Upload
jinderation
View
222
Download
0
Embed Size (px)
Citation preview
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
1/84
GEOTECTONICSGEOTECTONICS
BS Geology(4BS Geology(4thth semester)semester)
BAHRIA UNIVERSITY ISLAMABADBAHRIA UNIVERSITY ISLAMABAD
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
2/84
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
3/84
HISTORICAL PERSPECTIVE OFHISTORICAL PERSPECTIVE OF
PLATE TECTONICSPLATE TECTONICS
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
4/84
Historical Perspective
The theory of plate tectonics has largelybeen developed since 1967 but the historyof ideas concerning the mobilist view of theearth extends back considerably longer
The theory of plate tectonics states thatthe Earths outermost layer is fragmentedinto a dozen of large & small plates that
are moving relative to one another on thetop of mobile asthenosphere.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
5/84
Before the advent of plate tectonics
,however, some people already believedthat the presentday continents were thefragmented pieces of preexisting largerlandmasses (supercontinents).
Plate tectonics is the relatively newscientific concept, introduced in the 19th
centuary. The theory has unified the study
of the earth by drawing together manybranches of earth sciences, frompaleontology to seismology.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
6/84
Plate tectonics theory has provided
explanation to the distribution ofearthquakes & volcanic active zone aroundthe globe.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
7/84
Abraham Ortelius(1527-1598)
He was the first to note the similarity& suggest an ancient separation in1756. He suggested that theAmericas were torn away fromEurope & Africa by earthquake &floods.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
8/84
Abraham OrteliusAbraham Ortelius(Abraham Ortels) (April(Abraham Ortels) (April14, 152714, 1527 June 28, 1598)June 28, 1598)was awas a FlemishFlemish cartographercartographerandand geographergeographer, generally, generallyrecognized as the creator ofrecognized as the creator of
the firstthe first modernmodern atlasatlas, the, theTheatrum Orbis TerrarumTheatrum Orbis Terrarum
(Theatre of the World). He(Theatre of the World). Heis also believed to be theis also believed to be the
first person to imagine thatfirst person to imagine thatthe continents were joinedthe continents were joinedtogether before drifting totogether before drifting totheir present positions.their present positions.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
9/84
Theatrum Orbis TerrarumTheatrum Orbis Terrarum
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
10/84
Sir Francis Bacon:
In 1620, he commented on thesimilar form of the west coasts ofAfrica & South America. He alsonoted the similar configuration of theNew & Old world, both of which arebroad & extended towards the north,narrow & pointed towards south.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
11/84
Sir Francis Bacon
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
12/84
Theodor Christoph Lilienthal:
Theodor Christoph, Professor ofTheology at Konigberg in Germany,
also note A fit of Atlantic Coasts ofSouth America & Africa & Suggestthat they might once have been side
by side
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
13/84
Alexander Von Humbolt:
The German explorer Humbolt alsonoted the geometric & geologicalsimilarities of the opposing shores ofthe Atlantic but also suggested thatthe Atlantic ocean was formed bycatastrophic event.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
14/84
Catastrophism VsCatastrophism VsUniformitarianismUniformitarianismCatastrophismCatastrophism
A principle that statesA principle that statesthat catastrophicthat catastrophicevents have beenevents have beenimportant in Earthimportant in Earthhistory and modifyhistory and modifythe path of slowthe path of slowchangechange..
UniformitarianismUniformitarianism
The principle that states thatThe principle that states thatgeological change occurs overgeological change occurs over
long periods of time, bylong periods of time, bysequence of almostsequence of almostimperceptible events.imperceptible events.
In addition, processes andIn addition, processes andscientific laws operating todayscientific laws operating today
also operated in the past andalso operated in the past andthus past geologic events canthus past geologic events canbe explained by forcesbe explained by forcesobservable today.observable today.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
15/84
In the mid of 19th centuary concept ofcatastrophism is replaced by that ofuniformitarianism or actualism asproposed by the Scottish geologist JamesHutton in 1785.
