1,720,973 research outputs found
Alpine-Apennine ophiolitic peridotites: new concepts on their composition and evolution.
No full textStructure and petrology of the Erro-Tobbio metaperidotite (Voltri Massif, Western Alps):some inferences on the alpine tectonics
No full textMelt migration in ophiolitic peridotites: the message from Alpine-Appennine peridotites and implication from embryonic ocean basins.
No full textMelt/peridotite interaction in the Southern Lanzo peridotite: Field, textural and geochemical evidence
No full textThis paper presents field, petrographic–structural and geochemical data on spinel and plagioclase peridotites from the
southern domain of the Lanzo ophiolitic peridotite massif (Western Alps). Spinel lherzolites, harzburgites and dunites crop out at Mt. Arpone and Mt. Musinè. Field evidence indicates that pristine porphyroclastic spinel lherzolites are transformed to
coarse granular spinel harzburgites, which are in turn overprinted by plagioclase peridotites, while strongly depleted spinel
harzburgite and dunite bands and bodies replace the plagioclase peridotites. On the northern flank of Mt. Arpone, deformed,
porphyroclastic (lithospheric) lherzolites, with diffuse pyroxenite banding, represent the oldest spinel-facies rocks. They show
microstructures of a composite subsolidus evolution, suggesting provenance from deeper (asthenospheric) mantle levels and
accretion to the lithosphere. These protoliths are locally transformed to coarse granular (reactive) spinel harzburgites and
dunites, which show textures reminiscent of melt/rock reaction and geochemical characteristics suggesting that they are
products of peridotite interaction with reactively percolating melts. Geochemical data and modelling suggest that <1–5%
fractional melting of spinel-facies DMM produced the injected melts. Plagioclase peridotites are hybrid rocks resulting from
pre-existing spinel peridotites and variable enrichment of plagioclase and micro-gabbroic material by percolating melts. The
impregnating melts attained silica-saturation, as testified by widespread orthopyroxene replacement of olivine, during open
system migration in the lithosphere. At Mt. Musinè, coarse granular spinel harzburgite and dunite bodies replace the
plagioclase peridotites. Most of these replacive, refractory peridotites have interstitial magmatic clinopyroxene with trace
element compositions in equilibrium with MORB, while some Cpx have REE-depleted patterns suggesting transient
geochemical features of the migrating MORB-type melts, acquired by interaction with the ambient plagioclase peridotite.
These replacive spinel harzburgite and dunite bodies are interpreted as channels exploited for focused and reactive migration of silica-undersaturated melts with aggregate MORB compositions. Such melts were unrelated to the silica-saturated melts that refertilized the pre-existing plagioclase peridotites. Finally, MORB melt migration occurred along open fractures, now recorded as gabbroic dikes. Our data document the complexity of rock-types and mantle processes in the South Lanzo peridotite massif and describe a composite tectonic and magmatic scenario that is not consistent with the “asthenospheric scenario” proposed by previous authors. We envisage a “transitional scenario” in which extending subcontinental lithospheric mantle was strongly modified (both depleted and refertilized) by early melts with MORB-affinity formed by decompression partial melting of the upwelling asthenosphere, during pre-oceanic rifting and lithospheric thinning in the Ligurian Tethys realm
Ophiolitic peridotites of the Alpine-Apennine system: mantle processes and geodynamic relevance.
No full textB, Cl, Li Variability in the Subducted Oceanic Mantle and in Antigorite-Breakdown Fluids: Implications for Fluid Processes and Light Element Recycling
No full textThe pre-alpine to alpine structural and tectonic evolution of sub continental mantle: a comparison of the Erro-Tobbio peridotite (Voltri Massif, Ligurian Alps) and the Malenco ultramafics (Val Malenco, Central Eastern Alps)
No full textRevisiting the Lanzo peridotite (NW-Italy): ‘asthenospherization’ of ancient mantle lithosphere.
No full textIn this paper, we comipled previous investigations and summarized recent results to show that the Lanzo peridotite records a sequence of deep lithospheric igneous events that largely obliterated the previous subcontinental history. Field, microtextural and trace element data indicate the progressive evolution of an igneous system that forms above an upwelling asthenosphere, most probably during the transition from a rifted system to the establishement of an (ultra-) slow spreading ridge of the Piedmont Ligurian ocean. Pervasive porous flow of melt forming 'reactive' spinel peridotites followed by plagioclase peridotite is later replaced by focused porous flow, reflected by a sysstem of replacive harzburgite and dunites. Cooling of the Lanzo peridotite leads to the interstitial crystallization of clinopyroxene and plagioclase, and finally to the formation of gabbro dikes. Thus, the Lanzo peridotite may indicate the extension-driven 'asthenospherization' of lithospheric mantle is an important process in the development of embryonic ocean basins
The variability of boron and chlorine concentrations in the subducted hydrous oceanic mantle
No full text- …
