Element and isotopic signature of re-fertilized mantle peridotite as determined by nanopowder and olivine LA-ICPMS analyses
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Element and isotopic signature of re-fertilized mantle peridotite as determined by nanopowder and olivine LA-ICPMS analyses. / Lawley, Christopher; Pearson, D. Graham; Waterton, Pedro; Zagorevski, Alex; Bedard, Jean; Jackson, Simon E.; Petts, Duane; Kjarsgaard, Bruce; Zhang, Shuangquan; Wright, Donald.
I: Chemical Geology, Bind 536, 119464, 2020.Publikation: Bidrag til tidsskrift › Tidsskriftartikel › Forskning › fagfællebedømt
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T1 - Element and isotopic signature of re-fertilized mantle peridotite as determined by nanopowder and olivine LA-ICPMS analyses
AU - Lawley, Christopher
AU - Pearson, D. Graham
AU - Waterton, Pedro
AU - Zagorevski, Alex
AU - Bedard, Jean
AU - Jackson, Simon E.
AU - Petts, Duane
AU - Kjarsgaard, Bruce
AU - Zhang, Shuangquan
AU - Wright, Donald
PY - 2020
Y1 - 2020
N2 - The lithospheric mantle should be depleted in base- and precious-metals as these elements are transferred to the crust during partial melting. However, some melt-depleted mantle peridotites are enriched in these ore-forming elements. This may reflect re-fertilization of the mantle lithosphere and/or sequestering of these elements by residual mantle phase(s). Both processes remain poorly understood because of the low abundances of incompatible elements in peridotite and the nugget-like distribution of digestion-resistant mantle phases that pose analytical challenges for conventional geochemical methods. Herein we report new major and trace element concentrations for a suite of mantle peridotite and pyroxenite samples from the Late Permian to Middle Triassic Nahlin ophiolite (Cache Creek terrane, British Columbia, Canada) using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) analysis of nanoparticulate powders and olivine. Compatible to moderately incompatible element concentrations suggest that Nahlin ophiolite peridotites represent residues after ≥20% melt extraction. Pyroxenite dykes and replacive dunite bands are folded and closely intercalated with residual harzburgite. These field relationships, coupled with the presence of intergranular base metal sulphide, clinopyroxene and Cr-spinel at the microscale, point to percolating melts that variably re-fertilized melt-depleted mantle peridotite. Radiogenic Pb (206Pb/204Pb = 15.402–19.050; 207Pb/204Pb = 15.127–15.633; 208Pb/204Pb = 34.980–38.434; n = 45) and Os (187Os/188Os 0.1143–0.5745; n = 58) isotope compositions for a subset of melt-depleted peridotite samples further support metasomatic re-fertilization of these elements. Other ore-forming elements are also implicated in these metasomatic reactions because some melt-depleted peridotite samples are enriched relative to the primitive mantle, opposite to their expected behaviour during partial melting. New LA-ICPMS analysis of fresh olivine further demonstrates that a significant proportion of the highly incompatible element budget for the most melt-depleted rocks is either hosted by, and/or occurs as trapped inclusions within, the olivine-rich residues. Trapped phases from past melting and/or re-fertilization events are the preferred explanation for unradiogenic Pb isotope compositions and Paleozoic to Paleoproterozoic Re-depletion model ages, which predate the Nahlin ophiolite by over one billion years.
AB - The lithospheric mantle should be depleted in base- and precious-metals as these elements are transferred to the crust during partial melting. However, some melt-depleted mantle peridotites are enriched in these ore-forming elements. This may reflect re-fertilization of the mantle lithosphere and/or sequestering of these elements by residual mantle phase(s). Both processes remain poorly understood because of the low abundances of incompatible elements in peridotite and the nugget-like distribution of digestion-resistant mantle phases that pose analytical challenges for conventional geochemical methods. Herein we report new major and trace element concentrations for a suite of mantle peridotite and pyroxenite samples from the Late Permian to Middle Triassic Nahlin ophiolite (Cache Creek terrane, British Columbia, Canada) using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) analysis of nanoparticulate powders and olivine. Compatible to moderately incompatible element concentrations suggest that Nahlin ophiolite peridotites represent residues after ≥20% melt extraction. Pyroxenite dykes and replacive dunite bands are folded and closely intercalated with residual harzburgite. These field relationships, coupled with the presence of intergranular base metal sulphide, clinopyroxene and Cr-spinel at the microscale, point to percolating melts that variably re-fertilized melt-depleted mantle peridotite. Radiogenic Pb (206Pb/204Pb = 15.402–19.050; 207Pb/204Pb = 15.127–15.633; 208Pb/204Pb = 34.980–38.434; n = 45) and Os (187Os/188Os 0.1143–0.5745; n = 58) isotope compositions for a subset of melt-depleted peridotite samples further support metasomatic re-fertilization of these elements. Other ore-forming elements are also implicated in these metasomatic reactions because some melt-depleted peridotite samples are enriched relative to the primitive mantle, opposite to their expected behaviour during partial melting. New LA-ICPMS analysis of fresh olivine further demonstrates that a significant proportion of the highly incompatible element budget for the most melt-depleted rocks is either hosted by, and/or occurs as trapped inclusions within, the olivine-rich residues. Trapped phases from past melting and/or re-fertilization events are the preferred explanation for unradiogenic Pb isotope compositions and Paleozoic to Paleoproterozoic Re-depletion model ages, which predate the Nahlin ophiolite by over one billion years.
U2 - 10.1016/j.chemgeo.2020.119464
DO - 10.1016/j.chemgeo.2020.119464
M3 - Journal article
VL - 536
JO - Chemical Geology
JF - Chemical Geology
SN - 0009-2541
M1 - 119464
ER -
ID: 234468963