Formation of layered structure in the Murotomisaki gabbroic complex, especially picrite gabbro, Kochi Prefecture, Japan. Quantitative evaluation of crystal accumulation.

貴史, 赤塚; 正明, 小畑; 久芳, 横瀬

doi:10.5575/geosoc.105.771

Cited by 13 publications

(33 citation statements)

References 8 publications

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“…The calculation result is illustrated in Figure 4, compared with actual compositional trend of the Murotomisaki gabbros. According to these calculation, the initial liquidus phase was olivine of composition Fo 84 , which nearly coincides with the observed value in the core of phenocrysts of the chilled marginal rocks (Akatsuka et al, 1999); and the subsequent liquidus phase was An 75 plagioclase. As crystallization proceeds, MgO decreases and CaO and FeO slightly increase in the early stages of the fractionated melt.…”

Section: Formation Of Anorthositic Magmasupporting

confidence: 49%

“…Whole rock compositions of various rock types from the Murotomisaki Gabbroic Complex have been reported in Akatsuka et al (1999) with an illustration of a stratigraphic variation diagram. They are plotted in FeO MgO and CaO MgO variation diagrams in Figure 2 for the study of whole rock compositional systematics.…”

Section: The Whole-rock Composition and Its Systematicsmentioning

confidence: 99%

“…With the recognition of the AC zone and the GR zone, we noted that the AC zone rocks and GR zone rocks define separate trends (Figure 2). The AC zone trend goes through the initial melt composition that had been deduced from chilled marginal composition by Akatsuka et al (1999) and extends toward the olivine composition of Fo 83 the core composition of the phenocrysts of the lower chilled marginal rocks. We interpret this AC trend to represent a mixing between the initial melt and phenocrystic olivine (i.e., olivine crystal accumulation trend), being guided by the crystal accumulation hypothesis (Hoshide et al, 2006).…”

Section: The Whole-rock Composition and Its Systematicsmentioning

confidence: 99%

“…We utilized the computer software "PELE" (Boudreau, 1999) which is a PC window version of MELTS (Ghiorso and Sack, 1995). Calculations were made starting from the initial melt composition determined by Akatsuka et al, (1999). 1.0 wt% water content was assumed for the initial melt, a typical value for fresh tholeiitic basalts (McBirney, 1993).…”

Section: Formation Of Anorthositic Magmamentioning

confidence: 99%

“…The intrusion has attracted much petrological works because of its well developed layered structure, that was presumably formed through igneous differentiation processes (Yoshizawa, 1953(Yoshizawa, , 1954Yajima, 1972aYajima, , 1972bAkatsuka et al, 1999;Hoshide et al, 2006). An investigation of olivine crystal size and crystal number densities, identified an olivine crystal accumulation zone (AC zone) in the lower part of the intrusion and an olivine crystal growth zone (GR zone) directly above the AC zone (Hoshide et al, 2006).…”

Section: Introductionmentioning

confidence: 99%

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Magmatic differentiation by means of segregation and diapiric ascent of anorthositic crystal mush - the Murotomisaki Gabbroic Complex, Shikoku, Japan

Hoshide

Obata

Akatsuka³

2006

Journal of Mineralogical and Petrological Sciences

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The Murotomisaki Gabbro is a sill like layered igneous complex that contains several layers of olivine enrichment. In our previous paper (Hoshide et al, 2006), we have identified two zones of olivine enrichment: 'the crystal accumulation zone (AC zone)', formed by gravity settling and accumulation of olivine crystals, and 'the crystal growth zone (GR zone)', in which increase of modal olivine was caused by crystal growth of olivine and not by crystal accumulation.Based on whole rock compositional data, we have found that the AC zone rocks define a linear compositional trend (termed as 'AC trend') which is consistent with the crystal settling and accumulation hypothesis. However the GR zone data define another linear trend with a slope different from that of the AC trend. Moreover, the compositions of the coarse gabbros and the upper olivine gabbros that occur above the GR zone and an anorthosite vein from the GR zone roughly lie on the same trend, but on the opposite side of the GR zone composition, defining the 'GR trend' as a whole. Some anorthositic veins and wavy pegmatitic veins have plume like structures, suggesting that these veins are remnant of crystal mushes that have been mobilized and ascended diapirically during magmatic differentiation.Considering the observed compositional relationships and the mode of occurrences of the anorthosite and wavy pegmatitic veins, we conclude that the segregation and separation of anorthositic material out of semi solidified crystallization boundary layers was responsible for the formation of the GR zone and the GR trend. Phase equilibrium calculations reveal that the hypothetical anorthosite material was a mixture of fractionated melt and plagioclase crystals that precipitated from the melt. The GR zone represents a residue from the separation of anorthositic crystal mushes and the coarse gabbros and the upper olivine gabbro parts represent mixtures of the crystal mush and the initial melt.

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Section: Formation Of Anorthositic Magmasupporting

confidence: 49%

Section: The Whole-rock Composition and Its Systematicsmentioning

confidence: 99%