P-T history of a mantle diapir: the Horoman peridotite complex, Hokkaido, northern Japan
P-T history of a mantle diapir: the Horoman peridotite complex, Hokkaido, northern Japan
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地幔底辟的 P-T 历史：日本北部北海道霍罗马橄榄岩杂岩
DOI：
10.1007/bf00306505
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发表时间：
1995
影响因子：
3.5
通讯作者：
N. Takahashi
中科院分区：
文献类型：
--
作者：
K. Ozawa;N. Takahashi
日本北海道霍罗马橄榄岩杂岩根据对比的地质特征分为下区和上区。该杂岩记录了斜长石二辉橄榄岩中辉石和斜长石化学分带的连续减压历史，这被解释为通过固相线下减压反应衍生自石榴石二辉橄榄岩。在下带，大型辉石碎斑岩中清晰地保留了早期的减压历史，显示出明显的M形Al分带，其特征是核心处Al浓度较低（Al=0.12/6个氧），向边缘区逐渐增加，向边缘快速减少。核心中的 Ca 含量几乎恒定（Ca=0.03/6 个氧），向边缘略有增加，然后向边缘突然减少。上带斜长石二辉石核（Al=0.22，Ca=0.055/6 个氧）的斜辉石核中 Al 和 Ca 含量远高于下带，并且 Al 含量通常从核到边缘单调递减，但有一些例外，表现出较差的 M 形分带剖面。根据辉石核心成分推断，最早的 P-T 条件为下区 900–950°C 和 ∼20 kbar，上区 1100–1150°C 和 ∼20 kbar。推断铝从核心到边缘的增加是由于从这些条件进入尖晶石橄榄岩相的近绝热减压所致。该杂岩体经历了从尖晶石稳定场到斜长石稳定场的进一步减压，这是根据主要由斜长石、铬铁矿尖晶石和橄榄石与少量辉石组成的细粒聚集体中的斜长石带推断的。每个斜长石颗粒的 Na-Ca 比率从核心到边缘逐渐降低，表明辉石和尖晶石不断发生减压反应，产生橄榄石和斜长石。朝向边缘的钙含量急剧增加表明，与减压相关的相当快速的冷却对于形成和保留标记的分区是必要的。 Al 和 Ca 含量向斜方辉石边缘急剧下降也是在该复合体的最后上升过程中形成的。下带和上带之间的矿物学和岩石学特征的系统变化表明霍罗曼杂岩保留了与上地幔不同的温度变化。上部区域被解释为遵循比下部区域更高的温度减压路径，并且可能代表从上地幔中超过 60 公里的深度上升的地幔底辟的相对较热的部分。
The Horoman peridotite complex, Hokkaido, Japan is divided into Lower and Upper zones on the basis of contrasting geological features. The complex recorded a consecutive decompression history in chemical zoning of pyroxenes and plagioclase in plagioclase lherzolite, which is interpreted to have been derived from garnet lherzolite by subsolidus decompression reactions. In the Lower Zone, and earlier decompression history is clearly preserved in large pyroxene porphyroclasts, which show marked M-shaped Al zoning characterized by low Al concentration at the core (Al=0.12/6 oxygens), gradual increase toward the marginal region, and rapid decrease toward the rim. The Ca content in the core is nearly constant (Ca=0.03/6 oxygens) with slight increase toward the margin followed by abrupt decrease toward the rim. The Al and Ca contents in the core of orthopyroxene in plagioclase lherzolite from the Upper Zone (Al=0.22, Ca=0.055/6 oxygens) are much higher than those for the Lower Zone, and the Al content typically decreases monotonously from the core to the rim with several exceptions that show poorly developed M-shaped zoning profiles. The earliestP-Tconditions, inferable from the core compositions of pyroxenes are 900–950°C and ∼20 kbar for the Lower Zone and 1100–1150°C and ∼20 kbar for the Upper Zone. The increase of Al from the core to the margin is inferred to have resulted from nearly adiabatic decompression from these conditions into spinel peridotite facies. The complex experienced further decompression from the spinel stability field into the plagioclase stability field, which is inferred from plagioclase zoning in fine-grained aggregates composed mostly of plagioclase, chromite spinel, and olivine with minor pyroxenes. The Na-Ca ratio of each plagioclase grain decreases from the core to the rim, suggesting continuous decompression reaction producing olivine and plagioclase from pyroxenes and spinel. The sharp increase in Ca content toward the rim indicates that fairly rapid cooling associated with decompression is necessary to form and preserve the marked zoning. The sharp decrease in Al and Ca contents toward the rim of orthopyroxene was also formed during this final ascent of the complex. The systematic changes of the mineralogic and petrographic features that are gradational between the Lower and Upper zones suggest that the Horoman complex retains a temperature variation from the upper mantle. The Upper Zone is interpreted to have followed a higher temperature decompression path than the Lower Zone and probably represents a relatively hotter portion of a mantle diapir ascending from a depth greater than 60 km in the upper mantle.
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。”
DOI：
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发表时间：
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期刊：
影响因子：
--
作者：
通讯作者：
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影响因子：
3.9
作者：
MCKENZIE, D;BICKLE, MJ
通讯作者：
BICKLE, MJ