1860-Ma within-plate mafic rocks of the Eastern Murman Sill Province were studied in the northern part of the Murmansk Craton, where they compose sheet bodies (sills) up to 100 m thick in Archean granitoids and gneisses. The sills have a simple inner structure, show no macroscopic signs of in situ differentiation even in large bodies, and consist of homogenous medium-grained poikilophitic dolerites weakly varying in composition. Minor variations in mineral and chemical composition of the rocks allow us to regard the mafic sills as I-shaped sills. Their homogeneity is likely caused by the rapid crystallization of aphyric magmas. The studied sills are close to N-MORB in major-element composition, but significantly differ in trace element signatures. The low Cr and Ni concentrations in the dolerites indicate the high degrees of fractional crystallization, while the low HREE and HFSE contents suggest that primary komatiite melts were formed through the high-degree melting of a depleted mantle source. The absence of phenocrysts in chilled dolerites prevented the use mineralogic and petrographic criteria for estimating the crystallization conditions in intermediate magma chambers. AlphaMELTS 1.9 and PRIMELT3 MEGA modelling results indicate that the primary melts could be formed through a high-degree melting of ascending high-temperature mantle plume, with subsequent contamination and fractional crystallization in mid-crustal intermediate magma chambers. The Nd and Sr isotopic composition of the dolerites and constituent minerals suggests that the crustal contamination included several stages. The first, most significant crustal contribution (up to 10%) was related to the contamination by Archean tonalites in the intermediate mid-crustal chambers. This provided negative ε_Nd values and radiogenic Sr isotopic composition (Sr_i = 0.702–0.704) in the dolerites. The second stage included the upper-crustal contamination during lateral propagation of melts along gentle weakened zones, which resulted in the wide variations of Sr-Nd isotopic composition in rocks and minerals. The third stage was related to the contamination by ⁸⁷Sr-enriched fluid that is supported by the sharp increase of Sr_i (up to 0.708) at constant Nd isotopic composition in gabbro-pegmatites. Such fluid could be formed via biotite dehydration caused by heating of host granites by large volume of emplaced mafic melts. The age, volume, and composition of the studied dolerites and similarity with coeval mafic rocks in the Superior Craton indicate that the I-shaped mafic sills in the Murmansk Craton could be formed on the periphery of the Circum Superior large igneous province. It suggests that the Murmansk Craton of the Fennoscandian Shield and the Superior Craton of the Canadian Shield at 1860 Ma were joined into a single consolidated lithospheric block that host within-plate mafic rocks and likely represented an early core of the Paleoproterozoic Nuna supercontinent.

中文翻译：

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芬诺斯堪的亚东部摩尔曼斯克克拉通的1860-Ma型I型基岩基岩：努纳集会期间板内基性事件的岩石学和构造环境

在摩尔曼斯克克拉通北部研究了东摩尔曼西尔省的1860-Ma板内镁铁质岩石，在那里它们组成了高达100 m厚的太古宙花岗岩和片麻岩片状体（基岩）。窗台有一个简单的内部结构，显示出没有宏观迹象原位甚至在大的物体中也可以分化，并且由组成微弱变化的均质的中粒粒滑钙质白云岩组成。岩石中矿物和化学成分的微小变化使我们可以将铁镁石窗台视为I形窗台。它们的同质性可能是由于岩浆岩浆的快速结晶造成的。所研究的窗台在主要元素组成上接近N-MORB，但痕量元素特征差异很大。白云岩中低的Cr和Ni浓度表明高分馏结晶度，而低的HREE和HFSE含量表明初级科莫长岩熔体是通过贫化地幔源的高度熔融形成的。冷却的白云岩中不存在隐晶石，因此无法使用矿物学和岩相学标准来估算中岩浆室内的结晶条件。AlphaMELTS 1.9和PRIMELT3 MEGA建模结果表明，初熔体可能是通过高温上升的地幔羽流的高度融化而形成的，随后在中地壳中部岩浆室内发生了污染和部分结晶。白云岩和组成矿物的Nd和Sr同位素组成表明地壳污染包括几个阶段。首先，最重要的地壳贡献（高达10％）与中间中地壳室内太古宙同色岩的污染有关。这提供了负ε 图9和PRIMELT3的MEGA建模结果表明，初生熔体可能是通过高温上升的地幔羽流的高度融化而形成的，随后在中地壳中部岩浆室内发生了污染和部分结晶。白云岩和组成矿物的Nd和Sr同位素组成表明地壳污染包括几个阶段。最重要的地壳贡献（最多达10％）与中间中地壳室内太古宙同色岩的污染有关。这提供了负ε 图9和PRIMELT3的MEGA建模结果表明，初生熔体可能是通过高温上升的地幔羽流的高度融化而形成的，随后在中地壳中部岩浆室内发生了污染和部分结晶。白云岩和组成矿物的Nd和Sr同位素组成表明地壳污染包括几个阶段。最重要的地壳贡献（最多达10％）与中间中地壳室内太古宙同色岩的污染有关。这提供了负ε 白云岩和组成矿物的Nd和Sr同位素组成表明地壳污染包括几个阶段。最重要的地壳贡献（最多达10％）与中间中地壳室内太古宙同色岩的污染有关。这提供了负ε 白云岩和组成矿物的Nd和Sr同位素组成表明地壳污染包括几个阶段。最重要的地壳贡献（最多占10％）与中间中地壳室内太古宙同色岩的污染有关。这提供了负ε白云岩中的_Nd值和放射源Sr同位素组成（Sr _i = 0.702–0.704）。第二阶段包括熔体沿缓和弱化带横向传播期间的上地壳污染，这导致岩石和矿物中Sr-Nd同位素组成的广泛变化。第三阶段与富集⁸⁷ Sr的流体的污染有关，这受Sr _i的急剧增加的支持。辉长岩斜晶岩中Nd同位素组成恒定时（最高0.708）。这种流体可能是由于黑云母脱水而形成的，黑云母脱水是由于大量的镁铁质熔体加热主体花岗岩而引起的。研究的白云岩的年龄，体积和组成以及与上克拉通上的中世纪镁铁质岩石的相似性表明，摩尔曼斯克克拉通的I形镁铁基岩可能形成于上环大火成岩省的外围。这表明芬诺斯堪的纳斯盾的摩尔曼斯克克拉通和1860 Ma的加拿大盾的上等克拉通被合并成一个单一的整合岩石圈块体，该板块容纳板状镁铁质岩石，并可能代表了古元古代努纳超大陆的早期核心。