Le Roux Véronique

Last Name

Le Roux

First Name

Véronique

ORCID

0000-0002-5855-4888

Full item page

Search Results

Now showing 1 - 11 of 11

Sources of dehydration fluids underneath the Kamchatka arc

(Nature Research, 2022-08-02) Shu, Yunchao ; Nielsen, Sune G. ; Le Roux, Véronique ; Wörner, Gerhard ; Blusztajn, Jerzy S. ; Auro, Maureen E.

Fluids mediate the transport of subducted slab material and play a crucial role in the generation of arc magmas. However, the source of subduction-derived fluids remains debated. The Kamchatka arc is an ideal subduction zone to identify the source of fluids because the arc magmas are comparably mafic, their source appears to be essentially free of subducted sediment-derived components, and subducted Hawaii-Emperor Seamount Chain (HESC) is thought to contribute a substantial fluid flux to the Kamchatka magmas. Here we show that Tl isotope ratios are unique tracers of HESC contribution to Kamchatka arc magma sources. In conjunction with trace element ratios and literature data, we trace the progressive dehydration and melting of subducted HESC across the Kamchatka arc. In succession, serpentine (<100 km depth), lawsonite (100–250 km depth) and phengite (>250 km depth) break down and produce fluids that contribute to arc magmatism at the Eastern Volcanic Front (EVF), Central Kamchatka Depression (CKD), and Sredinny Ridge (SR), respectively. However, given the Tl-poor nature of serpentine and lawsonite fluids, simultaneous melting of subducted HESC is required to explain the HESC-like Tl isotope signatures observed in EVF and CKD lavas. In the absence of eclogitic crust melting processes in this region of the Kamchatka arc, we propose that progressive dehydration and melting of a HESC-dominated mélange offers the most compelling interpretation of the combined isotope and trace element data.
Barium isotope evidence for pervasive sediment recycling in the upper mantle

(American Association for the Advancement of Science, 2018-07-11) Nielsen, Sune G. ; Horner, Tristan J. ; Pryer, Helena V. ; Blusztajn, Jerzy S. ; Shu, Yunchao ; Kurz, Mark D. ; Le Roux, Véronique

The upper mantle, as sampled by mid-ocean ridge basalts (MORBs), exhibits significant chemical variability unrelated to mechanisms of melt extraction at ridges. We show that barium isotope variations in global MORBs vary systematically with radiogenic isotopes and trace element ratios, which reflects mixing between depleted and enriched MORB melts. In addition, modern sediments and enriched MORBs share similar Ba isotope signatures. Using modeling, we show that addition of ~0.1% by weight of sediment components into the depleted mantle in subduction zones must impart a sedimentary Ba signature to the overlying mantle and induce low-degree melting that produces the enriched MORB reservoir. Subsequently, these enriched domains convect toward mid-ocean ridges and produce radiogenic isotope variation typical of enriched MORBs. This mechanism can explain the chemical and isotopic features of enriched MORBs and provide strong evidence for pervasive sediment recycling in the upper mantle.
Causes of oceanic crustal thickness oscillations along a 74-M Mid-Atlantic ridge flow line

(American Geophysical Union, 2019-11-19) Shinevar, William J. ; Mark, Hannah F. ; Clerc, Fiona ; Codillo, Emmanuel A. ; Gong, Jianhua ; Olive, Jean-Arthur ; Brown, Stephanie M. ; Smalls, Paris T. ; Liao, Yang ; Le Roux, Véronique ; Behn, Mark D.

Gravity, magnetic, and bathymetry data collected along a continuous 1,400‐km‐long spreading‐parallel flow line across the Mid‐Atlantic Ridge indicate significant tectonic and magmatic fluctuations in the formation of oceanic crust over a range of time scales. The transect spans from 28 Ma on the African Plate to 74 Ma on the North American plate, crossing the Mid‐Atlantic Ridge at 35.8°N. Gravity‐derived crustal thicknesses vary from 3–9 km with a standard deviation of 1.0 km. Spectral analysis of bathymetry and residual mantle Bouguer anomaly show a diffuse power at >1 Myr and concurrent peaks at 390, 550, and 950 kyr. Large‐scale (>10 km) mantle thermal and compositional heterogeneities, variations in upper mantle flow, and detachment faulting likely generate the >1 Myr diffuse power. The 550‐ and 950‐kyr peaks may reflect the presence of magma solitons and/or regularly spaced ~7.7 and 13.3 km short‐wavelength mantle compositional heterogeneities. The 390‐kyr spectral peak corresponds to the characteristic spacing of faults along the flow line. Fault spacing also varies over longer periods (>10 Myr), which we interpret as reflecting long‐lived changes in the fraction of tectonically versus magmatically accommodated extensional strain. A newly discovered off‐axis oceanic core complex (Kafka Dome) found at 8 Ma on the African plate further suggests extended time periods of tectonically‐dominated plate separation. Fault spacing negatively correlates with gravity‐derived crustal thickness, supporting a strong link between magma input and fault style at mid‐ocean ridges.
Postmelting hydrogen enrichment in the oceanic lithosphere

