The 560.8 ± 2.4 Ma old Okamutambo Pluton is the easternmost intrusion of the syn-collisional Otjimbingwe Alkaline Complex (OAC; Damara Belt, Namibia) and consists of mafic to intermediate alkaline rocks that belong to the monzodiorite-syenite series. The studied samples are potassic (K₂O/Na₂O > 1) and have moderately high magnesium (MgO: 5.7–2.6 wt%), nickel (Ni: 66–26 ppm), and chromium (Cr: 223–62 ppm) concentrations. LILE (Ba: 2425–1243 ppm; Sr: 1359–941 ppm) and HFSE (Zr: 447–202 ppm, Nb: 32.8–16.4 ppm, Hf: 4.7–9.4 ppm, Ta: 1.2–2.0 ppm) contents are also high. Strontium and Nd isotope data reveal the existence of two magmatic suites indicating a multi-source origin. Group 1 monzonites-quartz monzonites have moderately evolved Sr and Nd isotopic compositions (initial ⁸⁷Sr/⁸⁶Sr: 0.7066 to 0.7073; initial ε_Nd: −3.5 to −5.0) and radiogenic Pb isotope ratios (²⁰⁶Pb/²⁰⁴Pb: 17.65–18.02; ²⁰⁷Pb/²⁰⁴Pb: 15.62–15.67; ²⁰⁸Pb/²⁰⁴Pb: 38.19–38.32). In contrast, group 2 monzodiorites-syenites display more evolved Sr and Nd isotopic compositions (initial ⁸⁷Sr/⁸⁶Sr: 0.7088 to 0.7090; initial ε_Nd: −6.7 to −7.1) but similar Pb isotope ratios (²⁰⁶Pb/²⁰⁴Pb: 17.63–17.82; ²⁰⁷Pb/²⁰⁴Pb: 15.64–15.66; ²⁰⁸Pb/²⁰⁴Pb: 38.21–38.37). Differentiation involved AFC processes in group 1 monzonites-quartz monzonites whereas group 2 monzodiorites-syenites were modified by fractional crystallization. Although second-order processes were operative, high total alkali contents, incompatible trace element concentrations in excess of bulk crustal values, and evolved isotopic compositions of the most primitive samples are source-controlled and provide insight into the origin of the parental magmas. With reference to experimental data from the literature, it is inferred that the Okamutambo alkaline rocks represent evolved melts that were generated through melting of enriched lithospheric mantle (phlogopite-lherzolite). The observed negative Nb-Ta and Ti anomalies and positive Pb anomalies in primitive mantle-normalized trace element patterns are in line with a mantle source that contains a recycled crustal component. Isotopic compositions indicate that mantle enrichment is an ancient feature that might be linked to Proterozoic subduction. At 561 Ma, the geodynamic regime in the Damara Orogen was mainly characterized by compression during convergence and continental collision between the Congo and Kalahari cratons which is difficult to reconcile with the generation of the OAC as alkaline magmatism is commonly associated with extensional tectonic regimes. The OAC is, however, associated with a major suture zone that may have been involved in localized transtensional tectonics during oblique flat subduction and thus enabled the generation and ascent of mantle-derived alkaline melts.

在560.8±2.4马老Okamutambo岩体是最东端入侵顺-collisional Otjimbingwe碱性络合物（OAC;达马拉腰带，纳米比亚）和由镁铁质的到属于monzodiorite正长岩系列中间碱性岩。研究的样品是钾（K ₂ O / Na ₂O> 1) 且镁（MgO：5.7-2.6 wt%）、镍（Ni：66-26 ppm）和铬（Cr：223-62 ppm）浓度适中。LILE（Ba：2425-1243 ppm；Sr：1359-941 ppm）和HFSE（Zr：447-202 ppm，Nb：32.8-16.4 ppm，Hf：4.7-9.4 ppm，Ta：1.2-2.0 ppm）的含量高的。锶和 Nd 同位素数据揭示了两个岩浆组的存在，表明存在多源成因。组1二长岩-二长岩石英已适度发展Sr和Nd同位素组成（初始⁸⁷ SR / ⁸⁶ SR：0.7066至0.7073;初始ε_的Nd：-3.5至-5.0）和放射铅同位素比（²⁰⁶ PB / ²⁰⁴的Pb：17.65- 18.02; ²⁰⁷ Pb / ²⁰⁴ Pb：15.62-15.67; ²⁰⁸ Pb /²⁰⁴铅：38.19-38.32)。相比之下，第 2 组二长闪长岩 - 正长岩显示出更多演化的 Sr 和 Nd 同位素组成（初始⁸⁷ Sr / ⁸⁶ Sr：0.7088 至 0.7090；初始 ε _Nd：-6.7 至 -7.1）但类似的 Pb 同位素比（²⁰⁶ Pb / ²⁰⁴ Pb） 17.63-17.82；²⁰⁷铅/ ²⁰⁴铅：15.64-15.66；²⁰⁸铅/ ²⁰⁴铅：38.21-38.37）。分化涉及第 1 组二长岩 - 石英二长岩中的 AFC 过程，而第 2 组二长闪长岩 - 正长岩通过分步结晶进行改性。尽管二级过程是有效的，但总碱含量高、微量元素浓度超过大块地壳值的不相容微量元素浓度以及最原始样品的演化同位素组成是受源控制的，并提供了对母岩浆起源的深入了解。参考文献中的实验数据，推断奥卡穆坦博碱性岩是由富集岩石圈地幔（金云母-二辉长岩）熔融形成的演化熔体。在原始地幔归一化微量元素模式中观察到的负 Nb-Ta 和 Ti 异常和正 Pb 异常与包含循环地壳成分的地幔源一致。同位素组成表明地幔富集是一个古老的特征，可能与元古代俯冲有关。561 Ma时，达马拉造山带的地球动力学制度主要表现为刚果和喀拉哈里克拉通在辐合和大陆碰撞过程中的挤压，这与OAC的产生难以协调，因为碱性岩浆作用通常与伸展构造制度有关。然而，OAC 是