Akira Ishikawa et al. (2004) Layered Lithospheric Mantle Beneath the Ontong Java Plateau: Implications from Xenoliths in Alnoite, Malaita, Solomon Islands, Journal of Petrology, 45, 2011-2044, doi: 10.1093/petrology/egh046. < 20120620142742-148-279 > pub

Map on Earth or stone. Places and analyses are shown.

  • abstract:

    A varied suite of mantle xenoliths from Malaita, Solomon Islands, was investigated to constrain the evolution of the mantle beneath the Ontong Java Plateau. Comprehensive petrological and thermobarometric studies make it possible to identify the dominant processes that produced the compositional diversity and to reconstruct the lithospheric stratigraphy in the context of a paleogeotherm. P–T estimates show that both peridotites and pyroxenites can be assigned to a shallower or deeper origin, separated by a garnet-poor zone of 10 km between 90 and 100 km. This zone is dominated by refractory spinel harzburgites (Fo91–92), indicating the occurrence of an intra-lithospheric depleted zone. Shallower mantle (∼Moho to 95 km) is composed of variably metasomatized peridotite with subordinate pyroxenite derived from metacumulates. Deeper mantle (∼95–120 km) is represented by pyroxenite and variably depleted peridotites that are unevenly distributed; the least-depleted garnet lherzolite (Fo90–91) lies just below the garnet-poor depleted zone (∼100–110 km), whereas the presence of pyroxenite is restricted to the deepest region (∼110–120 km), together with relatively Fe-enriched garnet lherzolite (Fo87–88). This depth-related variation (including the depleted zone) can be explained by assuming that the degree of melting for a basalt–peridotite hybrid source was systematically different at each level of arrival depth within a single adiabatically ascending mantle plume: (1) the depleted zone at the top of the mantle plume, where garnet was totally consumed in the residual solid; (2) an intermediate part of the plume dominated by the least-depleted garnet lherzolite just above the depth of the peridotite solidus; (3) the deepest pyroxenite-rich zone, whose petrochemical variation is best explained by the interaction between peridotite and normative quartz-rich basaltic melt, below the solidus of peridotite and liquidus of basalt. We explain the obvious lack of pyroxenites at shallower depths as the effective extraction of hybrid melt from completely molten basalt through the partially molten ambient peridotite, which caused the voluminous eruption of the Ontong Java Plateau basalts. From these interpretations, we conclude that the lithosphere forms a genetically unrelated two-layered structure, comprising shallower oceanic lithosphere and deeper impinged plume material, which involved a recycled basaltic component, now present as a pyroxenitic heterogeneity. This interpretation for the present lithospheric structure may explain the seismically anomalous root beneath the Ontong Java Plateau.

