Petrology and geochemistry of the Batchingou anorthositic suite rocks (Bana volcano-plutonic complex, Cameroon Volcanic Line): Inference on their origin and relation with host granites,Geological Journal

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Petrology and geochemistry of the Batchingou anorthositic suite rocks (Bana volcano-plutonic complex, Cameroon Volcanic Line): Inference on their origin and relation with host granites
Geological Journal ( IF 1.4 ) Pub Date : 2022-07-11 , DOI: 10.1002/gj.4543
Morel Ziada Tabengo ₁ , Bernard Tassongwa ₁ , Jules Tamen ₁ , Charles Nkoumbou ₂ , Théophile Njanko _{1,

3} , Asobo Nkengmatia Elvis Asaah _{4,

5} , Sylvin Sans Terre Tedonkenfack ₁ , Armand Sylvain Ludovic Wouatong ₁

Affiliation

This study focusses on field mapping, petrographic description, and geochemical analyses of the Batchingou anorthositic suite rocks (Bana Plutono-volcanic Anorogenic Complex, Cameroon Volcanic Line). This suite consists of gabbroic (gabbro, gabbronorite, norite, and anorthosite) and charnockitic (mangerite, jotunite, enderbite, and monzogranite) rocks and intrude Ypresian granites (51 ± 1 Ma), within an elliptically shaped corridor of 1200 × 600 m². Gabbroic rocks evolved by crystal fractionation of olivine, hypersthene, augite, plagioclase, and ilmenite following the path: gabbro → gabbronorite → norite → anorthosite. There is little or no crustal assimilation in this suite, contrarily to the charnockitic suite which likely evolved from a jotunite melt by assimilation of the Pan-African granito-gneissic basement rocks. Anorthosite has high Eu/Eu* (2.04–2.66), typical of anorthosites formed as cumulates. The La/Ta ratios (9.75–20.1 in gabbro, 21–45 in anorthosite and 23–76 charnockitic rocks), La/Yb_N (4.2–19.5), Nb/U (22–90), and Nb/Th (5–23) suggest that the parental magma of the Batchingou anorthositic suite rocks is an alkaline basaltic melt deriving from a garnet-bearing asthenospheric mantle, but was variably modified during ascent by lithospheric spinel lherzolites and crustal rocks. The Batchingou gabbro has characteristics of evolved tholeiites and match the composition of the Laramie high-Al gabbro, whereas jotunite shows compositional affinity to ferrodiorites from Proterozoic anorthosite complexes. The gabbro Ni (19–39 ppm) and Cu (44–118 ppm) contents are low, indicating that their parental melt is not primitive. The Batchingou anorthositic suite differentiated from a different magma batch postdating the host granitoids and is similar to the anorthosite dykes of the Mboutou ring complex (Cameroon) and most of the ring complexes of the Aïr Province (Niger).

中文翻译：

Batchingou 斜长岩套岩（巴纳火山-深成杂岩，喀麦隆火山线）的岩石学和地球化学：对其起源和与宿主花岗岩关系的推断

本研究的重点是对 Batchingou 斜长岩组岩（Bana Plutono-volcanic Anorogenic Complex, Cameroon Volcanic Line）进行实地测绘、岩相描述和地球化学分析。该套组由辉长岩（辉长岩、辉长岩、钠长石和钙长石）和红绿长石（芒长石、黄褐斑、尾长岩和二长花岗岩）岩石和侵入伊普勒斯花岗岩（51 ± 1 Ma）组成，位于 1200 × 600 m ^{2的椭圆形走廊内}. 辉长岩是由橄榄石、超辉石、辉石、斜长石和钛铁矿的结晶分馏演化而成的，其路径是：辉长岩→辉长石→钠长石→斜长岩。在这个套件中几乎没有或没有地壳同化，这与可能是通过泛非花岗-片麻岩基底岩石的同化从黄钾长石熔体演变而来的软黄褐质套件相反。钙长石具有高 Eu/Eu* (2.04–2.66)，典型的钙长石形成。La/Ta 比（辉长岩为 9.75-20.1，斜长岩为 21-45，松软岩为 23-76），La/Yb _N(4.2-19.5)、Nb/U (22-90) 和 Nb/Th (5-23) 表明 Batchingou 斜长岩套岩的母岩浆是源自含石榴石软流圈地幔的碱性玄武质熔体，但在上升过程中受到岩石圈尖晶石亮辉石和地壳岩石的不同修饰。Batchingou辉长岩具有演化拉斑矿的特征，与Laramie高铝辉长岩的成分相匹配，而jotunite对来自元古代斜长石复合体的铁闪长岩表现出成分亲和性。辉长岩 Ni (19-39 ppm) 和 Cu (44-118 ppm) 含量较低，表明它们的母体熔体不是原始的。

更新日期：2022-07-11

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