Abstract

A supracrustal sequence of biotite gneisses, light coloured garnet-biotite gneisses (metasediments) and metabasite rocks is bounded to the north-west and south-east by basement rocks of biotite (± hornblende) gneisses and metabasites. The supracrustal sequence lies in the core of a major F3 synform. Metabasite horizons are used as marker horizons to elucidate the structure of the area. Hornblende-granulite subfacies metamorphism accompanied the F3 folding; later retrograde metamorphism only affected the rocks along master joints and thrusts. Structural analysis of the basement rocks indicates at least two folding phases older than the F3 folding of the supracrustal sequence; the supracrustals also show minor folds of a fourth phase.

Highlights

  • In the summer of 1966 detailed mapping was started in the Agto area of western Greenland under the leadership of Erling Bondensen (Bondesen, 1966, 1968)

  • Within the key area the F i fold phase is represented by a synform and an antiform, which are refolded about a steep north-plunging F2 fold axis; the axial plane strikes ENE-WSW and dips to the NNW

  • To the north-east the flanks of the F2 fold are pressed together, forming a fan fold, the axial plane of which strlkes ENE-WSW and dips steeply to the NNW; see map 2 and three successive cross-sections on fig. 9

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Summary

INTRODUCTION

In the summer of 1966 detailed mapping was started in the Agto area of western Greenland under the leadership of Erling Bondensen (Bondesen, 1966, 1968). The work was a university research project and formed a part of the mapping programme carried out by the Geological Survey of Greenland (GrØnlands Geologiske Undersøgelse). Ikorlat lies within the Isortoq complex of the Nagssugtoqidian fold belt, a name proposed by Ramberg (1948) and later discussed by Noe-Nygaard (1952) and Pulvertaft (1968). Ikorlat can geologically be divided into three areas; two of the areas are essentially similar, but are separated by a synformal area which differs structurally and lithologically from the two others. During the mapping it was found that the dark metabasite horizons formed suitable key horizons for a structural analyses

Lithological units
Metamorphic facies
ANALYSIS OF THE STRUCTURES
GEOMETRICAL DESCRIPTION OF THE STRUCTURES
The synformal area
FOLD CHRONOLOGY
STRUCTURAL CONCLUSION
Thrusts in the major synform
Major joints and faulls
RELATIONS OF FOLDING AND METAMORPHISM
Full Text
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