K. A. Savko, A. V. Samsonov, S. V. Tsybulyaev, N. S. Bazikov, E. Kh. Korish, R. A. Terentiev
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引用次数: 0
摘要
摘要 在萨尔马特的库尔斯克地块首次发现了碳酸盐-生物岩成分的沸石尖晶石,它们与古近纪带铁地层相交。它们的年龄为 2.10-2.07 Ga。闪长岩尖晶石经历了闪长岩-闪长岩面变质作用(550°С,2-3千巴),并发生了变形和褶皱。原生岩浆橄榄石和辉石没有保存下来。从地球化学角度来看,库尔斯克区块的超基性岩化石类似于典型的岩浆岩。它们的 SiO2 和 Al2O3 含量低,而 MgO、TiO2、K2O、Cr、Ni 和 Nb 含量高,LREE 和 HREE 分馏度高。高放射性钕同位素组成表明榴辉岩来源于幼年富集(变质)地幔。正的 Nb 和 Ti 异常表明,在 Tim 后弧盆地打开的情况下,OIB 熔体对贫化的岩石圈地幔进行了变质改造。Dubravinsky复合体的箭云母尖晶石和碳酸盐岩可能是在一个单一的深岩石圈源的不同熔融程度下形成的,在熔融前不久富含亲岩元素,可能是在大约2.1 Ga的超俯冲环境中形成的。
First Discovery of Paleoproterozoic Aillikite Dikes in Sarmatia: Geochemistry and Petrogenesis
Abstract
Aillikite dikes of carbonate–biotite composition, intersecting Paleoproterozoic banded iron formations, were discovered in the Kursk block of Sarmatia for the first time. Their age is 2.10–2.07 Ga. The aillikite dikes underwent epidote–amphibolite facies metamorphism (550°С, 2–3 kbar), and they are deformed and foliated. Primary magmatic olivine and pyroxene were not preserved. In terms of geochemistry, ultramafic lamprophyres of the Kursk block are similar to petrotypical aillikites. They are depleted in SiO2 and Al2O3 and enriched in MgO, TiO2, K2O, Cr, Ni, and Nb with highly fractionated LREE and HREE. The highly radiogenic neodymium isotopic composition is indicative of a juvenile enriched (metasomatized) mantle source of aillikites. Positive Nb and Ti anomalies suggest metasomatic alterations of the depleted lithosphere mantle by OIB melts under opening of the Tim back-arc basin. The aillikite dikes and carbonatites of the Dubravinsky complex could have been formed at different melting degrees of a single deep, lithospheric source, enriched in lithophile elements shortly before the melting episode, possibly in a suprasubduction setting about 2.1 Ga.
期刊介绍:
Doklady Earth Sciences is a journal that publishes new research in Earth science of great significance. Initially the journal was a forum of the Russian Academy of Science and published only best contributions from Russia. Now the journal welcomes submissions from any country in the English or Russian language. Every manuscript must be recommended by Russian or foreign members of the Russian Academy of Sciences.