Abstract The Superior craton is bordered on its northern and eastern sides by the approximately coeval Cape Smith fold belt and the Labrador Trough, two major Paleoproterozoic volcano-sedimentary belts that record broadly similar tectonic evolution but which show some distinctive characteristics and have notably different mineral resource endowments. The Roberts Lake Syncline, situated directly between the Cape Smith and Labrador Trough, hosts two Paleoproterozoic mafic volcanic sequences and has uncertain tectonic affinities to its neighboring fold belts. It was previously linked to Labrador Trough magmatism but re-interpretation of the regional geology suggests a closer resemblance to the successions of the Cape Smith belt. We present new lithogeochemistry that shows that the Roberts Lake Syncline comprises two distinct magmatic events rather than the single event previously interpreted. The lower and more voluminous suite of the Roberts Lake Syncline lavas comprises multiply-saturated basalts characterized by normalized trace element patterns similar to E-type mid-ocean ridge basalts (E-MORB). The upper suite of the Roberts Lake Syncline stratigraphy is composed of volcanic rocks with depleted, N-MORB-like trace element signatures rocks spanning a range from komatiites and picrites with near-primary compositions to high-Mg basalts with flat normalized trace element patterns. Both suites were apparently undersaturated with sulfide liquid in their mantle source. The E-MORB magmas were affected by a sulphide-saturation event, leading to widespread and variable degrees of depletion of chalcophile elements, despite showing no significant crustal contamination. The N-MORB magmas also underwent saturation with sulfide melt, generating minor occurrences of magmatic sulfide mineralization hosted by ultramafic intrusions within the older volcanic suite and small but significant depletions in chalcophile elements in the erupted picritic basalts. The geochemistry of the lower E-MORB suite is similar to that of the 2170 Ma Biscotasing dike swarm that occurs in and near the Labrador Trough and the 1998 Ma Minto-Povungnituk large igneous province (LIP) of the Cape Smith belt, whereas the upper N-MORB-like suite in the Roberts Lake Syncline has compositions resembling those of the 1880 Ma Circum-Superior LIP. Our detailed geochemical comparison suggests a close resemblance to the chemical stratigraphy observed within the Cape Smith belt, leading us to consider the Roberts Lake Syncline as the southeasternmost portion of the Ungava Orogen rather than the northernmost part of the Labrador Trough. These insights contribute to a revised LIP and plume centre map for this NE portion of the Superior craton and help to constrain the large-scale tectonic architecture of the margins of the Superior Province.

中文翻译：

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罗伯茨湖向斜镁铁质熔岩（东北苏必利克拉通）：史密斯角带的拟议延伸

摘要 苏必利尔克拉通的北部和东部与大约同时期的史密斯角褶皱带和拉布拉多海槽相邻，这两个主要的古元古代火山-沉积带记录了大体相似的构造演化，但表现出一些独特的特征和明显不同的矿产资源。禀赋。罗伯茨湖向斜直接位于史密斯角和拉布拉多海槽之间，拥有两个古元古代基性火山序列，与其相邻的褶皱带具有不确定的构造亲缘关系。它以前与拉布拉多海槽岩浆作用有关，但对区域地质的重新解释表明它与史密斯角带的序列更相似。我们提出了新的岩石地球化学，表明罗伯茨湖向斜包含两个不同的岩浆事件，而不是先前解释的单一事件。罗伯茨湖向斜熔岩的下部和体积更大的岩层包括多饱和玄武岩，其特征是归一化的微量元素模式，类似于 E 型大洋中脊玄武岩 (E-MORB)。罗伯茨湖向斜地层的上层由火山岩组成，其具有耗尽的、类似 N-MORB 的微量元素特征岩石，范围从科马提岩和具有近原生成分的苦冰岩到具有平坦归一化微量元素模式的高镁玄武岩。两套地幔源中的硫化物液体显然都不饱和。E-MORB 岩浆受到硫化物饱和事件的影响，尽管没有显示出明显的地壳污染，但导致了广泛和不同程度的亲硫元素消耗。N-MORB 岩浆也经历了硫化物熔体的饱和，产生了少量岩浆硫化物矿化，这些岩浆硫化物矿化由较旧的火山岩套内的超基性侵入体和喷发的苦味玄武岩中的小而显着的亲硫元素消耗所承载。下部 E-MORB 组的地球化学与发生在拉布拉多海槽和 1998 年 Ma Minto-Povungnituk 大型火成岩省 (LIP) 及其附近的 2170 Ma Biscotasing 堤群相似，而上部Roberts Lake Syncline 中类似 N-MORB 的组曲具有类似于 1880 Ma Circum-Superior LIP 的乐曲。我们详细的地球化学比较表明与在史密斯角带内观察到的化学地层非常相似，使我们将罗伯茨湖向斜视为 Ungava 造山带的最东南部，而不是拉布拉多海槽的最北部。这些见解有助于为苏必利尔克拉通东北部部分修订 LIP 和羽流中心图，并有助于约束苏必利尔省边缘的大规模构造结构。