39

TEKTONIKA PLOČA

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Tektonika ploča

• fundamentalna koncepcija u geoznanosti

• potaknuta iz geologije i paleontologije• prihvaćena nakon geofizičkih dokaza

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Mozaik Zemlje

Peter W. Sloss, NOAA-NESDIS-NGDC

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• prijašnji način tumačenja zajedničke pojave dva kompleksa stijena koji imaju sasvim različitu genezu

• teorija geosinklinala istisnuta pojavom teorije tektonike ploča

stabilna platforma miogeosinkilnala geoantiklinala eugeosinklinala rubna zona

Geosinklinala

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Ploče

• grupe stijena koje se kreću u istom smjeru

• mogu sadržavati oceansku i kontinentalnu koru ili samo jednu od njih

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Tipovi granica ploča

• divergentne

• konvergentne

• transformne

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Divergentne granice ploča

• obično se počinju razvijati unutar kontinenta gdje kasnije može nastati ocean

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Osobine srednjeoceanskog hrbta

• središnja riftna dolina

• plitki potresi

• efuzije bazalta

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Kontinentalni riftovi

• Istočna Afrika, Rio Grande rift

• početak nastanka oceana

• specifične stijene

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Riftanje i širenje morskoga dna

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Riftanje i

širenje morskoga

dna duž srednjeoce-

anskog hrbta

Peter W. Sloss, NOAA-NESDIS-NGDC

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Početak riftanja unutar kontinenta

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Početak riftanja duž Istočnoafri-

čkog riftnog sustava

Peter W. Sloss, NOAA-NESDIS-NGDC

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Delta Nila

Sueskizaljev

‘Aqabazaljev

Crvenomore

Earth Satellite Corp.

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Kalifornijski zaljev

formiran riftanjem

Worldsat International/Photo Researchers

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Podudaranje granica

kontinenata

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Neobična distribucija fosila

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Konvergentne granice

• posljedica stvaranja nove kore na srednjeoceanskom hrbtu

• različita gustoća kora i astenosfere

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Konvergentne granice

• Tri tipa:

– ocean–ocean– ocean–kontinent– kontinent–kontinent

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Ocean–ocean

• otočni lukovi: – potresi– vulkanizam– podmorski rov (trench)

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Ocean–ocean

subdukcijska zona

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Ocean–kontinent

• kontinentalni lukovi:

– aktivni vulkani– kompresija gornje kore

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Ocean-kontinentsubdukcijska zona

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Kontinent–kontinent

• kolizijska konvergencija nošenasubdukcijom

• konvergencija udružena s:– boranjem– pružnim rasjedanjem– podvlačenjem

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Kontinent-kontinent kolizija

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Himalaja i plato Tibeta

• produkt kolizije Indije i Azije

• počela prije 45 mil. god.

• prije kolizije južna Azija poput današnjih Anda

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Zone širenja oceana presječene transformnim granicama

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Wilsonov ciklus

• ponavljanje procesa uzrokovanog tektonikom ploča:– otvaranje i zatvaranje oceana

• tektonika ploča (ili nešto slično) aktivna od početka povijesti Zemlje

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Današnji primjeri granica ploča

O-Okonvergentna

O-Odivergentna

O-Kkonvergentna

O-Kkonvergentna

O-Odivergentna

K-Kdivergentna

O-Odivergentna

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Ocean–kontinent konvergentne

granice

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Kontinent–kontinent konvergentna

granica

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Brzina kretanja ploča

• brzina dobivena iz magnetskih anomalija u stijenama morskoga dna

– brzo širenje– sporo širenje

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Magnetskeanomalije

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Starost oceanske kore

R. Dietmar Muller, 1997

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Relativna brzina i smjer kretanja ploča

Iz C. Demets, R.G> Gordon, D.F. Argus, and S. Sten, Model Nuvel-1, 1990

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Otvaranje Atlans-

kog oceana

kretanjem ploča

Prema Phi llips & Forsyth, 1972

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Zajednice stijena i tektonika ploča

• veza tektonike ploča i grupa stijena

• istraživanje stijenskih zapisa

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Idealizirani

ofioliti

Dubokovodni sedimenti: šejlovi, vapnenci, rožnjaci, turbiditi, fosili morskih pelagičkih organizama.

Bazaltna pillow lava ispresijecana dajkovima.

Gabro, naznake metamorfizma.

Peridotiti i druge mafitne stijene, često pokazuju metamorfizam.

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Model formiranja oceanske kore na srednjeoceanskom hrbtu

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Vulkanski i nemarinski sedimenti taloženi u riftnoj dolini

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Hlađenje i spuštanje rubova rifta omogućava taloženje marinskih

naslaga

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Razvijanje karbonatnih platformi

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Kontinentalni rub raste jer se opskrbljuje materijalom zbog erozije

kontinenta

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Dijelovi ocean–ocean konvergentne granice ploča

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Dijelovi ocean–kontinentkonvergentne granice ploča

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Kontinentalna subdukcija

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Kontinent–kontinent

kolizija

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Približavanje luka kontinentu

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Kolizija

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Područje prirasta mikroploče

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Tektonska rekonstrukcija• Različiti dokazi kretanja kontinenata

kroz vrijeme:– paleomagnetizam– deformacijske strukture– taložni okoliši– fosili

– distribucija vulkana

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Nastanak Pangee

I.W.D. Dalziel, 1995

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Dezintegracija Pangee

prije 200 mil. god.

PremaDietz & Holden, 1970

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Dezintegracija Pangee

prije 140 mil. god.

PremaDietz & Holden, 1970

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Dezintegracija Pangee

prije 65 mil. god.

PremaDietz & Holden, 1970

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Dezintegracija Pangee

danas

PremaDietz & Holden, 1970

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Mehanizmi pokretanja tektonike ploča

• konvekcija

• transfer energije

• izokrenuta astenosfera

Mehanizmi kretanja ploča

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Ostali faktori

• podvlačenje u rovovima

• izguravanje od hrbta

Glavni događaji na rubovima ploča

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Što nam objašnjava tektonika ploča

• distribuciju potresa i vulkana• odnos starosti i visine planinskih

lanaca• distribuciju starosti oceanske kore• magnetske informacije u stijenama

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Posljedice

• klimatske i ekološke barijere

• interakcija vjetra i oceanskih struja

• pad temperature od ekvatora prema polovima

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• formiranje geografske barijere: divergencija vrsta

– vrlo različiti uvjeti s obje strane– prilagodba– nove vrste

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a) prevlaka Paname

b) divergencija vrsta mekušaca

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Neriješena pitanja

• problem konvekcije

• neki kontinenti u potpunosti okruženi divergentnim granicama

• različitost tektonike u kontinentalnoj kori i oceanskoj kori

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