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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Petrology and Sr-Nd-Pb isotope geochemistry of Late Cretaceous continental rift ignimbrites, Kap Washington peninsula, North Greenland
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Petrology and Sr-Nd-Pb isotope geochemistry of Late Cretaceous continental rift ignimbrites, Kap Washington peninsula, North Greenland

机译：北格陵兰Kap华盛顿半岛晚白垩世大陆裂谷火成岩的岩石学和Sr-Nd-Pb同位素地球化学

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摘要

The Late Cretaceous-Palaeocene (71-61 Ma) Kap Washington Group (KWG) volcanic sequence is exposed at the north coast of Greenland. The sequence is bimodal and was erupted in a continental rift setting during the opening of the Arctic Ocean. The succession exposed on the Kap Washington peninsula, which forms the bulk of the KWG sequence (>5 km thick), has been sampled along four traverses with a combined stratigraphic thickness of ca. 1500 m. The sampled sequence is dominated by silicic ignimbrites (69-79 wt.% SiO_2) showing geochemical features typical of ferroan, A-type granitoids. The ignimbrites range from sparsely phyric, mildly peraluminous compositions [ASI = Al_2O_3/(CaO + Na_2O + K_2O) = 1.05-1.20] to feldspar + quartz ± sodic am-phibole ± Fe-Ti oxide phyric peralkaline compositions [PI = (Na_2O + K_2O)/Al_2O_3 = 1.00-1.40]. The peraluminous ignimbrites appear to overlie the peralkaline ignimbrites, although stratigraphy is complicated by faulting. Fiamme imbrication indicates that both types were erupted from a vent area located north of the Kap Washington peninsula. The peralkaline ignimbrites have Sr-Nd-Pb isotopic compositions which overlap with the compositions of KWG basalts, indicating a dominantly basaltic source. The more peralkaline compositions were generated by up to ca. 50% fractional crystallisation of alkali feldspar-quartz-dominated assemblages from mildly peralkaline parental magmas, themselves probably derived by fractionation of trachytic magmas. The peraluminous ignimbrites have slightly negative ε_(Nd(i)) and more radiogenic ~(207)Pb/~(204)Pbi and ~(208)Pb/~(204)Pb_i. Modelling indicates that they are not cogenetic with the peralkaline ignimbrites and they are inferred to have originated by partial melting of hybridised mafic crust. Petrographic evidence suggests that magma mixing was an important process and variations in Nd-Pb isotopes and trace element ratios indicate mixing between peralkaline and peraluminous magma batches.
机译：晚白垩世-古新世（71-61 Ma）的卡普华盛顿组（KWG）火山序列暴露于格陵兰岛的北海岸。该序列是双峰序列，在北冰洋开放期间在大陆裂谷环境中爆发。沿着Kap华盛顿半岛暴露的演替形成了KWG序列的主体（> 5 km厚），已沿4条导线进行了采样，总地层厚度约为。 1500米样品序列以硅质火成岩（69-79 wt。％SiO_2）为主导，显示出铁氧体，A型花岗岩典型的地球化学特征。着火点的范围从稀疏的，轻度的高铝成分[ASI = Al_2O_3 /（CaO + Na_2O + K_2O）= 1.05-1.20]到长石+石英±钠盐双闪石±Fe-Ti氧化物的过高碱性成分[PI =（Na_2O + K_2O）/ Al_2O_3 = 1.00-1.40]。尽管地层因断层而复杂化，但高铝辉石似乎覆盖在高碱性辉石上。 Fiamme振动表明这两种类型都是从位于Kap Washington半岛北部的通风口喷出的。周碱性火成岩具有Sr-Nd-Pb同位素组成，与KWG玄武岩的组成重叠，表明主要为玄武岩来源。高碱性的组合物最多可生成约20个。碱性长石-石英为主的集合体的50％分数结晶，其来自温和的碱性碱性亲本岩浆，它们本身很可能是由trachytic岩浆分离而成的。钙铝辉石具有略微负的ε_（Nd（i））和更多的放射源〜（207）Pb /〜（204）Pbi和〜（208）Pb /〜（204）Pb_i。建模表明，它们与过碱性的火成岩不是共生的，并且推断它们是由杂化的铁镁铁壳的部分融化引起的。岩相学证据表明，岩浆混合是重要的过程，Nd-Pb同位素的变化和微量元素的比例表明，高碱性碱和高铝质岩浆之间存在混合。

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