FINDING OF CORUNDUM-BEARING GABBRO BOULDER POSSIBLY DERIVED FROM THE HOROMAN PERIDOTITE COMPLEX, HOKKAIDO, NORTHERN JAPAN
FINDING OF CORUNDUM-BEARING GABBRO BOULDER POSSIBLY DERIVED FROM THE HOROMAN PERIDOTITE COMPLEX, HOKKAIDO, NORTHERN JAPAN
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发现可能源自日本北部北海道 HOROMAN 橄榄岩群的含刚玉辉长岩巨石
DOI：
10.2465/ganko.93.52
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发表时间：
1998
期刊：
影响因子：
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通讯作者：
T. Kodera
中科院分区：
文献类型：
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作者：
T. Morishita;T. Kodera
日本北海道萨玛尼镇Ponsanushibetsu河中的一块巨石中发现了含有辉长岩的粗粒刚玉。根据矿物组合和化学成分，其起源很可能是霍罗曼橄榄岩杂岩中的GBII辉长岩(Shiotani和Niida，1997)。根据刚玉与其他矿物之间的结构关系推断，在最近的变质条件下，刚玉在辉长岩中不稳定。刚玉的分解反应可能表现为：刚玉+单斜辉石=尖晶石+斜长石(I)。这一反应表明，GBII原岩经历了加热或减压，或两者兼而有之，导致了刚玉的破裂。另一方面，我们可以估计刚玉形成的两个可能的反应。首先，刚玉可以通过(I)在形成尖晶石后的冷却或压缩过程中的反应而形成，如：olivine+anorthite=orthopyroxene+clinopyroxene+spinel(Ii)，在相对铝质的原岩(例如，富含斜长石的原岩)中。其次，在更高的压力下形成刚玉也是可能的，反应是：单斜辉石中的CA-Tschermaks=刚玉+粗粒(III)。这一反应意味着含铝单斜辉石可以在高压下形成含刚玉的石榴石-单斜辉石。最近对霍罗曼橄榄岩杂岩的解释为从石榴石稳定区上升的地幔底辟(Ozawa和Takahashi，1995)，这可能有利于后一种过程，即刚玉的高压起源。GBII辉长岩可能是在高温高压条件下变质形成刚玉后，作为地幔底辟的一员而上升的。
Coarse-grained corundum bearing gabbro was found as a boulder in the Ponsanushibetsu river of the Samani Town, Hokkaido, Japan. Its provenance is most probably the GBII gabbro (Shiotani and Niida, 1997) of the Horoman peridotite complex on the basis of mineral assemblage and chemical composition. Deduced from textural relationships between corundum and other minerals, corundum has not been stable in the gabbro under the latest metamorphic condition. The reaction for the corundum breakdown is possibly shown as: corundum+clinopyroxene=spinel+plagioclase (i). This reaction suggests that the GBII protolith had experienced heating or decompression or both to cause the corundum breakdown. On the other hand, we can estimate two possible reactions for corundum formation. First, corundum can be formed by a reaction (i) during cooling or compression after the formation of spinel by a reaction, which is shown as: olivine+anorthite=orthopyroxene+clinopyroxene+spinel (ii), in relatively aluminous protoliths (e.g., plagioclase-rich protoliths). Second, formation of corundum at much higher pressures is also possible by a reaction: Ca-tschermaks in clinopyroxene=corundum+grossular (iii). This reaction means that corundum-bearing garnet-clinopyroxenite can be formed from aluminous clinopyroxenite at high-pressure. The recent interpretation of the Horoman peridotite complex as a mantle diapir ascended from the garnet stability field (Ozawa and Takahashi, 1995) may favor the latter process, the high-pressure origin of the corundum. The GBII gabbro possibly ascended as one of the member of the mantle diapir after it had been metamorphosed under high P-T conditions to form corundum as one of high-pressure minerals.
Frey, F. A.：“日本北海道 Horoman 橄榄岩下层带内的成分变化：熔体-固体偏析模型的限制。”
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