Sm-Nd and Lu-Hf isotope and trace-element systematics of Mesoarchaean amphibolites, inner Ameralik fjord, southern West Greenland
Sm-Nd and Lu-Hf isotope and trace-element systematics of Mesoarchaean amphibolites, inner Ameralik fjord, southern West Greenland
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DOI：
10.1180/minmag.2015.079.4.02
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发表时间：
2015-08
影响因子：
2.7
通讯作者：
K. Szilas;J. Hoffmann;Christina Hansmeier;J. Hollis;C. Münker;S. Viehmann;H. Kasper
中科院分区：
文献类型：
--
作者：
K. Szilas;J. Hoffmann;Christina Hansmeier;J. Hollis;C. Münker;S. Viehmann;H. Kasper
碎屑状表壳岩是太古宙高等级片麻岩地体的典型组成部分，如北大西洋克拉通。本文首次对西格陵兰岛南部Ameralik峡湾南部地区收集的角闪岩进行了主要、微量元素和Nd-Hf同位素数据分析。此外，在周围TTG片麻岩中获得了新的U-Pb锆石年龄。根据其微量元素模式，可以区分出两组不同的角闪岩。在筛选岩浆后蚀变和离群e值后，简化样本集确定147Sm/143Nd回归年龄为3038 Ma±310 Ma (MSWD = 9.2)， 176Lu/176Hf回归年龄为2867±160 Ma （MSWD = 5.5）。蚀变最小角闪岩的初始εNd2970Ma值在0.0 ~ +5.7之间，初始εHf2970Ma值在+0.7 ~ +10.4之间，表明其地幔源和地壳源具有明显的非均质性。令人惊讶的是，那些显然是最进化和不相容元素丰富的角闪岩却有最耗尽的hf同位素组成。这种明显的矛盾可以解释为，在俯冲带火山活动期间，对一个具有古熔体枯竭的局部地幔源区进行采样，该区域被一种流体成分重新富集，或者在富集岩石的地幔源区中，一种古代辉石岩成分的优先熔融。
Abstract Fragmented supracrustal rocks are typical components of Archaean high-grade gneiss terranes, such as those in the North Atlantic Craton. Here we present the first major, trace element and Nd-Hf isotope data for amphibolites collected in the yet poorly studied southern inner Ameralik fjord region of southern West Greenland. In addition, new U-Pb zircon ages were obtained from the surrounding TTG gneisses. Based on their trace-element patterns, two different groups of amphibolites can be distinguished. Following screening for post-magmatic alteration and outlying e values, a reduced sample set defines a 147Sm/143Nd regression age of 3038 Ma ±310 Ma (MSWD = 9.2) and a 176Lu/176Hf regression age of 2867 ± 160 Ma (MSWD = 5.5). Initial εNd2970Ma values of the least-altered amphibolites range from 0.0 to +5.7 and initial εHf2970Ma range from +0.7 to +10.4, indicating significant isotopic heterogeneity of their mantle sources with involvement of depleted domains as well as crustal sources. Surprisingly, the amphibolites which are apparently most evolved and incompatible element-rich have the most depleted Hf-isotope compositions. This apparent paradox may be explained by the sampling of a local mantle source region with ancient previous melt depletion, which was re-enriched by a fluid component during subduction zone volcanism or alternatively by preferential melting of an ancient pyroxenite component in the mantle source of the enriched rocks.