inclusions ◽  
Source Heterogeneity

scholarly journals Thallium isotope ratios record a transition to melting of hydrated oceanic crust at the Hadean-Archean boundary

2021 ◽  
Author(s):  
Mathias Schannor ◽  
Heye Freymuth ◽  
Jesse Reimink ◽  
Mark Rehkämper ◽  
Helen Williams
Keyword(s):  
Oceanic Crust ◽  
Isotope Ratios

A myriad of melt inclusions: a synchrotron microtomography study of melt inclusions and vapour bubbles from Colli Albani (Italy)

2021 ◽  
Author(s):  
Corin Jorgenson ◽  
Luca Caricchi ◽  
Michael Stueckelberger ◽  
Giovanni Fevola ◽  
Gregor Weber
Keyword(s):  
Melt Inclusions ◽  
Melt Inclusion ◽  
Fluid Phase ◽  
Volcanic Eruptions ◽  
Mineral Chemistry ◽  
Magma Ascent ◽  
Vapour Bubble ◽  
Electron Synchrotron ◽  
Colli Albani ◽  
Synchrotron Microtomography

<p>Melt inclusions provide a window into the inner workings of magmatic systems. Both mineral chemistry and volatile distributions within melt inclusions can provide valuable information about the processes modulating magma ascent and preceding volcanic eruptions. Many melt inclusions host vapour bubbles which can be rich in CO<sub>2</sub> and H<sub>2</sub>O and must be taken into consideration when assessing the volatile budget of magmatic reservoirs. These vapour bubbles can be the product of differential volumetric contraction between the melt inclusion and host phase during an eruption or indicate an excess fluid phase in the magma reservoir. Thus, determining the distribution of volatiles between melt and vapour bubbles is integral to our fundamental understanding of melt inclusions, and by extension the evolution of volatiles within magmatic systems.</p><p>A large dataset of 79 high-resolution tomographic scans of clinopyroxene and leucite phenocrysts from the Colli Albani Caldera Complex (Italy) was recently acquired at the German Electron Synchrotron (DESY). These tomograms allow us to quantify the volume of melt inclusions and associated vapour bubble both glassy and microcrystalline melt inclusions. Notably, in the glassy melt inclusions the vapour bubbles exist either as a single large vapour bubble in the middle of the melt inclusion or as several smaller vapour bubbles distributed around the edge of the melt inclusion. These two types of melt inclusions can coexist within a single crystal. We suggest that the occurrence of these rim- bubbles is caused by one of two exsolution pathways, either pre-entrapment and bubble migration or post entrapment with preferential exsolution at the rims. By combining the analysis of hundreds of melt inclusions with the chemistry of the host phase we aim to unveil magma ascent rates and distribution of excess fluids within the magmatic system of Colli Albani, which produced several mafic-alkaline large volume ignimbrites.</p>

scholarly journals The Petrogenesis of the Permian Podong Ultramafic Intrusion in the Tarim Craton, Western China: Constraints from C-He-Ne-Ar Isotopes

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-14 ◽  
Author(s):  
Mingjie Zhang ◽  
Pengyu Feng ◽  
Tong Li ◽  
Liwu Li ◽  
Juerong Fu ◽  
...  
Keyword(s):  
Oceanic Crust ◽  
Mantle Plume ◽  
Mantle Source ◽  
Noble Gas ◽  
Western China ◽  
Crustal Material ◽  
Sulfide Mineralization ◽  
Hydrocarbon Gases ◽  
Isotopic Compositions ◽  
Ultramafic Intrusion

The Podong Permian ultramafic intrusion is only one ultramafic intrusion with massif Ni-Cu sulfide mineralization in the Pobei layered mafic-ultramafic complex, western China. It is obviously different in sulfide mineralization from the nearby coeval Poyi ultramafic intrusion with the largest disseminated Ni-Cu sulfide mineralization and mantle plume contribution (Zhang et al., 2017). The type and addition mechanism of the confirmed crustal contaminations and possible mantle plume involved in the intrusion formation require evidences from carbon and noble gas isotopic compositions. In the present study, we have measured C, He, Ne, and Ar isotopic compositions of volatiles from magmatic minerals in the Podong ultramafic intrusion. The results show that olivine, pyroxene, and plagioclase minerals in the Podong intrusion have variable δ13C of CO2 (-24.5‰ to -3.2‰). The CH4, C2H6, C3H8, and C4H10 hydrocarbon gases show normal or partial reversal distribution patterns of carbon isotope with carbon number and light δ13C1 value of CH4, indicating the hydrocarbon gases of biogenic origin. The δ13C of CO2 and CH4 suggested the magmatic volatile of the mantle mixed with the volatiles of thermogenic and crustal origins. Carbon and noble gas isotopes indicated that the Podong intrusion could have a different petrogenesis from the Poyi ultramafic intrusion. Two types of contaminated crustal materials can be identified as crustal fluids from subducted altered oceanic crust (AOC) in the lithospheric mantle source and a part of the siliceous crust. The carbon isotopes for different minerals show that magma spent some time crystallizing in a magma chamber during which assimilation of crustal material occurred. Subduction-devolatilization of altered oceanic crust could be the best mechanism that transported large proportion of ASF (air-saturated fluid) and crustal components into the mantle source. The mantle plume existing beneath the Poyi intrusion could provide less contribution of real materials of silicate and fluid components.

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