Lecture 12 - Rocks and Time

Lecture 12 - Rocks and Time - Start - Tuesday, October 11th...

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Unformatted text preview: Start - Tuesday, October 11th 2011 !""#$"%&'&"()* !  !"#$%&'()!"#$%&'()*+,-."(/0+1(%+(234567385%9:( !  *++'),--"./'%/$-)01)23-$)/3'%(( ;<=(/503(((((>(6(?@#A1+( <--- My room !  B87(/5/3((((?,(6(<.C+,@( !  B82(55/3(((((<A,(6(DEA#*( !  !  4+5)!678)0&"/.)1+5&)-$5#%/$)9:);3&#)3/#)</+=)1+5&) >30)-%;$"+/)/5'0%&?( !  !"#$%&')@+A%&3.%BC+&'3$( !  %FF(F.*+E".G(%@$(F%-(9%+."#%F(EH(+,(%@$(#@*FE$#@A(+1.(IJK( F.*+E".:( !  !  !  L%"+(>3(M.N@#+#,@G(O/5(PE.G+#,@Q(/5(9%"RGS( L%"+(T3(U,*%F(>".%(OV(PE.G+#,@GQ(/5(9%"RGS( L%"+(;3(K1,"+(>@GC."(OW(PE.G+#,@GQ(8/(9%"RGS( !  73'D>%)!"#$%&')E5%-$"+/-)D+-$%#)+/),A%/5%?( !""#$"%&'&"()* !  X%*Y,*RG(ZE#[(*F,G.G(%+(0345H9(,@(!"#$%&'()*+,-."( /0+1( !  <,(U%-G(C..R(,\()*+,-."(/5+1( !  <,(U%-()]*.(=,E"G(C..R(,\()*+,-."(/5+1( !  ;,@+.@+()]*.(=,E"G( !  ^.$@.G$%&'()*+,-."(/8+1(\",9(864345(#@(TKT(405T( +,-./*01*2345* /:  ^1&($,(",*RG(\,F$(%@$(\%EF+_( !  G+".GG'(G+"%#@( 8:  I.,F,A#*(G+"E*+E".G( !  !,F$G( !  !%EF+G( 4:  Y.F%+#`.($%+#@A( Y,*RG(%".(GE-a.*+(+,3( force )7$&%--)b((( per unit area ::%@$(E@$."A,( change in size/shape in response )7$&3"/(b(() b  (( COMPRESSIONAL STRESS - forces pushing together ex. plates colliding !#A:(//:8( .:A:(*,FF#G#,@%F(HF%+.( 9%"A#@G( TENSIONAL STRESS - forces pulling apart !#A:(//:8( .:A:((( divergent plate margins SHEAR STRESS - parallel, opposing forces !#A:(//:4( .:A:(+"%@G\,"9(HF%+.(9%"A#@G( ELASTIC - deformed body recovers when stress removed - beyond elastic limit, permanent deformation PLASTIC - bends but does not return to original shape - rocks under high temperature/pressure - ex: glacial ice, asthenosphere (pretty much whole canadian shield has gone through this) mtn eroded away B RITTLE - breaks or fractures, ex: faults -much more common in surface rocks b/c rocks are colder and more malliable can measure the offset and see how much pressure was i nvolved and when occured !"#$%&'%(')&*%+,%-'./%+,&+.#$01! C+>#-) b  ((- bends in layered rock - plastic strain ANTICLINE - upward arching fold (accordian type structure (loopy type); the arching fold is called the anticline) * looks l ike an egg SYNCLINE - downward arching fold *accordian pushed together axis F"/.%)>"/%)b((( of the fold containing all ,G"3>)D>3/%((-)planelines of a fold hinge !#A:(//://( 6(7&8*(9:&)*#;*;#<=)>* * need to know how anti/syncline folds work and reproduce a diagram if you know these 4 then you'll be fine anticline on a slight angle !#A:(//:/W( C&3;$5&%-)"/)&+;<( H+"/$-) b rock fractures, no displacement (( dependent on the nature of the rock i tself C35>$-) Fractures along which movement has taken place an active fault has to be within 11,000 years "#$%&'!()*+$(b((( movement with last 11,000 years ,-.!/-!.'!/%0$%12*%03!/%4'5'1$!$67'0!-(!()*+$08! * on final exam 0#'&*(&8'?"#<#@9>* HANGING WALL BLOCK overlies an inclined fault plane FOOTWALL BLOCK - underlies an inclined fault plane !#A:(//:88( understand this b/c it will be on final exam NORMAL FAULT - hanging wall block moves D OWNWARD relative to the footwall block - can produce a GRABEN or a HORST - ex: rift valleys !#A:(//:8/( !#A:(//:84( *%A%&-%)I35>$) UPWARD b  !hanging wall block movesblock relative to ( footwall 8J&5-$)I35>$) b  (reversefault plane (doesnt (angle fault with very low happen very often) 7$&"<%K->"D)I35>$-) b - (horizontal movement parallel to strike of fault ( - right-lateral (dextral) or left-lateral (sinistral) displacement - ex: San Andreas fault Which is the oldest event/unit? Which is the youngest event/unit? of valley would be youngest but erosion the youngest unit is the Osoyoos Lake Limestone b/c its on top, then penticton, then okanagan, then dike, then revelstoke, then granite, unconformity is missing time *Question like this on final exam Stopped Tuesday October 11, 2011 Started Thursday October 13th, 2011 2. Relative Geologic Time In a sedimentary succession, how can we tell which rocks are older or younger than others? - if something cross-cut other l ayers, - ones on top are most likely younger especially if things are relatively flat unconformity - gap in because the geologic time angle changes - oldest at base, youngest on top when dating sedimentary rock it is hard because you are measuring the sediment not the actual time of lithification !  Relative geologic time !  Understanding when events occured relative to one another !  which came first? !  Absolute geologic time !  understanding when events actually happened !  how old is it? Principle of Superposition (Steno, 1669): !  in any undisturbed series of sedimentay rocks, the oldest layer will be at the bottom, successively younger layers on top Caution: make sure the rocks are ‘undisturbed’, right way up How can we tell if the rocks in one layer are the same age? Principle of original horizontality !  beds of sediment laid down in water form horizontal or near-horizontal layers What can you say about the relative ages of deposits in this situation? Principle of cross-cutting relationships (Lyell, 1830) - A geological feature that cuts across or penetrates another body of rock must be younger than the rock mass penetrated Which is older? A or B? Principle of Inclusions (Lyell, 1830) !  fragments included in the host rock are older than the host rock there are bits of A in B so A is older How can we match the age of rocks from one area to another? Correlation : –  - determining time equivalency of rock units - similiarity in lithology and/or fossils Principle of Faunal Successions (Smith, 1800): –  - fossil species succeed one another in a recognizable order - index fossils relate to specific time periods –  Three types of unconformities D ISCONFORMITY - layers above and below the unconformity are parallel to one another ANGULAR UNCONFORMITY - younger beds overlie tilted or folded beds NONCONFORMITY - younger beds overlie much older metamorphic or plutonic rocks What sequence of events is recorded here? A7?"@)*9#$*7BC&*(#*=#D* Y.%$(;1%H+."(//( L%+>+.";)7$&5;$5&%-) >@GC."(+1#G(PE.G+#,@3( F+=)#+)-3>$)#+'%-)I+&'M) NJ1)3&%)$J%1)"'D+&$3/$)$+)$J%)&%-+5&;%)"/#5-$&1M) ...
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This note was uploaded on 11/28/2011 for the course ENV SCI 1G03 taught by Professor Padden during the Fall '11 term at McMaster University.

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