Transformation of two‐pyroxene hornblende granulite to garnet granulite involving simultaneous melting and fracturing of the lower crust, Fiordland, New Zealand
Transformation of two‐pyroxene hornblende granulite to garnet granulite involving simultaneous melting and fracturing of the lower crust, Fiordland, New Zealand
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双辉石角闪石麻粒岩向石榴石麻粒岩的转变涉及下地壳的同时熔融和破裂，新西兰峡湾
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发表时间：
2001
期刊：
影响因子：
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通讯作者：
K. Klepeis
中科院分区：
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作者：
N. Daczko;G. Clarke;K. Klepeis
新西兰米尔福德湾彭布罗克谷的粒岩相辉长岩和闪长质片麻岩被垂直和平面石榴石反应带以直线图案切割。在辉长岩片麻岩中，斜长岩隐色体的狭窄岩脉被细粒石榴石麻粒岩包围，这些石榴石麻粒岩在 750°C 和 14kbar 的条件下取代了主体双辉石角闪石麻粒岩。主量和微量元素全岩地球化学数据表明，再结晶主要是等化学的。斜长岩脉切割了辉长片麻岩和闪长片麻岩之间的接触面，但接触处的形态发生了变化，从辉长片麻岩中被石榴子麻粒岩反应带包围的斜长岩脉，到闪长片麻岩中被斜长岩隐色体包围的粗粒石榴石隔带。闪长质片麻岩还含有被无色体包围的孤立的石榴石颗粒，以及由无色体连接的石榴石颗粒的短平面序列。闪长质片麻岩的部分熔化，主要是由角闪石在水不饱和条件下的分解控制的，推测是产生了隐色体。无色体的形式与熔体分离和断裂扩展辅助的传输一致；有限的倒退表明大量的融化逃逸。据推断，闪长片麻岩的堤坝和熔体逃逸已将裂缝传播到辉长片麻岩中。迁移的熔体从周围的辉长片麻岩中清除水分，并引起石榴石麻粒岩的有限替代。
Granulite facies gabbroic and dioritic gneisses in the Pembroke Valley, Milford Sound, New Zealand, are cut by vertical and planar garnet reaction zones in rectilinear patterns. In gabbroic gneiss, narrow dykes of anorthositic leucosome are surrounded by fine‐grained garnet granulite that replaced the host two‐pyroxene hornblende granulite at conditions of 750 °C and 14 kbar. Major and trace element whole‐rock geochemical data indicate that recrystallization was mostly isochemical. The anorthositic veins cut contacts between gabbroic gneiss and dioritic gneiss, but change in morphology at the contacts, from the anorthositic vein surrounded by a garnet granulite reaction zone in the gabbroic gneiss, to zones with a septum of coarse‐grained garnet surrounded by anorthositic leucosome in the dioritic gneiss. The dioritic gneiss also contains isolated garnet grains enclosed by leucosome, and short planar trains of garnet grains linked by leucosome. Partial melting of the dioritic gneiss, mostly controlled by hornblende breakdown at water‐undersaturated conditions, is inferred to have generated the leucosomes. The form of the leucosomes is consistent with melt segregation and transport aided by fracture propagation; limited retrogression suggests considerable melt escape. Dyking and melt escape from the dioritic gneiss are inferred to have propagated fractures into the gabbroic gneiss. The migrating melt scavenged water from the surrounding gabbroic gneiss and induced the limited replacement by garnet granulite.