Metamorphism and origin of ultramafic bodies of the Sanbagawa metamorphic belt in central Shikoku
Metamorphism and origin of ultramafic bodies of the Sanbagawa metamorphic belt in central Shikoku
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四国中部三波川变质带超镁铁质体的变质作用及成因
DOI：
10.2465/ganko1941.79.20
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发表时间：
1984
期刊：
影响因子：
--
通讯作者：
K. Kunugiza
中科院分区：
文献类型：
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作者：
K. Kunugiza
在四国中部的三巴川变质带中，与米纳瓦组上段和奥连组泥质片岩互插着大量的双质和威氏超基岩体。变质橄榄岩（p型）和变质蛇纹岩（s型）。对变质蛇纹岩进行了变质分区填图。矿物组合按变质品位递增顺序依次为辉长岩-水辉石-透辉石（I区）、橄榄石-辉长岩-透辉石（II区）和橄榄石-辉长岩-透辉石（III区）。带的分布与变质地的热结构一致。遗迹矿物学研究表明，三八川变质带大部分超镁铁质体原产于上地幔尖晶石和石榴石—辉橄榄岩相沉积。其中一单晶变质蛇纹岩（Shiraga体），其铬铁矿显示Cr-Al取代（Cr/(Cr+Al)=0.85 ~ 0.5），没有Fe3+和Ti的变化，可能是地幔橄榄岩部分熔融后的残余物。在成因和热历史方面，三巴川变质带至少有4种类型的超镁铁质体；(1) p型，积云石榴石橄榄岩；(2)p型，积云尖晶石橄榄岩；(3)s型，积云尖晶石橄榄岩；(4)s型，残余尖晶石橄榄岩。源区和热史的多样性表明，米纳瓦组上段和奥join组可能是超镁质体构造侵位的混杂岩带。由于超镁铁质体的变质等级与其周围片岩的变质等级相协调，在达到三巴川变质的最高温度之前，超镁铁质体的构造侵位就停止了。
In the Sanbagawa metamorphic belt of central Shikoku, many dunitic and wehrlitic ultramafic bodies occur intercalated with the pelitic schists of the Upper member of the Minawa Formation and of the Ojoin Formation. They are metamorphosed peridotite (P-type) and metamorphosed serpentinite (S-type). Metamorphic zonal mapping was made on the metamorphosed serpentinites. Mineral assemblages are, in the order of increasing metamorphic grade, antigorite-brucite-diopside (zone I), olivine-antigorite-diopside (zone II), and olivine-antigorite-tremolite (zone III). The distribution of zones is consistent with the thermal structure of the metamorphic terrain. Relic mineralogy indicates that most of ultramafic bodies of the Sanbagawa metamorphic belt are originally cumulates formed at the spinel and garnet lherzolite facies in the upper mantle. One dunitic metamorphosed serpentinite (Shiraga body), of which chromite indicates Cr-Al substitution (Cr/(Cr+Al)=0.85 to 0.5) without Fe3+ and Ti variations, may have been originally a residue after partial melting of mantle peridotite. With regard to the origin and thermal history, there are at least 4 types of ultramafic bodies in the Sanbagawa metamorphic belt ; (1) P-type, cumulus garnet peridotite, (2) P-type, cumulus spinel peridotite, (3) S-type, cumulus spinel peridotite, and (4) S-type, residual spinel peridotite. The diversity of origin and thermal history indicates that the Upper member of the Minawa Formation and the Ojoin Formation were probably melange zones into which ultramafic bodies were tectonically emplaced. As metamorphic grade of ultramafic bodies is in harmoneous with that of their surrounding schists, tectonic emplacement of ultramafic bodies ceased before the maximum temperature of the Sanbagawa metamorphism was reached.