浅部软流圈和深部岩石圈中的锆石残存
Zircon survival in shallow asthenosphere and deep lithosphere
摘要：
锆石是最常用的矿物地球和地球外的岩石定年。然而，镁铁质/超镁铁质熔体中的锆石系统很少被实验探索，大多数现有的基于长英质、中间和/或合成系统的模型可能不适用于预测陆地浅部软流圈中锆石的存活。为了确定在这样的自然系统中的锆石的稳定性，我们进行了高温实验的锆石溶解在天然洋中脊玄武岩和合成haplobasaltic熔体加上在高电流的实验产品的原位电子探针显微分析。考虑到电子探针分析过程中锆石玻璃对中的二次荧光效应，我们计算了预测拉斑玄武岩组成的软流圈熔体中锆石存活所需的锆扩散系数。这些数据表明，典型的100微米锆石溶解迅速（在10小时内），并在地幔压力下与玄武质熔体反应后一致。我们观察到不一致的（晶体氧化锆和二氧化硅在熔体中）溶解的锆石在自然洋中脊玄武岩熔体在低压和单玄武岩熔体在高压下。我们的实验数据提出了问题的起源锆石在镁铁质和超镁铁质岩石，特别是在浅洋软流圈和岩石圈深部，以及从这些矿物的组成估计的锆石年龄的意义。金伯利岩、橄榄岩、碱性玄武岩等岩浆中的大尺寸锆石巨晶表明锆石与熔体之间的快速输运和短暂的相互作用，锆石巨晶的成因可能与Zr交代加入地幔有关，因为任何地幔熔融事件都应将其消除。
英文摘要：
Zircon is the most frequently used mineral for dating terrestrial and extraterrestrial rocks. However, the system of zircon in mafic/ultramafic melts has been rarely explored experimentally and most existing models based on the felsic, intermediate and/or synthetic systems are probably not applicable for prediction of zircon survival in terrestrial shallow asthenosphere. In order to determine the zircon stability in such natural systems, we have performed high-temperature experiments of zircon dissolution in natural mid-ocean ridge basaltic and synthetic haplobasaltic melts coupled with in situ electron probe microanalyses of the experimental products at high current. Taking into account the secondary fluorescence effect in zircon glass pairs during electron microprobe analysis, we have calculated zirconium diffusion coefficient necessary to predict zircon survival in asthenospheric melts of tholeiitic basalt composition. The data imply that typical 100 micron zircons dissolve rapidly (in 10 hours) and congruently upon the reaction with basaltic melt at mantle pressures. We observed incongruent (to crystal ZrO2 and SiO2 in melt) dissolution of zircon in natural mid-ocean ridge basaltic melt at low pressures and in haplobasaltic melt at elevated pressure. Our experimental data raise questions about the origin of zircons in mafic and ultramafic rocks, in particular, in shallow oceanic asthenosphere and deep lithosphere, as well as the meaning of the zircon-based ages estimated from the composition of these minerals. Large size zircon megacrysts in kimberlites, peridotites, alkali basalts and other magmas suggest the fast transport and short interaction between zircon and melt.The origin of zircon megacrysts is likely related to metasomatic addition of Zr into mantle as any mantle melting episode should obliterate them.
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