Tectonics of the Isua Supracrustal Belt 1: P‐T‐X‐d Constraints of a Poly‐Metamorphic Terrane. Issue 3 (15th March 2021)

• Record Type: Journal Article
• Authors: Ramírez‐Salazar, Anthony; Müller, Thomas; Piazolo, Sandra; Webb, A. Alexander G.; Hauzenberger, Christoph; Zuo, Jiawei; Haproff, Peter; Harvey, Jason; Wong, Tsz Kin; Charlton, Callum
• Is Part Of: Tectonics. Volume 40:Issue 3(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-03-15
• Subjects: Archean geodynamics -- Archean metamorphism -- geothermobarometry -- Isua supracrustal belt -- nonuniformitarian tectonics; Geology, Structural -- Periodicals; 551.8
• DOI: 10.1029/2020TC006516
• Languages: English
• ISSNs: 0278-7407

Abstract

Abstract: The Eoarchean Isua supracrustal belt (ISB) has been interpreted as one of the earliest records of subduction processes, leading to the conclusion that a plate tectonic geodynamic system was likely operating since the early Archean. However, proposed tectonic models remain difficult to evaluate as our understanding of the metamorphic and structural evolution remains fragmentary. Here, we present a metamorphic study of the supracrustal rocks of the ISB. We used petrographic and microstructural observations, phase equilibria, isopleth geothermobarometry, and conventional thermometry to explore the prograde, peak, and retrograde metamorphic evolution of the northeastern ISB. Our results show that the ISB records a syn‐tectonic, amphibolite facies metamorphic event (M1 ) with peak conditions of 550°C–600°C and 0.5–0.7 GPa. M1 was followed by a static, lower amphibolite facies metamorphic event (M2 ; <540°C and <0.5 GPa). Published constraints suggest that M1 and M2 occurred in the late Eoarchean (>3.5 Ga) and the Neoarchean (<2.9 Ga), respectively. These events are partially overprinted by late low temperature (<500°C) retrogression (M3 ) that is most intensely developed in the northeastern part of the belt; it typically overprints some peak mineral phases while preserving the peak fabric. Our findings are consistent with spatially homogeneous syn‐tectonic amphibolite facies metamorphism and macroscale folding. Such features are predicted by a heat‐pipe tectonic model. Therefore, our findings permit the interpretation of the ISB as a record of early nonuniformitarian tectonic processes. Key Points: The Isua supracrustal belt (ISB) records three tectono‐metamorphic events Petrographic observations and geothermobarometry show no clear metamorphic gradients in the ISB Syn‐tectonic metamorphic records are consistent with heat‐pipe model predictions for the evolution of the belt