Abstract
Peridotitic sulfide inclusions in diamonds from the central Slave craton constrain the age and origin of their subcontinental lithospheric mantle (SCLM) source. In the Re-Os isochron diagram, sulfides form two ca 3.4 Ga age arrays with variably elevated initial 187Os/188Os indicative of enriched sources. Archean to recent plume-derived melts carry a subducted crust (eclogite) signature [1], and some cratonic mantle lithosphere may have been generated in plumes by extraction of komatiitic liquids [2]. We explain our data by melting in a hybrid mantle plume that contains domains of recycled eclogite [1] and/or (?plume-initiated) subduction of proximal evolved lithospheric material [3].
In upwelling hybrid mantle, eclogite will melt first. Melts will react with olivine in surrounding peridotites to form orthopyroxene (opx), convert peridotite to pyroxenite [1] and confer their crustal isotope signatures. Upon further decompression, pyroxenitic melts [1] pervade the near-solidus mantle, helping local isotopic homogenization and adding aluminous opx. The subsequent partial melting of this opx- (Al- and Si-) enriched source generated komatiites and complementary ultradepleted cratonic mantle residues.
Subduction still is needed to explain many cratonic features. Nonetheless, this model satisfies several key observations: (1) suprachondritic initial 187Os/188Os in subsets of lithospheric mantle samples and in some coeval Archaean komatiites; (2) variable aluminous opx enrichment and (3) high Mg# combined with high opx content in cratonic SCLM [2] due to higher melt productivity of an Al- and Si-richer source [4], in addition to higher Archean temperatures. The model also alleviates a mass balance problem [2, 4] because it predicts a hybrid mantle source with variably higher SiO2 than pyrolite, and contrary to a primitive mantle source is able to reconcile compositions of komatiites and complementary cratonic mantle residues.
In upwelling hybrid mantle, eclogite will melt first. Melts will react with olivine in surrounding peridotites to form orthopyroxene (opx), convert peridotite to pyroxenite [1] and confer their crustal isotope signatures. Upon further decompression, pyroxenitic melts [1] pervade the near-solidus mantle, helping local isotopic homogenization and adding aluminous opx. The subsequent partial melting of this opx- (Al- and Si-) enriched source generated komatiites and complementary ultradepleted cratonic mantle residues.
Subduction still is needed to explain many cratonic features. Nonetheless, this model satisfies several key observations: (1) suprachondritic initial 187Os/188Os in subsets of lithospheric mantle samples and in some coeval Archaean komatiites; (2) variable aluminous opx enrichment and (3) high Mg# combined with high opx content in cratonic SCLM [2] due to higher melt productivity of an Al- and Si-richer source [4], in addition to higher Archean temperatures. The model also alleviates a mass balance problem [2, 4] because it predicts a hybrid mantle source with variably higher SiO2 than pyrolite, and contrary to a primitive mantle source is able to reconcile compositions of komatiites and complementary cratonic mantle residues.
Original language | English |
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Pages (from-to) | A37-A37 |
Number of pages | 1 |
Journal | Geochimica et Cosmochimica Acta |
Volume | 74 |
Issue number | 12, Supplement |
DOIs | |
Publication status | Published - Jun 2010 |
Externally published | Yes |
Event | Goldschmidt Conference (20th : 2010) - Knoxville, United States Duration: 13 Jun 2010 → 18 Jun 2010 |