Petrology of the Pan-African high-K alkali-calcic Bocaranga plutonic complex in the Adamawa-Yadé domain (Central African Republic): Nature, origin and contribution to geodynamic reconstruction of the Central African fold belt

IF 2 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY Solid Earth Sciences Pub Date : 2024-10-11 DOI:10.1016/j.sesci.2024.100211
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Abstract

The Bocaranga plutonic complex belongs to the northwestern extension Adamawa-Yadé Domain of the Central African Fold Belt (CAFB) in the Central African Republic (CAR). Six petrographical units are recorded in the Bocaranga plutonic complex: (i) a coarse-grained biotite granite, (ii) hornblende-biotite granite, (iii) fine-grained biotite granite, and (iv) two micas granite emplaced in Pan-African metamorphic basement rocks composed of (v) gneisses and (vi) amphibolites. Their chemical compositions are similar to quartz monzonites, monzogranite, syenogranite and alkali granite, respectively. The pluton rocks are metaluminous to weakly peraluminous I-type granitoids, hornblende-biotite granite are magnesian and high-K alkaline, while grained biotite granite and fine-grained biotite granite are ferroan, alkalic-calcic and shoshonitic, whereas the two micas granite are weakly to strongly peraluminous and calc-alkaline. The evolution of the major elements (Al2O3 and CaO) and some trace elements (Sr) suggest that fractional crystallization controlled by plagioclase is the main magma differenciation process which influenced the magmatic evolution in this plutonic complex. However, the presence of gneiss xenoliths and mafic enclaves within the plutonic complex, combined to the geochemical data, indicate that the Bocaranga plutonic complex is most likely the result of mixing between mantle- and crust-derived magmas, with high crustal implication for coarse-grained biotite granite, fine-grained biotite granite and two micas granite and high mantle one for hornblende-biotite granite. High U–Th content displays by two-mica granite the high REE content display by all the plutonic rocks indicate that these rocks appear to be respectively favourable for mineralisation in the aforemention elements, thus indicating that the Bocaranga area may represents a potential exploration target for U–Th and REE deposits. The Bocaranga plutonic complex is a synkinematic pluton whose emplacement is synchronuous to the D2 ductile deformation phase related to linear lithospheric delamination along the MBéré Shear Zone around 620-550 Ma during the late-to post-collisional history the Pan-African orogeny. Such granitic plutons are common in the Orogenic Belt of Central Africa and the Brasiliano Belt.
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阿达马瓦-亚代地区(中非共和国)泛非高 K 碱钙质博卡兰加岩浆复合体的岩石学:性质、起源及对中非褶皱带地球动力学重建的贡献
博卡兰加岩浆岩复合体属于中非共和国中部非洲褶皱带(CAFB)的西北延伸阿达马瓦-亚代域(Adamawa-Yadé Domain)。博卡兰加岩浆岩群中有六个岩相单元:(i) 粗粒生物花岗岩,(ii) 角闪石-生物花岗岩,(iii) 细粒生物花岗岩,(iv) 两种云母花岗岩,它们被安放在由(v) 片麻岩和(vi) 闪长岩组成的泛非变质基底岩中。它们的化学成分分别类似于石英独居岩、独居岩、正长岩和碱性花岗岩。深成岩为金属铝质至弱过铝质的 I 型花岗岩,角闪石-黑云母花岗岩为镁质和高 K 碱性,粒状黑云母花岗岩和细粒黑云母花岗岩为铁质、碱性-钙质和霰石质,而两种云母花岗岩为弱至强过铝质和钙碱性。主要元素(Al2O3 和 CaO)和一些微量元素(Sr)的演化表明,由斜长石控制的碎裂结晶是影响这个岩浆复合体岩浆演化的主要岩浆分异过程。然而,该深成岩复合体中存在片麻岩异长岩和黑云母飞地,再加上地球化学数据,表明 Bocaranga 深成岩复合体很可能是地幔和地壳岩浆混合的结果,粗粒生物花岗岩、细粒生物花岗岩和两种云母花岗岩具有较高的地壳影响,而角闪石-生物花岗岩则具有较高的地幔影响。双云母花岗岩显示的高铀-钍含量和所有深成岩显示的高稀土元素含量表明,这些岩石似乎分别有利于上述元素的成矿,从而表明博卡兰加地区可能是铀-钍和稀土元素矿床的潜在勘探目标。博卡兰加岩浆岩复合体是一种同源岩浆岩,其形成与泛非造山运动晚期至碰撞后历史时期约 620-550 马年沿 MBéré 剪切带的线性岩石圈分层相关的 D2 延展变形阶段同步。这种花岗岩柱岩在中非造山带和巴西利亚诺带很常见。
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来源期刊
Solid Earth Sciences
Solid Earth Sciences GEOSCIENCES, MULTIDISCIPLINARY-
CiteScore
3.60
自引率
5.00%
发文量
20
审稿时长
103 days
期刊最新文献
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