Basaltic liquids and harzburgitic residues in the Garrett Transform: A case study at fast-spreading ridges

Niu, Yaoling and Hékinian, Roger (1997) Basaltic liquids and harzburgitic residues in the Garrett Transform: A case study at fast-spreading ridges. Earth and Planetary Science Letters, 146 1-2: 243-258.

Author Niu, Yaoling
Hékinian, Roger
Title Basaltic liquids and harzburgitic residues in the Garrett Transform: A case study at fast-spreading ridges
Journal name Earth and Planetary Science Letters   Check publisher's open access policy
ISSN 0012-821X
Publication date 1997-01-01
Sub-type Article (original research)
Open Access Status Not yet assessed
Volume 146
Issue 1-2
Start page 243
End page 258
Total pages 16
Language eng
Subject 1908 Geophysics
1906 Geochemistry and Petrology
1901 Earth and Planetary Sciences (miscellaneous)
1912 Space and Planetary Science
Abstract The peridotite-basalt association in the Garrett Transform, ∼13°28′S, East Pacific Rise (EPR), provides a prime opportunity for examining mantle melting and melt extraction processes from both melts and residues produced in a common environment beneath fast-spreading ridges. The peridotites are highly depleted, clinopyroxene-poor, harzburgites. Residual spinel, orthopyroxene and clinopyroxene in these harzburgites are extremely depleted in AlO, and plot at the most depleted end of the abyssal peridotite array defined by samples from slow-spreading ridges (including samples from hotspot-influenced ridges), suggesting that these harzburgites are residues of very high extents of melting. The residual peridotites from elsewhere at the EPR (i.e., Hess Deep and the Terevaka Transform) also are similarly depleted. This suggests that the extent of melting beneath the EPR is similar to, or even higher than, beneath ridges influenced by hotspots (e.g., Azores hotspot in the Atlantic Ocean and Bouvet hotspot in the Indian Ocean), and is significantly higher than ≤10%, a value that has been advocated to be the average extent of melting beneath global ocean ridges. Many of these harzburgite samples, however, show whole-rock incompatible element abundances higher than expected. These same samples also have various amounts of excess olivine with forsterite contents as low as Fo. The total olivine modes correlate inversely with olivine forsterite contents, and positively with whole-rock incompatible element abundances. These correlations suggest that the excess olivine and incompatible element enrichment are both the result of melt-solid re-equilibration. The buoyant melts that ascend through previously depleted residues crystallize olivine at shallow levels as a result of cooling. Entrapment of these melts leads to whole-rock incompatible element enrichment. These observations contrast with the notion that melts formed at depth experience little low pressure equilibration during ascent.
Keyword East Pacific Rise
Harzburgite
Mantle
Melts
Mid-ocean ridge basalts
Mid-ocean ridges
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collection: Scopus Import - Archived
 
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Created: Fri, 29 Dec 2017, 11:05:28 EST