ZIRCON SATURATION REVISITED - TEMPERATURE AND COMPOSITION EFFECTS IN A VARIETY OF CRUSTAL MAGMA TYPES
ZIRCON SATURATION REVISITED - TEMPERATURE AND COMPOSITION EFFECTS IN A VARIETY OF CRUSTAL MAGMA TYPES
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DOI：
10.1016/0012-821x(83)90211-x
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发表时间：
1983-01-01
影响因子：
5.3
通讯作者：
HARRISON, TM
中科院分区：
文献类型：
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作者：
WATSON, EB;HARRISON, TM
750-1020°C温度范围内的热液实验确定了地壳深熔熔体中锆石的饱和行为是温度和成分的函数。结果提供了一个锆石溶解度模型，由下式给出：InDZrzirconz/melt=-3.80-[0.85（M-1）]+12900/T其中DZrzirconz/melt是化学计量锆石中Zr与熔体中Zr的浓度比，T是绝对温度，M是阳离子比（Na + K + 2Ca）/（Al · Si）。该溶解度模型主要基于860°、930°和1020°C下的实验，但也已在高达1500°C的温度下（M = 1.3）得到证实。最低温度实验（750°和800°C）得到相对不精确的低溶解度，但测量值（有指定的误差）与模型的预测结果一致。对于M = 1.3（正常过铝质花岗岩），这些结果预测锆石溶解度范围为750°C时的100 ppm溶解Zr至1020°C时的1330 ppm溶解Zr。因此，鉴于在地壳花岗岩类中观察到的大量Zr浓度范围（0.50 -350 ppm），很明显，深熔岩浆可以显示出与源岩中锆石相反的行为。那些在熔化过程中锆含量不足以使锆石饱和的熔体只能通过消耗源中的所有锆石来实现该条件。另一方面，具有较高Zr含量（适于锆石饱和）的熔体必须被视为不能溶解额外的锆石，无论其位于残留岩石中还是作为离开熔体部分中夹带的晶体。这后一种可能性特别令人感兴趣，因为熔体不能消耗锆石意味着未溶解锆石中所含的关键地球化学“指标”（例如重稀土、Hf、U、Th和放射成因Pb）只能通过固态扩散与接触熔体平衡，这相对于熔化事件的时间尺度可能是缓慢的。
Hydrothermal experiments in the temperature range 750–1020°C have defined the saturation behavior of zircon in crustal anatectic melts as a function of both temperature and composition. The results provide a model of zircon solubility given by: InDZrzircon/melt= −3.80−[0.85(M−1)]+12900/T whereDZrzircon/meltis the concentration ratio of Zr in the stoichiometric zircon to that in the melt,Tis the absolute temperature, andMis the cation ratio (Na + K + 2Ca)/(Al · Si). This solubility model is based principally upon experiments at 860°, 930°, and 1020°C, but has also been confirmed at temperatures up to 1500°C forM= 1.3. The lowest temperature experiments (750° and 800°C) yielded relatively imprecise, low solubilities, but the measured values (with assigned errors) are nevertheless in agreement with the predictions of the model.ForM= 1.3 (a normal peraluminous granite), these results predict zircon solubilities ranging from ∼ 100 ppm dissolved Zr at 750°C to 1330 ppm at 1020°C. Thus, in view of the substantial range of bulk Zr concentrations observed in crustal granitoids (∼ 50–350 ppm), it is clear that anatectic magmas can show contrasting behavior toward zircon in the source rock. Those melts containing insufficient Zr for saturation in zircon during melting can have achieved that condition only by consuming all zircon in the source. On the other hand, melts with higher Zr contents (appropriate to saturation in zircon) must be regarded as incapable of dissolving additional zircon, whether it be located in the residual rocks or as crystals entrained in the departing melt fraction. This latter possibility is particularly interesting, inasmuch as the inability of a melt to consume zircon means that critical geochemical “indicators” contained in the undissolved zircon (e.g. heavy rare earths, Hf, U, Th, and radiogenic Pb) can equilibrate with the contacting melt only by solid-state diffusion, which may be slow relative to the time scale of the melting event.