The Principle of uniformity is commonlystated as:
The present is Key to the past
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
16/84
James Hutton
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
17/84
It means that slow processes going onat & beneath the Earths surface todayhave been going on throughoutgeological time & have shaped the
surface record. However the geologic forces &
processes are gradual as well as
catastrophic, acting on the Earth todayare the same as those that have actedin the geologic past.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
18/84
For the first time it was considered
that drift is taking place today & hastake place at least through the past100-200 Ma of Earth history.
In this way drift was considered toaccount for the geometric &geological similarities of the trailing
edges of the continents around theAtlantic & Indian oceans & theformation of the young fold mountain
systems at their leading edges.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
19/84
Continental drift
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
20/84
Continental drift & AlfredWegners Theory
In 1912, the German meteorologist AlfredWegener (1880-1930), first proposed thetheory of continental drift , which statethat parts of the Earths crust slowly driftatop of a mobile asthenosphere.
Wegener detailed much of the older, pre-drift, geological data & maintained that
the continuity of older structures,formations & fossils faunas & floras acrosspresent continental shorelines was morereadily understood on predrift
reconstruction.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
21/84
Alfred LotharAlfred LotharWegenerWegener(1880(1880--1930),1930),the originatorthe originatorof the theory ofof the theory ofcontinentalcontinental
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
22/84
Wegener hypothesized that all the
continents were assembled intosupersontinents 200 Ma ago, which henamed Pangaea, meaning All earth.
Pangaea was a supercontinent consistingof all of Earths land masses.
It existed from Permian to Jurassic periods. It began breaking up during the Jurassic
period, forming two supercontinents
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
23/84
Pangaea(all earth)
Laurasia(from Laurentia,a region of Canada
& Asia )
Gondwanaland(literally land of Gonds, after
an ancient tribe of northern India)
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
24/84
Laurasia:
It is the northern portion of
supercontinents & consists ofNorth America, Greenland,Europe & Asia.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
25/84
Gondwanaland
It is the southern portion of
Supercontinent & includeSouth America, Antarctica,Africa, Madagascar, India &
Australia.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
26/84
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
27/84
These two supercontinents wasseparated by palaeo-Thethysocean (after the Greek goddess
of the sea).The ocean surrounding themwas Panthalassa (literally all
ocean).
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
28/84
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
29/84
Alfred SupercontinentsAlfred Supercontinents
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
30/84
Position of Continents inPosition of Continents in
different periodsdifferent periods
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
31/84
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
32/84
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
33/84
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
34/84
Wegener proposed hisContinental drift hypothesis inbook Die Entstehung der
kontinente und ozeane (Theorigin of continents & oceans)
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
35/84
Drawbacks of Alfred Wegeners
Theory Lack of plausible driving force was
missing.
Wegener suggested that continents driftoccurred in response to the centripitalforce experienced by the continents
because of the Earths rotation but it is nottrue
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
36/84
Wegeners theory vindication
Although Wegener s continental theorywas rejected during his life time due tolack of reasonable mechanism forcontinental drift.
Later on, the British geologist ArthurHolmes championed the theory ofcontinental drift & proposed that
continents were moved by convectioncurrent powered by the heat ofradioactive decay.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
37/84
However, after his death, new evidencefrom ocean floor exploration and otherstudies rekindled interest in Wagener'stheory, ultimately leading to the
development of the theory of platetectonics
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
38/84
Evidences of Continental driftEvidences of Continental drift
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
39/84
Wegener devoted his life to
doggedly pursuing additionalevidence to defend his theory.
The evidence used by Wegener,du Toit, and others to support thehypothesis of continental drift are
as follow;
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
40/84
1)GEOMETRICAL1)GEOMETRICAL FIT OF CONTINENTSFIT OF CONTINENTS
Wegener, like some before him, was impressedby the close resemblance between the coastlinesof continents on opposite sides of the Atlantic
Ocean, particularly between South America andAfrica. He argued that continents are fit togetherlike pieces of a giant jigsaw puzzle.
