纳米比亚西北部达马拉兰火成岩省二叠纪-三叠纪岩浆作用：Ondurakorume碱性碳酸盐岩杂岩

IF 2.6 3区地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS

Chemie Der Erde-Geochemistry Pub Date : 2025-03-27 DOI:10.1016/j.chemer.2025.126287

Andreja Ladisic , Michael A.W. Marks , Benjamin F. Walter , R. Johannes Giebel , Aratz Beranoaguirre , Gregor Markl

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引用次数: 0

摘要

Kalkfeld、Ondurakorume、Osongombo和Etaneno四个空间关联的火成岩杂岩体位于纳米比亚西北部的达马拉兰火成岩省（Damaraland）内，形成于早白垩世南大西洋的裂谷作用。锆石和钛石的LA-ICP MS U-Pb年龄确定了Etaneno的白垩纪年龄（平均139.2±6.7 Ma），而Kalkfeld的榴石正长岩（249.6±3.2和249.4±2.9 Ma）和ondurakorme的（272.1±1.5 Ma）则确定了三叠纪和二叠纪的侵位年龄。此外，Etaneno的霞石正长岩（平均122.8±3.8 Ma）和Kalkfeld的（平均217.4±24.5 Ma）以及Ondurakorume的碳酸盐岩（平均248.1±4.8 Ma）的磷灰石年龄与锆石和钛矿年龄基本一致，而基底大理岩的磷灰石年龄可能为479.6±2.6 Ma和465.1±7.0 Ma。对Ondurakorume的正长岩、霞石正长岩、碳酸盐岩、硅碳酸盐岩和灰长岩进行了详细的岩石学分析，揭示了碱硅酸盐岩与碳酸盐岩之间不同的相互作用过程。正长岩和霞石正长岩含有间质方解石，内含银斑岩或碳碳石包裹体（常见于方解石碳酸盐中）和坏辉石-锆石替代结构。在某些碳酸盐和硅碳酸盐中，局部受（榴石）正长岩和花岗质基底的污染，导致硅活度升高，引发斜辉石、角闪洞和云母的形成增强。释放的溶出液中斜辉石的组成变化表明，近端虫体样品中的近端成员艾格石（Aeg69-91Di0-10Hed0-7）和远端虫体样品中的低钠艾格石（Aeg54-96Di0-17Hed0-16），后者含有额外的钠质角闪孔。与霞石正长岩和碳酸盐岩中的斜辉石相比，白云石中的斜辉石钛含量升高（主要为>；0.05 apfu Ti），其中远端白云石的斜辉石钛含量最高（高达0.22 apfu Ti），表明钛具有流动性。这些变化表明，要么是流体-岩石相互作用期间的成分演化，要么是两种不同的流体来源（分别是碳酸岩和（霞石）正长岩）。

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Permo-Triassic magmatism in the Damaraland Igneous Province, NW Namibia: The Ondurakorume alkaline‑carbonatite complex

The four spatially associated igneous complexes of Kalkfeld, Ondurakorume, Osongombo and Etaneno are situated within the Damaraland Igneous Province (northwestern Namibia), which formed in response to the rifting of the South Atlantic during the early Cretaceous. Spatially-resolved LA-ICP MS U-Pb age dating on zircon and titanite confirms the Cretaceous age for Etaneno (mean of 139.2 ± 6.7 Ma), while Triassic and Permian emplacement ages are indicated for nepheline syenites from Kalkfeld (249.6 ± 3.2 and 249.4 ± 2.9 Ma) and Ondurakorume (272.1 ± 1.5 Ma). Furthermore, apatite ages for nepheline syenites from Etaneno (mean of 122.8 ± 3.8 Ma) and Kalkfeld (217.4 ± 24.5 Ma), and for carbonatites of Ondurakorume (248.1 ± 4.8 Ma) broadly agree with the zircon and titanite ages, while apatite from basement marbles yields a presumably metamorphic age of 479.6 ± 2.6 Ma and 465.1 ± 7.0 Ma.

Detailed petrographic analysis of syenites, nepheline syenites, carbonatites, silicocarbonatites and fenites from Ondurakorume reveals variable interaction processes between alkaline-silicate rocks and carbonatites. Syenites and nepheline syenites contain interstitial calcite with burbankite or carbocernaite inclusions (as commonly found in calcite carbonatites) and baddeleyite-zircon replacement textures. In some carbonatites and in silicocarbonatites, local contamination with (nepheline) syenites and granitic basement caused elevated Si activity, triggering enhanced formation of clinopyroxene, amphibole and mica.

Compositional variations in the released fenitizing fluids are indicated by clinopyroxene compositions that vary from nearly end-member aegirine (Aeg_69-91Di_0-10Hed_0-7) in proximal fenites to less sodic aegirine-augite (Aeg_54-96Di_0-17Hed_0-16) in more distal fenite samples, with the latter containing additional sodic amphibole. Compared to clinopyroxene in nepheline syenites and carbonatites, clinopyroxene in fenites shows elevated Ti contents (mostly >0.05 apfu Ti) that are highest in distal fenites (up to 0.22 apfu Ti), suggesting Ti mobility. These changes suggest either a compositional evolution during fluid-rock interaction or two different fluid sources (carbonatites and (nepheline) syenites, respectively).

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来源期刊

Chemie Der Erde-Geochemistry 地学-地球化学与地球物理

CiteScore

7.10

自引率

0.00%

发文量

审稿时长

3.0 months

期刊介绍： GEOCHEMISTRY was founded as Chemie der Erde 1914 in Jena, and, hence, is one of the oldest journals for geochemistry-related topics. GEOCHEMISTRY (formerly Chemie der Erde / Geochemistry) publishes original research papers, short communications, reviews of selected topics, and high-class invited review articles addressed at broad geosciences audience. Publications dealing with interdisciplinary questions are particularly welcome. Young scientists are especially encouraged to submit their work. Contributions will be published exclusively in English. The journal, through very personalized consultation and its worldwide distribution, offers entry into the world of international scientific communication, and promotes interdisciplinary discussion on chemical problems in a broad spectrum of geosciences. The following topics are covered by the expertise of the members of the editorial board (see below): -cosmochemistry, meteoritics- igneous, metamorphic, and sedimentary petrology- volcanology- low & high temperature geochemistry- experimental - theoretical - field related studies- mineralogy - crystallography- environmental geosciences- archaeometry