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The Melville Bugt Dyke Swarm across SE Greenland : A closer link to Mesoproterozoic AMCG-complexes

Klausen, M. B. and Nilsson, M. K.M. LU (2019) In Precambrian Research 329. p.88-107
Abstract

Following upon previous work on the 1630 Ma Melville Bugt Dyke Swarm (MBDS) along the NW coast of Greenland, this paper confirms its proposed continuation in SE Greenland, into an extraordinary >2000 km long trans-Greenlandic dyke swarm. This correlation is not only based on the swarm's continuous pattern, but now also by a matching 1630 ± 4 Ma U-Pb baddeleyite age determination and similar bulk rock compositions, as well as distinctive outcrop characteristics. A greater number of thinner dykes across SE Greenland supports a previous notion of the MBDS being emplaced laterally from a more southerly located magma chamber; whereas, a doubling of both individual and cumulative dyke thicknesses towards the north may relate to how the... (More)

Following upon previous work on the 1630 Ma Melville Bugt Dyke Swarm (MBDS) along the NW coast of Greenland, this paper confirms its proposed continuation in SE Greenland, into an extraordinary >2000 km long trans-Greenlandic dyke swarm. This correlation is not only based on the swarm's continuous pattern, but now also by a matching 1630 ± 4 Ma U-Pb baddeleyite age determination and similar bulk rock compositions, as well as distinctive outcrop characteristics. A greater number of thinner dykes across SE Greenland supports a previous notion of the MBDS being emplaced laterally from a more southerly located magma chamber; whereas, a doubling of both individual and cumulative dyke thicknesses towards the north may relate to how the swarm's laterally emplaced blade-shaped dyke geometries are exposed in greater abundance farther from its source. Remarkably homogenous yet differentiated, transitional to trachybasaltic compositions indicate a single magma chamber source that was buffered by between 4 and 7 wt% MgO, through magma replenishments and cotectic plagioclase-olivine fractionation at lower crustal depths for >13 ± 6 Myrs (published age range). Geochemical signatures – of particularly high Ba and other LILE's, negative Nb-Ta spikes and otherwise slightly enriched HFSE patterns – bear a conspicuous resemblance to >100 Myr-older late- to post-Ketilidian appinites (orogenic lamprophyres), which are both thought to have been derived from a common highly metasomatised, young sub-continental lithospheric mantle. The dry mineralogy of the MBDS and a geologically based Nuna supercontinent reconstruction is more consistent with a breakup setting, which together with neighbouring coeval AMCG-complexes may arguably combine into an unusual LIP. However, such a relatively short-lived LIP-setting may be questioned if the plagioclase-phyric MBDS was derived from a similar deep crustal magma chamber source, as proposed for four Mesoproterozoic cycles of AMCG-emplacements during a >500 Myr Nuna –Rodinia supercontinental transition. Consequently, arguing for a longer-lived active continental margin, as suggested by palaeomagnetically based Nuna supercontinent reconstructions.

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published
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Precambrian Research
volume
329
pages
88 - 107
publisher
Elsevier
external identifiers
  • scopus:85048524463
ISSN
0301-9268
DOI
10.1016/j.precamres.2018.06.001
language
English
LU publication?
yes
id
8ea77746-2113-4d5e-858a-aaa8cde6f2e1
date added to LUP
2018-07-03 11:04:56
date last changed
2019-09-11 03:59:49
@article{8ea77746-2113-4d5e-858a-aaa8cde6f2e1,
  abstract     = {<p>Following upon previous work on the 1630 Ma Melville Bugt Dyke Swarm (MBDS) along the NW coast of Greenland, this paper confirms its proposed continuation in SE Greenland, into an extraordinary &gt;2000 km long trans-Greenlandic dyke swarm. This correlation is not only based on the swarm's continuous pattern, but now also by a matching 1630 ± 4 Ma U-Pb baddeleyite age determination and similar bulk rock compositions, as well as distinctive outcrop characteristics. A greater number of thinner dykes across SE Greenland supports a previous notion of the MBDS being emplaced laterally from a more southerly located magma chamber; whereas, a doubling of both individual and cumulative dyke thicknesses towards the north may relate to how the swarm's laterally emplaced blade-shaped dyke geometries are exposed in greater abundance farther from its source. Remarkably homogenous yet differentiated, transitional to trachybasaltic compositions indicate a single magma chamber source that was buffered by between 4 and 7 wt% MgO, through magma replenishments and cotectic plagioclase-olivine fractionation at lower crustal depths for &gt;13 ± 6 Myrs (published age range). Geochemical signatures – of particularly high Ba and other LILE's, negative Nb-Ta spikes and otherwise slightly enriched HFSE patterns – bear a conspicuous resemblance to &gt;100 Myr-older late- to post-Ketilidian appinites (orogenic lamprophyres), which are both thought to have been derived from a common highly metasomatised, young sub-continental lithospheric mantle. The dry mineralogy of the MBDS and a geologically based Nuna supercontinent reconstruction is more consistent with a breakup setting, which together with neighbouring coeval AMCG-complexes may arguably combine into an unusual LIP. However, such a relatively short-lived LIP-setting may be questioned if the plagioclase-phyric MBDS was derived from a similar deep crustal magma chamber source, as proposed for four Mesoproterozoic cycles of AMCG-emplacements during a &gt;500 Myr Nuna –Rodinia supercontinental transition. Consequently, arguing for a longer-lived active continental margin, as suggested by palaeomagnetically based Nuna supercontinent reconstructions.</p>},
  author       = {Klausen, M. B. and Nilsson, M. K.M.},
  issn         = {0301-9268},
  language     = {eng},
  pages        = {88--107},
  publisher    = {Elsevier},
  series       = {Precambrian Research},
  title        = {The Melville Bugt Dyke Swarm across SE Greenland : A closer link to Mesoproterozoic AMCG-complexes},
  url          = {http://dx.doi.org/10.1016/j.precamres.2018.06.001},
  volume       = {329},
  year         = {2019},
}