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Weathering profiles developed on gneisses from Batchenga and Doua areas, central Cameroon: Climate and topography controls
Journal of African Earth Sciences ( IF 2.3 ) Pub Date : 2021-08-27 , DOI: 10.1016/j.jafrearsci.2021.104367
Jean-Marc Kessoum Adamou 1 , Sylvie Désirée Noa Tang 2 , Elisé Sababa 1 , Vincent Laurent Onana 1
Affiliation  

Two weathering profiles from Batchenga and Doua areas in Central Cameroun developed under contrasting equatorial climate conditions and located in different morphological units have been selected to constraint the variability of their morphology, mineralogy, and geochemistry. The parent rock is a biotite and amphibole gneiss with a heterogranular granoblastic texture. The weathering profiles are typical lateritic materials formed in a humid tropical climate zone. They comprise, from bottom to top, coarse saprolite, fine saprolite, nodular horizon and loose clayey horizon. The Doua weathered materials are more clay-rich as a result of intense chemical weathering (CIA: 95.0–99.5%) than those of Batchenga (CIA: 51.3–87.8%). The weathering profile of Doua is thicker (12.00 m) than that of Batchenga (6.30 m). The intense chemical weathering and the total leaching of mobile elements as a consequence of good drainage led to the formation of a hard nodular horizon in the Doua weathering profile. The mineral composition is dominated by quartz, kaolinite, muscovite, illite, hematite/goethite, gibbsite and anatase. Illite is particularly abundant in the Batchenga weathering profile. Among trace elements, Ba, V, Zr, Sr, and Cr have high contents while REE show moderate contents with the highest contents in the Batchenga weathering profile. The oxidizing conditions favor positive Ce anomalies while positive Eu anomalies are due to the resistance of Eu mineral bearers. Geochemical mass balance results suggest that climate and topographic position which influence the quality of drainage greatly influence the distribution patterns of major, trace and rare earth elements in the weathering profiles. Apart from Al, Fe, and P, major elements have been much leached than trace elements during chemical weathering. Thus, the important variations are explained by the variation in the annual rainfall and topographic conditions.



中文翻译:

喀麦隆中部 Batchenga 和 Doua 地区片麻岩的风化剖面:气候和地形控制

来自喀麦隆中部 Batchenga 和 Doua 地区的两个风化剖面在对比鲜明的赤道气候条件下形成并位于不同的形态单位,已被选择以限制其形态、矿物学和地球化学的变异性母岩是黑云母和角闪石片麻岩,具有异粒粒晶质结构。风化剖面是在潮湿的热带气候区形成的典型红土材料。它们从下到上包括粗腐泥土、细腐泥土、结节层和疏松粘土层。由于强烈的化学风化作用(CIA:95.0-99.5%),Doua 风化材料比 Batchenga(CIA:51.3-87.8%)更富含粘土。Doua 的风化剖面 (12.00 m) 比 Batchenga (6.30 m) 厚。由于排水良好,强烈的化学风化作用和流动元素的完全浸出导致在杜阿风化剖面中形成硬结节层。矿物成分以石英、高岭石、白云母、伊利石、赤铁矿/针铁矿、三水铝石和锐钛矿为主. 伊利石在 Batchenga 风化剖面中特别丰富。在微量元素中,Ba、V、Zr、Sr 和 Cr 含量较高,而 REE 含量适中,在 Batchenga 风化剖面中含量最高。氧化条件有利于 Ce 正异常,而 Eu 正异常是由于 Eu 矿物载体的抵抗。地球化学质量平衡结果表明,影响排水质量的气候和地形位置极大地影响了风化剖面中主要、微量和稀土元素的分布格局。除了 Al、Fe 和 P 之外,主要元素在化学风化过程中比微量元素浸出得更多。因此,重要的变化可以用年降雨量和地形条件的变化来解释。

更新日期:2021-09-02
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