地质学基础地质构造.docx
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地质学基础地质构造.docx
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地质学基础地质构造
ChapterTwoGeologicalStructure
§2-1geologicaltimeandChronologicalscale
一、GeologicalTime
Geologicaltimeisamethodoforderingandmeasuringpastevents.Theorderingofeventsusesagroupofobservationalmethodsknownas:
absolutedatingmethodsandrelativedatingmethodsd
1AbsoluteDatingmethods
Absolutedatingmethodsarethosethatgenerateanageinyears.Therearetwoprincipalmethods:
oneisthemethodwhichrelyoneventinthegeologicalrecordwithverystrongannualcyclicity(周期性),suchastreegrowthrings,coralgrowthcyclesvarves(annualclaysedimentlayers).AnotherMethodsismorecommonlyusednowdayswhichrelyonthedecayofnaturallyoccurringradiogenicisotopes:
Radiometricdatingisnotwithoutdifficultiesbutisbyfarthemostwidespreadmethodappliedtodetermineabsoluteagesbetween100and4500My.ThesamedecayprocessisresponsibleforthetemperaturegradientwithintheEarth(geothermalgradient).Uranium(铀),Thorium(钍)andPotassium(钾)arebyfarthemostcommonradiogenicisotopesintheEarth'scrust.Radiocarbonisimportantindatingorganicremainsfromtherelativelyrecentpast.
2Relativedatingmethods
Relativedatingmethodsusegeologicalprinciplestoplaceeventsinchronologicalorder,whichincludestratasuperpositionmethod,fossilsuccessionmethod,themethodofrocklayerscontactrelation.
(1)Theprincipleofsuperpositionstatesthatolderbedsarecoveredbyyoungerbeds.Inotherword,theyoungestunitisusuallyatthetopinasedimentarysequence.
(2)Theprincipleoffossilsuccessionstatesthatorganismsevolvethroughtimesothatparticularformscanbeusedasagemarkerswherevertheyarefound.
(3)Themethodofrocklayerscontactrelationstatesthatthecontactrelationsamongrocklayersisthehistoryrecordsofcrustmovement,magmaactivities.Sogeologicaleventscanbeorderedbytherelationofrocklayers,theseincludestherelationsamongsedimentaryrock,therelationsamongtheigneousrock,therelationbetweensedimentaryrockandigneousrock.
(a)Therelationsamongsedimentaryrock
Therelationsamongsedimentaryrockcanbedividedintoconformityandunconformity.
Theconformitymeansthatstratawasformedinastablesedimentaryenvironment,thedipandstrikeofstrataarebasicallythesame.Seediagram(a).
Theunconformitymeanthereisabreakinsedimentation,aperiodoferosionoranepisodeofdeformation,Unconformitiesrangefromminorerosionalbreakstostrongangulardiscordancesinbedding.Anunconformityindicatesaperiodwherenorockrecordisaccumulated.Theyaretime-breaksofindeterminatelength.Thediagrams(b),(c)illustratevariouskindsofunconformities.
(b)Therelationsamongigneousrock
Cross-cuttingrelationshipsamongigneousrocks(seediagrambellow)indicatethatintrusionrocksmustbeyoungerthantherockstheycut.
(c)therelationbetweensedimentaryrockandigneousrock.
Cross-cuttingrelationshipsbetweenigneousrocksandsedimentaryrock
Indicatethatsedimentaryrockincludedpebblesandfragmentsmustbeolderthanthehostrockcontainingthem.
Deformationanyrockseffectedbyadeformationevent(foldingortilting)mustpre-datethedeformationepisode.
二Chronologicalscale
Thegeologictimescalewasoriginallyasetofrelativedatesbutthevariouseons,eras,periodsandepochshavenowbeenaccuratelydatedwiththeaidofradiometricmethods.
Theimportantdatesare:
4,600My-theageoftheEarthandSolarSystem
3,600My-theearliestlife
570My-thefirstappearanceofabundantandvariedorganicforms
200My-thebreak-upofthesupercontinentPangea
66My-thedisappearanceofthedinosaurs
Thegeologictimescaleisusuallypresentedinadistortedform-87%ofthetotaltimespanisrepresentedbytheProterozoicandArcheaneonsofthePrecambrian.
GeologicalTimeScale
EON
(宇)
ERA
(代)
PERIOD
(纪)
EPOCH
(世)
MILLIONYEAR
(距今百年)
顯生宙
Phanerozoic
新生代
Cenozoic
第四纪
Quaternary
Holocene
全新世
現代Today--0.01
Pleistocene
更新世
0.01--1.8
第三紀
Tertiary
上新世
Pliocene
1.8--5.3
中新世
Miocene
5.3--23
漸新世
Oligocene
23--36.5
始新世
Eocene
36.5--53
古新世
Palaeocene
53--65
中生代
Mesozoic
白堊紀
Cretaceous
65--145
侏羅紀
Jurassic
145--208
三疊紀
Triassic
208--248
古生代
Palaeozoic
二疊紀
Permian
248--290
石炭紀
Carboniferous
290--360
泥盆紀
Devonian
360--410
志留紀
Silurian
410--438
奧陶紀
Ordovician
438--510
寒武紀
Cambrian
510--570
元古宙
Precambrian
元古代
Proterozoic
震旦紀
Sinian
570--800
800--2,500
太古宙
Archaean
太古代
Archaeozoic
2,500--4,600
Initialstageofearthformation(before3600)
Archaeozoicera:
(3600--2500)→Ar
crustmovementintensively,nowater,nolife,atheendthiserasea
Proterozoicera:
(2500-570)→Pt
(Pt1→upperpro…
Pt2→lowerpro…)
Sedimentaryrock’sformationalgae(earliest)appeared
Paleozoicera:
(570-230)→Pz
InPz1:
theseaintrusion,attheendofOrdovicianreachitspeak,hugeofsedimentaryrockwasformedintheinthisenvironment;flourishinginthesealivingthing
InPz2:
landvegetabledeveloped,foresthugecoalwasformedatthistimethrivinginamphibiousanimal.
