Lithogeochem_II

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Unformatted text preview: be strongly partitioned into heavy mineralrich sands during sorting (e.g., high Zr/Sc, Hf/Sc, and Sn/ Sc may indicate heavy mineral-rich sediments) (e.g., McLennan, 2003). Monday, 13 August, 12 Provenance of Clastic Sedimentary Rocks • Key with provenance is the usage of elements with short residence time in water. • These elements are deposited rapidly from water and reflect source regions from which elements were derived. • These elements must also be relatively immobile and insensitive to diagenetic effects. • Best elements are REE, HFSE, and transition elements. Monday, 13 August, 12 8.0 U Rb log 6.0 4.0 REE,Y,Sc 2.0 0.0 Fe Si V Ba Cr Ni Hf Zr Ti Pb Mn Co Al Th -8.0 -6.0 -4.0 Na K Mg Sr Ca Ocean Mixing Time -2.0 0.0 log KSW From McLennan (1989) and McLennan et al. (2003) Monday, 13 August, 12 Useful Trace Elements and Trace Element Ratios for Provenance • • • Cr, Ni, V, Sc = reflect mafic and ultramafic sources. • La/Sm, La/Yb = gives degree of LREE-enrichment of source (more upper crustal more LREE-enriched). • Gd/Yb = gives degree of MREE/HREE fractionation - useful for identifying monazite, etc. Monday, 13 August, 12 Th, Al, LREE, Zr = reflect felsic and upper crustal sources. Th/Sc, Th/Co, Th/Ni, Th/Cr, La/Sc, La/Co, La/Ni, La/Cr = ratio of upper-crustal (Th, La) to more mafic source (Sc, Co, Ni, Cr) - can tell more juvenile detritus from more upper crustal detritus. Useful Trace Elements and Trace Element Ratios for Provenance • Zr/Sc, Hf/Sc = indentifying heavy mineral enrichment (i.e., zircon enriched in Zr and Hf but not Sc). • • Cr/V - useful in identifying chromite detritus (Cr/V-Y/Ni diagram). • Nb/Ta - extremely sensitive to crustal (Nb/Ta ~12) versus mantle/ mafic contributions (Nb/Ta ~17) in sediments. Monday, 13 August, 12 Nb/Th - useful for identifying crustal and arc-related detritus (low Nb/Th, Nb/La) from more mafic material (higher Nb/Th, Nb/ La). Rock / Post-Archeann Shale Identifying Heavy Mineral Accumulation 10000 1000 100 Monazite Allanite 10 Zircon 1 .1 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu From McLennan (1989) Monday, 13 August, 12 100 Zircon = ZrSiO4 Zircon Addition 800 400 Zr = 1500 ppm 1000 600 Ybn 10 Shale Zr = 1500 ppm 0.020%0.016% 0.012% 0.008% 1000 800 600 400 1 0.6 0.7 0.8 0.9 1.0 1.1 1.2 Sandstone 1.3 1.4 1.5 1.6 Gd/Ybn 100 Monazite Addition Monazite = SmPO4 [Sm0.2Gd0.2Th0.15Ce0.15Ca0.1Nd0.1(PO4)0.9] 30 15 Gdn Shale .033% 20 30 .017% 12 10 20 .008% 15 .003% Th = 12 ppm Sandstone From McLennan (1989) 1 0 1 2 3 Gd/Ybn Monday, 13 August, 12 4 5 6 7 Identifying Heavy Mineral Accumulation 10 Sediment Recycling (Zircon Addition) Upper Crust 1 Th/Sc Andesite Compositional Variations .1 Passive Margin Turbidites Active Margin Turbidittes MORB .01 .1 1 10 Zr/Sc From McLennan et al. (1993, 2003) Monday, 13 August, 12 100 1000 Sediment Provenance 10 UCC GLOSS 1 PASC BCC LCC La/Co .1 N-MORB .01 Depleted Mantle Primitive Mantle .001 Chondrite .0001 .00001 .0001 .001 .01 Th/Co Monday, 13 August...
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This document was uploaded on 03/06/2014 for the course ES 4502 at Memorial University.

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