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Age and origin of the major syenite centers in the Gardar province of south Greenland: Rb-Sr studies

1978; Geological Society of America; Volume: 89; Issue: 2 Linguagem: Inglês

10.1130/0016-7606(1978)89 2.0.co;2

1943-2674

Alan B. Blaxland, O. van Breemen, C. H. Emeleus, James G. Anderson,

Geological Studies and Exploration

Research Article| February 01, 1978 Age and origin of the major syenite centers in the Gardar province of south Greenland: Rb-Sr studies ALAN B. BLAXLAND; ALAN B. BLAXLAND 1Isotope Geology Division, Scottish Universities Research and Reactor Centre, East Kilbride, Glasgow G75 0QU, Scotland4Present address: Institut für Mineralogie, Universität Münster, Gievenbecker Weg 61, D-44 Münster, West Germany Search for other works by this author on: GSW Google Scholar OTTO VAN BREEMEN; OTTO VAN BREEMEN 1Isotope Geology Division, Scottish Universities Research and Reactor Centre, East Kilbride, Glasgow G75 0QU, Scotland Search for other works by this author on: GSW Google Scholar C. HENRY EMELEUS; C. HENRY EMELEUS 2Department of Geological Sciences, University of Durham, South Road, Durham DH1 3LE, England Search for other works by this author on: GSW Google Scholar JAMES G. ANDERSON JAMES G. ANDERSON 3Department of Geology and Mineralogy, University of Aberdeen, Aberdeen AB9 1AS, Scotland Search for other works by this author on: GSW Google Scholar Author and Article Information ALAN B. BLAXLAND 1Isotope Geology Division, Scottish Universities Research and Reactor Centre, East Kilbride, Glasgow G75 0QU, Scotland4Present address: Institut für Mineralogie, Universität Münster, Gievenbecker Weg 61, D-44 Münster, West Germany OTTO VAN BREEMEN 1Isotope Geology Division, Scottish Universities Research and Reactor Centre, East Kilbride, Glasgow G75 0QU, Scotland C. HENRY EMELEUS 2Department of Geological Sciences, University of Durham, South Road, Durham DH1 3LE, England JAMES G. ANDERSON 3Department of Geology and Mineralogy, University of Aberdeen, Aberdeen AB9 1AS, Scotland Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1978) 89 (2): 231–244. https://doi.org/10.1130/0016-7606(1978)89 2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation ALAN B. BLAXLAND, OTTO VAN BREEMEN, C. HENRY EMELEUS, JAMES G. ANDERSON; Age and origin of the major syenite centers in the Gardar province of south Greenland: Rb-Sr studies. GSA Bulletin 1978;; 89 (2): 231–244. doi: https://doi.org/10.1130/0016-7606(1978)89 2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Rb-Sr whole-rock isochron data for nine intrusive centers (including the major oversaturated and undersaturated syenite bodies) in the Precambrian Gardar alkalic igneous province of south Greenland complete a systematic isotopic study of the major complexes of the region (15 distinct igneous centers). The new data show that magmatic activity occurred throughout the region over a period in excess of 150 m.y. and that there is a clear distinction between two major magmatic events — an early Gardar (∼1,300 m.y. old) event and a more widespread late Gardar (∼1,160 m.y. old) event, which also involved extensive east-northeast-trending dike emplacement. Two relatively small intrusions in the western part of the province have middle Gardar (∼1,250 m.y. old) ages. There does not appear to be any relationship between emplacement age and geographic location, mode of emplacement, or the recognized petrologic division into saturated or undersaturated types; indeed, some adjacent complexes with strikingly similar petrologic characteristics have originated during different events, and, conversely, adjacent complexes with very different compositions are chronologically indistinguishable with present techniques.Initial 87Sr/86Sr ratios for the Gardar rocks are broadly divisible into three groups. Low (0.702 to 0.704) ratios are characteristic of most of the intrusions in the province, including most of the syenites (both undersaturated and oversaturated) and gabbros —which indicates a primitive (mantle) origin for the parental Gardar magmas. Intermediate ratios (0.704 to 0.707) are observed in fewer centers, particularly in the Nunarssuit complex (gabbro, oversaturated syenites, and granites). For these centers, the possibility of closed-system enrichment in 87Sr (by decay of 87Rb during a complex molten history extending throughout 150 m.y. of Gardar time) is rejected as unlikely, as is a direct origin by partial melting of older crust; field, chemical, and isotopic evidence presented here strongly support a bulk-assimilation hypothesis. Only two complexes have high (>0.707)ratios; both show evidence of introduction of radiogenic 87Sr into their magmas at a late stage of development through selective leaching of radiogenic 87Sr from older crust, and both of these complexes are associated with mineralization. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.