Recycling process and proto-kimberlite melt metasomatism in the lithosphere-asthenosphere boundary beneath the Amazonian Craton recorded by garnet xenocrysts and mantle xenoliths from the Carolina kimberlite

• Published in: 地学前缘（英文版） 2022, Vol.13 (5), p.89-105
• Main Authors: Fernanda Gervasoni, Tiago Jalowitzki, Marcelo Peres Rocha, Ricardo Kalikowski Weska, Eduardo Novais-Rodrigues, Rodrigo Antonio de Freitas Rodrigues, Yannick Bussweiler, Elisa Soares Rocha Barbosa, Jasper Berndt, Elton Luiz Dantas, Valmir da Silva Souza, Stephan Klemme
• Format: Article
• Language: English
• ISSN: 1674-9871

Here we present new data on the major and trace element compositions of silicate and oxide minerals from mantle xenoliths brought to the surface by the Carolina kimberlite,Pimenta Bueno Kimberlitic Field,which is located on the southwestern border of the Amazonian Craton.We also present Sr-Nd iso-topic data of garnet xenocrysts and whole-rocks from the Carolina kimberlite.Mantle xenoliths are mainly clinopyroxenites and garnetites.Some of the clinopyroxenites were classified as GPP-PP-PKP(garnet-phlogopite peridotite,phlogopite-peridotite,phlogopite-K-richterite peridotite)suites,and two clinopyroxenites(eclogites)and two garnetites are relicts of an ancient subducted slab.Temperature and pressure estimates yield 855-1102℃and 3.6-7.0 GPa,respectively.Clinopyroxenes are enriched in light rare earth elements(LREE)(LaN/YbN=5-62;CeN/SmN=1-3;where N=primitive mantle normal-ized values),they have high Ca/Al ratios(10-410),low to medium Ti/Eu ratios(742-2840),and low Zr/Hf ratios(13-26),which suggest they were formed by metasomatic reactions with CO2-rich silicate melts.Phlogopite with high TiO2(＞2.0 wt.％),Al2O3(＞12.0 wt.％),and FeOt(5.0-13.0 wt.％)resemble those found in the groundmass of kimberlites,lamproites and lamprophyres.Conversely,phlogopite with low TiO2(＜1.0 wt.％)and lower Al2O3(＜12.0 wt.％)are similar to those present in GPP-PP-PKP,and in MARID(mica-amphibole-rutile-ilmenite-diopside)and PIC(phlogopite-ilmenite-clinopyorxene)xenoliths.The GPP-PP-PKP suite of xenoliths,together with the clinopyroxene and phlogopite major and trace element signatures suggests that an intense proto-kimberlite melt metasomatism occurred in the deep cratonic lithosphere beneath the Amazonian Craton.The Sr-Nd isotopic ratios of pyrope xenocrysts(G3,G9 and G11)from the Carolina kimberlite are characterized by high 143Nd/144Nd(0.51287-0.51371)and εNd(+4.55 to+20.85)accompanied with enriched 87Sr/86Sr(0.70405-0.71098).These results suggest interac-tion with a proto-kimberlite melt compositionally similar with worldwide kimberlites.Based on Sr-Nd whole-rock compositions,the Carolina kimberlite has affinity with Group 1 kimberlites.The Sm-Nd iso-chron age calculated with selected eclogitic garnets yielded an age of 291.9±5.4 Ma(2 σ),which repre-sents the cooling age after the proto-kimberlite melt metasomatism.Therefore,we propose that the lithospheric mantle beneath the Amazonian Craton records the Paleozoic subduction with the attach-ment of an eclogitic slab into the cratonic ma