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Mineralogy, geochemistry, and Nd isotope composition of the Rainbow hydrothermal field, Mid-Atlantic Ridge 总被引:3,自引:0,他引:3
Petrological, geochemical, and Nd isotopic analyses have been carried out on rock samples from the Rainbow vent field to assess the evolution of the hydrothermal system. The Rainbow vent field is an ultramafic-hosted hydrothermal system located on the Mid-Atlantic Ridge characterized by vigorous high-temperature venting (∼365°C) and unique chemical composition of fluids: high chlorinity, low pH and very high Fe, and rare earth element (REE) contents (Douville et al., Chemical Geology 184:37–48, 2002). Serpentinization has occurred under a low-temperature (<270°C) retrograde regime, later overprinted by a higher temperature sulfide mineralization event. Retrograde serpentinization reactions alone cannot reproduce the reported heat and specific chemical features of Rainbow hydrothermal fluids. The following units were identified within the deposit: (1) nonmineralized serpentinite, (2) mineralized serpentinite—stockwork, (3) steatite, (4) semimassive sulfides, and (5) massive sulfides, which include Cu-rich massive sulfides (up to 28wt% Cu) and Zn-rich massive sulfide chimneys (up to 5wt% Zn). Sulfide mineralization has produced significant changes in the sulfide-bearing rocks including enrichment in transition metals (Cu, Zn, Fe, and Co) and light REE, increase in the Co/Ni ratios comparable to those of mafic Cu-rich volcanic-hosted massive sulfide deposits and different 143Nd/144Nd isotope ratios. Vent fluid chemistry data are indicative of acidic, reducing, and high temperature conditions at the subseafloor reaction zone where fluids undergo phase separation most likely under subcritical conditions (boiling). An explanation for the high chlorinity is not straightforward unless mixing with high salinity brine or direct contribution from a magmatic Cl-rich aqueous fluid is considered. This study adds new data, which, combined with the current knowledge of the Rainbow vent field, brings compelling evidence for the presence, at depth, of a magmatic body, most likely gabbroic, which provides heat and metals to the system. Co/Ni ratios proved to be good tools used to discriminate between rock units, degree of sulfide mineralization, and positioning within the hydrothermal system. Deeper units have Co/Ni <1 and subsurface and surface units have Co/Ni >1. 相似文献
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Sub-solidus Oligocene zircon formation in garnet peridotite during fast decompression and fluid infiltration (Duria, Central Alps) 总被引:1,自引:0,他引:1
Summary A garnet peridotite lens from Monte Duria (Adula nappe, Central Alps, Northern Italy) contains porphyroblastic garnet and
pargasitic amphibole and reached peak metamorphic conditions of ∼830 C, ∼2.8 GPa. A first stage of near isothermal decompression
to pressures <2.0 GPa is characterised by domains where fine grained spinel, clinopyroxene, orthopyroxene and amphibole form.
The newly formed amphibole contains elevated levels of fluid mobile elements such as Rb, Ba and Pb indicating that recrystallization
was assisted by infiltration of a crustal-derived fluid. Further decompression and cooling to ∼720 °C, 0.7–1.0 GPa associated
with limited fluid influx is documented by the formation of orthopyroxene-spinel-amphibole symplectites around garnet.
Zircon separated from this garnet peridotite exhibits two distinct zones. Domain 1 displays polygonal oscillatory zoning and
high trace element contents. It contains clinopyroxene and amphibole inclusions with the same composition as the same minerals
formed during the spinel peridotite equilibration, indicating that this domain formed under sub-solidus conditions during
decompression and influx of crustal fluids. Domain 2 has no zoning and much lower trace element contents. It replaces domain
1 and is likely related to zircon recrystallization during the formation of the symplectites. SHRIMP dating of the two domains
yielded ages of 34.2 ± 0.2 and 32.9 ± 0.3 Ma, respectively, indicating fast exhumation of the peridotite within the spinel
stability field. We suggest that the Duria garnet peridotite originates from the mantle wedge above the tertiary subduction
of the European continental margin and that it was assembled to the country rock gneisses between 34 and 33 Ma.
Third author was Deceased 相似文献
970.
V. A. Marinov S. V. Meledina O. S. Dzyuba O. S. Urman O. V. Yazikova V. A. Luchinina A. G. Zamirailova A. N. Fomin 《Stratigraphy and Geological Correlation》2006,14(4):418-432
Paleontological study of Upper Jurassic and Lower Cretaceous sediments recovered by boreholes in the Agan-Vakh and Nadym-Vengapur interfluves clarified environments of their deposition. As is shown, influx of siliciclastic material to central areas of the West Siberian sea basin varied through time. Taxonomic composition and ecological structure of nektonic and benthic fossil assemblages are analyzed and considered in terms of environmental factors such as hydrodynamics, aeration, temperature, and salinity of seawater. 相似文献