@misc{10481/71057,
year = {2021},
month = {8},
url = {http://hdl.handle.net/10481/71057},
abstract = {A variety of base-metal minerals (BMM) may form during hydration-dehydration of ultramafic rocks within
subduction zones. However, the trace element fingerprints of these minerals and their relation to different stages
of the subduction cycle are still unexplored. Here, we present the first comprehensive in situ analysis by Laser
Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) of (semi)-metals (Ni, Fe, As, Sb, Co, Bi, Te,
Pb, Cd, Se, Cu, Zn, and Mn) and precious metals (Os, Ir, Rh, Pt, Pd, Au, and Ag) for Ni–Fe–S–As minerals in
subducted serpentinites from the La Caba˜na area (South-Central Chile). The targeted rocks are medium- and
high-pressure serpentinites recording the entire cycle of burial-exhumation within a subduction zone. A first
stage of hydration of upper mantle peridotites within the mantle wedge led to formation of lizardite after
magmatic olivine at ~300 ◦C. This stage was followed by prograde hydration (i.e., antigoritization at
~320–400 ◦C; <1GPa) and subsequent partial dehydration (formation of prograde olivine at ~600 ◦C and 1.1
GPa) within the subduction channel, and final exhumation of the serpentinites and incorporation in the accretionary
prism still in the stability field of antigorite (>300 ◦C). The Ni–Fe–S–As minerals in these serpentinites
include Ni-Fe-rich sulfides [pentlandite (Ni,Fe)9S8), smythite (Fe9S11), heazlewoodite (Ni3S2), millerite (NiS)],
arsenides [orcelite (Ni5-xAs2), nickeline (NiAs) and maucherite (Ni11As8)] and, to a lesser extent, alloy (awaruite,
Ni3Fe) and sulfarsenides (gerdorffite, NiAsS). Their abundance, morphology and chemistry strongly vary with the
degree of serpentinization and style of deformation of the host rock. Thus, euhedral grains of heazlewoodite ±
awaruite ± magnetite formed in equilibrium with lizardite when magmatic olivine was hydrated within the
mantle wedge. Once the lizardite-olivine serpentinites were incorporated into the subduction serpentinite
channel, the infiltration of hotter (S-As-Sb)-bearing fluids promoted antigoritization under static regime and
precipitation of orcelite and pentlandite in equilibrium with antigorite. Channelling of fluids in zones of focussed
strain enhanced further antigoritization in some schistose serpentinites at decreasing fO2 and fS2, resulting in the
transformation of pentlandite into a second generation of heazlewoodite–awaruite–magnetite. After relic olivine
exhaustion, fO2 and fS2 increased promoting the replacement of the secondary heazlewoodite to millerite. No
significant variations in terms of trace elements were observed during these mineral replacements associated to
hydration upon prograde metamorphism and/or increasing of strain. In contrast, partial dehydration of serpentinites
under high-pressure conditions (> 1GPa) generated Ni-rich awaruite in equilibrium with the prograde
assemblage antigorite-metamorphic olivine. These awaruites are depleted in trace elements, indicating substantial
(semi)-metal and precious metal mobility during high P-T metamorphism within the subduction channel.
During the final stage of deformation linked to exhumation inside the accretionary prism some orcelite grains
formed during early antigoritization recrystallized without substantial change in trace element concentration. At this stage, nickeline singularly enriched in gold formed in equilibrium with the recrystallizing orcelite. These
results demonstrate that Ni–Fe–S–As minerals formed or modified during the entire subduction cycle of upper
mantle rocks have their own characteristic trace element signature (i.e., depletion in precious metals and
enrichment in As, Sb, Te, Bi and Pb) that distinguish them from magmatic counterparts.},
organization = {"Ministerio de Ciencia, Innovacion y Universidades"	RTI2018099157-A-I00},
organization = {Spanish Government	RYC-2015-17596},
organization = {Miguel Angel Hidalgo Laguna (CIC)},
publisher = {Elsevier},
keywords = {Subduction channel},
keywords = {Serpentinite},
keywords = {Base-metal mineral},
keywords = {Sulfides},
keywords = {Arsenides},
title = {Trace element fingerprints of Ni–Fe–S–As minerals in subduction channel serpentinites},
doi = {10.1016/j.lithos.2021.106432},
author = {González Jiménez, José María and Marchesi, Claudio and Padrón Navarta, José Alberto and Ramón Fernández, María and Gervilla Linares, Fernando},
}