Deciphering the parent-daughter relationship between Ediacaran high-silica ignimbrites and their complementary silicic cumulates: Insights from zircon trace element composition

Author(s)

Lino, Lucas Martins ; Quiroz-Valle, Francy Roxana ; Vlach, Silvio Roberto Farias ; Basei, Miguel Angelo Stipp ; Vilalva, Frederico Castro Jobim ; Hueck, Mathias ; Martins, Jose Vinicius

• Document type: Journal article
• Source: CHEMICAL GEOLOGY; v. 635, p. 20-pg., 2023-09-30.

Abstract

The Ediacaran Campo Alegre-Corup & PRIME;a Basin (CACB) comprises a rare and excellent exposure of caldera-forming pyroclastic rocks and their cogenetic underlaying plutons. The CACB experienced at least two major episodes of bimodal volcanic activity. The Basin Stage (-605-590 Ma), characterized by transitional OIB-like basaltic lava flows with minor trachydacites and rhyolites, interbedded with surge-like, silicic pyroclastic deposits, and the Caldera Stage (-583-577 Ma), marked by at least one cycle of silicic alkaline, caldera-forming eruption, dominated by rhyolitic to trachytic ignimbrites and lava flows/domes with subordinate IAB-like basalts. During the Caldera Stage, granitoid plutons were emplaced at shallow crustal levels (-5-8 km deep), correlating with the depth of the magma chamber responsible for the contemporaneous large silicic eruption(s). Previous studies have suggested a genetic connection between the post-collisional volcanic and plutonic rocks based on their similar ages, composition, and Sr-Nd-Hf isotopic signatures. In this study, we analyze zircon trace elements from the volcanic rocks of both stages in the CACB to constrain their evolutive compositional patterns, redox conditions, and Ti-in-zircon saturation temperatures. We compare our results with zircon compositions of the cogenetic granitoids, focusing on the Corup & PRIME;a Pluton, which likely supplied the magma for the caldera-forming eruption(s). By examining whole-rock and zircon chemical compositions, we establish a petrogenetic link between the volcanic rocks and their potential remnant magma reservoir. Our findings indicate that the silicic volcanic rocks from the Caldera Stage represent highly evolved compositions extracted from a crystal mush that solidified as a syenitic intrusion. During the evolution of the volcanic-plutonic system, zircon crystals tracked compositional changes associated with the extraction of residual silicic liquids from crystal mushes and the formation of intermediate-silicic cumulates. Unique variations in zircon compositions of volcanic and plutonic rocks, such as Eu/Eu*, Zr/Hf, and Th/U ratios support such a connection and suggest crystal-melt segregation processes at relatively low crystallinities (< 30 vol%). Additionally, our trace element data supports the occurrence of intense hydrothermal-induced recrystallization of zircon within the caldera structure, as suggested by the morphologic aspects of crystals previously analyzed for U-Pb and Lu-Hf isotopes. (AU)

• FAPESP's process: 19/17343-4 - Geochemical and textural properties of accessory minerals as petrological and geochronological indicators in granitic rocks and associated greisens
• Grantee: Silvio Roberto Farias Vlach
• Support Opportunities: Regular Research Grants
• FAPESP's process: 15/03737-0 - The Rio de La Plata Craton and the Western Gondwana Assembly
• Grantee: Miguel Angelo Stipp Basei
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 19/06838-2 - Pan-African shear zones in the Kaoko Belt (Namibia) and links across Southwestern Gondwana: Neoproterozoic evolution and Phanerozoic reactivation
• Grantee: Mathias Hueck
• Support Opportunities: Scholarships in Brazil - Post-Doctoral