TY - JOUR
T1 - New age (ca 2970Ma), mantle source composition and geodynamic constraints on the Archean Fiskenæsset anorthosite complex, SW Greenland
AU - Polat, Ali
AU - Frei, Robert
AU - Scherstén, Anders
AU - Appel, Peter W.U.
N1 - Funding Information:
We thank R. Kerrich, S. Moobath and B. Windley for reviewing the initial draft of the manuscript. This contribution is supported by NSERC grants 250926 to A. Polat. R. Frei is supported by FNU (Forskningsrådet for Natur of Univers) grant nr. 21-01-0492 56493 . Field work was supported by the Bureau of Minerals and Petroleum in Nuuk and the Geological Survey of Denmark and Greenland (GEUS) . Any anonymous reviewer is acknowledged for the constructive comments, which have resulted in significant improvements to the paper. A. Polat thanks Mr. Tekin Demir for helping his family during fieldwork in Greenland. P. Kalvig, J. Kolb, D. Schlatter, A. Dziggel, A. Kisters, J. Schumacher, O. Dahl, S. Weatherly, M. Ghisler, W. Heijlen and D. Herwartz are acknowledged for discussions of geological and geochemical problems in various contexts.
PY - 2010/10
Y1 - 2010/10
N2 - The Archean Fiskenæsset
Complex, SW Greenland, consists of an association of ca. 550-meter-thick
layered anorthosite, leucogabbro, gabbro, and ultramafic rocks
(peridotite, pyroxenite, dunite, hornblendite). The complex was intruded
by tonalite, trondhjemite, and granodiorite (TTG) sheets (now
orthogneisses) during thrusting that was followed by several phases of
isoclinal folding. The trace element systematics of the Fiskenæsset
Complex and associated volcanic rocks are consistent with a
supra-subduction zone geodynamic setting.The Fiskenæsset anorthosites, leucogabbros, gabbros and ultramafic rocks collectively yield an Sm–Nd errorchron age of 2973 ± 28 Ma (MSWD = 33), with an average initial εNd = + 3.3 ± 0.7, consistent with a long-term depleted mantle source. Regression of Pb isotope data define an age of 2945 ± 36 Ma (MSWD = 44); and the regression line intersects the average growth curve at 3036 Ma.
Slightly lower Pb–Pb errorchron age is interpreted as reflecting
partial disturbance of the U–Pb system in gabbros, leucogabbros and
ultramafic rocks during intrusion of TTGs.Complex
internal structures in zircons from orthogneisses reveal several
episodes of zircon growth and recrystallization taking place between ca.
3200 and 2650 Ma. Zircon ages peak at about 3200, 3100, 3000, 2950, 2820, and 2750 Ma. The 3200–3000 Ma zircon cores are interpreted as inherited xenocrysts from older reworked crustal rocks. 2950 Ma is considered as an approximate intrusion age of sampled TTGs. The 2940–2650 Ma
ages are attributed to metamorphic overgrowth and recrystallization in
response to multiple tectonothermal events that affected the Fiskenæsset
region.On the basis of recently published trace
element data, and new Nd and Pb isotope and U–Pb zircon age data, a
three-stage geodynamic model is proposed to explain the evolution of the
Fiskenæsset Complex. Stage 1 represents the formation of depleted
shallow mantle source > 3000 Ma (εNd = + 3.3 ± 0.7) for the complex. Stage 2 corresponds to the development of an intra-oceanic island arc between 3000–2950 Ma.
Stage 3 is characterized by the collision of the island arc with either
a passive continental margin or with an older arc between 2950–2940 Ma.
AB - The Archean Fiskenæsset
Complex, SW Greenland, consists of an association of ca. 550-meter-thick
layered anorthosite, leucogabbro, gabbro, and ultramafic rocks
(peridotite, pyroxenite, dunite, hornblendite). The complex was intruded
by tonalite, trondhjemite, and granodiorite (TTG) sheets (now
orthogneisses) during thrusting that was followed by several phases of
isoclinal folding. The trace element systematics of the Fiskenæsset
Complex and associated volcanic rocks are consistent with a
supra-subduction zone geodynamic setting.The Fiskenæsset anorthosites, leucogabbros, gabbros and ultramafic rocks collectively yield an Sm–Nd errorchron age of 2973 ± 28 Ma (MSWD = 33), with an average initial εNd = + 3.3 ± 0.7, consistent with a long-term depleted mantle source. Regression of Pb isotope data define an age of 2945 ± 36 Ma (MSWD = 44); and the regression line intersects the average growth curve at 3036 Ma.
Slightly lower Pb–Pb errorchron age is interpreted as reflecting
partial disturbance of the U–Pb system in gabbros, leucogabbros and
ultramafic rocks during intrusion of TTGs.Complex
internal structures in zircons from orthogneisses reveal several
episodes of zircon growth and recrystallization taking place between ca.
3200 and 2650 Ma. Zircon ages peak at about 3200, 3100, 3000, 2950, 2820, and 2750 Ma. The 3200–3000 Ma zircon cores are interpreted as inherited xenocrysts from older reworked crustal rocks. 2950 Ma is considered as an approximate intrusion age of sampled TTGs. The 2940–2650 Ma
ages are attributed to metamorphic overgrowth and recrystallization in
response to multiple tectonothermal events that affected the Fiskenæsset
region.On the basis of recently published trace
element data, and new Nd and Pb isotope and U–Pb zircon age data, a
three-stage geodynamic model is proposed to explain the evolution of the
Fiskenæsset Complex. Stage 1 represents the formation of depleted
shallow mantle source > 3000 Ma (εNd = + 3.3 ± 0.7) for the complex. Stage 2 corresponds to the development of an intra-oceanic island arc between 3000–2950 Ma.
Stage 3 is characterized by the collision of the island arc with either
a passive continental margin or with an older arc between 2950–2940 Ma.
KW - Anorthosite
KW - Archean
KW - Fiskenæsset Complex
KW - Geochronology
KW - Isotopes
KW - SW Greenland
UR - http://www.scopus.com/inward/record.url?scp=77956615577&partnerID=8YFLogxK
U2 - 10.1016/j.chemgeo.2010.06.016
DO - 10.1016/j.chemgeo.2010.06.016
M3 - Article
VL - 277
SP - 1
EP - 20
JO - Chemical Geology
JF - Chemical Geology
SN - 0009-2541
IS - 1-2
ER -