Basin evolution and destruction in an Early Proterozoic continental margin: the Rinkian fold–thrust belt of central West Greenland

John Grocott,Kenneth J W Mccaffrey

doi:10.1144/jgs2016-109

Abstract

In central West Greenland, early Palaeoproterozoic siliciclastic and carbonate sequences of the Karrat Group (shelf sequences of the Rae craton margin) were deposited in sedimentary basins controlled by NW- and SW-trending linked extensional fault systems. The shelf basins were later filled and overtopped by turbidite systems filling a foredeep advancing ahead of a thrust system – the Karrat Fjord thrust system – that propagated west to east. Deformation culminated in emplacement of basement-cored nappes, progressive deformation and high-grade metamorphism at c. 1.87 Ga. Reactivation of lower plate growth faults formed dome- and basin-like folds and related thrusts that refolded the structure of the Karrat Fjord thrust system and inverted the shelf basins. The southern Karrat Fjord thrust system was reworked in a belt of intense ductile NW-directed thrusting – the Nunaarsussuaq thrust system – formed at c. 1.84 Ga at the northern limit of the Nagssugtoqidian orogen. Kinematics of these events are at odds with the consensus view that the Rinkian fold–thrust belt is a northward extension of the Nagssugtoqidian orogen resulting from north–south convergence between the Rae and North Atlantic cratons. Application of structural restoration techniques to basin analysis of Palaeoproterozoic rocks has potential to provide new insights into Proterozoic orogenic processes worldwide.

Highlights

The Rinkian fold–thrust belt was recognized as a discrete Palaeoproterozoic geological entity by Escher & Pulvertaft (1976) based on structural style and the observation that it contained a distinctive stratigraphic sequence, the Karrat Group, thought to have been deposited on a continental margin
The zircon data show that the bulk of the clastic material making up the Nûkavsak Formation was derived from a Palaeoproterozoic magmatic source, supporting the earlier conclusions of Kalsbeek et al (1998) that the Nûkavsak Formation was deposited in a basin within an active margin setting
What is the significance of our work for the idea that the Nagssugtoqidian orogen and the Rinkian fold–thrust belt are a single orogen some 1100 km wide formed by north–south convergence between the Rae and North Atlantic cratons? The regional thrust transport direction in the earliest Rinkian thrust system, the Karrat Fjord thrust system, was WSW–ENE and transport was to the ENE

Summary

Introduction

The Rinkian fold–thrust belt was recognized as a discrete Palaeoproterozoic geological entity by Escher & Pulvertaft (1976) based on structural style and the observation that it contained a distinctive stratigraphic sequence, the Karrat Group, thought to have been deposited on a continental margin. The outcomes provide insight into previously obscure fundamental characteristics of the Rinkian fold–thrust belt, including strike of the orogen, pattern of metamorphic grade zonation and large-scale vergence, direction to the foreland and tectonic transport direction(s), and constrain future attempts to reconstruct the Palaeoproterozoic plate-tectonic framework of the Canadian and Greenland margins of Baffin Bay. The Karrat Group is widely exposed in the Uummannaq region and northward to the Melville Bugt (Fig. 1). Stratigraphic columns for the Qeqertarssuaq Formation were constructed using data from geological survey maps supplemented by field observations and thicknesses calculated from cross-sections (Fig. 3) They were drawn for locations where there is thought to have been little duplication by thrusting or other significant structural thickening. We have used thickness and lithology variation expressed in the stratigraphic columns with a reinterpretation of outcrop patterns and a structural contour map drawn for the base of the Nûkavsak Formation (Henderson 1969) to infer the position of some of the main basin boundary faults that controlled the deposition of the formation (Fig. 3)

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Conclusion