片狀紋理
片狀紋理（英語：Schistosity）是由變質作用產生的岩石薄層結構，使岩石很容易分裂成小於 5 至 10 毫米（0.2 至 0.4 英寸）厚的薄片[1] [2]。具片狀紋理的變質岩，稱爲片岩。片麻岩，片狀紋理發育不良，層狀較厚。
形成機制
[編輯]當岩石在一個方向比在其他方向（非靜水應力）被更強力壓縮時，在高溫下會，垂直於最大壓縮方向產生片狀紋理。此種構造是由於片狀礦物在壓力下被旋轉或重結晶而形成平行的層理[3]。 片狀或細長礦物最容易被重新排列，但石英或方解石也可能被選向排列[4]。
分類
[編輯]片狀紋理，分為內部及外部片理，內部片理是在顯微鏡下，斑狀變晶內的包裹體的取向排列。外部片理，為岩石中顆粒的取向排列[4]。 片狀紋理亦可按應力不同而區分[5]。發育於壓性斷裂帶內 的片狀紋理產狀與斷層面的產狀一致或 近於一致；發育於壓扭性斷裂帶內的片狀紋理產狀與斷層面的產狀斜交；在強烈褶皺軸部岩層中發育的片狀紋理 與褶皺軸面平行或大致平行，而在褶皺兩翼發育的片理產狀與岩層產狀趨於一致[6]。
原岩成分
[編輯]形成片狀紋理，岩石需要含能形成板狀礦物的成分。例如，當泥岩中的粘土礦物變質為雲母，形成雲母片岩[7]。早期的變質作用將泥岩轉化為稱為板岩，是一種的細粒的變質岩，進一步變質造成細粒的千枚岩。再進一步變質，造成雲母重結晶，產生中粒雲母片岩。如果變質作用再進一步，會使雲母片岩發生脫水反應，將片狀礦物轉化為長石等粒狀礦物，降低片狀紋理並將岩石變成片麻岩[3]。
在片岩中亦有其他片狀礦物，包括綠泥石、滑石和石墨。綠泥石片岩和滑石片岩通常由超鎂鐵質火成岩的變質作用形成 [8][9] [10][11]。滑石片岩也可由含滑石碳酸鹽岩經熱液變質成而形成的[12]。石墨片岩並不常見，但是由含有豐富有機碳的沉積層變質形成的[13]。 有機碳也可能是來源於藻類[14]。 火山灰經由變質後，能形成石英白雲母片岩[4]。
參考文獻
[編輯]- ^ 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.