Behaviour of zircon and monazite during crustal melting
Behaviour of zircon and monazite during crustal melting
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DOI：
10.1144/jgs2013-115
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发表时间：
2014-05
影响因子：
2.7
通讯作者：
C. Yakymchuk;Michael Brown
中科院分区：
文献类型：
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作者：
C. Yakymchuk;Michael Brown
从高品位变质岩中的附属矿物中获得的年代对地壳深部构造变质过程的时间和速率具有重要的限制作用。在超固体岩石中，锆石和独居石的溶解和生长强烈地依赖于变质作用的P-T条件和溶出的溶出液的化学成分和数量。沿顺时针P-T路径，固相上方的渐进式加热导致熔体损失和熔体化学变化，这对锆石和独居石的溶解和生长具有重要意义。在这项研究中，开放体系熔融的相平衡模型与锆石和独居石溶解度的实验数据相结合，沿着几个示意图顺时针P-T路径评估这些矿物在超固体条件下的稳定性。在混辉岩黑素体和残余麻粒岩中，一些锆石有望在加热至峰值温度和随后的等温减压中幸存下来，而独居石可能被完全消耗，这与在独居石中遗传岩心比在锆石中更少的观察结果一致。减压后，在冷却至固相的过程中，新的锆石和独居石在黑素体和残余麻粒岩中沿晶界被熔体捕获，预计会受到限制。相比之下，混辉岩和浅灰花岗岩中的白色小体预计主要含有新形成的锆石和独居石，遗传成分很少，除非这些矿物从源头被大量夹带。在新形成的锆石中保存的岩心，正如在许多无净质花岗岩中观察到的那样，表明分离、上升和就位通常足够快，足以限制这些遗传颗粒的溶解。
Ages retrieved from accessory minerals in high-grade metamorphic rocks place important constraints on the timing of events and the rates of tectonometamorphic processes operating in the deep crust. In suprasolidus rocks, the dissolution and growth of zircon and monazite are strongly dependent on the P–T conditions of metamorphism and the chemistry and quantity of anatectic melt present. Along a clockwise P–T path, prograde heating above the solidus leads to episodic melt loss and changes in melt chemistry that have important implications for the dissolution and growth of zircon and monazite. In this study, phase equilibria modelling of open-system melting is coupled with experimental data on zircon and monazite solubility to evaluate the stability of these minerals at suprasolidus conditions along several schematic clockwise P–T paths. In migmatite melanosomes and residual granulites, some zircon is expected to survive heating to peak temperature and subsequent isothermal decompression, whereas monazite may be completely consumed, consistent with the observation that inherited cores are less common in monazite than in zircon. After decompression, during cooling to the solidus, new zircon and monazite growth from melt trapped along grain boundaries in melanosomes and residual granulites is expected to be limited. By contrast, leucosomes in migmatites and anatectic granites are predicted to contain mostly newly formed zircon and monazite with minimal inherited components, unless significant entrainment of these minerals from the source occurs. The preservation of cores inside newly formed zircon, as observed in many anatectic granites, demonstrates that segregation, ascent and emplacement is commonly fast enough to limit dissolution of these inherited grains.