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CLASTIC ROCKS-COMPOSITION

CLASTIC ROCKS-COMPOSITION. Clastic Components. detrital grains f. grained matrix authigenic minerals. Mineral Abundance. Depends on: source rk mechanical/chemical stability. Chemical Stability. qtz, zircon, tourmaline most stable: least stable pyroxene, olivine; feldspars in between.

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CLASTIC ROCKS-COMPOSITION

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  1. CLASTIC ROCKS-COMPOSITION

  2. Clastic Components • detrital grains • f. grained matrix • authigenic minerals

  3. Mineral Abundance • Depends on: • source rk • mechanical/chemical stability

  4. Chemical Stability • qtz, zircon, tourmaline most stable: • least stable pyroxene, olivine; feldspars in between

  5. Mechanical Stability • depends on hardness & if cleavage present • qtz hard, rk frags= weak http://cmsc.minotstateu.edu/Labs/web%20minerals/Albite.html

  6. TYPES OF DETRITAL GRAINS

  7. TYPES OF DETRITAL GRAINS • C. Quartz • most common, most stable • average s.s. = 65% qtz; some up to 100% • source = plutonic/gneisses/schists • have mono/polyxline; undulose vs nonundulose • difficult to tell source rk from qtz • qtz volcanics--nonundulose, monoxline • polyxline= meta source-many xls • hydrothermal-much inclusions; mono or coarse polxline • monoxline qtz w/undulose ext & polyxline least stable Petrographic Textures of Detrital Polycrystalline Quartz as an Aid to Interpreting Crystalline Source Rocks Steven W. Young (2)Journal of Sedimentary Research Volume 46 (1976) http://plaza.snu.ac.kr/~lee2602/atlas/quartz.html

  8. FELDSPAR • s.s. avg. 10-15%, arkoses up to 50% • destroyed during transport: • felds to sericite, clays (kaol./illite) • felds common from granite/gneiss • humid climate= felds dissolution; arid= felds survive • humid & rapid uplift--felds survive Elemental Mobility in Sandstones Duping Burial: Whole-Rock Chemical and Isotopic Data, Frio Formation, South Texas K.L. Milliken, L.E. Mack, L.S. LandJournal of Sedimentary Research Volume 64a (1994) http://www.endeeper.com

  9. Micas & Clays • common in matrix and mudrocks • biotite & chlorite may form large grains on bedding plane • Heavy Minerals • usually 1 % • provenance-garnet, epidote,staurolite-metamorphic terrain • rutile, apatite & tourmaline-most common ig. rocks • Other Minerals • Carbonate fossils; oolites, pellets, intraclasts • phosphate, glauconite

  10. Classification of Sandstones • Over 50 proposed • Based on: • texture • composition/mineralogy/ presence or absence of matrix

  11. Textural Classification • congl/breccia, ss, mudrocks (siltstones, mudstones, claystones) • use sand, silt, clay as end members, also gravel

  12. Compositional/ mineralogical classification • qtz, felds, rk frags common in ss • matrix may be present • most use trangular QFL/QFR plots • qtz arenites, arkoses, lithic arenites matrix-free • wackes greater than 5% matrix • Graywacke problem • matrix-rich ss, chlorite matrix From F.J. Pettijohn, P.E. Potter, and R. Siever, Sand and Sandstone (1987), 2nd ed., Springer-Verlag, Berlin

  13. Provenance • Mineralogy clue to eroded source • rk fragments most important • K felds mostly alkalic ig/met rks • fresh angular felds = high relief source or arid or cold climate • small, rounded weathered = low relief or warm humid climate • be ware of diagenesis

  14. Tectonic Setting • What is tectonic setting of source rocks? • 3 major tectonic settings • continental block provenances • magmatic arc provenances • recycled orogen provenances

  15. Continental Block • In continental masses • May have passive/active margins • Composed of plutonic, meta, and sed rocks, few volcanics • Generate qtzose sands, high K to Ca felds ratios • Meta and sed rk frags http://csmres.jmu.edu/geollab/Fichter/SedRx/Clastic.html

  16. Recycled orogen • Plate collision zones with uplift at suture • Have sed and met rks present prior to collision • Produce: • sed/met rk frags • moderate qtz, high qtz, felds ratio • If have magmatic arc/cont collision have: • volcanics, ultramafics, chert, argillite, lithic ss, and ls.

  17. Magmatic Arc • Plate convergence zone with arc • Have volcanic highlands • Produce: • volcaniclastic debris • qtz & K felds rare except at arc dissection • deposition in trench

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