TY - JOUR
T1 - The Mesoarchaean Akia terrane, West Greenland, revisited
T2 - new insights based on spatial integration of geophysics, field observation, geochemistry and geochronology
AU - Steenfelt, Agnete
AU - Hollis, Julie
AU - Kirkland, Christopher L.
AU - Sandrin, Alessandro
AU - Gardiner, Nicholas J.
AU - K. H. Olierook, Hugo
AU - Szilas, Kristoffer
AU - Waterton, Pedro
AU - Yakymchuk, Chris
N1 - NJG thanks Australian Research Council grant FL160100168 for financial support.
PY - 2021/1
Y1 - 2021/1
N2 - The northern part of the North Atlantic
Craton (NAC) in southern West Greenland comprises a large tract of
exposed Meso-Neoarchaean continental crust, divided into the ca
3300–2900 Ma Akia and ca 2900–2500 Ma Tuno terranes. We combine
aeromagnetic, stream sediment geochemical, new litho-chemical and zircon
geochronological data with previously published data to re-evaluate the
crustal architecture and evolution of the Akia terrane and its boundary
towards the Tuno terrane.The previously recognised,
but overlooked, Alanngua complex, situated between the Akia and Tuno
terranes is bounded by aeromagnetic lineaments interpreted as
Neoarchaean shear zones and has a distinct spectrum of Neoarchaean
magmatic and metamorphic zircon ages that are rare in the Akia terrane.
The Alanngua complex comprises components derived from both the Akia and
Tuno terranes and is interpreted as a tectonic melange created during
the Neoarchaean assembly of the NAC.Within the Akia
terrane, the chemistry of orthogneiss samples indicate that a large
percentage is too mafic to classify as TTG s.s., implying that not only
partial melting of mafic crust, but also some yet unaddressed mantle
involvement is necessary in their formation. Previous models for the
generation of the ca. 3015–2990 Ma quartz-dioritic Finnefjeld and
Taserssuaq complexes conflict with their geochemical variation. The
complexes are spatially associated with strong aeromagnetic responses
that are interpreted to reflect a large gabbro-diorite intrusion, and we
propose that the protoliths of the Finnefjeld and Taserssuaq complexes
are genetically linked to such intrusion. Formed at same time are
carbonatite, high-Mg gabbro and tonalite-trondhjemite, and we propose
that this wide spectrum of rocks could have formed by lithospheric and
crustal melting in response to asthenospheric upwelling possibly in an
extensional setting.Periods of extensive magmatism in
the Akia terrane were previously recognised at ca. 3220-3180 Ma and
3070-2970 Ma. We now subdivide the latter period into three episodes:
juvenile basaltic-andesitic volcanism at 3070–3050 Ma; tonalitic and
dioritic plutonism at 3050–3020 Ma, and gabbroic-dioritic plus
tonalitic-trondhjemitic plutonism at 3020–2985 Ma. This last episode was
immediately followed by crustal reworking during collision at 2980–2950
Ma.
AB - The northern part of the North Atlantic
Craton (NAC) in southern West Greenland comprises a large tract of
exposed Meso-Neoarchaean continental crust, divided into the ca
3300–2900 Ma Akia and ca 2900–2500 Ma Tuno terranes. We combine
aeromagnetic, stream sediment geochemical, new litho-chemical and zircon
geochronological data with previously published data to re-evaluate the
crustal architecture and evolution of the Akia terrane and its boundary
towards the Tuno terrane.The previously recognised,
but overlooked, Alanngua complex, situated between the Akia and Tuno
terranes is bounded by aeromagnetic lineaments interpreted as
Neoarchaean shear zones and has a distinct spectrum of Neoarchaean
magmatic and metamorphic zircon ages that are rare in the Akia terrane.
The Alanngua complex comprises components derived from both the Akia and
Tuno terranes and is interpreted as a tectonic melange created during
the Neoarchaean assembly of the NAC.Within the Akia
terrane, the chemistry of orthogneiss samples indicate that a large
percentage is too mafic to classify as TTG s.s., implying that not only
partial melting of mafic crust, but also some yet unaddressed mantle
involvement is necessary in their formation. Previous models for the
generation of the ca. 3015–2990 Ma quartz-dioritic Finnefjeld and
Taserssuaq complexes conflict with their geochemical variation. The
complexes are spatially associated with strong aeromagnetic responses
that are interpreted to reflect a large gabbro-diorite intrusion, and we
propose that the protoliths of the Finnefjeld and Taserssuaq complexes
are genetically linked to such intrusion. Formed at same time are
carbonatite, high-Mg gabbro and tonalite-trondhjemite, and we propose
that this wide spectrum of rocks could have formed by lithospheric and
crustal melting in response to asthenospheric upwelling possibly in an
extensional setting.Periods of extensive magmatism in
the Akia terrane were previously recognised at ca. 3220-3180 Ma and
3070-2970 Ma. We now subdivide the latter period into three episodes:
juvenile basaltic-andesitic volcanism at 3070–3050 Ma; tonalitic and
dioritic plutonism at 3050–3020 Ma, and gabbroic-dioritic plus
tonalitic-trondhjemitic plutonism at 3020–2985 Ma. This last episode was
immediately followed by crustal reworking during collision at 2980–2950
Ma.
KW - Mesoarchean crust formation
KW - Diorite
KW - TTG
KW - Aeromagnetometry
KW - North Atlantic Craton
KW - Akia terrane
KW - Zircon geochronology
U2 - 10.1016/j.precamres.2020.105958
DO - 10.1016/j.precamres.2020.105958
M3 - Article
SN - 0301-9268
VL - In press
JO - Precambrian Research
JF - Precambrian Research
M1 - 105958
ER -