sec 3 ihe ge 2014/chan ml
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Sec 3 IHE GE 2014/Chan ML. Fold is a bend in the rock strata caused by compression. Fold. Folds are formed by compression resulting in shortening and thickening of the crust. Parts of a fold: 1) limbs - the two sides of a fold. - PowerPoint PPT PresentationTRANSCRIPT
Sec 3 IHE GE 2014/Chan ML
Fold
» Fold is a bend in the rock strata caused by compression
Folding
» Folds are formed by compression resulting in shortening and thickening of the crust.
» Parts of a fold:1) limbs - the two sides of a fold.2) axial plane - an imaginary surface that divides a fold as symmetrically as possible, with one limb on either side of the plane.3) fold axis - a line drawn along the points of maximum curvature of each layer.Also defined as the intersection of the axial plane with the beds. In some folds, the axis is completely horizontal.
In more complex folding, the fold axis is ofteninclined at an angle known as the plunge - a plunging fold.
http://pirate.shu.edu/~schoenma/mountains.htm
Types of fold
1) anticline - formed by upfolding, or arching, of rock layers. It is a structure in which the oldest strata are found in the center.
2) syncline - a downfold, or trough, with youngest strata in the center.
Symmetrical when the limbs on either side of the axialplane diverge at the same angle and asymmetrical when they do not.
Asymmetrical fold is said to be overturned if one limb is tilted beyond the vertical.Some folds are said to be plunging since the axis of the fold penetrates into the ground.
http://www.bcminerals.ca/pdf/Geo12-activityHH.pdf
Limb
Fold mountains
Formation:» two plates converge
˃ two continental plates or˃ a continental and an oceanic plate. Usually found along
continents’ edges » When the plates converge, the accumulated layers of
rock crumple as sedimentary rocks are forced upwards into a series of folds
young fold mountains (10 to 25 million years), (Rockies and Himalayas)
old fold mountains (over 200 million years), (Urals and Appalachians)
The French Alps
http://www.deskpicture.com/DPs/Places/FrenchAlps.jpg
Folding
www.indiana.edu/~g103/G103/week9/wk9.html
Overturned Folding
www.indiana.edu/~g103/G103/week9/wk9.html
Faulting
Faults are fractures in the crust along which displacement has taken place.
Faults can occur as single discrete breaks, or as part of a large fault system (the San Andreas fault has displacement of hundreds of kilometers and consist of many interconnecting fault surfaces). These so called fault zones can be several kilometers wide.
Sudden movements along faults are the cause of most earthquakes.
http://facweb.bhc.edu/academics/science/harwoodr/Geol101/study/Images/D041-716.jpg
Formation of Block Mountains by:
TENSION COMPRESSION- Reverse faults- Rock layers are compressed- Central block is pushed upwards- Overhanging escarpment
- Normal Faults- Rock layers are pulled apart- Side blocks are lowered relative to
the central block Examples: Sierra Nevada (USA), Flinders Range (Australia), The Tetons (USA)Examples: Death Valley, California
(USA), Black Forest (Germany)
Formation of Rift Valleys by: TENSION COMPRESSION
- Normal Faults- Rock layers are pulled
apart- Central block is loweredExample: Great Rift Valley, East Africa
- Reverse Faults- Rock layers are
compressed- Side blocks are pushed up- Overhanging escarpmentExample: Great Glenn Fault, Scotland
Strike-Slip Faults
» Dominant displacement horizontal and parallel to the strike of the fault plane.
» Rather than a single fracture along which movement takes place, large strike-slip faults consist of a zone of roughly parallel fractures up to several kilometers in width.
» They DO NOT produce a fault scarp, like the normal and reverse faults
» Many major strike slip faults cut through the lithosphere and accommodatemotion between two large crustal plates - transform fault.
» Examples: San Andreas Fault, Anatolian Fault (Turkey)
http://teachers.sduhsd.k12.ca.us/gstimson/faultmac.gif
New Madrid
http://www.showme.net/~fkeller/quake/images/tennesseeguy.wordpressblog.jpg
California
http://pirate.shu.edu/~schoenma/mountains.htm
http://www.geo.arizona.edu/~cparkjr/hebgen/page2.html
Strike Slip fault
Case Study
The Great Rift Valley System(Africa)
» +9656 km crack (fissure) in the earth's crust, » stretching from Lebanon to Mozambique. » It divides Kenya into two segments. » formed by violent subterranean forces that tore
apart the earth's crust. » forces caused huge chunks of the crust to sink
between parallel fault lines and force up molten rock in volcanic eruptions.
» this process, called rifting, is still in progress » many active and semi-active volcanoes; and
hotsprings are along the Rift.
http://images.encarta.msn.com/xrefmedia/aencmed/targets/maps/map/000edd0e.gif
http://www.munoz-group.net/pics/map_africa.jpg
Stages of Formation
» 2 continental plates moving apart (African Plate: Nubian) and Somalian Subplate
» Due to the rising convection currents» Producing Normal Faults» The central block is lowered relative to the adjacent
blocks» The process is accompanied by earthquakes and volcanic
eruptions» This process is widening the valley» The Somalian plate may be pulled apart from Africa, just
like what happened to Madagascar
The continent of Africa is thought to have been split by a series of rift valleys in various states of development. Those in East Africa are still in thick crust. Those in West Africa are associated with thick oil-bearing sediments. In the Red Sea area the rifting has gone so far as to form a narrow ocean. In the south-east Madagascar has been completely separated from Africa by rifting.
Madagascar
R e f e r e n c e s
» http://geology.rutgers.edu/~feigy/LectureNotes/12StructuralGeol.pdf» http://www.berghuis.co.nz/abiator/patana/6t/index/humanities/mountains/geofaulting/flash/main.swf
» Chong, Marianne. Aspects of Physical Geography» Waugh, David. Integrated Approach