New petrographic, geochemical, and isotopic (Sr, Nd, and δ¹⁸О) data on olivine and pyroxene phenocrysts provide constraints on the composition and crustal evolution of primary melts of Paleoproterozoic (2.40 Ga) picrodoleritic sills in the northwest Kola province, Fennoscandian Shield. The picrodolerites form differentiated sills with S-shaped compositional profiles. Their chilled margins comprise porphyritic picrodolerite (upper margin) and olivine gabbronorite (bottom) with olivine and clinopyroxene phenocrysts. Analysis of the available data allows us to recognize three main stages in the crystallization of mineral assemblages. The central parts of large (up to 2 mm) olivine phenocrysts (Ol–1–C) crystallized at the early stage. This olivine (Mg# 85–92) is enriched in Ni (from 2845 to 3419 ppm), has stable Ni/Mg ratio, low Ti, Mn and Co concentrations, and contains tiny (up to 10 μm) diopside–spinel dendritic lamella that probably originated due to the exsolution from high Ca- and Cr- primary magmatic olivine. All these features of Ol–1–C are typical of olivine from primitive picritic and komatiitic magmas (De Hoog et al., 2010; Asafov et al., 2018). Ol–1–C contains large (up to 0.25 mm) crystalline inclusions of high-Al enstatite (Mg# 80–88) and clinopyroxene (Mg# 82–90), occasionally in association with Ti-pargasite and chromian spinel (60.4 wt.% Al₂O₃). These inclusions are regarded as microxenoliths of wall rock that were captured by primary melt at depths more than 30 km and preserved due to the conservation in magmatic olivine. The second stage was responsible for the crystallization of Ol–1 rim (Ol–1–R), small (up to 0.3 mm) olivine (Ol–2, Mg# 76–85) grains, and central parts of large (up to 1.5 mm) clinopyroxene (Cpx–C) phenocrysts in the mid-crustal transitional magma chamber (at a depth of 15–20 km) at 1160–1350°C. At the third stage, Cpx–C phenocrysts were overgrown by low-Mg rims (Mg# 70–72) similar in composition to the groundmass clinopyroxene from chilled picrodolerite and gabbro-dolerite in the central parts of the sills. This stage likely completed the evolution of picrodoleritic magma and occurred in the upper crust at a depth of about 5 km. All stages of picrodoleritic magma crystallization were accompanied by contamination. Primary melts were contaminated by upper mantle and/or lower crust as recognized from xenocrystic inclusions in Ol–1–C. The second contamination stage is supported by the negative values of ε_Nd(2.40) = –1.1 in clinopyroxene phenocrysts. At the third stage, contamination likely occurred in the upper crust when ascending melts filled gentle fractures. This caused vertical whole-rock Nd heterogeneity in the sills (Erofeeva et al., 2019), and difference in Nd isotopic composition of clinopyroxene phenocrysts and doleritic groundmass. It was also recognized that residual evolved melts are enriched in radiogenic strontium but have neodymium isotopic composition similar to other samples. It could be explained by the interaction of the melts with fluid formed via decomposition of biotite from surrounding gneisses under the effect of high-temperature melts.

中文翻译：

---

橄榄石和斜辉石酚类单体替代了原始地幔熔体的起源和地壳演化：以北芬诺斯堪的亚州科拉-挪威地层中的2.40 Ga铁镁基岩为例

新的岩相，地球化学和同位素的（Sr，Nd和δ ¹⁸ О）上橄榄石和辉石斑晶数据提供关于组合物和古元（2.40 Ga）的在西北科拉省，芬诺斯堪底亚盾picrodoleritic窗台的主熔体的地壳演化约束。吡咯石形成具有S形组成轮廓的差异基石。它们的冷却边缘包括斑状的亚闪闪石（上部边缘）和橄榄石辉长石（底部）以及橄榄石和斜辉石型隐晶石。对可用数据的分析使我们能够识别矿物集合体结晶的三个主要阶段。大（最大2毫米）橄榄石隐晶石的中央部分（Ol–1–C）在早期结晶。该橄榄石（Mg＃85–92）富含镍（从2845至3419 ppm），具有稳定的Ni / Mg比，低的Ti，Mn和Co浓度，并且包含微小的（最多10μm）透辉石-尖晶石树突状薄片这可能是由于高钙和铬初生岩浆橄榄石的析出。Ol –1–C的所有这些特征都是原始的浅云母和科马特岩浆岩中典型的橄榄石（De Hoog等，2010； Asafov等，2018）。Ol –1–C包含高铝顽石（Mg＃80–88）和斜辉石（Mg＃82–90）的大（最大0.25 mm）晶体夹杂物，偶有钛辉石和铬尖晶石（60.4 wt 。％Al ₂ O ₃）。这些包裹体被认为是壁岩的微异岩体，它们在30 km以上的深度被一次初熔体捕获，并由于岩浆橄榄石的保存而得以保留。第二阶段负责Ol -1边缘（Ol –1–R），小（最大0.3毫米）橄榄石（Ol –2，Mg＃76–85）晶粒以及大（最大至1.5毫米）单斜辉石（单斜辉石在中间地壳过渡岩浆室（在15-20公里的深度-C）斑晶）在1160至1350年℃。在第三阶段，Cpx低碳镁沿（Mg＃70-72）长满了-C隐晶，其组成与基部中央的冷黄粉铁矿和辉长辉石-辉长岩的地基斜辉石组成相似。这个阶段很可能完成了软岩质岩浆的演化，并发生在上地壳中约5 km的深度。浅岩质岩浆结晶的所有阶段都伴随着污染。从Ol – 1C中的异相夹杂物可以看出，初熔体被上地幔和/或下地壳污染。第二污染级由ε的负值支持_的Nd（2.20）= –1.1在环吡咯烯单晶中。在第三阶段，上升的熔体填充缓和的裂缝时，上地壳可能会发生污染。这导致了基岩中垂直全岩Nd的异质性（Erofeeva等人，2019），以及斜辉石斑晶和白垩质地层的Nd同位素组成存在差异。还认识到，残留的析出熔体富含放射性锶，但钕同位素组成与其他样品相似。这可以通过熔体与高温熔体作用下黑云母从周围片麻岩分解而形成的流体的相互作用来解释。