He cited these similarities as partialevidence that the continents were at onetime joined together as a supercontinentthat subsequently split apart.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
41/84
As his critics pointed out, though, theconfiguration of coastlines result from erosional
and depositional processes and therefore iscontinually being modified. So even if thecontinents had separated during the MesozoicEra, as Wegener proposed, it is not likely that thecoastlines would fit exactly.
A more realistic approach is to fit thecontinents together along the continental
slope where erosion would be minimal.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
42/84
In 1965 Sir Edward Bullard, an Englishgeophysicist, and two associates showedthat the best fit between the continentsoccurs along the continental slope at adepth of about 2,000m.
Since then, other reconstructions using thelatest ocean basin data have confirmed theclose fit between continents when they are
reassembled to form Pangaea.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
43/84
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
44/84
2)Similarity of Rock Sequences andMountain Ranges
If the continents were at one time joined,then the rocks and mountain ranges of thesame age in adjoining locations on theopposite continents should closelymatch. Such is the case for the Gondwanacontinents. Marine, non-marine, and glacial
rock sequences of Pennsylvanian to Jurassicage are almost identical for all five Gondwanacontinents, strongly indicating that they werejoined together at one time.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
45/84
The continuity of Paleozoic fold beltsacross the assembled Laurasia &Gondwanaland also support thehypothesis of continental drift.
The continuation of Appalachian foldbelt of North America with theCaledonian fold belt of northernEurope was noted.
Similarly the sedimentary depositsassociated with these fold belts also
supported theory.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
46/84
The grain size & chemical compositionof the sediments can be used todetermine the nature & direction of thesource.
The source of the sediments inCaledonian fold belt of northern Europelies to the west in location nowoccupied by Atlantic ocean, indicatethat in past both continents were sideby side.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
47/84
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
48/84
3) Age provinces3) Age provinces
The correlation of the patterns ofages across the southern Atlantic is
also noted. He observed similar rockunits up to Jurassic.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
49/84
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
50/84
4) Igneous provinces4) Igneous provinces
The igneous rocks of similar age canbe traced b/w various continents.
This consists of both extrusive &intrusive e.g. the Mesozoic doloritesspread through Africa, Antarctica,
America.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
51/84
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
52/84
4) Glacial Evidence
During the Late Paleozoic Era, massiveglaciers covered large continental areas of
the Southern Hemisphere. Evidence forthis glaciation includes layers of till(sediments deposited by glaciers) andstriations (scratch marks) in the bedrockbeneath the till.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
53/84
Fossils and sedimentary rocks of the sameage from the Northern Hemisphere,
however, give no indication ofglaciation. Fossil plants found in coalsindicate that the Northern Hemisphere had
a tropical climate during the time that theSouthern Hemisphere was glaciated.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
54/84
All of the Gondwana continents except
Antarctica are currently located near theequator in subtropical to tropicalclimates. Mapping of glacial striations inbedrock in Australia, India, and South
America indicates that the glaciersmoved from the areas of the present-day oceans onto land. This would be
highly unlikely because large continentalglaciers flow outward from their centralarea of accumulation toward the sea.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
55/84
If the continents did not move duringthe past, one would have to explainhow glaciers moved from the oceansonto land and how large-scalecontinental glaciers formed near theequator.
But if the continents are reassembledas a single landmass with South Africalocated at the south pole, the directionof movement of Late Paleozoiccontinental glaciers makes sense.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
56/84
Furthermore, this geographicarrangement places the northerncontinents nearer the tropics, which isconsistent with the fossil andclimatological evidence from Laurasia.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
57/84
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
58/84
5) Fossil Evidences5) Fossil Evidences
Some of the most compelling evidence forcontinental drift comes from the fossil
record.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
59/84
a)Glossopteris flora
Glossopteris, a tree-like plant from thePermian through the Triassic Period. It
had tongue-shaped leaves and was about12 ft (3.7 m) tall. It was the dominantplant ofGondwana.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
60/84
Eduard Suess was an Austrian geologistwho first realized that there had once been
a land bridge between South America,Africa, India, Australia, and Antarctica. Henamed this large land mass Gondwanaland
(named after a district in India where thefossil plant Glossopteris was found).
