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首页> 外文期刊>Journal of African Earth Sciences >The geology and geochemistry of the Espungabera Formation of central Mozambique and its tectonic setting on the eastern margin of the Kalahari Craton
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The geology and geochemistry of the Espungabera Formation of central Mozambique and its tectonic setting on the eastern margin of the Kalahari Craton

机译：莫桑比克中部埃斯彭加贝拉组的地质地球化学及其在卡拉哈里克拉通东缘的构造环境

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摘要

Whole rock major and trace element chemistry as well as radiogenic isotope data from the Espungabera Formation of central Mozambique are compared with published data from the Umkondo Formation lavas in SE Zimbabwe and Straumsnutane Formation lavas in western Dronning Maud Land, Antarctica. These formations form part of the ～1100Ma Umkondo Igneous Province in southern Africa and are now preserved on the Grunehogna (in Antarctica) and Zimbabwe (in Zimbabwe) Cratons. The chemical data indicate that the Espungabera Formation lavas are dominantly tholeiitic and basaltic to basaltic andesitic in composition. The Espungabera lavas are dominated by plagioclase, clinopyroxene and Fe-Ti oxides. Metamorphic mineral assemblages indicate the lavas have been metamorphosed under mid-greenschist facies on a retrograde path to prehnite-pumpellyite facies conditions. The decrease in FeO_t with increasing MgO content in the Espungabera lavas and the slight decrease in TiO_2 with increasing MgO indicates fractionation of Fe-Ti oxides. The lavas are characterised by negative Nb anomalies; enriched LILE's and high ~(87)Sr/~(86)Sr isotopic ratios. The ~(87)Sr/~(86)Sr data calculated at 1100 Ma suggest contamination by continental crust during the petrogenesis of the lavas. The Espungabera volcanics have negative eNd values (-2.83 to -3.49) also suggesting that the magma was contaminated by older crust. Comparison of the chemical data from the Espungabera Formation with data from the Umkondo Group basalts from SE Zimbabwe and the Straumsnutane Formation lavas from Dronning Maud Land, Antarctica shows that they are similar. These similarities, along with similarities in the available geochronological data suggest that these rocks are comagmatic. Both units are also geochemically similar to some rock units that form part of the Umkondo Large Igneous Province (i.e. Zimbabwe basalts that were regarded as Umkondo basalts by Munyanyiwa (1999), Waterberg sills, Umkondo sills and Type Ⅲ Mutare and Guruve dykes identified by Ward (2002)), and therefore we conclude that the Espungabera lavas in Mozambique also form part of the Umkondo Igneous Province. The craton-based tholeiitic Umkondo Igneous Province is broadly coeval with tonalitic calc-alkaline and granitic gneisses in the Nampula and Maud Terranes in Mozambique and Antarctica respectively, immediately east of the Kalahari Craton in a reconstructed Gondwana. These data can be interpreted to indicate that the Espungabera and Straumsnutane lavas form part of a back-arc complex, west of a volcanic arc/subduction zone along the eastern margin of the Kalahari Craton at ～1100 Ma.
机译：将来自莫桑比克中部埃斯彭加贝拉组的整个岩石主化学和微量元素化学以及放射性同位素数据与来自津巴布韦东南部的Umkondo组熔岩和南极Dronning Maud Land西部的Straumsnutane组熔岩的公开数据进行了比较。这些岩层构成了南部非洲〜1100Ma Umkondo火成岩省的一部分，现在被保存在Grunehogna（南极洲）和津巴布韦（津巴布韦）克拉通地区。化学数据表明，埃斯彭加贝拉组熔岩的成分主要为高生质和玄武质至玄武质安山岩。 Espungabera熔岩以斜长石，斜辉石和Fe-Ti氧化物为主。变质矿物组合表明熔岩已在中绿片岩相下变质，朝着早老石-粉晶岩相条件逆行。 FeO_t的减少随Espungabera熔岩中MgO含量的增加而降低，而TiO_2随MgO的增加而略有降低，表明Fe-Ti氧化物的分馏。熔岩的特征是负Nb异常。富集了LILE和高〜（87）Sr /〜（86）Sr同位素比在1100 Ma处计算出的〜（87）Sr /〜（86）Sr数据表明，在熔岩成岩过程中被大陆壳污染。 Espungabera火山的eNd值为负值（-2.83至-3.49），也表明该岩浆被较旧的地壳污染了。来自Esungabera组的化学数据与来自津巴布韦东南部的Umkondo Group玄武岩的数据和来自南极洲Dronning Maud Land的Straumsnutane组熔岩的比较表明，它们是相似的。这些相似之处以及可用的地质年代数据中的相似之处表明，这些岩石是岩浆。这两个单元在地球化学上也与构成Umkondo大火成岩省一部分的某些岩石单元相似（例如，津巴布韦玄武岩被Munyanyiwa（1999）视为Umkondo玄武岩，Waterberg窗台，Umkondo窗台以及Ward鉴定的Ⅲ型Mutare和Guruve堤坝。 （2002年），因此我们得出的结论是，莫桑比克的Espungabera熔岩也构成了Umkondo火成岩省的一部分。以克拉通为基础的Umkondo火成岩省大致与莫桑比克和南极的Nampula和Maud Terranes的tonalitic钙碱性和花岗片麻岩同时存在，在重建的冈瓦纳省卡拉哈里克拉通以东。这些数据可以解释为表明埃斯彭加贝拉和Straumsnutane熔岩形成了后弧复合体的一部分，该复合体位于卡拉哈里克拉通东缘约1100 Ma的火山弧/俯冲带以西。

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