1,721,053 research outputs found
Genesis of quartz-rich geodes from peculiar aqueous fluids in a Cu-Zn-Pb skarn (Temperino mine, Italy) and relations with ore bodies
No full textThe Temperino deposit is an historical Cu-Zn-Pb skarn
located in the the Tuscan magmatic province of Italy. It
consists mainly of massive lenses of sulfide bodies, enclosed
within white marble, from which chalcopyrite, sphalerite, and
galena were exploited in the past. These bodies occur close
to trachyandesite and rhyolite porphyry dikes and within
NNW-SSE trending, en-echelon and discontinuous ilvaite and
hedenbergite skarn masses.
A peculiar characteristics of this deposit is the presence of
quartz-rich geodes wthin the ilvaite and hedenbergite skarns.
The geodes occur close to the sulfide lenses, have variable
volumes (range: from 10-20 cm3 to 2-3 m3), and are enclosed within the massive ilvaite and hedenbergite skarns. They represent the end of the main mineralizing event at
Temperino. In addition to large euhedral quartz crystals (up to
15 cm in legth), geodes contain ilvaite, calcite, epidote, and
small propostions of ore minerals.
We determined the physical-chemical properties of the
geode fluid combining microthermometry, Raman
spectrometry, EMPA, CL imaging, and LA-ICP-MS of fluid
inclusions entrapped at several stages of euhedral quartz
growth. The crystals show alternations of 100 micron- to 1 mm thick bands variably enriched in Al, Na, Li, Rb, Sr, Sb, Ba,
Mn, B, Cs, and Zn, so they are chemically zoned. This zoining
was accounted for in the determination of inclusion
compositions. Fluid inclusions host two- (L, V) to five phase
(L,V, and 3 solids) aqueous fluids. Depite this, their estimated
bulk salinity is unexpectedly low (0.4-2.9 wt% NaCl eq.) and
does not change systematically within the crystals. The
Th(total) of all fluids is consistently in the 220-260 °C range
and homogenzation occurs mainly by bubble disappearance.
The main inclusion components are (in order of relative
abundance) Na, K, B, Sr, Sb, Ba, Mn, Rb, Cs, Zn, Pb, and Cu,
i.e., the same that make the quartz zoning
Orogenic garnet peridotites as tracers of mantle wedge transformations and metasomatism by subduction fluids
No full textSerpentine dehydration recorded by garnet peridotites and chlorite harzburgites from Cima di Gagnone.
No full textPetrology and Trace Element Budgets of High-pressure Peridotites Indicate Subduction Dehydration of Serpentinized Mantle (Cima di Gagnone, Central Alps, Switzerland)
No full textISSN:0022-3530ISSN:1460-2415ISSN:1460-241
Fluid-mobile elements in serpentinites: Constraints on serpentinisation environments and element cycling in subduction zones.
No full textFluid-mobile element (FME) systematics in serpentinites are key to unravel the environments of mantle rock hydration, dehydration, and element recycling in subduction zones. Here we compile serpentinite geochemical data and, for the first time, report discriminative FME enrichment trends for mid ocean ridge vs. forearc serpentinisation by applying alkali element-U ratios. Characteristic element fractionations are thereby governed by redox-dependent differential U mobility at mid ocean ridges and in forearcs, and by high Cs input in forearcs due to fluids equilibrated with sediments. Simple modelling reproduces the observed enrichment trends in serpentinites that range over several orders of magnitude. From these systematics, first constraints on potentially discriminative fractionation trends for unconventional fluid tracers such as B, As, and Sb can be deduced. Prominent W enrichments that correlate with FMEs suggest significant W mobility in low-temperature serpentinising environments. Application of the alkali element-U systematics to the subducted metaperidotites of Erro Tobbio (recording initial brucite + antigorite breakdown during subduction) and Almirez (recording final antigorite breakdown) reveal that pre-subduction FME enrichment signatures are retained in progressively subducted hydrous mantle rocks to beyond subarc levels. Associated dehydration veins and fluid inclusions reveal subordinate alkali element-U fractionation trends during dehydration. Subducted hydrous mantle rocks therefore may introduce characteristic element signatures and thus contribute towards mantle geochemical heterogeneities
Ophiolitic peridotites of the Alpine-Apennine system: mantle processes and geodynamic relevance.
No full textThe fate of B, Cl and Li in the subducted oceanic mantle and in the antigorite breakdown fluids
No full textFluid-induced crystallization of majoritic garnet during Scandian continental subduction, Western Gneiss Region, Norway
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