Honors 1360 Planet Earth Last time: Obs : Volcanism at plate boundaries Obs : “Normal” geotherm...
-
Upload
angelica-kennedy -
Category
Documents
-
view
225 -
download
1
Transcript of Honors 1360 Planet Earth Last time: Obs : Volcanism at plate boundaries Obs : “Normal” geotherm...
Honors 1360 Planet Earth
Last time:
Obs: Volcanism at plate boundaries Obs: “Normal” geotherm < melt temperature
Hyp: Volcanism in rift zones geotherm raised by rock “rising to fill” vacated space
Hyp: Hotspots: Some volcanoes far from plate boundaries temperature raised by mantle plumes (convection)Pred: Should see “hotspot tracks” in direction of plate motion Obs: Volcanoes over 100-km depth contour of subducting slabHyp: Water released by slab lowers melt temperature
Today:• Mountain Building• Rock Cycle & Geologic Time
29 September 2008
Read for Mon: 213-241Exam Date: Oct 10
Global Elevation (Shuttle Radar Topography Mission)
Global Plate Motions
Plate Tectonics
& Mountains
Two major processes by which mountains develop:
Orogeny: At convergent plate boundaries, get: -- Thrust faulting in the near-surface -- Flow of weak crustal rocks at depth -- Isostatic response to thicker (buoyant) crust Mountains (Himalaya, Andes)
Epeirogeny: At divergent plate boundaries and continental rifts, get: -- Thinning of the crust and lithosphere -- Hot rock brought nearer the Earth’s surface -- Isostatic response to (buoyant) higher temperature rock Mountains (Basin & Range, Rio Grande Rift, mid-ocean ridges)
An easy way to tell the difference is by crustal thickness:
Orogeny: Himalayan Plateau
40 km65 km
Crust Mantle
Epeirogeny: Mid-Ocean Ridge
I. Weathering, Erosion, & Deposition
Weathering describes all the processes that break up / alter / remove rock from the surface:• Includes mechanical processes of fracturing/jointing, freeze/thaw, glacial “scraping”, plant roots;• chemical/biological processes (acids in rainwater and biological waste products)
Erosion is the transport process:• Mass-wasting, glaciation, wind and water
Deposition is the accumulation process wherever it ends up!
The Rest of the Rock Cycle:
Weathering…
Biological
Physical
Chemical
Erosion…
200,000 tons of soil removed per year, per dot
Results in Sedimentary Rocks
Note These Rocks Contain Clues to the Past!