Nanoscale Structure of Zoned Laurites from the Ojen Ultramafic Massif, Southern Spain
Por:
Baurier-Aymat, Sandra, Jimenez-Franco, Abigail, Roque-Rosell, Josep, Maria Gonzalez-Jimenez, Jose, Gervilla, Fernando, Proenza, Joaquin A., Mendoza, Joan, Nieto, Fernando
Publicada:
1 may 2019
Resumen:
We report the first results of a combined focused ion beam and
high-resolution transmission electron microscopy (FIB/HRTEM)
investigation of zoned laurite (RuS2)-erlichmanite (OS2) in
mantle-hosted chromitites. These platinum-group minerals form isolated
inclusions (<50 mu m across) within larger crystals of unaltered
chromite form the Ojen ultramafic massif (southern Spain).
High-magnification electron microscopy (HMEM), high angle-annular dark
field (HAADF) and precession electron diffraction (PED) data revealed
that microscale normal zoning in laurite consisting of Os-poor core and
Os-rich rims observed by conventional micro-analytical techniques like
field emission scanning electron microscope and electron microprobe
analysis (FE-SEM and EPMA) exist at the nanoscale approach in single
laurite crystals. At the nanoscale, Os poor cores consist of relatively
homogenous pure laurite (RuS2) lacking defects in the crystal lattice,
whereas the Os-richer rim consists of homogenous laurite matrix hosting
fringes (10-20 nm thickness) of almost pure erlichmanite (OsS2).
Core-to-rim microscale zoning in laurite reflects a nonequilibrium
during laurite crystal growth, which hampered the intra-crystalline
diffusion of Os. The origin of zoning in laurite is related to the
formation of the chromitites in the Earth's upper mantle but fast
cooling of the chromite-laurite magmatic system associated to fast
exhumation of the rocks would prevent the effective dissolution of Os in
the laurite even at high temperatures (1200 degrees C), allowing the
formation/preservation of nanoscale domains of erlichmanite in laurite.
Our observation highlights for the first time the importance of
nanoscale studies for a better understanding of the genesis of
platinum-group minerals in magmatic ore-forming systems.
Filiaciones:
Baurier-Aymat, Sandra:
Univ Barcelona, Dept Mineral Petrol & Geol Aplicada, Marti & Franques S-N, E-08028 Barcelona, Spain
Jimenez-Franco, Abigail:
Univ Barcelona, Dept Mineral Petrol & Geol Aplicada, Marti & Franques S-N, E-08028 Barcelona, Spain
Univ Barcelona, Inst Nanociencia & Nanotecnol, Fac Quim IN2UB, Av Diagonal 645, E-08028 Barcelona, Spain
Univ Nacl Autonoma Mexico, Posgrad Ciencias Tierra, Ciudad Univ, Cd De Mexico 04510, Mexico
Roque-Rosell, Josep:
Univ Barcelona, Dept Mineral Petrol & Geol Aplicada, Marti & Franques S-N, E-08028 Barcelona, Spain
Univ Barcelona, Inst Nanociencia & Nanotecnol, Fac Quim IN2UB, Av Diagonal 645, E-08028 Barcelona, Spain
Maria Gonzalez-Jimenez, Jose:
Univ Granada, Dept Mineral & Petrol, Fac Ciencias, Avda Fuentenueva S-N, Granada 18002, Spain
Gervilla, Fernando:
Univ Granada, Dept Mineral & Petrol, Fac Ciencias, Avda Fuentenueva S-N, Granada 18002, Spain
CSIC UGR, IACT, Avda Palmeras 4, Granada 18100, Spain
Proenza, Joaquin A.:
Univ Barcelona, Dept Mineral Petrol & Geol Aplicada, Marti & Franques S-N, E-08028 Barcelona, Spain
Univ Barcelona, Inst Nanociencia & Nanotecnol, Fac Quim IN2UB, Av Diagonal 645, E-08028 Barcelona, Spain
Mendoza, Joan:
Univ Barcelona, Ctr Cient & Tecnol, Lluis Sole & Sabaris 1-3, E-08028 Barcelona, Spain
Nieto, Fernando:
Univ Granada, Dept Mineral & Petrol, Fac Ciencias, Avda Fuentenueva S-N, Granada 18002, Spain
CSIC UGR, IACT, Avda Palmeras 4, Granada 18100, Spain
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