Copper and Noble Metal Enrichments Across the Lithosphere--Asthenosphere Boundary of Mantle Diapirs: Evidence from the Lanzo Lherzolite Massif

Lorand, Jean Pierre; Keays, Reid R.; Bodinier, Jean-Louis

doi:10.1093/petrology/34.6.1111

Cited by 97 publications

(47 citation statements)

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“…The mean of 28 ppm Cu found in the Kane Megamullion spinel harzburgites is close to typical depleted mantle values (Garuti et al, 1984;Lorand, 1989a;1991;Lorand et al, 1993;Fig. 5).…”

Section: Evidence For Melt Refertilizationsupporting

confidence: 72%

“…The chalcophile element contents of the serpentinized spinel harzburgites (Table 2) are in the compositional range of primitive mantle estimates (Sun, 1982;McDonough and Sun, 1995) and most fresh peridotites from orogenic and ophiolitic massifs (Garuti et al, 1984;Lorand, 1989a;Lorand, 1991;Lorand et al, 1993) (Fig. 5).…”

Section: Bulk-rock Trace-element Contentsmentioning

confidence: 95%

“…Although Cu has been partially redeposited by secondary processes (Goettler et al, 1976;Begemann et al, 2010), the data from our study and the characteristic distribution of the ancient mining sites imply that the first stage of Cu enrichment may have been magmatic. In the ophiolitic peridotites from the Lanzo massif in Italy, dunitic bands that are a product of melt percolation in the mantle are enriched in Cu (Lorand et al, 1993).…”

Section: Mechanism Of Melt Refertilizationmentioning

confidence: 99%

“…Where the bars are not visible, 1 SE is <4 ppm. Source of data for orogenic peridotites: Lanzo (Lorand et al, 1993), Western Pyrenean Massif (Lorand, 1991), Eastern…”

mentioning

confidence: 99%

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Sulfide enrichment at an oceanic crust-mantle transition zone: Kane Megamullion (23°N, MAR)

Ciążela

Koepke

Dick

et al. 2018

Geochimica et Cosmochimica Acta

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ABSTRACT:The Kane Megamullion oceanic core complex located along the Mid-Atlantic Ridge (23°30'N, 45°20'W) exposes lower crust and upper mantle directly on the ocean floor. We studied chalcophile elements and sulfides in the ultramafic and mafic rocks of the crust-mantle transition and the mantle underneath. We determined mineralogical and elemental composition and the Cu isotope composition of the respective sulfides along with the mineralogical and elemental composition of the respective serpentines. The rocks of the crust-mantle transition zone (i.e., plagioclase harzburgite, peridotite-gabbro contacts, and dunite) overlaid by troctolites are by one order of magnitude enriched in several chalcophile elements with respect to the spinel harzburgites of the mantle beneath. Whereas the range of Cu concentrations in spinel harzburgites is 7-69 ppm, the Cu concentrations are highly elevated in plagioclase harzburgites with a range of 90-209 ppm. The zones of the peridotite-gabbro contacts are even 2 more enriched, exhibiting up to 305 ppm Cu and highly elevated concentrations of As, Zn, Ga, Sb and Tl.High Cu concentrations show pronounced correlation with bulk S concentrations at the crust-mantle transition zone implying an enrichment process in this horizon of the oceanic lithosphere. We interpret this enrichment as related to melt-mantle reaction, which is extensive in crust-mantle transition zones. In spite of the ubiquitous serpentinization of primary rocks, we found magmatic chalcopyrites [CuFeS 2 ] as inclusions in plagioclase as well as associated with pentlandite [(Fe,Ni) indicate that the metal enrichment, increased sulfide modes, and potentially formation of small sulfide deposits could be expected globally along the petrological Moho.

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“…The mean of 28 ppm Cu found in the Kane Megamullion spinel harzburgites is close to typical depleted mantle values (Garuti et al, 1984;Lorand, 1989a;1991;Lorand et al, 1993;Fig. 5).…”

Section: Evidence For Melt Refertilizationsupporting

confidence: 72%

Section: Bulk-rock Trace-element Contentsmentioning

confidence: 95%

Section: Mechanism Of Melt Refertilizationmentioning

confidence: 99%

“…Where the bars are not visible, 1 SE is <4 ppm. Source of data for orogenic peridotites: Lanzo (Lorand et al, 1993), Western Pyrenean Massif (Lorand, 1991), Eastern…”

mentioning

confidence: 99%

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Sulfide enrichment at an oceanic crust-mantle transition zone: Kane Megamullion (23°N, MAR)

Ciążela

Koepke

Dick

et al. 2018

Geochimica et Cosmochimica Acta

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“…It has been suggested that the typical mantle xenoliths and Alpinetype orogenic peridotites have flat PGE patterns, in which the PGEs are not fractionated [3]. Furthermore, partial melting would lead to depletion of PPGEs over IPGEs in the mantle residues, which should display flat to negative PGE patterns [3,22,28,29]. Therefore, we suggest that the Bixiling garnet peridotites are refractory mantle residues after melt extraction but represent fractional crystallization products of mantle-derived melts, which is also supported by both trace-element and isotope compositions as discussed above.…”

