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An overview of the lithological and geochemical characteristics of the Mesoarchean (ca. 3075 Ma) Ivisaartoq greenstone belt, southern West Greenland

Ali Polat, Robert Frei, Peter W. U. Appel, Brian Fryer, Yildirim Dilek and Juan C. Ordonez-Calderon
An overview of the lithological and geochemical characteristics of the Mesoarchean (ca. 3075 Ma) Ivisaartoq greenstone belt, southern West Greenland (in When did plate tectonics begin on planet Earth?, Kent C. Condie (editor) and Victoria Pease (editor))
Special Paper - Geological Society of America (2008) 440: 51-76

Abstract

In this review we summarize the major lithological and geochemical characteristics of the Mesoarchean (ca. 3075 Ma) Ivisaaroq greenstone belt, Nuuk region, southern West Greenland. In addition, the geological characteristics of the Ivisaartoq greenstone belt are compared with those of other Archeam greenstone belts in the area. The Ivisaartoq greenstone belt is the largest Mesoarchean supracrustal lithotectonic assemblage in the Nuuk region. The belt contains well-preserved primary magmatic structures including pillow lavas, volcanic breccias, and cumulate (picrite) layers. It also includes variably, deformed gabbroic to dioritic dikes, actinolite schists, serpentinites, siliciclastic sediments, and minor cherts. The Ivisaaroq rocks underwent at least two stages of postmagmatic metamorphic alteration, including seafloor hydrothermal alteration and syn- to post-tectonic calc-silicate metasomatism, between 3075 and 2961 Ma. The trace element systematics of the least altered rocks are consistent with a subduction zone geodynamik setting. On the basis of lithological similarities between the Ivisaartoq greenstone belt and Phanerozoic forearc/backarc ophiolites, and intra-oceanic island acres, we suggest that the Ivisaartoq greenstone belt represents a relic of dismembered Mesoarchean suprasubduction zone oceanic crust. The Sm-Nd isotope system appears to have remain relatively undisturbed in picrites, tholeiitic pillow lavas, gabbros, and diorites. As a group, picrites have more depleted initial Nd isotopic signatures (epsilon (sub Nd) = +4.2 to +5.0) than gabbros, diorites, and tholeiitic basalts (epsilon (sub Nd) = +0.3 to +3.1), consistent with a strongly depleted mantle source. In some areas gabbros include up to 15 cm long white inclusions (xenoliths). These inclusions are composed primarily (>90%) of Ca-plagioclase and are interpreted as anorthositic cumulates of the lower oceanic crust brought to the surface by upwelling gabbroic magmas. Alternatively, the inclusions may represent the xenoliths from older (>3075 Ma) anorthositic crust onto which the Ivisaartoq magmas were emplaced as an autochthonous sequence. However, no geological evidence has been found for such older anorthositic crust in the region. The anorthositic cumulates have significantly higher initial epsilon (sub Nd) values (+4.8 to +6.0) than the surrounding gabbroic matrix (+2.3 to +2.8), suggesting two different mantle sources for these rocks.


ISSN: 0072-1077
EISSN: 2331-219X
Coden: GSAPAZ
Serial Title: Special Paper - Geological Society of America
Serial Volume: 440
Title: An overview of the lithological and geochemical characteristics of the Mesoarchean (ca. 3075 Ma) Ivisaartoq greenstone belt, southern West Greenland
Title: When did plate tectonics begin on planet Earth?
Author(s): Polat, AliFrei, RobertAppel, Peter W. U.Fryer, BrianDilek, YildirimOrdonez-Calderon, Juan C.
Author(s): Condie, Kent C.editor
Author(s): Pease, Victoriaeditor
Affiliation: University of Windsor, Department of Earth and Environmental Sciences, Windsor, ON, Canada
Affiliation: New Mexico Institute of Mining and Technology, Department of Earth and Environmental Science, Socorro, NM, United States
Pages: 51-76
Published: 2008
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
Meeting name: Penrose Conference
Meeting location: Lander, WY, USA, United States
Meeting date: 20060613June 14-18, 2006
References: 117
Accession Number: 2008-124314
Categories: Igneous and metamorphic petrologySolid-earth geophysics
Document Type: Serial Conference document
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables, geol. sketch map
N42°40'00" - N42°40'00", W50°00'00" - W50°00'00"
Secondary Affiliation: Stockholm University, SWE, SwedenGeological Institute, DNK, DenmarkGeolgoical Survey of Denmark and Greeland, DNK, DenmarkGreat Lakes Institute for Environmental Research, CAN, CanadaMiami University, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200848
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