New isotopic data for Mid-Atlantic Ridge basalts from the Arkhangelsk-Sierra Leone fracture zone (central Atlantic)
New isotopic data for Mid-Atlantic Ridge basalts from the Arkhangelsk-Sierra Leone fracture zone (central Atlantic)
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阿尔汉格尔斯克-塞拉利昂断裂带（大西洋中部）大西洋中脊玄武岩的新同位素数据
DOI：
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发表时间：
2014
影响因子：
0.9
通讯作者：
S. Skolotnev
中科院分区：
文献类型：
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作者：
S. Skolotnev
本研究提供了阿尔汉格尔斯克转换断层和5° N之间MAR轴上玄武岩的Sr、Nd和Pb同位素数据。阿尔汉格尔斯克断层和韦尔纳茨基断层之间的MAR段玄武岩的同位素数据表明，在14° N地球化学异常的位置，存在N-MORB亏损拉斑玄武岩，这与佛得角断层和马拉松断层之间的MAR段的一些玄武岩相似。从南到北，同位素值沿轴向有很大的正梯度（143 Nd/144 Nd为负梯度），叠加在9.6° N异常玄武岩的同位素变化上。南北增加（La/Sm）n表明较小程度的部分熔融。波格丹诺夫断层以南玄武岩的同位素变化范围与更偏南的1.7° N异常处的玄武岩相似。在5.4° N海隆附近广泛分布着P-MORB成分，其中类HIMU成分占很大比例。同位素比值逐渐减少（增加143 Nd/144 Nd）进一步向北向波格丹诺夫转换断层。对于（La/Sm）n观察到类似的趋势。因此，Bogdanov断裂南北两侧玄武岩的放射性同位素富集具有不同的来源：5.4° N和9.6° N隆起。在Vernadsky转换断层以北发现的玄武岩具有较高的143 Nd/144 Nd和较低的206 Pb/204 Pb，87 Sr/86 Sr比值相似。我们的结论是，富集玄武岩的同位素特征接近于HIMU样地幔柱衍生组分的局部表现，包括14° N和1.7° N的地球化学异常，可能是由软流圈地幔流夹带在上地幔底部的微地幔柱形成的，这些微地幔柱排列成直径为450-500 km的圆柱形对流单体系统。波格丹诺夫变换以北，上地幔被下陆壳物质所混染，这些物质是在冈瓦纳大陆赤道段之下岩石圈的构造侵蚀过程中被夹带的。
This study presents Sr, Nd, and Pb isotopic data for basalts collected from the MAR axis between the Arkhangelsk transform fault and 5° N. The isotopic data for basalts from the MAR segment between the Arkhangelsk and Vernadsky faults indicate the presence of N-MORB depleted tholeiites, which are similar to some basalts from the MAR segment between the Cape Verde and Marathon faults, at the location of the 14° N geochemical anomaly. Broad positive along-axis gradients in isotopic values (and negative for 143Nd/144Nd) are observed from south to north, superimposed by isotopic variations in the 9.6° N anomalous basalts. A north-south increase in (La/Sm)n suggests a smaller degree of partial melting. The range of isotopic variations in basalts south of the Bogdanov fault is similar to that of basalts recovered at the more southerly 1.7° N anomaly. P-MORB compositions with a large proportion of the HIMU-like component are widely distributed in the vicinity of the 5.4° N rise. The isotopic ratios decrease gradually (with increasing 143Nd/144Nd) farther to the north toward the Bogdanov transform fault. A similar trend is observed for (La/Sm)n. Therefore, the basalts recovered to the south and north of Bogdanov fault have different sources of radiogenic isotope enrichment: 5.4° N and 9.6° N rises. Basalts recovered to the north of the Vernadsky transform fault have higher 143Nd/144Nd and lower 206Pb/204Pb at similar 87Sr/86Sr ratios. We conclude that the localized manifestations of enriched basalts with isotopic characteristics close to the HIMU-like plume-derived component, including the 14° N and 1.7° N geochemical anomalies, may have been formed by microplumes entrained at the base of the upper mantle by asthenospheric mantle flows arranged into a system of cylindrical convective cells, 450–500 km in diameter. Northward of the Bogdanov transform, the upper mantle is contaminated with lower continental crust material, which was entrained during tectonic erosion of the lithosphere beneath the equatorial segment of Gondwanaland during its late stage opening.