Fractionation Of Heavy Rare Earth Elements Research Articles

Eocene Challis-Kamloops volcanism in central British Columbia: an example from the Buck Creek basin

Eocene volcanic rocks of the Buck Creek basin in central British Columbia are part of the Challis-Kamloops volcanic belt extending from the United States across British Columbia to central Yukon. The volcanic rocks include two units, the Buck Creek Formation, composed of high-K calc-alkaline rocks with predominant andesitic composition, and the overlying Swans Lake unit made up of intraplate tholeiitic basalts. Whole rock 40Ar/39Ar data for both units show that they were emplaced at 50 Ma. They have similar mantle-normalized trace element patterns characterized by a large-ion lithophile element enrichment and Nb-Ta depletion, similar chondrite-normalized rare earth element patterns with (La/Yb)n ~4-14 and heavy rare earth element fractionation, and overlapping epsilonNd values (2.4-3.1) and initial Sr-isotope ratios ( ~ 0.704). These features suggest derivation of these two units from a similar mantle source, probably garnet-bearing subcontinental lithosphere. The differences between tholeiitic and calc-alkaline suites can be due, in part, to differences in the depth of fractional crystallization and the crystallizing mineral assemblage. Fractional crystallization of the calc-alkaline magmas began at a greater (mid-crustal) depth and included fractionation of Fe-Ti oxides. The volcanic rocks are probably related to subduction of the Farallon plate under the North American continent in a regime characterized by transcurrent movements and strike-slip faulting.

Trace Elements in Continental-Margin Magmatism: Part II. Trace Elements in Ben Ghnema Batholith and Nature of the Precambrian Crust in Central North Africa

Research Article| August 01, 1980 Trace Elements in Continental-Margin Magmatism: Part II. Trace Elements in Ben Ghnema Batholith and Nature of the Precambrian Crust in Central North Africa John J. W. Rogers; John J. W. Rogers 1Department of Geology, University of North Carolina at Chapel Hill, Mitchell Hall 029A, Chapel Hill, North Carolina 27514 Search for other works by this author on: GSW Google Scholar Kip V. Hodges; Kip V. Hodges 1Department of Geology, University of North Carolina at Chapel Hill, Mitchell Hall 029A, Chapel Hill, North Carolina 27514 Department of Earth and Planetary Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 Search for other works by this author on: GSW Google Scholar Mohamed A. Ghuma Mohamed A. Ghuma 2Department of Geology, Faculty of Science, Al Fateh University, P.O. Box 13258, Tripoli, Libyan Arab People's Socialist Jamahiriya Search for other works by this author on: GSW Google Scholar Author and Article Information John J. W. Rogers 1Department of Geology, University of North Carolina at Chapel Hill, Mitchell Hall 029A, Chapel Hill, North Carolina 27514 Kip V. Hodges 1Department of Geology, University of North Carolina at Chapel Hill, Mitchell Hall 029A, Chapel Hill, North Carolina 27514 Mohamed A. Ghuma 2Department of Geology, Faculty of Science, Al Fateh University, P.O. Box 13258, Tripoli, Libyan Arab People's Socialist Jamahiriya Department of Earth and Planetary Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 Publisher: Geological Society of America Received: 17 May 1979 Revision Received: 13 Mar 1980 Accepted: 19 Mar 1980 First Online: 02 Mar 2017 Online Issn: 1943-2674 Print Issn: 0016-7606 © 1980 The Geological Society of America, Inc. GSA Bulletin (1980) 91 (8_Part_II): 1742–1788. https://doi.org/10.1130/GSAB-P2-91-1742 Article history Received: 17 May 1979 Revision Received: 13 Mar 1980 Accepted: 19 Mar 1980 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation John J. W. Rogers, Kip V. Hodges, Mohamed A. Ghuma; Trace Elements in Continental-Margin Magmatism: Part II. Trace Elements in Ben Ghnema Batholith and Nature of the Precambrian Crust in Central North Africa. GSA Bulletin 1980;; 91 (8_Part_II): 1742–1788. doi: https://doi.org/10.1130/GSAB-P2-91-1742 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 The Ben Ghnema bacholith is in the northwestern part of the Tibesti massif of southern Libya. It was formed as a series of separate plutons about 550 m.y. ago (Pan-African time). The batholith is lithologically and compositionally similar to the Sierra Nevada batholith, thus suggesting that the Ben Ghnema batholith was also formed by subduction of oceanic crust under a cratonic margin. Areal variation from tonalite and granodiorite (on the east side) to granite (on the west) indicates that ocean basin occurred to the east of the batholith and craton to the west.Several compositional properties indicate that the plutons of the Ben Ghnema batholith represent a series of partial melts instead of a sequence formed by fractional crystallization. This conclusion is supported by the pronounced increase of K2O with SiO2, the lack of variation in Zr/Y ratios, and the lack of fractionation of heavy rare-earth elements (REE) in the more silicic rocks.The dominant rock type of the Ben Ghnema batholith is an adamellite (65% to 70% SiO2). The average composition of the adamellite is 68.1% SiO2; 0.49% TiO2; 15.7% Al2O3; 3.8% total iron as Fe2O3; 1.4% MgO; 3.0% CaO; 3.3% Na2O; 4.2% K2O; 156 ppm Rb; 220 ppm Sr; 25 ppm Y; 169 ppm Zr; 11 ppm Nb; 564 ppm Ba; 25 ppm V; 87 ppm Cr; and 6 ppm Ni. This rock contains slightly more K2O and Rb and less Sr than typical calc-alkalic subduction-zone suites. This composition is consistent with intrusion of the batholith into the margin of a thick, well-formed, possibly Archean craton (the East Saharan craton of Bertrand and Caby). 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.

Trace elements in continental-margin magmatism: Part II. Trace elements in Ben Ghnema batholith and nature of the Precambrian crust in central North Africa: Summary

The Ben Ghnema bacholith is in the northwestern part of the Tibesti massif of southern Libya. It was formed as a series of separate plutons about 550 m.y. ago (Pan-African time). The batholith is lithologically and compositionally similar to the Sierra Nevada batholith, thus suggesting that the Ben Ghnema batholith was also formed by subduction of oceanic crust under a cratonic margin. Areal variation from tonalite and granodiorite (on the east side) to granite (on the west) indicates that ocean basin occurred to the east of the batholith and craton to the west. Several compositional properties indicate that the plutons of the Ben Ghnema batholith represent a series of partial melts instead of a sequence formed by fractional crystallization. This conclusion is supported by the pronounced increase of K 2 O with SiO 2 , the lack of variation in Zr/Y ratios, and the lack of fractionation of heavy rare-earth elements (REE) in the more silicic rocks. The dominant rock type of the Ben Ghnema batholith is an adamellite (65% to 70% SiO 2 ). The average composition of the adamellite is 68.1% SiO 2 ; 0.49% TiO 2 ; 15.7% Al 2 O 3 ; 3.8% total iron as Fe 2 O 3 ; 1.4% MgO; 3.0% CaO; 3.3% Na 2 O; 4.2% K 2 O; 156 ppm Rb; 220 ppm Sr; 25 ppm Y; 169 ppm Zr; 11 ppm Nb; 564 ppm Ba; 25 ppm V; 87 ppm Cr; and 6 ppm Ni. This rock contains slightly more K 2 O and Rb and less Sr than typical calc-alkalic subduction-zone suites. This composition is consistent with intrusion of the batholith into the margin of a thick, well-formed, possibly Archean craton (the East Saharan craton of Bertrand and Caby).