Lecture 4 Summary and Notes

Important concepts for the day...

1. Metamorphic rocks rocks are, by definition, rocks in which mineralogical changes have occurred in response to changes in pressure, temperature, or transient fluids. Pressure and temperature increase together with increasing depth and the temperature range at which metamorphic rocks form varies from either 150 or 200 degrees Celsius (depending on the author) to between 700 and 1400 degrees Celsius (depending on the rock type present and the pressure). Below the arbitrary 150 or 200 degrees Celsius, reactions and their resultant minerals and rocks are considered to be sedimentary (diagenetic) and above 700 degrees, rocks start to melt. The amount (high vs. low) of pressure is important as is the nature of that pressure (lithostatic vs. differential) since rocks that are deformed in the presence of differential pressure (sigma 1 >> sigma 2 > sigma 3) develop foliation (a planar arrangement of the minerals in 3-D space).

2. Most of the time when metamorphic rocks are discussed, we envision a system that is closed at the handsample (sub-meter) scale. An important consideration for metamorphic processes that concentrate MSI is that water-rich (hydrothermal) fluids can import and export elements to or from a system in a process that is called metasomatism.

3. Continental drift is the concept that the Earth's continents have moved (and are moving) throughout Earth's history both with respect to one another and with respect to the underlying mantle asthenosphere.

4. This movement of continents is achieved through plate tectonics. Plate tectonics is commonly referred to as the "unifying theory of geology" because it is useful in explaining so many geologic phenomena.

5. Plate boundaries are defined by the relative motion between plates (convergent, divergent, or transform) and the "tectonic setting" of an area describes a location with respect to a plate and its boundaries.

6. In order to be able to predict the distribution of some types of MSI (particularly fossil fuels) at the global level, it is important to understand not only the present tectonic setting of an area and the modern processes that are affecting it but also how the tectonic setting and location of the area has changed throughout time.

Wednesday, we will begin our discussion with a look at how the position of the continents has changed through Earth's history before moving onto how hydrocarbon reservoirs form. Slides from lecture today are posted on the course Sakai site. The readings assignments for Wednesday can be found in Friday's lecture summary.