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首页> 外文期刊>Contributions to Mineralogy and Petrology >Patterns of Nd and Sr isotopic ratios produced by magmatic and post-magmatic processes in the Shiant Isles Main Sill, Scotland
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Patterns of Nd and Sr isotopic ratios produced by magmatic and post-magmatic processes in the Shiant Isles Main Sill, Scotland

机译：苏格兰Shiant Isles Main Sill岩浆和后岩浆过程产生的Nd和Sr同位素比的模式

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The Shiant Isles Main Sill of the British Tertiary Igneous Province is a classic example of a differentiated, alkaline basic sill. Four separate intrusions, each emplaced internally in rapid succession, form a 165-m-thick sill hosted by Lower Jurassic sedimentary rocks. Extensive Nd and Sr isotopic studies were conducted on samples from a vertical section through the still where the relationships of samples to one another are well defined. The results illuminate patterns of modification of isotopic ratios and clarify the petrogenesis (magma sources, crustal contamination), magmatic processes (bulk mixing, interstitial liquid mixing), and post-magmatic alteration (hydrothermal effects on Sr and Nd). Overall, the whole-rock initial ~(87)Sr/~(86)Sr ratios range from approx 0.7037 to 0.7061 while initial ~(143)Nd/~(144)Nd ratios vary from approx 0.51243 to 0.51286 (#epsilon#_(Nd) approx -0.7 to +5.7) - values that contrast markedly with those of the country rock. Acid leaching (HCl) of the whole-rock samples that removes analcime indicates that most of the scatter in the ~(87)Sr/~(86)Sr is caused by the ubiquitous subsolidus, aqueous alteration during which more-radiogenic Sr was introduced into the sill, especially along the margins, and also reveals magmatic isotopic ratios. In contrast, Nd was immobile during fluid interaction so that the sill ~(143)Nd/~(144)Nd ratios were not affected, even <1 m from the country-rock contact. Using leached rock values, ~(87)Sr/~(86)Sr and ~(143)Nd/~(144)Nd ratios are inversely correlated from magmatic processes. Magmas with two distinct isotopic compositions were involved: a more primitive one with ~(143)Nd/~(144)Nd approx 0.51285 and ~(87)Sr/~(86)Sr approx 0.7035 that produced the first two intrusions and a more evolved one (with 0.51252 and 0.7048) that produced the third intrusion. Mixing of the two magmas was very limited, restricted to near contacts between units, and apparently occurred by interstitial melt migration. The more evolved crinanitic magma was probably produced from a batch of the more primitive picritic melt by a small degree of crustal contamination and crystal fractionation during a short crustal residence prior to ascent and emplacement.
机译：英国第三纪火成岩省的Shiant Isles主门槛是区分碱性碱性门槛的经典例子。四个独立的侵入体，每个侵入体都在内部快速相继形成，形成了一个厚度为165 m的门槛，由下侏罗统沉积岩构成。对从垂直截面到静止的样品的Nd和Sr同位素进行了广泛的研究，其中样品之间的关系已得到很好的定义。结果阐明了同位素比率改变的模式，并阐明了成岩作用（岩浆源，地壳污染），岩浆过程（大体积混合，间隙液体混合）和后岩浆蚀变（水热对Sr和Nd的影响）。总体而言，整个岩石的初始〜（87）Sr /〜（86）Sr比率范围约为0.7037至0.7061，而初始〜（143）Nd /〜（144）Nd比率范围约为0.51243至0.51286（＃epsilon＃_ （Nd）约为-0.7到+5.7）-与乡村岩石明显不同的值。全岩样的酸浸（HCl）去除了Analcime，表明〜（87）Sr /〜（86）Sr中的大部分散射是由普遍存在的亚固相线引起的，水相改变是在此过程中引入了更具放射性的Sr。进入窗台，特别是沿边缘，并且还揭示了岩浆同位素比。相比之下，Nd在流体相互作用过程中是不动的，因此基岩〜（143）Nd /〜（144）Nd的比值不受影响，即使与乡村岩石接触不到1 m。使用浸出的岩石值，〜（87）Sr /〜（86）Sr和〜（143）Nd /〜（144）Nd比与岩浆过程成反比。涉及具有两种不同同位素组成的岩浆：更原始的岩浆具有〜（143）Nd /〜（144）Nd约0.51285和〜（87）Sr /〜（86）Sr约0.7035产生了前两次侵入。进化出一个（具有0.51252和0.7048）产生了第三次入侵。两种岩浆的混合非常有限，仅限于单元之间的近距离接触，并且显然是由间隙熔体迁移引起的。上升较早的皮特克熔融岩可能是由一批较原始的皮特质熔岩产生的，其发展较早。

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