Mtn Bldg

	Mountains and Mountain Building	Welcome to	Updated on 05.05.15
		Poorna's Pages at the Glendale Community College

Welcome! Thanks for visiting Poorna's Pages at the Glendale Community College. These pages and the links therein introduce you to the fascinating worlds of Physical Geology, Environmental Geology and Oceanography. We offer 3-unit lecture and 1-unit laboratory classes in these areas, all at the freshman level, that satisfy the GE Physical Science requirement and therefore transfer to UC, CSU, USC and all other North American universities/colleges for the baccalaureate degree. This page presents a general outline of the topic named at the top of the page and links to some sites of interest, including Poorna's PowerPoint Presentations (as ppt as well as pdf files) and hand-outs/overviews (as pdf files). Please do feel free to contact me if you have any questions, wish to seek any clarifications, or have some suggestions that would improve this page.

Home My Book Geol-101 (Earth Revealed Telecourse) Geol-101 (Physical Geology) Geol-102 (Environmental Geology) Geol-112 (Environmental Geology Lab) Ocean-115 (Oceanography) Ocean-116 (Oceanography Lab)
		Access Columbia Earthscape
		click here to e-mail me 4

Poorna's Outlines: Mountain Building You may need to download the Adobe Acrobat Reader to view this PDF file
Click on the image above to browse the PDF version of USGS publication "Birth of the Mountains: The Geologic Story of the Southern Appalachian Mountains"

Click on this map of Asia in order to browse an interesting research paper (PDF) on measuring the crustal shortening in Central Asia

Southern California Mountains and Seismicity

The Transverse Ranges of Southern California, as can be seen in this map, comprise a number of east-west trending mountain blocks bounded by major faults and interspersed with broad valleys. The aftershock areas of 1994 Northridge, 1987 Whittier Narrows, and 1971 San Francisco earthquakes and principal faults are shown for their relations to physiography.








Source:
http://pubs.usgs.gov/of/1996/ofr-96-0263/p22study.jpg

Poorna's Web Notes

Mountain Belts and the Continental Crust

Locally, mountains can be simple topographic features that form by differential erosion, folding and/or faulting, volcanism etc. Our interest here is on a broad regional scale, however.

Mountain belts

World’s major mountain ranges were created
by convergent tectonics. A ~400 Ma old North America-Africa collision probably created the Appalachians, for instance, much like the way Himalayas, now the world’s tallest mountains, formed 55-70 Ma ago when the northerly moving Indian plate collided with rest of Eurasia.

The major mountain belts worldwide ...

are long continuous chains comprising numerous mountain ranges or groups of closely spaced parallel to sub-parallel ridges (e.g., from the Aleutian Islands to Coastal Ranges and Rocky mountains in the North American Cordillera);
often (but not necessarily always) tend to be
- younger than the surrounding continental and/or oceanic regions; and
- taller the younger they are;
usually carry thick sedimentary columns, mostly marine, compared to the thinner sedimentary cover elsewhere;
commonly have metamorphosed, often granitized, cores and intensely folded and faulted sections; and
overlie appreciably thicker crust than the average continent.

Folded mountain belts are believed to evolve in three main stages:

the uplift or block-faulting stage of “isostatic readjustment” and normal faults and block faulting;
the accumulation stage creates a thick pile of mostly marine sediments and volcanics;
the orogenic stage of intense deformation made up of folding accompanied with reverse and thrust faulting and followed by metamorphism and/or plutonic emplacements); and

The Example of Himalayas

Himalayas display all these characteristics. Of the two peaks shown alongside, the one on the left, Mt. Annapurna, is made up of limestones (i.e., marine rocks) with ~200 Ma old Ammonite fossils. These suggest that a deep ocean then existed here. The peak shown on the right is Mt. Everest, the world’s tallest peak. It is a gneissic (a metamorphic rock) dome. As for the crustal thickness, gravity and seismic studies confirm the crust beneath the Himalayas to be <70 km, compared to 30-35 km thickness of the average continental crust (click on the picture to read about the Himalayas).

A schematic cross-section across the Nepal Himalayas (MBT: Main Boundary Thrust, MT: Mahabharat Thrust, MCT: Main Central Thrust, STDS: South Tibetan Detachment System).

Taken from "Initiation of the Himalayan Orogen as an Early Paleozoic Thin-skinned Thrust Belt" by G.F. Gehrels, P.G. DeCelles, A. Martin, T.P. Ojha, G. Pinhassi and B.N. Upreti: "GSA Today", vol. 13, no. 9, pp. 4-9 (Sept. 2003).

Collision of India and Asia (90 Ma to the present)

90 million years ago India rifted away from Madagascar and began its rapid movement northward, ultimately colliding with Asia between 55-50 million years ago. During the late Cretaceous (80 - 65 mya), India was moving at rates of more than 15 cm/year. No modern plate moves that fast. India's northward race towards Asia may be something of a plate tectonic speed record. The reason it moved so quickly was because it was attached to a large oceanic slab of lithosphere that was subducting beneath the southern margin of Asia.

As India moved northward a string of islands were created along its southeastern trailing edge. These islands form the 90 E Ridge and were generated at the Kerguelen hotspot (just southwest of Australia).

After India collided, Australia was released from Antarctica and it began to move northward towards S. E. Asia. Australia is currently in collision with Asia. In the future we can expect Australia to continue moving northward, rotating counter-clockwise as it swings past Borneo and arrives at China's doorstep.
(www.scotese.com/indianim.htm)

Rocky Mountains

Shown on the left is a view of Northern Teton Range in the Rocky Mountains. Click on this picture to visit the USGS/National Park Service website that this picture has been taken from.

Try these virtual excursions
The picture on the right shows Nanga Parbat, the fastest rising ranges in the Himalayas. Clicking on it will take you to Bob Taylor's site at the University of Leeds for a virtual excursion to the Himalayas.

Click on the picture on the right for a virtual excursion to the Alps, that on the left for sub-Alpine virtual trip, both at Bob Taylor's site at the University of Leeds.

Plate tectonics ascribes mountain building to convergent plate motions, which provide the required compressive forces in the orogenic stage, and thus distinguishes between:

the collision mountains like Alps, Himalayas and Urals, which involve the convergence of continental edges of plates; and
the cordilleran mountains like the Andes which involve the convergence of continental edge of one plate and the ocean edge of the other.

The "Wilson Cycle:

Thus, Wilson Cycle, shown below, identifies mountain building as the culmination of a process that begins with continental rifting, so completing a cycle that lasts for 250-400 Ma or longer, judging from the example of the Appalachians that probably closed a >400 Ma old version of the present Atlantic ocean.

Click here to learn more about the Wilson Cycle

A schematic cross-section across the Nepal Himalayas (MBT: Main Boundary Thrust, MT: Mahabharat Thrust, MCT: Main Central Thrust, STDS: South Tibetan Detachment System).
Taken from "Initiation of the Himalayan Orogen as an Early Paleozoic Thin-skinned Thrust Belt" by G.F. Gehrels, P.G. DeCelles, A. Martin, T.P. Ojha, G. Pinhassi and B.N. Upreti: "GSA Today", vol. 13, no. 9, pp. 4-9 (Sept. 2003).

Try these virtual excursions The picture on the right shows Nanga Parbat, the fastest rising ranges in the Himalayas. Clicking on it will take you to Bob Taylor's site at the University of Leeds for a virtual excursion to the Himalayas.

	Click on the picture on the right for a virtual excursion to the Alps, that on the left for sub-Alpine virtual trip, both at Bob Taylor's site at the University of Leeds.