(American Association for the Advancement of Science, 2021-06-09) Le Roux, Véronique ; Urann, Benjamin M. ; Brunelli, Daniele ; Bonatti, Enrico ; Cipriani, Anna ; Demouchy, Sylvie ; Monteleone, Brian D.

The large range of H2O contents recorded in minerals from exhumed mantle rocks has been challenging to interpret, as it often records a combination of melting, metasomatism, and diffusional processes in spatially isolated samples. Here, we determine the temporal variations of H2O contents in pyroxenes from a 24-Ma time series of abyssal peridotites exposed along the Vema fracture zone (Atlantic Ocean). The H2O contents of pyroxenes correlate with both crustal ages and pyroxene chemistry and increase toward younger and more refractory peridotites. These variations are inconsistent with residual values after melting and opposite to trends often observed in mantle xenoliths. Postmelting hydrogen enrichment occurred by ionic diffusion during cryptic metasomatism of peridotite residues by low-degree, volatile-rich melts and was particularly effective in the most depleted peridotites. The presence of hydrous melts under ridges leads to widespread hydrogen incorporation in the oceanic lithosphere, likely lowering mantle viscosity compared to dry models.
Experimental evidence for melt partitioning between olivine and orthopyroxene in partially molten harzburgite

(John Wiley & Sons, 2016-08-31) Miller, Kevin J. ; Zhu, Wenlu ; Montesi, Laurent G. J. ; Gaetani, Glenn A. ; Le Roux, Véronique ; Xiao, Xianghui

Observations of dunite channels in ophiolites and uranium series disequilibria in mid-ocean ridge basalt suggest that melt transport in the upper mantle beneath mid-ocean ridges is strongly channelized. We present experimental evidence that spatial variations in mineralogy can also focus melt on the grain scale. This lithologic melt partitioning, which results from differences in the interfacial energies associated with olivine-melt and orthopyroxene-melt boundaries, may complement other melt focusing mechanisms in the upper mantle such as mechanical shear and pyroxene dissolution. We document here lithologic melt partitioning in olivine-/orthopyroxene-basaltic melt samples containing nominal olivine to orthopyroxene ratio of 3 to 2 and melt fractions of 0.02 to 0.20. Experimental samples were imaged using synchrotron-based X-ray microcomputed tomography at a resolution of 700 nm per voxel. By analyzing the local melt fraction distributions associated with olivine and orthopyroxene grains in each sample, we found that the melt partitioning coefficient, i.e., the ratio of melt fraction around olivine to that around orthopyroxene grains, varies between 1.1 and 1.6. The permeability and electrical conductivity of our digital samples were estimated using numerical models and compared to those of samples containing only olivine and basaltic melt. Our results suggest that lithologic melt partitioning and preferential localization of melt around olivine grains might play a role in melt focusing, potentially enhancing average melt ascent velocities.
Fluorine and chlorine in mantle minerals and the halogen budget of the Earth’s mantle

( 2017-05-01) Urann, Benjamin M. ; Le Roux, Véronique ; Hammond, Keiji ; Marschall, Horst R. ; Lee, Cin-Ty A.

