GEOL 106 -February 27 Lecture.docx

4 Pages
Unlock Document

Queen's University
Geological Sciences and Geological Engineering
GEOL 106
John Hanes

GEOL 106: Lecture 17 February 27,2013 How can the “solid” mantle convect like a liquid?  Mantle: lithosphere + asthenosphere  Plate tectonics say that the mantle is liquid (it convects)  But, seismic studies say that the mantle is solid o Both are right o Think of the mantle as silly putty  The mantle, although solid, convects plastically  Behaves like silly putty (elastico-plastic behaviour)  With slow stress application over long geologic time, mantle is “liquid”  Rocks can flow like liquids although they are solids Theory of Plate Tectonics  1. The outer part of Earth consists of a number of rigid lithospheric plates o Plate boundaries are marked by earthquakes and volcanoes o Plates are approx. 100 thick o As though the outer 200 km is like a cracked egg shell  2. The plates slide about on the plastic asthenosphere beneath them o at rates of several cm per year (rate of fingernail growth)  3. Almost all igneous and “tectonic” (ex. Mountain building) activity is localized along plate margins Types of plate boundaries: o Constructive: pull apart like “normal dipslip faults” o Destructive: come together like “reverse dipslip faults” o Transform: slide past one another like “strike slip faults” 1. Constructive/ divergent: new plates are formed and o Upwelling part of the convective cycle o New lithospheric plates are produced and move apart o Constructs new lithospheric plates and moves apart o Convection cells go up (like silly putty – solid material acting like a liquid) o As it goes up, it melts a bit, where the lithosphere is infinitely thing, getting thicker as you move away from the crack o New ocean crust produced  If new plates pull apart, the ocean opens up bigger and bigger (i.e. Atlantic Ocean is getting bigger) o What if the hot mantle up-wells under a continent?  It can split a continent apart (ex. East Africa) o Mid-ocean ridges: World’s greatest mountain range. Underwater, there are mountain ranges along the oceans of the world seafloor in the middle of the ocean between different continents (ex. South America and Africa)  Ex. Red Sea, Mid-Atlantic Ridge (oceans open!) 2. Destructive Plate Margin  Down-going part of the convective cycle  Lithosphe
More Less

Related notes for GEOL 106

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.