  • doi: 10.1093/petrology/egh046
  • modified at 16 h ago


(a) EPMA on EPMA JEOL JXA-8800R
Img 4843 thumb SAX9 < 20111128094000-724-268 >pub
  • classification: xenolithic
  • physical-form: chunk
  • status: (unknown)
  • description: mostly garnet
  • modified at 2014-04-14
Img 3451 thumb sax33 < 20110311093015-253-429 >pub
  • classification: mineral:pyroxene
  • physical-form: fraction
  • status: (unknown)
  • modified at 2016-02-11
Cpx sax39c thumb cpx-sax39c < 20090611163644190.hkitagawa >pub
  • classification: mineral:pyroxene
  • physical-form: grain
  • status: (unknown)
  • modified at 2019-08-07
Img 4841 thumb SAE152C < 20111128093947-661-568 >pub
  • classification: xenolithic
  • physical-form: grain
  • status: (unknown)
  • description: Ontong Java Plateau, Malaitan xenoliths, garnet clinopyroxenite
  • modified at 2019-09-04
Img 4839 thumb SAE116 < 20111128093932-459-753 >pub
  • classification: xenolithic
  • physical-form: grain
  • status: (unknown)
  • description: Ontong Java Plateau, Malaitan xenoliths, garnet clinopyroxenite
  • modified at 2019-09-03
Img 7918@c81a46acd353dcfb42eb4a3 thumb cpx-SAE113 < 20130228090217-163-658 >pub
  • classification: mineral:pyroxene
  • physical-form: grain
  • status: (unknown)
  • modified at 2020-04-28
Img 7917@bfe761bb284ac27c7a1fa68 thumb grt-SAE113 < 20130228090210-831-232 >pub
  • classification: mineral:garnet
  • physical-form: grain
  • status: (unknown)
  • modified at 2020-04-28
Img 4820 thumb mount-cpx-SAX33 < 20111115092257-154-137 >pub
  • classification: mineral:pyroxene
  • physical-form: on mount
  • status: (unknown)
  • modified at 2013-11-20
Img 1831 thumb SAG1 < 20100824093538769.hkitagawa >pub
  • classification: xenolithic
  • physical-form: aliquot
  • status: (unknown)
  • description: Ontong Java Plateau, Malaitan xenoliths, garnet lherzolite
  • modified at 2019-09-02
Img 1977 thumb mnt-ol-sas21 < 20080404232645.mw >pub
  • physical-form: aliquot
  • quantity (g): 0.0
  • status: (zero)
  • modified at 2018-02-07
Img 1834 thumb SAS47 < 20100824093539091.hkitagawa >pub
  • status: (unknown)
  • modified at 2010-09-03
Img 1832 thumb SAS21 < 20100824093538865.hkitagawa >pub
  • classification: xenolithic
  • physical-form: aliquot
  • status: (unknown)
  • description: Ontong Java Plateau, Malaitan xenoliths, high-temperature spinel harzburgite
  • modified at 2019-09-02
Img 1973 thumb mnt-ol-sas44 < 20080404232604.mw >pub
  • classification: mineral:olivine
  • physical-form: on mount
  • quantity (g): 0.0
  • status: (zero)
  • modified at 2018-02-07
Optical thumb cpx-sag30 < 20090313101750331.hkitagawa >pub
  • classification: mineral:pyroxene
  • physical-form: on mount
  • status: (unknown)
  • description: Clinopyroxenes are picked from xenolith (Malalite, Solomon) and mounted by A. Ishikawa.
  • modified at 2020-05-09
Img 4842 thumb SAE113 < 20111128093953-463-537 >pub
  • classification: xenolithic
  • physical-form: grain
  • quantity (g): 0.0
  • status: (zero)
  • description: Ontong Java Plateau, Malaitan xenoliths, garnet clinopyroxenite
  • modified at 2019-09-02
Sax 44 thumb SAX-44 < 20091002093527757.hkitagawa >pub
  • classification: xenolithic
  • physical-form: aliquot
  • status: (unknown)
  • description: Mantle xenoliths and volcanic rocks from Malaita, Solomon, collected by TITEC group
  • modified at 2020-04-27
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grt-SAE152C pub SIMS Cameca ims-5f 18 20190904114122-554935
grt-SAE152C pub TIMS Finnigan MAT261, MAT262 and Triton TI 11 20190904142433-783215
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cpx-SAE116 pub TIMS Finnigan MAT261, MAT262 and Triton TI 11 20190904142431-207260
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grt-SAE116 pub TIMS Finnigan MAT261, MAT262 and Triton TI 11 20190904142431-157618
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cpx-SAE152C pub MC-ICP-MS Finnigan, Neptune 3 20200206105928-670146
cpx-SAE152C pub Q-ICPMS Agilent 7500cs 4 20200206105601-026245
grt-SAE152C pub TIMS Finnigan MAT261, MAT262 and Triton TI 4 20200206105628-713720
grt-SAE152C pub MC-ICP-MS Finnigan, Neptune 3 20200206105929-366205
grt-SAE152C pub Q-ICPMS Agilent 7500cs 4 20200206105602-885942
cpx-SAE116 pub TIMS Finnigan MAT261, MAT262 and Triton TI 4 20200206105627-178719
cpx-SAE116 pub MC-ICP-MS Finnigan, Neptune 3 20200206105928-082185
cpx-SAE116 pub Q-ICPMS Agilent 7500cs 4 20200206105601-071102
grt-SAE116 pub TIMS Finnigan MAT261, MAT262 and Triton TI 4 20200206105627-613780
grt-SAE116 pub MC-ICP-MS Finnigan, Neptune 3 20200206105928-188624
grt-SAE116 pub Q-ICPMS Agilent 7500cs 4 20200206105601-724576
primary Cpx-SAE116 pub EPMA JEOL JXA-8800R 11 20190902150854-544094
name spots global-id
caption ID assembly stone
Table 2. Major element compositions of constituent minerals from representative samples of Malaitan xenoliths pub 20190902113420-951165 major (Ishikawa et al., 2004) 15
Table 5. Clinopyroxene compositions from quartz-garnet clinopyroxenite pub 20190902150053-732001 major (Ishikawa et al., 2004 Table 5) 2
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  • name
  • Akira Ishikawa
  • Maruyama, Shigenori
  • Komiya, Tsuyoshi