Nesbitt and young 1984 al2o3 hornblende kaolinite

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Unformatted text preview: tial work of Nesbitt and Young (1984) Al2O3 Hornblende Kaolinite, Gibbsite Clinopyroxene Natural Waters CaO*+Na2O K2O Illite Musc Fsp Smec Toorongo Granodiorite Chl Hbl Cal CaO*+Na2O+K2O Monday, 13 August, 12 Diopside Bio Oxide OPX FeO*+MgO Weathering Average Granodiorite Cl ay s tz ar Qu Zone I ar s Zone II Zone III II Rock Fragments Vermiculite Fe ld sp I Smectite Composition of Sands Qz Rock/Minerals Ill ite Ka Gi bb sit e ol in ite Clay Minerals Zone IV Bedrock Ks Pl Composition of Muds A Zone I CIA 100 Zone II III Zone III 50 Zone IV Bedrock IV CN From Nesbitt (2003) based on initial work of Nesbitt and Young (1984) Monday, 13 August, 12 K Elemental Weathering Profiles I II III IV e.g., Al, Zr, Nb 0 -ve +ve e.g., Na, Ca -ve 0 +ve % Change in Ratio of EL/Ti From Nesbitt (2003) Monday, 13 August, 12 e.g., Mn, Fe 0 -ve +ve Diagenetic Effects • Generally a result of: • • • Monday, 13 August, 12 Addition of cement (silica or calcite); or Interaction with diagenetic fluids (i.e., K, Na, Mg metasomatism). Most can be viewed using A-CN-K and A-CNK-FM diagrams. Diagenetic Effects Al2O3 Kaolinite, Gibbsite, Chlorite 90 Smectite 80 70 CIA Muscovite Avg Shale Ca-metasomatism 60 50 Illite K-m eta Biotite so ma ti Plagioclase Granodiorite sm K-feldspar 40 30 20 10 0 Hornblende Clinopyroxene Natural Waters CaO*+Na2O From Fedo et al. (1995) and Nesbitt (2003) Monday, 13 August, 12 K2O Diagenetic Effects Al2O3 Kaolinite, Gibbsite Fsp Ca , Na ,K -m eta som ati sm Illite Musc Mg -m Smec eta so Toorongo Granodiorite ma tis m Hbl Cal CaO*+Na2O+K2O Modified from Nesbitt (2003) Monday, 13 August, 12 Diopside Chl Bio Oxide OPX FeO*+MgO Major Elements and Sedimentary Rocks: Summary • Increases in chemical weathering result in increases in CIA, Al2O3/alkali ratios, and abundances of clay minerals relative to feldpsar and mafic minerals. • More humid environments have more aluminous muds and quartz-rich sands relative to less humid environments. • More tectonically active environments have less chemical weathering and less aluminous muds and more feldspathic sands. • Diagenesis can lead to increases in CaO, SiO2, MgO, K2O and Na2O. Patterns readily observable on ternary plots. Monday, 13 August, 12 Provenance of Clastic Sedimentary Rocks • When studying provenance of sedimentary rocks we require elements that are unaffected by weathering, erosion, transport, and diagenesis and reflect the source rocks that the sediments were derived from. • In general, Al, Ti, HFSE (Th, Zr, Hf, Nb, Ta), REE, Sc, Cr, Ni, V, Co reflect particulate matter and in most cases source regions that sediments were derived from (e.g., Bhatia and Crook, 1983; McLennan, 1989, 2001; McLennan et al., 1990, 1993, 2003). Monday, 13 August, 12 Provenance of Clastic Sedimentary Rocks: Caveats • Al/Ti ratios can be fractionated from one another during intense weathering (e.g., Young and Nesbitt, 1998). • U, Th, V, Mo, Ni, and Cr are redox sensitive and can be effected by redox conditions in basins and are particularly enriched in organic-rich shales (e.g., Quinby-Hunt and Wilde, 1994). • Zr, Hf, Sn, can...
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This document was uploaded on 03/06/2014 for the course ES 4502 at Memorial University.

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