Amphibole genesis via metasomatic reaction with clinopyroxene in mantle xenoliths from Victoria Land, Antarctica
Amphibole genesis via metasomatic reaction with clinopyroxene in mantle xenoliths from Victoria Land, Antarctica
复制标题
DOI：
10.1016/j.lithos.2003.12.021
复制
发表时间：
2004-07-01
期刊：
影响因子：
3.5
通讯作者：
Siena, F
中科院分区：
文献类型：
--
作者：
Coltorti, M;Beccaluva, L;Siena, F
对墨尔本山和霸王山（南极洲维多利亚州）复合捕虏体中单斜辉石、角闪石和玻璃的岩相和主量和微量元素地球化学特征进行了研究。浸染在橄榄岩基质中的角闪石似乎在单斜辉石和尖晶石周围生长，并且通常与高 TiO2 硅酸盐玻璃伴生。单斜辉石呈现出多种成分，从原生未交代透辉石到高 MgO 盐岩，稀土元素模式从平坦（在 Yb-N 5X 球粒陨石）到较高 HREE 含量（Yb-N 9.3-14.3）的稍富集 [(La/Yb)(N) 2.7-4.2]。角闪石也出现在矿脉中，在少数情况下，这些矿脉在消失到橄榄岩中之前会分级为富含玻璃的矿脉。眼镜与角闪石不稳定无关；相反，它们似乎与其形成密切相关。与播散性角闪石或脉状角闪石相关的玻璃之间没有发现化学差异。它们的地球化学特征有利于钠碱性硅酸盐熔体作为交代剂。使用质量平衡计算来模拟从初级单斜辉石产生角闪石的反应，并强调交代剂的性质。推断熔体的微量元素含量与该地区发现的最不饱和岩浆的微量元素含量相当，表明交代作用与罗斯海裂谷系统的岩浆作用之间存在密切联系。与角闪石相关的单斜辉石 (cpx-A) 的微量元素模式与被宿主玄武岩污染的单斜辉石 (cpxBas) 的微量元素模式之间的类比进一步强化了这一假设。根据 Mg/Fe 扩散模型，这两种单斜辉石之间的 mg# 差异可用于估计玄武岩渗透和角闪石形成的时间。最后，回顾了播散和脉状角闪石关系的各种模型，并测试了它们在南极角闪石中的应用。事实上，浸染状角闪石的岩石学和地球化学特征并不支持它们可能源自脉状角闪石结晶后分异岩浆的假设。由于岩浆/围岩比例不同，这两种角闪石类型可能是在相似的时间跨度内形成的，而岩浆/围岩比例控制着熔体从多孔流动到破裂和破裂的迁移模式。 (C) 2004 Elsevier B.V. 保留所有权利。
Petrographic and major and trace element geochemical features of clinopyroxene, amphibole and glass from composite xenoliths from Mt. Melbourne and Mt. Overlord (Victoria Land, Antarctica) were investigated. Amphibole disseminated in the peridotite matrix appears to grow around clinopyroxene and spinel, and is often associated with high-TiO2 silicate glass. Clinopyroxene presents a wide range of compositions, from primary unmetasomatized diopside to high-MgO salite, with REE patterns varying from flat (at Yb-N 5Xchondrite) to slightly enriched [(La/Yb)(N) 2.7-4.2] at higher HREE contents (Yb-N 9.3-14.3). Amphibole also occurs in veins which, in few cases, grade into glass-rich veins before vanishing into the peridotite. Glasses are not related to amphibole destabilization; on the contrary, they appear to be strictly related to its formation. No chemical differences were noted between glasses related to disseminated or vein amphiboles. Their geochemical features favour a Na-alkaline silicate melt as the metasomatizing agent. Mass balance calculations were used to model the reactions producing amphibole from primary clinopyroxene, and to highlight the nature of the metasomatic agent/s. Trace element contents of the inferred melt/s are comparable to those of the most undersaturated magma found in the area, suggesting a strong link between metasomatism and the magmatism of the Ross Sea Rift system. This hypothesis is further strengthened by the analogy between trace element patterns of clinopyroxene associated with amphibole (cpx-A) and those of clinopyroxene contaminated by the host basalt (cpxBas). On the basis of the Mg/Fe diffusion model, the difference in mg# between these two clinopyroxenes was used to estimate the timing of the basalt infiltration and amphibole formation. Finally, various models for disseminated and vein amphibole relationships are recalled and their application to Antarctic amphiboles is tested. The petrographic and geochemical features of disseminated amphiboles, in fact, do not support the hypothesis that they may derive from differentiated magma after vein amphiboles have crystallized. Both amphibole types may have formed within a similar time span due to the different magma/wall rock ratios which control the mode of melt migration from porous flow to cracking and fracturing. (C) 2004 Elsevier B.V. All rights reserved.