On the Role of the Igneous Activities in the Tectonic Movement, With Special Reference to the Muroto Peninsula Igneous Zone

Yajima, Toru; Kajima, Mikio; Naganuma, Yukio

doi:10.5575/geosoc.83.395

Cited by 9 publications

(5 citation statements)

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“…2). The Shijujiyama sandstones have been considered to be a conformable member of the local sequence (Matsumoto & Terashima 1976;Yajima et al 1977), an olistolith in a melange (Sakai 1981), a fault bounded unit (Taira et al 1980) and a younger sequence that unconformably overlies the surrounding rocks (Katto & Arita 1966). Likewise, the volcanic rocks have been viewed as a conformable member of the sequence (Matsumoto & Terashima 1976;Yajima et al 1977) and as olistoliths in a mdange (Taira et al 1980;Sakai 1981).…”

Section: Previous Interpretationsmentioning

confidence: 98%

“…Opinions concerning the stratigraphic succession in the area have ranged from viewing the Oligocene-Miocene as a totally comformable sequence (Matsumoto & Terashima 1976;Yajima et al 1977) to considering it to be devoid of any recognizable stratigraphy (Sakai 1981(Sakai , 1988Fig. 2). In particular, the setting of both a distinct sandstone sequence in the area of Shijujiyama and of a volcanic unit in the area of Shiina-Hioki have been subject to a variety of interpretations (Fig.…”

Section: Previous Interpretationsmentioning

confidence: 99%

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Anomalous structural evolution of the Shimanto Accretionary Prism at Murotomisaki, Shikoku Island, Japan

1992

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The Late Oligocene-Early Miocene Nabae Sub-belt of the Shimanto Accretionary Prism was created coevally (ca 25-15 Ma) with the opening of the Shikoku back-arc basin, located to the south of the southwest Japan convergent margin. The detailed geology of the sub-belt has been controversial and the interaction of the Shimanto accretionary prism and the opening of the Shikoku Basin has been ambiguous. New structural analysis of the sub-belt has led to a new perception of its structural framework and has significant bearing on the interpretation of the Neogene tectonics of southwest Japan.The sub-belt is divided into three units: the Nabae Complex; the Shijujiyama Formation; and the Maruyama Intrusive Suite. The Nabae Complex comprises coherent units and melange, all of which show polyphase deformation. The first phase of deformation appears to have involved landward vergent thrusting of coherent units over the melange terrane. The second phase of deformation involved continued landward vergent shortening. The Shijujiyama Formation, composed mainly of mafic volcanics and massive sandstone, is interpreted as a slope basin deposited upon the Nabae Complex during the second phase of deformation. The youngest deformational pulse involved regional flexing and accompanying pervasive faulting. During this event, mafic rocks of the Maruyama Intrusive Suite intruded the sub-belt. Fossil evidence in the Nabae Complex and radiometric dates on the intrusive rocks indicate that this tectonic scheme was imprinted upon the sub-belt between -23 and -14 Ma.The timing of accretion and deformation of the sub-belt coincides with the opening of the Shikoku Basin; hence, subduction and spreading operated simultaneously. Accretion of the Nabae Sub-belt was anomalous, involving landward vergent thrusting, magmatism in newly accreted strata and regional flexing. It is proposed that this complex and anomalous structural history is largely related to the subduction of the active Shikoku Basin spreading ridge and associated seamounts.

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Section: Previous Interpretationsmentioning

confidence: 98%

Section: Previous Interpretationsmentioning

confidence: 99%

Anomalous structural evolution of the Shimanto Accretionary Prism at Murotomisaki, Shikoku Island, Japan

1992

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“…1.0 wt% water content was assumed for the initial melt, a typical value for fresh tholeiitic basalts (McBirney, 1993). We also assumed QFM buffer for the oxygen fugacity, and 1 kb for the pressure of crystallization (Yajima et al, 1977). The calculation result is illustrated in Figure 4, compared with actual compositional trend of the Murotomisaki gabbros.…”

Section: Formation Of Anorthositic Magmamentioning

confidence: 99%

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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“…Calculations were made starting from the initial melt composition of the intrusion (Akatsuka et al, 1999), assuming 1wt % H 2 O in of the initial meltça typical value for fresh tholeiitic basalts (McBirney, 1993). We also assumed NNO (nickel^nickel oxide) for the oxygen buffer and 1 kbar for the pressure of crystallization (Yajima et al, 1977). The bulk compositions of the O'-type MSI are closest to the initial melt composition IM, but have higher SiO 2 and MgO and lower FeO contents than IM (Table 7).…”

Section: B U L K C O M P O S I T I O N O F T H E M U Lt I P H a S E Smentioning

confidence: 99%

Amphibole-bearing Multiphase Solid Inclusions in Olivine and Plagioclase from a Layered Gabbro: Origin of the Trapped Melts

Hoshide

Obata

2012

Journal of Petrology

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This study presents new data regarding the petrographic and mineralogical characteristics of amphibole-bearing multiphase solid inclusions (MSI) enclosed in olivine and plagioclase from a well-characterized Japanese layered gabbro, the Murotomisaki Gabbroic Intrusion. Bulk compositions of the MSI were obtained using wavelength-dispersive (WDS) and energy-dispersive (EDS) techniques combined with modal analysis. Many MSI in olivines are spherical or polygonal in shape and are mainly composed of pargasitic amphibole, orthopyroxene, and mica (biotite and aspidolite). The MSI in olivine phenocrysts in the chilled margins of the intrusion are composed of plagioclase and hornblende rather than pargasite. Many of them are found to be enriched in olivine components in their bulk compositions, and therefore they cannot be regarded as simple trapped basaltic melts or their derivatives. The MSI in plagioclase are more irregular in shape and occur in the resorbed part of calcic plagioclase cores; they are mainly composed of pargasite and sodic plagioclase. Attempts were made to obtain the original composition of the MSI melts by applying a correction for Fe^Mg exchange reactions with the host olivine. It was found that after the correction, the MSI in the chilled margin were closest to the published initial basaltic melt composition, whereas the olivine-hosted MSI from the olivine gabbros were still fairly high in olivine components despite the correction. Such post-entrapment modification was probably minimal for the plagioclase-hosted MSI because plagioclase is essentially free of Mg and Fe, and therefore plagioclase-hosted MSI are believed to represent the compositions of the original trapped melts. These are characteristically enriched in plagioclase components. We believe that the anomalous compositions of the trapped melts (after the corrections) were generated by local dissolution of olivine and plagioclase caused by the introduction of water from lower horizons of the crystallization boundary layer in a magma chamber. The MSI are therefore considered to provide new evidence for the dissolution of silicates by hydrous fluxing in a lower crystallizing boundary layer of a magma reservoir during solidification of basaltic magma.

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On the Role of the Igneous Activities in the Tectonic Movement, With Special Reference to the Muroto Peninsula Igneous Zone

Cited by 9 publications

References 0 publications

Anomalous structural evolution of the Shimanto Accretionary Prism at Murotomisaki, Shikoku Island, Japan

Anomalous structural evolution of the Shimanto Accretionary Prism at Murotomisaki, Shikoku Island, Japan

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

Amphibole-bearing Multiphase Solid Inclusions in Olivine and Plagioclase from a Layered Gabbro: Origin of the Trapped Melts

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