(两牺)
(Flourishingthriving,prosperous)
Mesozoicera:
(230-65)→Mz
T:
North→land
South→shallowsea
J:
MostpartofChinaland→land
Dinosaurpopular(breast-feedanimals)
K:
Crustmovementmagmaactivities
Volcanicmaterialsdeposited
(ash,bomb,debris,gas)
Cenozoicera:
(65-now)→Kz
R:
breast,birddevelopedanddividedabruptly
Q:
loess,glacierhasformed,humanbeing…
§2-2Basicshapeandclassificationofgeologicalstructure
Geologicalstructureisthestudyofthepermanentdeformationandrockfailurecreatedbythechangesinstressthroughgeologictime.Itisbyfarthemostimportantaspectofgeologyfortheengineertounderstand.Tectonicprocessesareresponsibleforthemanydiscontinuityplanes(fractures,faults,joints)thatpermeaterockmassescontrollingtheirstrength,stress-straincharacteristicsandthetransmissionandstorageoffluids.
Structuresmaybeconvenientlysubdividedintotwogroups:
brittlestructures-recordingthebrittle-elasticfailureofrocksinthepast.Faultsandjointsfallinthisbroadcategory.
ductilestructures-preservingthepermanentviscoplasticdeformationofrockthroughoutgeologictime.Foldsandmetamorphicfoliationsaretheexpressionofthistypeofstructure.
Themoststrikingfeaturesofrocksasengineeringmaterialsisthattheyarenotsimple,isotropic,elasticandcontinuousbutverycomplex,stronglyanisotropic,anelasticdiscontinuous.Itisvirtuallyimpossibletodeducethestresshistoryofrocksfromtheirobserveddeformation.Therearealwaysmanyambiguousdeformationpathsthatcouldhavebeenfollowedtoproducewhatisobserved.
Thestudyofstructureinvolvesthecarefulrecordingoftheorientationoflinesandplanesinrockmassesinordertodeducethethree-dimensionalgeometryofthedistortedcrust.
一、岩层的产状要素
Planescanbedefinedinspacebytheirinclinationordipandtheirstrike,thebearingofthelineofintersectionoftheplaneandahorizontalsurface.Noticethatthebearingoftheprojectionofthediponahorizontalsurfaceisinadirectionatrightanglestothestrike.Thisiscalledthedipdirection.
Thelayerofsandstoneistiltedtothenorthatanangleofabout45degrees.Thedipandstrikeare45N/180.Thedipanddipdirectionare45/090.Noticethatifthedipweretothesouthwewouldwrite45S/180and45/270forthedip/strikeanddip/dip-directionrespectively.Engineerspreferthesecondnotationbecausethedirectionofdipisambiguouswhendip/strikepairsarerecorded.
二、水平构造和单斜构造(Horizootalandinclinedstructure)
三、Folding
1Thedefinitionoffolding
Foldsresultfromtheplasticdeformationofrocksatlowstrain-rates,usuallyunderelevatedtemperatureandpressureconditions.
2Theshapedescription
Foldsarebroadlysubdividedintoanticlines(upwardsconvex凸的)andsynclines(downwardsconvex).
Insynclinesandanticlines,theaxialplaneistheplaneofsymmetrypassingthroughtheapex(顶点)ofthefold.Thelineofintersectionofthefoldapexandthehorizontalplaneiscalledtheaxisofthefold.
3theclassificationoffolding
(1)AccordingtotheOrientationofaxialplane
Theorientationoftheaxialplanerelativetothehorizontaltogetherwiththeorientationoffoldlimbsallowsubdivisionintoupright(axialplanevertical,limbssymmetric),overturned(axialplanemoderatelyinclined,onelimboverturned),orrecumbent平卧的(axialplanenearhorizontal,onelimbinverted).
(2)accordingtopivotlocationstate
(3)Accordingtothetightnessoffolding
Thetighnessoffoldscanbedescribedasopen(limbsdipgently),tight(limbsdipsteeply)orisoclinal(limbsareparallel).
一、Fracturingstructure
Fragilerock
Fractureplane
Faultandjointing
block
(一)Jointing
1ThedefinitionofJointing
Jointsarediscontinuitiesonwhichtherehasbeenlittleornodisplacementinshear(incontrasttofaults).Jointsareubiquitous(普遍存在的)inigneous,metamorphicandsedimentaryrocks.Theyareevidenceofbrittlefailureoftherockmassatsomestageinthedeformationhistory.
2thefeaturesofjoints
Jointshavemanyimportantpropertiesasplanesofweaknessinrockmasses:
Orientation
-strikeanddipordipanddip-direction.
Spacing
-thefrequencyornumberofdiscontinuitiesperunitlength.
Aperture(口径,)
-themeandistancebetweenwallrocksurfaces.
Persistence(连续性)
-thecontinuityofjointsortracelength.
SurfaceRoughness
-thepropertycontrollingfrictionbetweensurfaces.
Infi
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