RECORDS OF GEOLOGIC PROCESSES

1、ROCKS:ROCKS:RECORDS OF GEOLOGIC PROCESSES (地質作用的紀錄地質作用的紀錄)ROCKROCK, by definition, is composed of an aggregate of mineralsminerals( (原素原素) )(礦物礦物)(岩石岩石) Appearance of a rock is related to: 1. Mineralogy = types and relative proportions of constituent minerals 2. Texture = size, shape and orientation

2、 of mineral grains These features relate to the origin and history of the rock. When many rocks are understood, the geologic history (and tectonic setting) of a region can be inferred.Where do we see rocks?Where do we see rocks? Not on the surface of course! They are at depth in most places covered

3、by soil and regolith (風化層風化層).Three general rock types:1. Igneous - formed by solidification of molten rock (700 C)2. Sedimentary - formed as burial products of sediments, on land or sea3.Metamorphic - formed by transformation in the solid state of pre-existing rock due to changing pressure and temp

4、erature.(火成岩火成岩)(沉積岩沉積岩)(變質岩變質岩)Sedimentary rocks comprise a majority of the surface of the Earth, but are a minor volume of the total volume of the crust. IGNEOUS ROCKS (火成岩火成岩)Definition: A rock formed by the solidification of magma (molten rock) Igneous environmentsIGNEOUS ROCKS (火成岩火成岩) Can be i

5、ntrusive (crystallizing below the surface of the Earth) or extrusive (crystallizing at the surface of the Earth) Textures in igneous rocks relates to the composition of the magma, rate of cooling of the magma and any flow features of the magma Extrusive (噴出噴出) rocks - rapid cooling, therefore fine-g

6、rained or glassy; some surface flows Intrusive (侵入侵入) rocks - slower cooling, therefore coarser grained; flow features possible IGNEOUS ROCKS (火成岩火成岩)SEDIMENTARY ROCKS (沉積岩沉積岩)Definition: A rock formed by the accumulation and cementation of mineral grains by wind, water or ice transportation to the

7、site of deposition, or by chemical precipitation at the site.Typical sedimentary depositional environments Sedimentary rocks - generally characterized by bedding i.e. parallel layers of sediments Textures of sedimentary rocks relate to the manner of sediment transport and deposition e.g. high vs. lo

8、w velocity transport This is an interface between the atmosphere, hydrosphere and lithosphere. SEDIMENTARY ROCKS (沉積岩沉積岩) Types:1. Clastic - physically deposited sedimentary particles (clasts - broken rocks, remains or products of animals or plants) transported and laid down by running water, wind o

9、r ice. Generally silicate minerals.2. Chemical and biochemical sediments -chemical precipitation of dissolved components of rocks at the depositional site e.g. halite, calcite3. Mixtures of both of the above Lithification of sedimentary rocks hardening into a solid rock due to compaction and cementa

10、tionMETAMORPHIC ROCKS (變質岩變質岩)Definition: A rock whose original mineralogy, texture, or composition has been changed by the effects of pressure, temperature, or the gain or loss of chemical components. Occurs between temperatures of roughly 250 C (end of sedimentary lithification processes) and melt

11、ing of the rock (700 C)Contact and regional metamorphism at plate-collisional mountain rangesBurial metamorphism in deep sedimentary rocksCataclastic metamorphism along faultsHydrothermal metamorphism at mid-oceanic ridgesContact and regional metamorphism at subduction zonesMETAMORPHIC ROCKS(變質岩變質岩)

12、 General classification of type of metamorphism relates to location of heat source1. Regional metamorphism - heat source in not apparent, but generally higher; associated with mountain building episodes extending over large regions2. Contact metamorphism - heat source is apparent i.e. associated wit

13、h intrusion of a magma that cooks the surrounding rocks Textures relate to the pressure, temperature and deformational history of metamorphic rockMetamorphic environmentsTHE ROCK CYCLE (岩石循環岩石循環) Inter-relationships among the three rock types The rock cycle is directly related to plate tectonics (板板塊構造塊構造) - in turn, the rocks that we currently see can infer tectonic conditions in the past. This is an interaction among the atmosphere, hydrosphere, lithosphere and asthenosphere (the mantle layer)