片状纹理
片状纹理（英语：Schistosity）是由变质作用产生的岩石薄层结构，使岩石很容易分裂成小于 5 至 10 毫米（0.2 至 0.4 英寸）厚的薄片[1] [2]。具片状纹理的变质岩，称为片岩。片麻岩，片状纹理发育不良，层状较厚。
形成机制
[编辑]当岩石在一个方向比在其他方向（非静水应力）被更强力压缩时，在高温下会，垂直于最大压缩方向产生片状纹理。此种构造是由于片状矿物在压力下被旋转或重结晶而形成平行的层理[3]。 片状或细长矿物最容易被重新排列，但石英或方解石也可能被选向排列[4]。
分类
[编辑]片状纹理，分为内部及外部片理，内部片理是在显微镜下，斑状变晶内的包裹体的取向排列。外部片理，为岩石中颗粒的取向排列[4]。 片状纹理亦可按应力不同而区分[5]。发育于压性断裂带内 的片状纹理产状与断层面的产状一致或 近于一致；发育于压扭性断裂带内的片状纹理产状与断层面的产状斜交；在强烈褶皱轴部岩层中发育的片状纹理 与褶皱轴面平行或大致平行，而在褶皱两翼发育的片理产状与岩层产状趋于一致[6]。
原岩成分
[编辑]形成片状纹理，岩石需要含能形成板状矿物的成分。例如，当泥岩中的粘土矿物变质为云母，形成云母片岩[7]。早期的变质作用将泥岩转化为称为板岩，是一种的细粒的变质岩，进一步变质造成细粒的千枚岩。再进一步变质，造成云母重结晶，产生中粒云母片岩。如果变质作用再进一步，会使云母片岩发生脱水反应，将片状矿物转化为长石等粒状矿物，降低片状纹理并将岩石变成片麻岩[3]。
在片岩中亦有其他片状矿物，包括绿泥石、滑石和石墨。绿泥石片岩和滑石片岩通常由超镁铁质火成岩的变质作用形成 [8][9] [10][11]。滑石片岩也可由含滑石碳酸盐岩经热液变质成而形成的[12]。石墨片岩并不常见，但是由含有丰富有机碳的沉积层变质形成的[13]。 有机碳也可能是来源于藻类[14]。 火山灰经由变质后，能形成石英白云母片岩[4]。
参考文献
[编辑]- ^ Schmid, R.; Fettes, D.; Harte, B.; Davis, E.; Desmons, J. (2007). "How to name a metamorphic rock.". Metamorphic Rocks: A Classification and Glossary of Terms: Recommendations of the International Union of Geological Sciences Subcommission on the Systematics of Metamorphic Rocks (PDF). Cambridge: Cambridge University Press. p. 7. Retrieved 28 February 2021.
- ^ Robertson, S. (1999). "BGS Rock Classification Scheme, Volume 2: Classification of metamorphic rocks" (PDF). British Geological Survey Research Report. RR 99-02: 5. Retrieved 27 February 2021.
- ^ 3.0 3.1 Blatt, Harvey; Tracy, Robert J. (1996). Petrology : igneous, sedimentary, and metamorphic (2nd ed.). New York: W.H. Freeman. p. 360. ISBN 0716724383.
- ^ 4.0 4.1 4.2 Yardley, B. W. D. (1989). An introduction to metamorphic petrology. Harlow, Essex, England: Longman Scientific & Technical. pp. 168–169. ISBN 0582300967
- ^ Wilson, G. (1982). Rock cleavage and schistosity. In: Introduction to Small~scale Geological Structures. Springer, Dordrecht. https://doi.org/10.1007/978-94-011-6838-0_6
- ^ Turner, F. J. (1948), Review of current hypotheses of origin and tectonic significance of schistosity (foliation) in metamorphic rocks, Eos Trans. AGU, 29( 4), 558– 564, doi:10.1029/TR029i004p00558.
- ^ Potter, Paul Edwin; Maynard, J. Barry; Pryor, Wayne A. (1980). Sedimentology of shale : study guide and reference source. New York: Springer-Verlag. p. 17. ISBN 0387904301.
- ^ Nokleberg, Warren J.; Jones, David L.; Silberling, Norman J. (1 October 1985). "Origin and tectonic evolution of the Maclaren and Wrangellia terranes, eastern Alaska Range, Alaska". GSA Bulletin. 96 (10): 1251–1270. Bibcode:1985GSAB...96.1251N. doi:10.1130/0016-7606(1985)96<1251:OATEOT>2.0.CO;2.
- ^ Esteban, J.J.; Cuevas, J.; Tubía, J.M.; Liati, A.; Seward, D.; Gebauer, D. (November 2007). "Timing and origin of zircon-bearing chlorite schists in the Ronda peridotites (Betic Cordilleras, Southern Spain)". Lithos. 99 (1–2): 121–135. Bibcode:2007Litho..99..121E. doi:10.1016/j.lithos.2007.06.006
- ^ Woguia, D.L.; Fagel, N.; Pirard, E.; Gourfi, A.; Ngo bidjeck, L.M.; El ouahabi, M. (June 2021). "Talc schist deposits from central Cameroon: Mineralogical and physico-chemical characterization". Journal of African Earth Sciences. 178: 104182.
- ^ Bibcode:2021JAfES.17804182W. doi:10.1016/j.jafrearsci.2021.104182. hdl:2268/258382. S2CID 233704877
- ^ Prochaska, W. (September 1989). "Geochemistry and genesis of Austrian talc deposits". Applied Geochemistry. 4 (5): 511–525. Bibcode:1989ApGC....4..511P. doi:10.1016/0883-2927(89)90008-5
- ^ Ukar, E.; Cloos, M. (April 2016). "Graphite-schist blocks in the Franciscan Mélange, San Simeon, California: Evidence of high- P metamorphism". Journal of Metamorphic Geology. 34 (3): 191–208. Bibcode:2016JMetG..34..191U. doi:10.1111/jmg.12174. S2CID 131721852
- ^ Lumpkin, B.; Stoddard, E.; Blake, D. (1994). "The Raleigh graphite schist". Geology and Field Trip Guide, Western Flank of the Raleigh Metamorphic Belt, North Carolina. Carolina Geological Society Field Trip Guidebook (PDF). Raleigh, NC: North Carolina Geological Survey. pp. 19–24. Retrieved 22 July 2021.