Abstract The Nkondjock area located in Western Cameroon is part of the Neoproterozoic Central African orogenic belt, at the northern border of the Congo craton. Rocks of the Nkondjock area are: two-mica orthogneisses, two-pyroxene orthogneisses and mylonitic orthogneisses. The protolith of two-mica, two-pyroxene and mylonitic orthogneisses crystallized at 607±4, 624.4±3.5 and 621±9.1Ma, respectively, and are thus consistent with the Central African Orogenic belt. Inherited zircons (2043±27 Ma) of mylonitic orthogneisses are interpreted as an inherited age of the metacratonization of the northern border of the Congo craton. S-type affinity of two-mica orthogneisses together with two-pyroxene orthogneisses (Mabombe) display geochemical affinities typical of adakite, including high La/YbN (29.7-55.6) and low Y (3.43-6.69 ppm) with low Mg# (30.8-55), eNd(t) (−8.6 to −6.5), high 87Sr/86Sri (0.70684-0.71063) and positive eHf(t) (+3 to +4.9), similar to those adakites formed by partial melting of thickened lower crust with some mantle input. Two-pyroxene orthogneisses (Ndogboni) and mylonitic orthogneisses display I-type granitoids affinity with A/CNK (0.93-1.06) and are depleted in Nb, Ta, Sr, P, Ti and enriched in Rb, Th, and Pb. They also have low eNd(t) (−10.3 to −11), high 87Sr/86Sri (0.71017-0.71063) and negative eHf(t) (−19.1 to −1) similar to melts derived from mature continental crust. Sr-Nd-Hf isotopes confirm heterogeneous source for these orthogneisses with bimodal distribution on eHf(t) and eNd(t) values, suggesting mixing between juvenile mafic melt and a mature continental crust during the evolution of the Central African Orogenic belt. We suggest that the protolith of these orthogneisses (S- and I-type granitoids) were formed during syn-collisional setting between the Congo and the West African craton which followed a subduction through partial melting of a thickened lower continental crust due to a thermal anomaly induced by upwelling of asthenosphere through slab break-off.

中文翻译：

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喀麦隆刚果克拉通北部边界 Nkondjock 地区的新元古代同碰撞岩浆活动：对中非造山带的地球动力学意义

摘要 位于喀麦隆西部的恩孔乔克地区是新元古代中非造山带的一部分，位于刚果克拉通的北部边界。Nkondjock 地区的岩石有：双云母正片麻岩、双辉石正片麻岩和糜棱正片麻岩。二云母、二辉石和糜棱正片麻岩的原岩分别在607±4、624.4±3.5和621±9.1Ma结晶，与中非造山带一致。糜棱正片麻岩的继承锆石 (2043±27 Ma) 被解释为刚果克拉通北部边界元克拉通化的继承时代。双云母正方麻岩和双辉石正方麻岩 (Mabombe) 的 S 型亲和力显示埃达克岩的典型地球化学亲和力，包括高 La/YbN (29.7-55.6) 和低 Y (3.43-6.69 ppm) 和低 Mg# (30.8) -55), eNd(t) (-8.6 to -6.5), 高 87Sr/86Sri (0.70684-0.71063) 和正 eHf(t) (+3 to +4.9), 类似于那些由加厚的下地壳和一些地幔部分熔融形成的埃达克岩输入。双辉石正片麻岩 (Ndogboni) 和糜棱正片麻岩显示出与 A/CNK (0.93-1.06) 的 I 型花岗岩类化合物，并且缺乏 Nb、Ta、Sr、P、Ti 并富含 Rb、Th 和 Pb。它们还具有低 eNd(t)（-10.3 至 -11）、高 87Sr/86Sri（0.71017-0.71063）和负 eHf(t)（-19.1 至 -1），类似于来自成熟大陆地壳的熔体。Sr-Nd-Hf 同位素证实了这些正方麻岩的异质来源，在 eHf(t) 和 eNd(t) 值上具有双峰分布，表明在中非造山带演化过程中，新生的基性熔体和成熟的大陆地壳之间存在混合。