NJG82-4-08
2002
40 Ar /39Ar geochronology and structural analysis: Basin evolution and detrital feedback mechanisms, Hold with Hope region, East Green land
82
4
pp. 341-358
82-92394-05-2

Detrital white-mica, single-grain laser  ages from five Permian to Cretaceous sedimentary packages in the Hold with Hope region, East Greenland, are compared to sup>40 Ar /39Ar cooling ages from nearby granitic domains. The data show that the variations in cooling ages between different basement units, separated by a detachment fault, are traceable into the overlying, proximal detritus and can be used to refine aspects of the basin-forming history in East Greenland. The two granitic samples, one above and one below the detachment, yield ages of 414 ± 2 Ma and 413-390 Ma, respectively, and imply younging structurally downwards. Younging downwards complies with models for gradual exhumation of high-grade rocks in East Greenland from Silurian through Early Carboniferous time. The detrital white micas from the Late Permian through Late Cretaceous sedimentary units show direct age relationships to these two granitic basement regions, with added detrital contributions to the Lower Triassic and Lower Cretaceous sands from other source areas. Specifically, the Lower Triassic sands may also include recycled Permian clasts, and sediments from a deeper (younger) basement unit that was not exposed or eroded in Permian time. The wide range of detrital mica ages in the Lower Cretaceous sands corresponds well to the major Late Jurassic-Early Cretaceous rift event documented in the Greenland-Norway corridor, and indicates extensive exposure and erosion of new provenance domains and basin cannibalization at this time. By the Late Cretaceous, sediment source areas appear to have become restricted again, coinciding with global eustatic sea-leve! rise and limited exposure of basement source regions. The study indicates that detrital, white-mica sup>40 Ar /39Ar geochronology is an effective way of differentiating contributions from different source regions and, in some cases, different tectonic events, as recorded in the basin detritus. When coupled with structural studies of controlling faults and constraints on the unroofing histories of basement domains, controls on sediment source regions, transport pathways and sedimentary recycling may also be provided.

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