The fluorine (F) and chlorine (Cl) contents of arc magmas have been used to track the composition of subducted components, and the F and Cl contents of MORB have been used to estimate the halogen content of depleted MORB mantle (DMM). Yet, the F and Cl budget of the Earth's upper mantle, and their distribution in peridotite minerals, remains to be constrained. Here we developed a method to measure low concentrations of halogens (≥ 0.4 μg/g F and ≥ 0.3 μg/g Cl) in minerals by secondary ion mass spectroscopy. We present a comprehensive study of F and Cl in natural olivine, orthopyroxene, clinopyroxene, and amphibole in seventeen samples from different tectonic settings. We support the hypothesis that F in olivine is controlled by melt polymerization, and that F in pyroxene is controlled by their Na and Al contents, with some effect of melt polymerization. We infer that Cl compatibility ranks as follows: amphibole > clinopyroxene > olivine ~ orthopyroxene, while F compatibility ranks as follows: amphibole > clinopyroxene > orthopyroxene ≥ olivine, depending on the tectonic context. In addition, we show that F, Cl, Be and B are correlated in pyroxenes and amphibole. F and Cl variations suggest that interaction with slab melts and fluids can significantly alter the halogen content of mantle minerals. In particular, F in oceanic peridotites is mostly hosted in pyroxenes, and proportionally increases in olivine in subduction-related peridotites. The mantle wedge is likely enriched in F compared to un-metasomatized mantle, while Cl is always low (< 1 μg/g) in all tectonic settings studied here. The bulk anhydrous peridotite mantle contains 1.4–31 μg/g F and 0.14–0.38 μg/g Cl. The bulk F content of oceanic-like peridotites (2.1–9.4 μg/g) is lower than DMM estimates, consistent with F-rich eclogite in the source of MORB. Furthermore, the bulk Cl budget of all anhydrous peridotites studied here is lower than previous DMM estimates. Our results indicate that nearly all MORB may be somewhat contaminated by seawater-rich material and that the Cl content of DMM could be overestimated. With this study, we demonstrate that the halogen contents of natural peridotite minerals are a unique tool to understand the cycling of halogens, from ridge settings to subduction zones.
Ophiolitic pyroxenites record boninite percolation in subduction zone mantle

(MDPI, 2019-09-18) Le Roux, Véronique ; Liang, Yan

The peridotite section of supra-subduction zone ophiolites is often crosscut by pyroxenite veins, reflecting the variety of melts that percolate through the mantle wedge, react, and eventually crystallize in the shallow lithospheric mantle. Understanding the nature of parental melts and the timing of formation of these pyroxenites provides unique constraints on melt infiltration processes that may occur in active subduction zones. This study deciphers the processes of orthopyroxenite and clinopyroxenite formation in the Josephine ophiolite (USA), using new trace and major element analyses of pyroxenite minerals, closure temperatures, elemental profiles, diffusion modeling, and equilibrium melt calculations. We show that multiple melt percolation events are required to explain the variable chemistry of peridotite-hosted pyroxenite veins, consistent with previous observations in the xenolith record. We argue that the Josephine ophiolite evolved in conditions intermediate between back-arc and sub-arc. Clinopyroxenites formed at an early stage of ophiolite formation from percolation of high-Ca boninites. Several million years later, and shortly before exhumation, orthopyroxenites formed through remelting of the Josephine harzburgites through percolation of ultra-depleted low-Ca boninites. Thus, we support the hypothesis that multiple types of boninites can be created at different stages of arc formation and that ophiolitic pyroxenites uniquely record the timing of boninite percolation in subduction zone mantle.
Arc-like magmas generated by mélange-peridotite interaction in the mantle wedge

(Nature Publishing Group, 2018-07-20) Codillo, Emmanuel A. ; Le Roux, Véronique ; Marschall, Horst R.

The mechanisms of transfer of crustal material from the subducting slab to the overlying mantle wedge are still debated. Mélange rocks, formed by mixing of sediments, oceanic crust, and ultramafics along the slab-mantle interface, are predicted to ascend as diapirs from the slab-top and transfer their compositional signatures to the source region of arc magmas. However, the compositions of melts that result from the interaction of mélanges with a peridotite wedge remain unknown. Here we present experimental evidence that melting of peridotite hybridized by mélanges produces melts that carry the major and trace element abundances observed in natural arc magmas. We propose that differences in nature and relative contributions of mélanges hybridizing the mantle produce a range of primary arc magmas, from tholeiitic to calc-alkaline. Thus, assimilation of mélanges into the wedge may play a key role in transferring subduction signatures from the slab to the source of arc magmas.
Causes of oceanic crustal thickness oscillations along a 74-Myr Mid-Atlantic Ridge flow line

( 2019-11-12) Shinevar, William J. ; Mark, Hannah F. ; Clerc, Fiona ; Codillo, Emmanuel A. ; Gong, Jianhua ; Olive, Jean-Arthur ; Brown, Stephanie M. ; Smalls, Paris T. ; Liao, Yang ; Le Roux, Véronique ; Behn, Mark D.

