Structural and tectonothermal evolution of the ultrahigh-temperature Bakhuis Granulite Belt, Guiana Shield, Surinam: Palaeoproterozoic to Recent

Frank Beunk*, Emond de Roever, Keewook Yi, F.M. Brouwer

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

We constrain the multistage tectonic evolution of the Palaeoproterozoic UHT metamorphic (P = 0.9-1.0 GPa, T>1000˚C, t = 2088-2031 Ma) Bakhuis Granulite Belt (BGB) in Surinam on the Guiana Shield, using large- to small-scale structures, Al-in-hornblende thermobarometry and published fluid inclusion and zircon geochronological data. The BGB forms a narrow, NE-SW striking belt between two formerly connected, ~E-W oriented granite-greenstone belts, formed between converging Amazonian and West African continental masses prior to collision and Transamazonian orogeny. Inherited detrital zircon in BGB metasediments conforms agewise to Birimian zircon of West Africa and suggests derivation from the subsequently subducted African passive margin. Ultrahigh-temperature metamorphism may have followed slab break-off and asthenospheric heat advection. Peak metamorphic structures result from layer-parallel shearing and folding, reflecting initial transtensional exhumation of the subducted African margin after slab break-off. A second HT event involves intrusion, at c. 0.49 GPa, of charnockites and metagabbros at 1993-1984 Ma and a layered anorthosite at 1980 Ma, after the BGB had already cooled to <400˚C. The event is related to northward subduction under the greenstone belts, along a new active margin to their south. A pronounced syntaxial bend in the new margin points northward towards the BGB and is likely the result of indentation by an anticlinorial flexural bulge of the subducting plate. Tearing of the subducting oceanic plate along this bulge explains why the charnockites are restricted to the BGB. The BGB subsequently experienced doming under an extensional detachment exposed in its southwestern border zone. Exhumation was focused in the BGB as a result of the flexural bulge in the subducting plate and localised heating of the overriding plate by charnockite magmatism. The present, straight NE-SW long-side boundaries of the BGB are superimposed mylonite zones, overprinted by pseudotachylites, previously dated at c. 1200 Ma and 950 Ma, respectively. The 1200 Ma mylonites reflect transpressional popping-up of the BGB, caused by EW-directed intraplate principal compressive stresses from Grenvillian collision preserved under the eastern Andes. Further exhumation of the BGB involved the 950 Ma pseudotachylite decorated faulting, and Phanerozoic faulting along reactivated Meso- and Neoproterozoic lineaments.
Original languageEnglish
Pages (from-to)677-692
Number of pages16
JournalGeoscience Frontiers
Volume12
Issue number2
Early online date16 Aug 2020
DOIs
Publication statusPublished - Mar 2021

Funding

FFB and EWFdR are indebted to the Dutch Dr. Schürmann Foundation (SF) for Precambrian research (www.dr-schuermannfonds.nl) for generous support for all field work since 2005, in particular grant numbers 86/2012 and 100/2014 for the present study. The SF also funded SHRIMP analyses by Keewook Yi (KBSI, Korea) and LA-ICP-MS analyses at Utrecht University and Münster University (Germany), for zircon U–Th–Pb geochronology. Dr. Sergei Matveev carried out the amphibole electron-microprobe analyses at VU Amsterdam. The Molengraaff Foundation and VU Amsterdam contributed travel subsidies to MSc-students participating in the field work. We specifically thank former VUA-students Fienke Nanne, Heleen Vos and Wouter van de Steeg for their contributions. The director of the Geological and Mining Service of Suriname (GMD) is thanked for support. We acknowledge an informal review of an early version of the manuscript by Dr. Wout Nijman, as well as journal reviews by Dr. Xiaofang He and an anonymous reviewer, all of which particularly helped us in structuring the paper.

FundersFunder number
Dutch Dr. Schürmann Foundation
Scioto Foundation

    Keywords

    • Bakhuis Granulite Belt; Guiana Shield; Transamazonian orogeny; UHT metamorphism; tectonics; P-T-t evolution

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