54 research outputs found
Melt migration and melt-rock reaction in the Alpine-Apennine peridotites: Insights on mantle dynamics in extending lithosphere
PETROLOGICAL CONSTRAINTS ON THE ORIGIN OF PYROXENITE DYKES IN THE LITHOSPHERIC MANTLE OF THE CHESHMEH-BID OPHIOLITIC MASSIF, SOUTHERN IRAN
The Cheshmeh-Bid ophiolitic massif in the Khajeh-Jamali district (Southern Iran) is dominated by harzburgite-dunite tectonites locally intruded by orthopy-roxenite dikes. These latter are composed of dominant coarse orthopyroxene with minor olivine, Cr-spinel, clinopyroxene and amphibole. Estimated equilibrium temperatures for Mg-hornblende and edenitic amphibole reveal a late stage magmatic origin.The Cheshmeh-Bid orthopyroxenites are characterized by very low Al2O3, CaO, Na2O and TiO2 abundances coupled to relatively high MgO and SiO2contents. They display U-shaped REE patterns, selective LILE enrichment and positive Pb and Sr anomalies. The host harzburgites are highly refractory mantle residues resulting from fluid-assisted melting. Field observations and mineral assemblages suggest that the pyroxenites formed by melt injection along fractures within rather cold ambient harzburgites and chromitites at moderate pressure (P > 1 GPa). Based on bulk-rock compositions and mineral chemistry, we infer that the Cheshmeh-Bid orthopyroxenites originated from the intrusion and crystallization of hydrous Si-rich, low-Ca melts with a boninite signature in a supra-subduction environment. Fine-grained neoblastic domains developed in the pyroxenites in response to subsolidus ductile deformation and recrystallization, which were most likely related to the exhumation of the Cheshmeh-Bid ophiolite massif
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Meter-scale Nd isotopic heterogeneity in pyroxenite-bearing Ligurian peridotites encompasses global-scale upper mantle variability
Pyroxenites embedded in peridotite are often invoked as a major cause of short-length scale isotopic heterogeneities in the upper mantle, but there has been little direct evidence. We report spatially controlled chemical and Sr-Nd isotopic compositions of pyroxenites and their host peridotites from an ophiolitic mantle sequence in the Northern Apennines, Italy, with depleted mantle compositions, representing a surface exposure of veined upper mantle, a potential source for mid-oceanic-ridge basalts (MORB). Interaction between pyroxenites and adjacent mantle rocks results in centimeter-scale chemical modifications in the host peridotites, systematically lowering their Sm/Nd ratios. Over time, this interaction causes the host peridotite at greater than 0.1 m scale to acquire an isotopic heterogeneity larger than the range defined by the peridotite and pyroxenite end-members. Moreover, the 143Nd/144Nd variation of a single outcrop covers most of the global Nd isotopic variability documented in abyssal peridotites. Such pyroxenite-peridotite veined mantle domains may represent the enriched component rarely found in abyssal peridotites, but often invoked to account for the low end of 143Nd/144Nd variations in MORB
Meter-scale Nd isotopic heterogeneity in pyroxenite-bearing Ligurian peridotites encompasses global-scale upper mantle variability
Pyroxenites embedded in peridotite are often invoked as a major cause of short-length scale isotopic heterogeneities in the upper mantle, but there has been little direct evidence. We report spatially controlled chemical and Sr-Nd isotopic compositions of pyroxenites and their host peridotites from an ophiolitic mantle sequence in the Northern Apennines, Italy, with depleted mantle compositions, representing a surface exposure of veined upper mantle, a potential source for mid-oceanic-ridge basalts (MORB). Interaction between pyroxenites and adjacent mantle rocks results in centimeter-scale chemical modifications in the host peridotites, systematically lowering their Sm/Nd ratios. Over time, this interaction causes the host peridotite at greater than 0.1 m scale to acquire an isotopic heterogeneity larger than the range defined by the peridotite and pyroxenite end-members. Moreover, the 143Nd/144Nd variation of a single outcrop covers most of the global Nd isotopic variability documented in abyssal peridotites. Such pyroxenite-peridotite veined mantle domains may represent the enriched component rarely found in abyssal peridotites, but often invoked to account for the low end of 143Nd/144Nd variations in MORB
Subsolidus phase relations in a mantle pyroxenite: an experimental study from 0.7 to 1.5 GPa
Melt migration and intrusion in the Erro-Tobbio peridotites (Ligurian Alps, Italy): Insights on magmatic processes in extending lithospheric mantle
The role of secondary pyroxenites in the composition of melts from veined mantle sources: experimental constraints
Forsterite-Anorthite-CaTschermak-Enstatite (FACE): A geobarometer for plagioclase-bearing peridotites
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