Age and geochemistry of Early Cambrian post-collisional granites from the Ambatondrazaka area in east-central Madagascar

作者：Zhou Jiu Long; Rasoamalala V; Razoeliarimalala M; Ralison B; Luo Zhao Hua^*

来源：Journal of African Earth Sciences, 2015, 106: 75-86.

DOI：10.1016/j.jafrearsci.2015.02.012

• East African Orogen
• Post-collisional magmatism
• Zircon Hf isotope
• Crustal anatexis
• Madagascar

New geochronological and geochemical data are presented on Early Cambrian granites from the Ambatondrazaka area in east-central Madagascar. U-Pb zircon dating reveals that these granites were emplaced at similar to 520 Ma within a post-collisional setting. They are metaluminous to weakly peraluminous and enriched in large ion lithophile elements. Using zircon Ce anomalies as proxy, it is indicated that they crystallized under moderately reduced conditions with an oxygen fugacity of FMQ+0.75/NNO-0.09. Their low initial Sr-87/Sr-86 ratios (0.706715 and 0.706869) and notably negative epsilon(Nd)(t) values (-24.1 and -23.4) imply a magma source of mafic continental crustal material, probably analogous to the Neoarchean mafic gneisses of the Tsaratanana Complex. The low zircon epsilon(Hf)(t) values (-16.4 to 12.9) further support a mafic crustal source with a Lu-176/Hf-177 ratio of similar to 0.017. On the other hand, their depletion in HREE and slight depletion in Nb help constrain the melting pressure between similar to 10 and 13 kbar. Taken together, a mafic lower crustal source is favored for these granites. Our results demonstrate the role of crustal anatexis in the origin of Late Ediacaran-Early Cambrian post-collisional magmatism in Madagascar.

• 出版日期2015-6
• 单位中国地质大学（北京）