Metamorphic P-T paths of metapelitic granulites from the Larsemann Hills, East Antarctica
Metamorphic P-T paths of metapelitic granulites from the Larsemann Hills, East Antarctica
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DOI：
10.1016/j.lithos.2014.01.013
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发表时间：
2014-04
期刊：
影响因子：
3.5
通讯作者：
L. Tong;Xiaohan Liu;Yanbin Wang;Xi-rong Liang
中科院分区：
文献类型：
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作者：
L. Tong;Xiaohan Liu;Yanbin Wang;Xi-rong Liang
通过详细的结构观察，在南极洲东部Larsemann Hills的一个结构早期富铝变质麻粒岩透镜体中发现了一个峰M1组合石榴石+正辉石+堇青石+钾长石。M1组合由M2堇青石电晕和M3正辉石+堇青石复合体叠印在石榴石晶粒上。利用THERMOCALC程序在KFMASH系统中对M1峰组合进行了定量模拟，结果表明，它是在6-8 kbar和840-880°C的P-T条件下，由石榴石+黑云母=堇青石+正辉石+钾长石+熔体的单一反应交叉形成的，然后是峰后近等压冷却。而含硼泥质麻粒岩的平均P-T计算表明，峰值M1条件达到~ 9.0 kbar和~ 900℃，而套印型M2组合形成于~ 7.0 kbar和800 ~ 850℃的P-T条件下，反映了峰后近等温减压。P-T估计表明M3条件达到4-5 kbar和700-750°C。这表明该地区M1变质演化表现出截然不同的P-T路径，而M2到M3变质演化则表现为减压-冷却过程。现有年表资料支持M1变质演化发生在晚元古代（1000 ~ 900 Ma） Grenvillian高等级挤压构造事件（D1），并伴有强烈的岩浆活动，与查尔斯王子山脉北部和Rayner杂岩有密切的亲缘关系。而套印的M2 - M3变质演化形成于早古生代（~ 530 Ma）泛非高等级构造事件（D2-D3），与一次重要的陆内改造有关。本研究为解释复杂的多变质史提供了一个范例。
Through detailed textural observations, a peak M1 assemblage garnet + orthopyroxene + cordierite + K-feldspar has been identified in a structurally early Al-rich metapelitic granulite lens from the Larsemann Hills, East Antarctica. The M1 assemblage has been overprinted by M2 cordierite corona and M3 orthopyroxene + cordierite symplectite on garnet grains. Quantitative modeling for the peak M1 assemblage via the THERMOCALC program in the KFMASH system suggests that it was formed by the crossing of the univariant reaction garnet + biotite = cordierite + orthopyroxene + K-feldspar + melt under P–T conditions of 6–8 kbar and 840–880 °C, followed by post-peak near isobaric cooling. However, the average P–T calculations for the boron-bearing pelitic granulite indicate that peak M1 conditions reached ~ 9.0 kbar and ~ 900 °C, and the overprinting M2 assemblage formed under P–T conditions of ~ 7.0 kbar and 800–850 °C, reflecting a post-peak near isothermal decompression. P–T estimates show that M3 conditions reached 4–5 kbar and 700–750 °C. These imply that the M1 metamorphic evolution of the region displays contrasting P–T paths, while M2 to M3 evolution indicates a decompression-cooling process. The available chronological data support that the M1 metamorphic evolution occurred during the late Proterozoic (1000–900 Ma) Grenvillian high-grade compression tectonic event (D1), and was accompanied by strong magmatism, showing a close affinity to the northern Prince Charles Mountains and the Rayner complex. However, the overprinted M2 to M3 metamorphic evolution formed during the early Palaeozoic (~ 530 Ma) Pan-African high-grade tectonic events (D2–D3), and was associated with an important intracontinental reworking. This study presents an example for interpreting a complex polymetamorphic history.