NDLI: An experimental study of focused magma transport and basalt–peridotite interactions beneath mid-ocean ridges: implications for the generation of primitive MORB compositions

Content Provider	Springer Nature Link
Author	Lambart, Sarah Laporte, Didier Schia, Pierre
Copyright Year	2008
Abstract	We performed experiments in a piston-cylinder apparatus to determine the effects of focused magma transport into highly permeable channels beneath mid-ocean ridges on: (1) the chemical composition of the ascending basalt; and (2) the proportions and compositions of solid phases in the surrounding mantle. In our experiments, magma focusing was supposed to occur instantaneously at a pressure of 1.25 GPa. We first determined the equilibrium melt composition of a fertile mantle (FM) at 1.25 GPa-1,310°C; this composition was then synthesised as a gel and added in various proportions to peridotite FM to simulate focusing factors Ω equal to 3 and 6 (Ω = 3 means that the total mass of liquid in the system increased by a factor of 3 due to focusing). Peridotite FM and the two basalt-enriched compositions were equilibrated at 1 GPa-1,290°C; 0.75 GPa-1,270°C; 0.5 GPa-1,250°C, to monitor the evolution of phase proportions and compositions during adiabatic decompression melting. Our main results may be summarised as follows: (1) magma focusing induces major changes of the coefficients of the decompression melting reaction, in particular, a major increase of the rate of opx consumption, which lead to complete exhaustion of orthopyroxene (and clinopyroxene) and the formation of a dunitic residue. A focusing factor of ≈4—that is, a magma/rock ratios equal to ≈0.26—is sufficient to produce a dunite at 0.5 GPa. (2) Liquids in equilibrium with olivine (±spinel) at low pressure (0.5 GPa) have lower SiO2 concentrations, and higher concentrations in MgO, FeO, and incompatible elements (Na2O, K2O, TiO2) than liquids produced by decompression melting of the fertile mantle, and plot in the primitive MORB field in the olivine–silica–diopside–plagioclase tetrahedron. Our study confirms that there is a genetic relationship between focused magma transport, dunite bodies in the upper mantle, and the generation of primitive MORBs.
Starting Page	429
Ending Page	451
Page Count	23
File Format	PDF
ISSN	00107999
Journal	Contributions to Mineralogy and Petrology
Volume Number	157
Issue Number	4
e-ISSN	14320967
Language	English
Publisher	Springer-Verlag
Publisher Date	2008-09-25
Publisher Place	Berlin/Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Dunite Peridotite Partial melting Focused magma transport Primitive MORB Magma/rock interactions Mineralogy Mineral Resources Geology
Content Type	Text
Resource Type	Article
Subject	Geochemistry and Petrology Geophysics

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