第一章变质作用及一些基本概念

1、 变质结晶作用变质结晶作用(Metamorphic crystallization )Figure 23-10. a. Dihedral angle between two mineral types. When the A-A grain boundary energy is greater than for A-B, the angle will decrease (b) so as to increase the relative area of A-B boundaries. Winter (2001) An Introduction to Igneous and Metamorphi

2、c Petrology. Prentice Hall. c. Sketch of a plagioclase (light)-clinopyroxene (dark) hornfels showing lower dihedral angles in clinopyroxene at most cpx-plag-plag boundaries. (c. from Vernon, 1976) Metamorphic Processes: Reactions and Microstructure Development. Allen & Unwin, London. c. Metamorp

3、hic differentiation成分层是强烈压扁的结果成分层是强烈压扁的结果Figure 1-9. Estimated ranges of oceanic and continental steady-state geotherms to a depth of 100 km using upper and lower limits based on heat flows measured near the surface. After Sclater et al. (1980), Earth. Rev. Geophys. Space Sci., 18, 269-311. Figure 2

4、1-4. A situation in which lithostatic pressure (Plith) exerted by the mineral grains is greater than the intergranular fluid pressure (Pfluid). At a depth around 10 km (or T around 300oC) minerals begin to yield or dissolve at the contact points and shift toward or precipitate in the fluid-filled ar

5、eas, allowing the rock to compress. The decreased volume of the pore spaces will raise Pfluid until it equals Plith. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.Figure 21-2. The three main types of deviatoric stress with an example of possible resulting structur

6、es. a. Tension, in which one stress in negative. “Tension fractures” may open normal to the extension direction and become filled with mineral precipitates. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.Figure 21-2. The three main types of deviatoric stress with a

7、n example of possible resulting structures. b. Compression, causing flattening or folding. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.Figure 21-2. The three main types of deviatoric stress with an example of possible resulting structures. b. Shear, causing slip

8、 along parallel planes and rotation. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.Figure 21-3. Flattening of a ductile homogeneous sphere (a) containing randomly oriented flat disks or flakes. In (b), the matrix flows with progressive flattening, and the flakes a

9、re rotated toward parallelism normal to the predominant stress. Winter (2001) An Introduction to Igneous and Metamorphic Petrology. Prentice Hall.构造超压构造超压(tectonic overpressure)：平均应力与负荷压力之差平均应力与负荷压力之差(0.1GPa).流体超压流体超压(fluid overpressure)：流体压力与负荷压力之差流体压力与负荷压力之差(0.1GPa).平均应力平均应力(mean stress)：(A+B)/2总压

10、力：总压力：P= P1+构造超压构造超压+流体超压流体超压进变质进变质(prograde metamorphism)：岩石在热峰前温度随时间而增加过程中发生岩石在热峰前温度随时间而增加过程中发生的变质结晶作用。的变质结晶作用。递增变质递增变质(progressive metamorphism)：一个变质地区地表一定方向热峰温度连一个变质地区地表一定方向热峰温度连续有规律地增加的变质作用。续有规律地增加的变质作用。变质级别变质级别增加增加Figure 21-14. Geologic Map and cross-section of the area around the Skiddaw gran

11、ite, Lake District, UK. After Eastwood et al (1968). Geology of the Country around Cockermouth and Caldbeck. Explanation accompanying the 1-inch Geological Sheet 23, New Series. Institute of Geological Sciences. London. Figure 21-17. Idealized N-S cross section (not to scale) through the quartz monz

12、onite and the aureole at Crestmore, CA. From Burnham (1959) Geol. Soc. Amer. Bull., 70, 879-920. s大小大小s形状形状s方向方向s温度温度s组分组分Schematic cross section across fault zones. After Mason (1978)Shatter cones in limestone from the Haughton Structure, Northwest Territories. Photograph courtesy Richard Grieve, N

13、atural Resources Canada.High Strain RocksProgressive mylonitization of a granite. From Shelton (1966). Geology Illustrated. Photos courtesy John Shelton.High Strain RocksAmguid crater with a diameter 0.45Km and less 0.1Ma, AlgeriaWorld Impact StructuresFigure 21-6. Schematic model for the sequential

14、 (a c) development of a “Cordilleran-type” or active continental margin orogen. The dashed and black layers on the right represent the basaltic and gabbroic layers of the oceanic crust. From Dewey and Bird (1970) J. Geophys. Res., 75, 2625-2647; and Miyashiro et al. (1979) Orogeny. John Wiley &

15、Sons. Figure 21-8. Regional metamorphic map of the Scottish Highlands, showing the zones of minerals that develop with increasing metamorphic grade. From Gillen (1982) Metamorphic Geology. An Introduction to Tectonic and Metamorphic Processes. George Allen & Unwin. London. (2) 洋底变质作用洋底变质作用洋底变质作用

16、形成于大洋板块和洋中脊区域洋底变质作用形成于大洋板块和洋中脊区域 玄武岩变质形成角闪岩玄武岩变质形成角闪岩(amphibolite)和绿岩和绿岩 (greenstone). 这些岩石是含水的这些岩石是含水的.After Minster et al. (1974) Geophys. J. Roy. Astr. Soc., 36, 541-576. The Mid-Ocean Ridge SystemTopic 1Section X-Y shows more detailFigure 21-10. Geologic sketch map of the South Island of New Zealand showing the Mesozoic metamorphic rocks east of the older Tasman Belt and the Alpine Fault. The Torlese Group is metamorphosed predominantly in the prehnite-pumpellyite zone, and the Otago Schist in higher grade zones. X-Y is the Haast River Section of Figur