Determination of Trace Element Mass Fractions in Ultramafic Rocks by <scp>HR</scp>‐<scp>ICP</scp>‐<scp>MS</scp>: A Combined Approach Using a Direct Digestion/Dilution Method and Preconcentration by Coprecipitation

Rospabé, Mathieu; Benoît, Mathieu; Candaudap, Frédéric

doi:10.1111/ggr.12181

Cited by 22 publications

(30 citation statements)

References 39 publications

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“…The along strike extent of the main faults exceeds several kilometers. 10% for LILE, REE, Pb, Th and U, and better than 20% for HFSE (see also Rospabé et al, 2018b). Grey fields represent the entire variation ranges described in Rospabé et al (2018).…”

Section: Resultsmentioning

confidence: 80%

Melt hybridization and metasomatism triggered by syn-magmatic faults within the Oman ophiolite: A clue to understand the genesis of the dunitic mantle-crust transition zone

Rospabé

Benoît

Ceuleneer

et al. 2019

Earth and Planetary Science Letters

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On Earth, most of the critical processes happen at the frontiers between envelopes and especially at the Moho between the mantle and the crust. Beneath oceanic spreading centres, the dunitic transition zone (DTZ) appears as a major interface between the upwelling and partially molten peridotitic mantle and the accreting gabbroic lower crust. Better constraints on the processes taking part in the DTZ allows improved understanding of the interactions between silicate melts and hydrated fluids, which act competitively to generate the petrological Moho. Here we combine mineral and whole rock major and trace element data with a structural approach along three cross-sections up to 300 m thick above the fossil Maqsad mantle diapir (Oman ophiolite) in order to understand the vertical organization of the DTZ with depth. Our results highlight that most of the faults or fractures cross-cutting the DTZ were ridge-related and active at an early, high temperature magmatic stage. Chemical variations along the cross-sections define trends with a characteristic vertical scale of few tens *Manuscript EPSL-D-18-00894R3 Click here to view linked References of meters. There is a clear correlation between the chemical variation pattern and the distribution of fault zones, not only for fluid-mobile elements but also for immobile elements such as REE and HFSE. Faults, despite displaying very limited displacements, enhanced both melt migration and extraction up to the crust and deep hydrothermal fluids introduction down to the Moho level. We propose that these faults are a vector for upwelling melt modification by hybridization, with hydrothermal fluids and/or silicic hydrous melts, and crystallization. Infiltration of these melts or fluids in the country rock governs part of the gradational evolutions recorded in composition of both the olivine matrix and interstitial phases away from faults. Finally, these faults likely control the thermal structure of the mantle-crust transition as evidenced by the spatial distribution of the crystallization products from percolating melts, organizing the transition zone into pure dunites to impregnated dunites horizons. In this context, the DTZ appears as a reactive interface that developed by the combination of three primary processes: tectonics, magmatism and deep, high temperature hydrothermal circulations. Accordingly, these features fundamentally contribute to the variable petrological and geochemical organization of the DTZ and possibly of the lower crust below oceanic spreading centers, and may be a clue to interpret part the heterogeneity observed in MORB signatures worldwide.

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Section: Resultsmentioning

confidence: 80%

Melt hybridization and metasomatism triggered by syn-magmatic faults within the Oman ophiolite: A clue to understand the genesis of the dunitic mantle-crust transition zone

Rospabé

Benoît

Ceuleneer

et al. 2019

Earth and Planetary Science Letters

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“…The concentrations in Li and Large Ion Lithophile Elements (LILE; Rb, Sr, Cs and Ba) and of most of transition elements (Cr, Mn, Co, Ni, Cu, Zn) and Ga were acquired after a direct digestion/dilution method. Sc, V, Rare Earth Elements (REE) and Y, High Field Strength Elements (HFSE; Zr, Hf, Nb, Ta, Ti) and U, Th and Pb contents were determined after the double coprecipitation procedure detailed in Rospabé et al (2018). BHVO-2 was used as calibrator following the values proposed by Barrat et al (2012).…”

Section: Methodsmentioning

confidence: 99%

“…Lee et al, 2007). The analytical method we developed (Rospabé et al, 2018) allowed us to establish with confidence that the extensive enrichment in LREE relative to MREE in pure dunites (Fig. 5) is a reliable result.…”

Section: About the Habitus Of Incompatible Trace Elements In The Dunimentioning

confidence: 97%

Extreme geochemical variability through the dunitic transition zone of the Oman ophiolite: Implications for melt/fluid-rock reactions at Moho level beneath oceanic spreading centers

