期刊
JOURNAL OF METAMORPHIC GEOLOGY
卷 30, 期 8, 页码 821-842出版社
WILEY
DOI: 10.1111/j.1525-1314.2012.01000.x
关键词
eclogite; fluid-rock interaction; Nb; Ta fractionation; rutile; vein
类别
资金
- Chinese Ministry of Science and Technology [2009CB825002]
- National Foundation of Science of China [40921002, 41090372]
- Knowledge Innovation Project of the Chinese Academy of Sciences [KZCX1-YW-15-3]
- Hundred Talent Program
Niobium and Ta concentrations in ultrahigh-pressure (UHP) eclogites and rutile from these eclogites and associated high pressure (HP) veins were used to study the behaviour of NbTa during dehydration and fluid-rock interaction. Samples were collected through a similar to 2 km profile at the Bixiling complex in the Dabie orogenic belt, Central-Eastern China. All but one eclogite away from veins (EAVs) display nearly constant Nb/Ta ratios ranging from 16.1 to 19.2, with an average of 16.9 +/- 0.8 (2 SE), similar to that of their gabbroic protolith from the Yangtze Block. Nb/Ta ratios of rutile from the EAVs range from 12.7 to 25.3 among different individual grains, with the average values close to those of the corresponding bulk rocks. These observations show that Nb and Ta were not significantly fractionated by prograde metamorphism up to eclogite facies when no significant fluid-rock interaction occurs. In contrast, Nb/Ta ratios of rutile from eclogites close to veins (ECVs) are highly variable from 17.8 to 49.8, which are systematically higher (by up to 17) than those of rutile from the veins. These observations demonstrate that Nb and Ta were mobilized and fractionated during localized fluid flow and intensive fluid-rock interaction. This is strongly supported by Nb/Ta zoning patterns in single rutile grains revealed by in situ LA-ICP-MS analysis. Ratios of Nb/Ta in the ECV-hosted rutile decrease gradually from cores towards rims, whereas those in the EAV-hosted rutile are nearly invariable. Furthermore, the vein rutile shows Nb/Ta zoning patterns that are complementary to those in rutile from their immediate hosts (ECVs), suggesting an internal origin for the vein-forming fluids. The Nb/Ta ratios of such fluids evolved from low values at the early stage of subduction to higher values at later supercritical conditions with increased temperature and pressure. Quantitative modelling was conducted to constrain the compositional evolution of metamorphic fluids during dehydration and fluid-rock interaction focusing on NbTa distribution. The modelling results based on our proposed multistage fluid phase evolution path can essentially reproduce the natural observations reported in the present study.
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据