Section: Bixiling Eclogites and Peridotitesmentioning

confidence: 99%

Different Origins of the Fractionation of Platinum-Group Elements in Raobazhai and Bixiling Mafic-Ultramafic Rocks from the Dabie Orogen, Central China

Liu

Hou

Xie

et al. 2012

Journal of Geological Research

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Concentrations of the platinum group elements (PGEs), including Ir, Ru, Rh, Pt, and Pd, have been determined for both Raobazhai and Bixiling mafic-ultramafic rocks from the Dabie Orogen by fire assay method. Geochemical compositions suggest that the Raobazhai mafic-ultramafic rocks represent mantle residues after variable degrees of partial melting. They show consistent PGE patterns, in which the IPGEs (i.e., Ir and Ru) are strongly enriched over the PPGEs (i.e., Pt and Pd). Both REE and PGE data of the Raobazhai mafic-ultramafic rocks suggest that they have interacted with slab-derived melts during subduction and/or exhumation. The Bixiling ultramafic rocks were produced through fractional crystallization and cumulation from magmas, which led to the fractionated PGE patterns. During fractional crystallization, Pd is in nonsulfide phases, whereas both Ir and Ru must be compatible in some mantle phases. We suggest that the PGE budgets of the ultramafic rocks could be fractionated by interaction with slab-derived melts and fractional crystallization processes.

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Refertilization of depleted mantle peridotite in the Nagaland–Manipur ophiolite, north‐east India: Constraints from PGE, mineral, and whole‐rock geochemistry

Chaubey

Singh

et al. 2022

Geological Journal

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This paper discusses whole‐rock geochemistry, mineral chemistry, and platinum group element (PGE) systematics of depleted mantle rocks (harzburgite and dunite) from the northern part of Nagaland–Manipur Ophiolite (NMO), north‐east India, to comprehend their source features, fractionation behaviour of PGE during magmatic evolution, and its tectonic origin. The studied ultramafic rocks are characterized by a low concentration of CaO (0.57–0.71 wt%), Al2O3 (0.18–0.92 wt%) with ∑REE of 1.135–2.702 ppm and high concentrations of MgO (38.70–44.21 wt%), Cr (1,843–4,572 ppm), and Ni (894–4,138 ppm). They show U‐shaped REE patterns [LREE and HREE enrichment (La/Sm)N = 1.85–4.11, (Dy/Yb)N = 0.51–0.85]. Olivine ranges Fo 88.18 to Fo92.23, whereas Cpx and Opx range En44.84 to En47.89 and En86.37 to En93.37 respectively. The chrome spinel Cr# [Cr/(Cr + Al)] and Mg# [Mg/(Mg + Fe2+)] are 0.47–0.83 and 0.31–0.60, respectively, which indicates recrystallization from a boninitic magma in a Supra‐Subduction Zone setting. Conventional thermometry indicates the equilibration temperatures of the dunite sample yielded high temperatures of ~850°C, suggesting their formation due to later interaction with high‐temperature percolating melts. The PGE contents in harzburgite are low (125.6–142.8 ppb) as compared to the dunite (248–360 ppb). They have high PPGE/IPGE and negative Pt* (Pt/Pt* = 0.73) anomaly, which is characteristic of re‐entry of PPGE into the system via reaction with percolating basaltic melt in the mantle wedge. Significantly higher concentration of PPGEs than IPGEs in the samples, indicating recrystallization of PPGEs with early sulphide fractionation. The presence of significant Rh and Pd enhancements relative to Pt in all samples suggests that Pt was removed during PGE fractionation. This could be one of the reasons for both harzburgite and dunite's sulphide undersaturation. PGE distribution in NMO ultramafic rocks was therefore validated as being governed by sulphide saturation in parental magma and altered not only by partial melting but also by fractionation during their production in the Supra‐Subduction Zone environment.

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Copper and Noble Metal Enrichments Across the Lithosphere--Asthenosphere Boundary of Mantle Diapirs: Evidence from the Lanzo Lherzolite Massif

Cited by 97 publications

References 0 publications

Sulfide enrichment at an oceanic crust-mantle transition zone: Kane Megamullion (23°N, MAR)

Sulfide enrichment at an oceanic crust-mantle transition zone: Kane Megamullion (23°N, MAR)

Different Origins of the Fractionation of Platinum-Group Elements in Raobazhai and Bixiling Mafic-Ultramafic Rocks from the Dabie Orogen, Central China

Refertilization of depleted mantle peridotite in the Nagaland–Manipur ophiolite, north‐east India: Constraints from PGE, mineral, and whole‐rock geochemistry

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