Zircon and monazite response to prograde metamorphism in the Reynolds Range, central Australia
Zircon and monazite response to prograde metamorphism in the Reynolds Range, central Australia
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DOI：
10.1007/pl00007673
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发表时间：
2001
影响因子：
3.5
通讯作者：
D. Rubatto;I. Williams;I. Buick
中科院分区：
文献类型：
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作者：
D. Rubatto;I. Williams;I. Buick
我们报告了一项广泛的野外研究，研究了澳大利亚中部雷诺兹山脉变质层序中的锆石和独居石，在连续的地壳剖面上记录了绿片岩-麻粒岩相变质作用。详细的阴极发光和背散射电子成像，在SHRIMP U-Pb测年的支持下，揭示了锆石和独居石在变质过程中的不同行为。独居石首次记录了区域变质年龄（1576±5 Ma），在角闪岩相等级，在~ 600°C。在麻粒岩相条件下，在部分熔体分离和残辉岩中均发现了丰富的独居石，年龄相近（1557±2 ~ 1585±3 Ma）。新锆石生长在1562±4 ~ 1587±4 Ma之间，但与独居石不同的是，新锆石只记录在熔融（≥700°C）存在的麻粒岩相岩石中。新的锆石似乎是在原有的碎屑和继承的岩心被部分吸收的情况下形成的。两副矿物的变质生长量随温度和变质品位的增加而增加。然而，新锆石的生长受岩石成分的影响和部分熔融的驱动，这些因素对变质独居石的形成影响不大。这些附属相的生长响应于变质作用，在一个稳定的高地热状态下延伸了30 Ma的熔融结晶期（1557-1587 Ma）。白粒体和抗蚀岩中锆石生长过量的稀土元素模式表明，在漫长的变质作用过程中，熔体-抗蚀岩达到了平衡。即使在750 ~ 800℃高温变质作用的极端条件下，碎屑锆石岩心中也广泛保留了Pb的遗传特征。在独居石中发现了遗传的痕迹，表明在较大的独居石晶体中，U-Pb体系的闭合温度可超过750 ~ 800℃。
We report an extensive field-based study of zircon and monazite in the metamorphic sequence of the Reynolds Range (central Australia), where greenschist- to granulite-facies metamorphism is recorded over a continuous crustal section. Detailed cathodoluminescence and back-scattered electron imaging, supported by SHRIMP U–Pb dating, has revealed the different behaviours of zircon and monazite during metamorphism. Monazite first recorded regional metamorphic ages (1576 ± 5 Ma), at amphibolite-facies grade, at ∼600 °C. Abundant monazite yielding similar ages (1557 ± 2 to 1585 ± 3 Ma) is found at granulite-facies conditions in both partial melt segregations and restites. New zircon growth occurred between 1562 ± 4 and 1587 ± 4 Ma, but, in contrast to monazite, is only recorded in granulite-facies rocks where melt was present (≥700 °C). New zircon appears to form at the expense of pre-existing detrital and inherited cores, which are partly resorbed. The amount of metamorphic growth in both accessory minerals increases with temperature and metamorphic grade. However, new zircon growth is influenced by rock composition and driven by partial melting, factors that appear to have little effect on the formation of metamorphic monazite. The growth of these accessory phases in response to metamorphism extends over the 30 Ma period of melt crystallisation (1557–1587 Ma) in a stable high geothermal regime. Rare earth element patterns of zircon overgrowths in leucosome and restite indicate that, during the protracted metamorphism, melt-restite equilibrium was reached. Even in the extreme conditions of long-lasting high temperature (750–800 °C) metamorphism, Pb inheritance is widely preserved in the detrital zircon cores. A trace of inheritance is found in monazite, indicating that the closure temperature of the U–Pb system in relatively large monazite crystals can exceed 750–800 °C.