Tracking crustal assimilation processes in kimberlites from the Alto Parana?ba Igneous Province, Brazil: Petrographic and geochemical controls and the role of perovskites

Author(s)

Azzone, Rogerio Guitarrari ; Pearson, David Graham ; Sarkar, Chiranjeeb ; Chmyz, Luanna ; Shibata, Camila Sayuri Vasconcelos ; Luo, Yan ; Ruberti, Excelso

• Document type: Journal article
• Source: LITHOS; v. 432-433, p. 22-pg., 2022-10-10.

Abstract

Anomalous kimberlite varieties from the Cretaceous Alto Paranaiba Igneous Province (APIP, Brazil) do not follow simple classification charts, showing abundant evidence of interaction with crustal xenoliths. In this paper, we track the potential effects of crustal assimilation processes on textural, mineralogical, geochemical and isotopic signatures. Formation of reaction diopside and poikilitic phlogopite, as well as Fe/Nb variations in perovskites, records progressive increases of not only alumina and K2O contents, but also of silica activity and fO2, compatible with the assimilation of and/or interaction with the Si-rich crust. High bulk rock "contamination indexes", decreasing Ce/Pb and Gd/Lu and slightly increasing Rb/Sr ratios are observed in the APIP kimberlite varieties and/or facies showing progressively more remarkable petrographic evidence of crustal contamination. Significant variability of 87Sr/86Sri ratios detected in whole rock, bulk perovskite concentrates (TIMS, MC-ICP-MS) and in-situ perovskite (multi-grain approach, LA-MC-ICP-MS) of the Indai ' a-I/Limeira-I intrusions (0.70507-0.70539) and their satellites Indaia-II/Limeira-II/III (0.70508-0.70592), of the different Pantano facies (0.70513-0.70551), and of the Catalao 1b (0.70495-0.706546) indicates a tendency to more radiogenic Sr isotope compositions during kimberlite open-system crystallization. Geochemical modeling indicates the important crustal contribution to the genesis of these anomalous occurrences, with an extensive crust input for the Indaia-II and Limeira-II/III occurrences, consistent with their petrographic evidence. The potassic to ultrapotassic geochemical affinity and the similarities between contaminated APIP kimberlite and bulk kamafugite compositions can be related to the incorporation/digestion of crustal components to the parental kimberlite magma. (AU)

• FAPESP's process: 19/22084-8 - The Paraná Magmatic Province: petrogenesis, chronology and environmental impact of Cretaceous tholeiitic, alkaline and silicic magmatism in the Brazilian Platform
• Grantee: Valdecir de Assis Janasi
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 17/03768-8 - Xenocryst and Antecryst compositional influence in basic to ultrabasic alkaline magmas
• Grantee: Rogério Guitarrari Azzone
• Support Opportunities: Regular Research Grants