Gravity, magnetic, and bathymetry data collected along a continuous 1400-km-long spreading-parallel flow line across the Mid-Atlantic Ridge indicate significant tectonic and magmatic fluctuations in the formation of oceanic crust over a range of timescales. The transect spans from 28 Ma on the African Plate to 74 Ma on the North American plate, crossing the Mid-Atlantic Ridge at 35.8 ºN. Gravity-derived crustal thicknesses vary from 3–9 km with a standard deviation of 1 km. Spectral analysis of bathymetry and residual mantle Bouguer anomaly (RMBA) show diffuse power at >1 Myr and concurrent peaks at 390, 550, and 950 kyr. Large-scale (>10-km) mantle thermal and compositional heterogeneities, variations in upper mantle flow, and detachment faulting likely generate the >1 Myr diffuse power. The 550- and 950-kyr peaks may reflect the presence of magma solitons and/or regularly spaced ~7.7 and 13.3 km short-wavelength mantle compositional heterogeneities. The 390-kyr spectral peak corresponds to the characteristic spacing of faults along the flow line. Fault spacing also varies over longer periods (>10 Myr), which we interpret as reflecting long-lived changes in the fraction of tectonically- vs. magmatically- accommodated extensional strain. A newly discovered off-axis oceanic core complex (Kafka Dome) found at 8 Ma on the African plate further suggests extended time periods of tectonically dominated plate separation. Fault spacing negatively correlates with gravity-derived crustal thickness, supporting a strong link between magma input and fault style at mid-ocean ridges.
Images of cellular ultrastructure of benthic foraminifera from Arctic seeps

(Woods Hole Oceanographic Institution, 2021-11-01) Bernhard, Joan M. ; Le Roux, Véronique ; Martin, Jonathan B.

Dissociation of methane hydrates due to ocean warming releases methane, a powerful greenhouse gas, to the atmosphere. Dissociation of gas hydrates may have led to rapid and dramatic environmental changes in the past. Thus, understanding the impact of those events requires information about their timing and magnitudes. While the foraminiferal fossil record provides a powerful tool to understand past environmental conditions, seep-endemic foraminifera are unknown, which limits evaluation of seep-specific information. However, geographically widespread benthic foraminifera do inhabit seep sites, as documented widely in the literature, and may provide information useful to the understanding of past methane releases. In an effort to better understand how benthic foraminifera inhabit this chemosynthesis-based ecosystem, and if they faithfully record the methane emissions, we conducted a multipronged analysis of foraminifera associated with a gas hydrate emission site in the Arctic. Our goal was to simultaneously assess, in single representative calcareous benthic foraminiferal individuals, the cell biology, test stable carbon isotope ratio, and carbonate microstructure (e.g., wall thickness, survey for authigenic overgrowths), from samples collected south of Svalbard, or on Vestnesa Ridge, west of Svalbard). Serially, each specimen was scanned with microCT (computerized tomography) to assess test characteristics, then the test dissolved by acidification while capturing gas to measure stable carbon isotope ratio via continuous-flow mass spectrometry, and finally the remaining soft parts embedded and examined for cell ultrastructure with a Transmission Electron Microscope (TEM). TEM). Data from isotopic analyses, microCT scans and TEM imaging are presented here.
Evolution of microstructural heterogeneity in the deep arc lithosphere during delamination

(American Geophysical Union, 2023-06-16) Gruber, Benjamin ; Chin, Emily J. ; Le Roux, Véronique

The microstructural properties of deep arc cumulates (arclogites) are poorly understood, but are essential in gaining a comprehensive picture of the rheology of continental lithosphere. Here, we analyze 16 arclogite xenoliths, comprising a low MgO and a high MgO suite, from Arizona, USA using electron backscatter diffraction to map microstructures, clinopyroxene shape preferred orientations (SPO), and clinopyroxene crystallographic preferred orientations (CPO). The lower pressure (∼1 GPa) low MgO arclogites show a variety of different clinopyroxene fabrics (S, L, and LS-type), whereas the high pressure (>2 GPa) high MgO arclogites show predominantly LS-type fabrics. Furthermore, clinopyroxenes in low MgO arclogites all show a pronounced correspondence between the long axis of their grain shape ellipsoids with the [001] crystal direction, indicating an SPO control on the CPO. In contrast, high MgO arclogite clinopyroxenes lack such a correspondence. We propose that both arclogite types originated as igneous cumulates, consistent with previous studies, but that the high MgO suite experienced substantial recrystallization which diminished the original igneous SPO-induced CPO. Using strain rates appropriate for arc settings, we calculate a strength profile for the lithosphere and argue that the deepest arclogite textures are consistent with lithospheric foundering through ductile deformation under high shear strain (10−14–10−12 s−1). Our study shows that there is a high degree of shear strain localization in deep arc roots while shallower portions are relatively undeformed.

Le Roux Véronique

Last Name

First Name

ORCID

Filters

Author

Subject

Date

Type

Has files

Settings

Sort By

Results per page

Search Results