TY - JOUR
T1 - Field and geochemical characteristics of the Mesoarchean (∼ 3075 Ma) Ivisaartoq greenstone belt, southern West Greenland
T2 - Evidence for seafloor hydrothermal alteration in supra-subduction oceanic crust
AU - Polat, Ali
AU - Appel, Peter W.U.
AU - Frei, Robert
AU - Pan, Yuanming
AU - Dilek, Yildirim
AU - Ordóñez-Calderón, Juan C.
AU - Fryer, Brian
AU - Hollis, Julie A.
AU - Raith, Johann G.
N1 - Funding Information:
We thank A. Trenhaile and R. Kerrich for reviewing the initial draft of the manuscript. Reviewers T. Kusky and H. Smithies are acknowledged for their constructive and incisive comments that have resulted in significant improvements to the paper. S. Maruyama and M. Santosh are acknowledged for inviting us to submit this contribution to Gondwana Research. We thank A. Nutman, C. Friend, A. Garde, J. van Gool, H. Stendal, A. Steenfelt, D. Frei, O. Stecher, C. Münker, and N. Kelly for helpful discussions in the field. T. Bonli, J.C. Barrette, J. Gagnon, and Z. Yang are acknowledged for their help during geochemical analyses, and D. Frei for geochronology support. This is a contribution of NSERC grants 250926 to AP and 83117 to B. Fryer. 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). A. Polat thanks Mr. Tekin Demir for helping his family during field work in Greenland.
PY - 2007/1
Y1 - 2007/1
N2 - The Mesoarchean (ca. 3075 Ma) Ivisaartoq greenstone belt in southern West Greenland includes variably deformed and metamorphosed pillow basalts, ultramafic flows (picrites), serpentinized ultramafic rocks, gabbros, sulphide-rich siliceous layers, and minor siliciclastic sedimentary rocks. Primary magmatic features such as concentric cooling-cracks and drainage cavities in pillows, volcanic breccia, ocelli interpreted as liquid immiscibility textures in pillows and gabbros, magmatic layering in gabbros, and clinopyroxene cumulates in ultramafic flows are well preserved in low-strain domains. The belt underwent at least two stages of calc-silicate metasomatic alteration and polyphase deformation between 2963 and 3075 Ma. The stage I metasomatic assemblage is composed predominantly of epidote (now mostly diopside) + quartz + plagioclase ± hornblende ± scapolite, and occurs mainly in pillow cores, pillow interstitials, and along pillow basalt-gabbro contacts. The origin of this metasomatic assemblage is attributed to seafloor hydrothermal alteration. On the basis of the common presence of epidote inclusions in diopside and the local occurrence of epidote-rich aggregates, the stage I metasomatic assemblage is interpreted as relict epidosite. The stage II metasomatic assemblage occurs as concordant discontinuous layered calc-silicate bodies to discordant calc-silicate veins commonly associated with shear zones. The stage II metasomatic assemblage consists mainly of diopside + garnet + amphibole + plagioclase + quartz ± vesuvianite ± scapolite ± epidote ± titanite ± calcite ± scheelite. Given that the second stage of metasomatism is closely associated with shear zones and replaced rocks with an early metamorphic fabric, its origin is attributed to regional dynamothermal metamorphism. The least altered pillow basalts, picrites, gabbros, and diorites are characterized by LREE-enriched, near-flat HREE, and HFSE (especially Nb)-depleted trace element patterns, indicating a subduction zone geochemical signature. Ultramafic pillows and cumulates display large positive initial ε
Nd values of + 1.3 to + 5.0, consistent with a strongly depleted mantle source. Given the geological similarities between the Ivisaartoq greenstone belt and Phanerozoic forearc ophiolites, we suggest that the Ivisaartoq greenstone belt represents Mesoarchean supra-subduction zone oceanic crust.
AB - The Mesoarchean (ca. 3075 Ma) Ivisaartoq greenstone belt in southern West Greenland includes variably deformed and metamorphosed pillow basalts, ultramafic flows (picrites), serpentinized ultramafic rocks, gabbros, sulphide-rich siliceous layers, and minor siliciclastic sedimentary rocks. Primary magmatic features such as concentric cooling-cracks and drainage cavities in pillows, volcanic breccia, ocelli interpreted as liquid immiscibility textures in pillows and gabbros, magmatic layering in gabbros, and clinopyroxene cumulates in ultramafic flows are well preserved in low-strain domains. The belt underwent at least two stages of calc-silicate metasomatic alteration and polyphase deformation between 2963 and 3075 Ma. The stage I metasomatic assemblage is composed predominantly of epidote (now mostly diopside) + quartz + plagioclase ± hornblende ± scapolite, and occurs mainly in pillow cores, pillow interstitials, and along pillow basalt-gabbro contacts. The origin of this metasomatic assemblage is attributed to seafloor hydrothermal alteration. On the basis of the common presence of epidote inclusions in diopside and the local occurrence of epidote-rich aggregates, the stage I metasomatic assemblage is interpreted as relict epidosite. The stage II metasomatic assemblage occurs as concordant discontinuous layered calc-silicate bodies to discordant calc-silicate veins commonly associated with shear zones. The stage II metasomatic assemblage consists mainly of diopside + garnet + amphibole + plagioclase + quartz ± vesuvianite ± scapolite ± epidote ± titanite ± calcite ± scheelite. Given that the second stage of metasomatism is closely associated with shear zones and replaced rocks with an early metamorphic fabric, its origin is attributed to regional dynamothermal metamorphism. The least altered pillow basalts, picrites, gabbros, and diorites are characterized by LREE-enriched, near-flat HREE, and HFSE (especially Nb)-depleted trace element patterns, indicating a subduction zone geochemical signature. Ultramafic pillows and cumulates display large positive initial ε
Nd values of + 1.3 to + 5.0, consistent with a strongly depleted mantle source. Given the geological similarities between the Ivisaartoq greenstone belt and Phanerozoic forearc ophiolites, we suggest that the Ivisaartoq greenstone belt represents Mesoarchean supra-subduction zone oceanic crust.
KW - Archean
KW - Epidosite
KW - Forearc
KW - Greenstone belt
KW - Ocelli
KW - Ophiolite
KW - Picrite
KW - Pillow basalt
UR - http://www.scopus.com/inward/record.url?scp=33845336094&partnerID=8YFLogxK
U2 - 10.1016/j.gr.2006.02.004
DO - 10.1016/j.gr.2006.02.004
M3 - Article
SN - 1342-937X
VL - 11
SP - 69
EP - 91
JO - Gondwana Research
JF - Gondwana Research
IS - 1-2
ER -