Rospabé

Benoît

Ceuleneer

et al. 2018

Geochimica et Cosmochimica Acta

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The Maqsad area in the Oman ophiolite exposes a >300 m thick dunitic mantle-crust transition zone (DTZ) that developed above a mantle diapir. The Maqsad DTZ is primarily f "p " w h scattered chromite and chromite seams) and " p g " which exhibit a significant lithological variability, including various kinds of clinopyroxene-, plagioclase-, orthopyroxene-, amphibole (hornblende/pargasite)bearing dunites. These minerals are interstitial between olivine grains and their variable abundance and distribution suggest that they crystallized from a percolating melt. Generally studied through in-situ mineral characterization, the whole rock composition of dunites is poorly documented. This study reports on whole rock and minerals major and trace element *Manuscript contents on 79 pure to variably impregnated dunites collected systematically along cross sections from the base to the top of the DTZ. In spite of its high degree of depletion, the olivine matrix is selectively enriched in the most incompatible trace elements such as LREE, HFSE, Th, U, Rb and Ba. These data support the view that this enrichment has been acquired early in the magmatic evolution of the DTZ, during the dunitization process itself. The dissolution of orthopyroxene from mantle harzburgites enhanced by the involvement of hydrothermal fluids produced low amounts of melts enriched in silica and in some trace elements that re-equilibrated with the olivine matrix. This pristine signature of the DTZ dunite was eventually variably altered by percolation of melts with a Mid-Ocean Ridge Basalt (MORB) affinity but displaying a wide spectrum of composition attributable to evolution by fractional crystallization and hybridization with the silica enriched, hydrated melts. The olivine matrix has been partially or fully re-equilibrated with these melts, smoothing the early strong concave-upward REE pattern in dunite. The chemical variability in the interstitial minerals bears witness of the percolation of MORB, issued from the mantle decompression melting, variably hybridized with melt batches produced within the DTZ by melt-rock reaction and poorly homogenized before reaching the lower crust. Our results lead to the conclusion that pure and impregnated dunites are end-members that recorded different stages of the same initial igneous processes: pure dunites are residues left after extraction of a percolating melt while impregnated dunites correspond to a stage frozen before complete melt extraction. Therefore dunites trace elements contents allow deciphering the multi-stage processes that led to their formation at the mantle-crust transition zone. Keywords Oman ophiolite; dunitic mantle-crust transition zone; trace elements; melt-rock reactions; melt percolation; refertilization 1995a; Kelemen et al., 1997b). In this way, the DTZ appears to be a reactive interface where melts are focused, transformed and potentially accumulated, then distributed beneath the midocean ridge. Crystallization associated to melt migration through the mantle-crust transition zone accou...

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“…; 0,0.94 μg g −1 , Rospabé et al . ). For REE, Y, Nb and HFSE (Hf, Ta, Th and U), the results we obtained are not in good agreement with literature data (Figure , Table and Table ).…”

Section: Resultsmentioning

confidence: 97%

“…, Rospabé et al . ). We show below that some of the matrix effects are easier to take into account using our fusion method.…”

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confidence: 97%

Rapid Determination of Trace Element Compositions in Peridotites by LA‐ICP‐MS Using an Albite Fusion Method

Zhang

Hou

et al. 2018

Geostandard Geoanalytic Res

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A rapid sample preparation procedure is described to determine trace element compositions of peridotites using LA-ICP-MS. Peridotite powders were fused with albite in a molybdenum-graphite assembly to obtain homogeneous glasses. Best conditions for the fusion procedure (heating at 1500-1550°C for 10-15 min with a sample-to-flux ratio of 1:2) were constrained with melting experiments on two USGS reference materials, PCC-1 and DTS-2B. Mass fractions of first series transition elements, Ba and Pb, in quenched glasses of PCC-1 and DTS-2B are consistent with published data within 10% RSD. Three spinel peridotite xenoliths from eastern China were analysed following both our method and conventional solution ICP-MS. Compared with solution ICP-MS, the relative deviations of our method for most elements were within 10%, while for the REE, Ta, Pb, Th and U, the relative deviations were within 20%. In particular, volatile elements (e.g., Pb and Zn) are retained in the glass. Compared with conventional wet chemistry digestion, our method is faster. Additional advantages are complete sample fusion, especially useful for samples with acid-resistant minerals (spinel and rutile), and long-term conservation of glasses allowing unlimited repeated measurements with microbeam techniques. The same approach can be used for analyses of other mantle rocks, such as eclogites and pyroxenites.

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Determination of Trace Element Mass Fractions in Ultramafic Rocks by HR‐ICP‐MS: A Combined Approach Using a Direct Digestion/Dilution Method and Preconcentration by Coprecipitation

Cited by 22 publications

References 39 publications

Melt hybridization and metasomatism triggered by syn-magmatic faults within the Oman ophiolite: A clue to understand the genesis of the dunitic mantle-crust transition zone

Melt hybridization and metasomatism triggered by syn-magmatic faults within the Oman ophiolite: A clue to understand the genesis of the dunitic mantle-crust transition zone

Extreme geochemical variability through the dunitic transition zone of the Oman ophiolite: Implications for melt/fluid-rock reactions at Moho level beneath oceanic spreading centers

Rapid Determination of Trace Element Compositions in Peridotites by LA‐ICP‐MS Using an Albite Fusion Method

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