A geochemical and Sr-Nd-O isotopic study of the Proterozoic Eriksfjord Basalts, Gardar Province, South Greenland: Reconstruction of an OIB signature in crustally contaminated rift-related basalts
A geochemical and Sr-Nd-O isotopic study of the Proterozoic Eriksfjord Basalts, Gardar Province, South Greenland: Reconstruction of an OIB signature in crustally contaminated rift-related basalts
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格陵兰岛南部加尔达尔省元古代埃里克斯峡湾玄武岩的地球化学和 Sr-Nd-O 同位素研究：重建地壳污染的裂谷相关玄武岩中的 OIB 特征
DOI：
10.1180/0026461036750147
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发表时间：
2003
影响因子：
2.7
通讯作者：
G. Markl
中科院分区：
文献类型：
--
作者：
R. Halama;T. Wenzel;B. Upton;W. Siebel;G. Markl
摘要南格陵兰加尔达省火山沉积型Eriksfjord组的玄武岩在约1.2 Ga时喷发成与裂谷有关的地堑构造。玄武岩成分介于拉斑玄武岩和碱性玄武岩之间，MgO含量<7 wt它们显示出相对于南极源的轻稀土元素富集。大部分微量元素和稀土元素特征与OIB型地幔源区玄武岩相似。单斜辉石的初始87 Sr/86 Sr比值为0.70278 ~ 0.70383，初始εNd值为-3.2 ~+2.1。最unradiogenic样品重叠的领域所定义的碳酸岩的年龄相似，可以解释为同位素贫化和富集地幔成分的混合。使用AFC模型方程，更多的放射性成因玄武岩的Sr-Nd同位素数据可以成功地模拟添加<5%的下地壳麻粒岩相片麻岩作为污染物。单斜辉石的δ 18 Ov-smow值为+5.2 ~+6.0%o，属于典型的幔源岩。然而，数据允许与平均下地壳成分混合高达10%。
Abstract Basalts from the volcano-sedimentaiy Eriksfjord Formation (Gardar Province, South Greenland) were erupted at around 1.2 Ga into rift-related graben structures. The basalts have compositions transitional between tholeiite and alkaline basalt with MgO contents <7 wt.% and they display LREE-enrichment relative to a chondritic source. Most of the trace element and REE characteristics are similar to those of basalts derived from OIB-Iike mantle sources. Initial 87Sr/86Sr ratios of clinopyroxene separates range from 0.70278 to 0.70383 and initial εNd values vary from -3.2 to +2.1. The most unradiogenic samples overlap with the field defined by carbonatites of similar age and can be explained by mixing of isotopically depleted and enriched mantle components. Using AFC modelling equations, the Sr-Nd isotope data of the more radiogenic basalts can successfully be modelled by addition of <5% lower crustal granulite-facies gneisses as contaminants. δ18Ov-smow values of separated clinopyroxene range from +5.2 to +6.0%o and fall within the range of typical mantle-derived rocks. However, up to 10% mixing with an average lower crustal component are permitted by the data.