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首页> 外文期刊>Geosciences >Zircons from a Pegmatite Cutting Eclogite (Gridino, Belomorian Mobile Belt): U-Pb-O and Trace Element Constraints on Eclogite Metamorphism and Fluid Activity
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Zircons from a Pegmatite Cutting Eclogite (Gridino, Belomorian Mobile Belt): U-Pb-O and Trace Element Constraints on Eclogite Metamorphism and Fluid Activity

机译：来自Pegmatite切割Eclogite（格里迪诺，Belomorian移动带）的锆石：U-PB-O和eClogite变质和流体活动的微量元素限制

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This report presents new data on U-Pb geochronology, oxygen isotopes, and trace element composition of zircon from a pegmatite vein crosscutting an eclogite boudin on Stolbikha Island, Gridino area, Belomorian mobile belt (BMB). The zircon grains occur as two distinct populations. The predominant population is pegmatitic and shows dark cathodoluminescence (CL); about a third of this population contains inherited cores. The second zircon population is typical of granulite and exhibits a well-defined sectorial (mosaic) zoning in CL. Both the inherited cores and sectorial in CL zircons appear to have been captured from metabasites as xenocrysts during the pegmatite vein formation. A U-Pb age of 1890 ± 2 Ma for the main zircon population is interpreted as the age of the pegmatite injection. This value is close to the age threshold for the BMB eclogites (~1.9 Ga) and unambiguously defines the upper age limit for the eclogite metamorphism. The pegmatite formation is thus related to partial melting events that occurred during the retrograde amphibolite-facies metamorphism shortly after the eclogitization. A U-Pb date of 2743 ± 10 Ma obtained for the sectorial in CL zircons is considered as the age of the granulite-facies metamorphism established previously within the BMB. The values of δ 18 O in the zircon populations overlap in a broad range, i.e., δ 18 O in the pegmatitic zircons varies from 6.1‰ to 8.3‰, inherited cores show a generally higher δ 18 O of 6.7–8.8‰, and in the captured granulitic zircons δ 18 O is 6.2–7.9‰. As a result of fluid attack during the final stage of the pegmatite vein formation, the composition of the pegmatitic zircons in terms of non-formula elements (REE, Y, Ca, Sr, Ti) has become anomalous, with the content of these elements having been increased by more than tenfold in the alteration zones. Our data provide new constraints on the timing of eclogite metamorphism within the BMB and show that the late-stage pegmatite-related fluids exerted a very pronounced influence on trace element abundances in zircon, yet had no significant impact on the isotopic composition of oxygen.
机译：本报告介绍了来自Pegmatite静脉的Zircon的U-PB地理学，氧同位素和痕量元素组成的新数据横切在斯托比里亚地区，贝诺里亚移动皮带（BMB）上横梳出Eclogite Boudin。锆石颗粒发生为两个不同的群体。主要群体是钉鼠并且显示暗阴极致发光（CL）;大约三分之一的人群包含遗传核心。第二个锆石种群是典型的颗粒石，在Cl中展示明确定义的扇形（马赛克）分区。在Pegmatite静脉形成期间，Cl Zircons的继承的核和Cl锆中的遗传术和扇形似乎已被捕获为XenoCrysts。对于主要锆石种群的U-PB年龄为1890±2 mA被解释为Pegmatite注射的年龄。该值接近BMB Eclogites（〜1.9 Ga）的年龄阈值，并明确定义Eclogite变质的上龄限制。因此，PEGMATITE形成与在eClogitization之后不久发生在逆行倒像倒像倒像倒像倒像倒话的部分熔化事件相关。在CL锆石中获得2743±10 mA的U-PB日期被认为是先前在BMB内建立的粒状相变质的年龄。锆石种群中的δ18O的值在宽范围内重叠，即悬臂中的δ180在褶皱锆中的δ180从6.1°变化到8.3‰，遗传芯显示出一般较高的δ180，为6.7-8.8‰，并且在捕获的粒度氧化锆δ180是6.2-7.9‰。由于在PEGMATITE静脉形成的最终阶段的流体攻击，在非公式元素（REE，Y，CA，SR，TI）方面的厚麦芽素氧化锆的组成变得异常，具有这些元素的含量在改变区域中已经增加了超过十倍。我们的数据在BMB内对Eclogite变质的时序提供了新的约束，并表明，阶段的Pegmatite相关的流体对锆石中的痕量元素丰度产生了非常明显的影响，对氧的同位素组成没有显着影响。

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