The present-day climates of South America,
Africa, India, Australia, and Antarcticarange from tropical to polar and are muchtoo diverse to support the type of plantsthat compose the Glossopteris flora.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
61/84
Distribution of GlosspterisDistribution of Glosspteris
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
62/84
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
63/84
b)Mesosaurus
It is freshwater reptile whose fossils arefound in Permian-aged rocks in certainregions of Brazil and South Africa andnowhere else in the world.
Because the physiology of freshwater andmarine animals is completely different, it ishard to imagine how a freshwater reptile
could have swum across the Atlantic Oceanand found a freshwater environment nearlyidentical to its former habitat.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
64/84
Mesosaurus
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
65/84
Moreover, if Mesosaurus could have swumacross the ocean, its fossil remains shouldbe widely dispersed. It is more logical toassume that Mesosaurus lived in lakes in
what are now adjacent areas of SouthAmerica and Africa, but were then unitedinto a single continent.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
66/84
c) Lystrosaurus and Cynognathus
Both are land-dwelling reptiles that livedduring the Triassic Period; their fossils are
found only on the present-day continentalfragments of Gondwana.
Because they are both land animals, theycertainly could not have swum across the
oceans currently separating the Gondwanacontinents. Therefore, the continentsmust once have been connected.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
67/84
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
68/84
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
69/84
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
70/84
d) Polar dinosaurs
Recently, paleontologists (specialists instudies of fossils) have carefully studied somewell-preserved dinosaur remains unearthed atDinosaur Cove, at the southeastern tip of
mainland Australia. Dinosaurs found in most other parts of the
world are believed to have lived in temperate
or tropical regions, but these Australianspecies, popularly called "polar" dinosaurs,seemed well adapted to cooler temperatureconditions.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
71/84
They apparently had keen night vision andwere warm-blooded, enabling them to
forage for food during long winter nights, atfreezing or sub-freezing temperatures.
The last of the dinosaurs became extinctduring a period of sharp global coolingtoward the end of the Cretaceous period(about 65 million years ago).
The discovery of the polar dinosaurs clearly
suggests that they survived the volcanicwinter that apparently killed other dinosaurspecies.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
72/84
Paleontologists do not have theanswers. Regardless, this recentlyacquired paleontologic evidenceconvincingly demonstrates thatAustralia has drifted north toward the
equator during the past 100 millionyears.
At the time when the Australian polar
dinosaurs thrived, their habitat wasmuch farther south, well within theAntarctic Circle.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
73/84
ApproximatelyApproximately100 million years100 million years
ago, the Dinosaurago, the DinosaurCove area (smallCove area (smallred outlinedred outlinedboxes) at theboxes) at the
southern end ofsouthern end ofAustralia was wellAustralia was wellwithin thewithin theAntarctic Circle,Antarctic Circle,
more than 40more than 40degrees closer todegrees closer tothe South Polethe South Polethan it is today.than it is today.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
74/84
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
75/84
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
76/84
Palaeoclimatology
& continental drift
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
77/84
Palaeoclimatology
It is the study of ancient climates. It may be used to demonstrate that
continents have drifted at least in a north-south direction.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
78/84
Factor controlling climate
Climate
Latitude Wind direction& ocean currents
Elevation &topographic barriers
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
79/84
1) Carbonates & reef deposits
Condition: restricted to warm water Latitude range: within 30 of the equator
at the present day. Temperature range: 25-30 C
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
80/84
2) Evaporites
Conditions: formed under hot aridconditions in regions where evaporations
exceeds sea water influx/precipitation. Latitude: arid subtropical high pressure
zones b/w about 10 & 40
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
81/84
3) Red-beds
Condition: hot climate Latitude: < 30
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
82/84
Coal & oil
Condition: warm humid climate isnecessary for accumulation & degradation
of organic matter. Latitude: < 30.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
83/84
5) Glacial deposits
Latitude: within 30 of pole
The result of applying thesepalaeoclimatic techniques strongly indicatethat continents have changed their
latitudinal position throughout geologicaltime.
8/3/2019 Historical Persp & Evidences of Cont. Drift. Lec#5 28th Sep_2011
84/84