白片岩

白片岩（英語：whiteschist）是一種少見的變質岩，在高壓到超高壓下形成。它特徵礦物是藍晶石 + 滑石的組合，這造成其為白色的原因。該名稱是由德國礦物學家和岩石學家 Werner Schreyer於 1973 年命名的^[1] 。這種岩石的形成與泥質岩、蒸發岩，變質玄武岩或長英質侵入岩體的變質有關^[2] ^[3] ^[4] 。白片岩在 MgO–Fe2O3–Al2O3–SiO2–H2O (MFASH) 系統中形成^[5]。具有這種主要化學成分的岩石非常稀有，大多是經由交代變質作用，去除了各種移動元素所造成的^[3]。

分佈

現在世界各地的九個造山帶中，已發現白片岩以透鏡體或構造板片的岩體，大小尺度從米到千米。中非有兩處，一處在塔斯馬尼亞，一處在挪威喀裡多尼德，兩處在阿爾卑斯山，三處在亞洲^[3]^[6] .最廣泛的白片岩露頭在 Lufilian Arc - Zambezi Belt 造山帶內。這個西北-東南走向的地帶延伸約 700 公里。白片岩與含有直閃石(anthophyllite)-堇青石-藍晶石和石榴石-十字石-藍晶石組合的岩石共生^[7]。最初白片岩被認為是變質沉積岩的蒸發岩或膨潤土。現在已認定白片岩是從原岩為變玄武岩到花崗岩變質產物^[3]。

形成

白片岩的化學成分很少作為岩石的主要成分出現。這指出它們只能在其他化學成分已被大規模交代變質作用去除，在強烈改變原始岩石成分的條件下形成。可去除的移動組分包括Na2O、CaO、K2O、MnO、P2O5、Rb、Ba、Th。白片岩的另一個特徵是鐵和錳僅以最高的氧化態出現，這指出交代變質作用的流體具有高氧逸度的特徵。它們形成過程中涉及的主要反應是：

鎂-綠泥石+ 石英 → 滑石 + 藍晶石

這反應已被用來定義白片岩組合的穩定性^[3]。

但在一個角閃岩中的變質反應為：

金雲母 + 角閃石 +斜長石 → 藍晶石 +滑石 + 石英 + Fe（赤鐵礦）+ Na、Ca、K、Mn（流體）

這就指出原始反應不能完全代表，在高氧逸度條件下，藍晶石 + 滑石組合的完整穩定性範圍^[3]。

參考文獻

^ Schreyer, W. (1973). "Whiteschist: a high-pressure rock and its geologic significance". The Journal of Geology. 81 (6): 735–739. Bibcode:1973JG.....81..735S. doi:10.1086/627926. JSTOR 30059001. S2CID 128944616.
^ Schreyer, W.; Abraham K. (1976). "Three-Stage Metamorphic History of a Whiteschist from Sar e Sang, Afghanistan, as Part of a Former Evaporite Deposit". Contributions to Mineralogy and Petrology. Springer-Verlag. 59 (2): 111–130. Bibcode:1976CoMP...59..111S. doi:10.1007/BF00371302. S2CID 129384880.
^ ^3.0 ^3.1 ^3.2 ^3.3 ^3.4 ^3.5 Johnson, J. "Preliminary investigation of in-situ, high-pressure, high-ƒO2 metasomatism and metamorphism of meta-basalt to whiteschist" (PDF). Frontier Research on Earth Evolution. 1. Retrieved 21 December 2011.
^ Rolfo, F.; Compagnoni R.; Xu S.; Jiang L. (2000). "First report of felsic whiteschist in the ultrahigh-pressure metamorphic belt of Dabie Shan, China". European Journal of Mineralogy. 12 (4): 883–898. doi:10.1127/0935-1221/2000/0012-0883. Retrieved 21 December 2011.
^ Wyllie, P.J. (1992). "Experimental petrology: Earth materials science". In Brown G., Hawkesworth C. & Wilson C. (ed.). Understanding the Earth (2 ed.). Cambridge University Press. pp. 82–84. ISBN 978-0-521-42740-1. Retrieved 21 December 2011.
^ Schreyer, W. (1977). "Whiteschists: Their compositions and pressure-temperature regimes based on experimental, field, and petrographic evidence". Tectonophysics. Elsevier. 43 (1–2): 127–144. Bibcode:1977Tectp..43..127S. doi:10.1016/0040-1951(77)90009-9.
^ John, T.; Schenk V.; Mezger K.; Tembo F. (2004). "Timing and PT evolution of whiteschist metamorphism in the Lufilian Arc-Zambezi Belt orogen (Zambia): Implications for the assembly of Gondwana". The Journal of Geology. 112 (1): 71–90. Bibcode:2004JG....112...71J. doi:10.1086/379693. S2CID 73549945. Retrieved 21 December 2011.

[”1”-1] Schreyer, W. (1973). "Whiteschist: a high-pressure rock and its geologic significance". The Journal of Geology. 81 (6): 735–739. Bibcode:1973JG.....81..735S. doi:10.1086/627926. JSTOR 30059001. S2CID 128944616.

[”2”-2] Schreyer, W.; Abraham K. (1976). "Three-Stage Metamorphic History of a Whiteschist from Sar e Sang, Afghanistan, as Part of a Former Evaporite Deposit". Contributions to Mineralogy and Petrology. Springer-Verlag. 59 (2): 111–130. Bibcode:1976CoMP...59..111S. doi:10.1007/BF00371302. S2CID 129384880.

[”3”-3] 3.0 ^3.1 ^3.2 ^3.3 ^3.4 ^3.5 Johnson, J. "Preliminary investigation of in-situ, high-pressure, high-ƒO2 metasomatism and metamorphism of meta-basalt to whiteschist" (PDF). Frontier Research on Earth Evolution. 1. Retrieved 21 December 2011.

[”4”-4] Rolfo, F.; Compagnoni R.; Xu S.; Jiang L. (2000). "First report of felsic whiteschist in the ultrahigh-pressure metamorphic belt of Dabie Shan, China". European Journal of Mineralogy. 12 (4): 883–898. doi:10.1127/0935-1221/2000/0012-0883. Retrieved 21 December 2011.

[”5”-5] Wyllie, P.J. (1992). "Experimental petrology: Earth materials science". In Brown G., Hawkesworth C. & Wilson C. (ed.). Understanding the Earth (2 ed.). Cambridge University Press. pp. 82–84. ISBN 978-0-521-42740-1. Retrieved 21 December 2011.

[”6”-6] Schreyer, W. (1977). "Whiteschists: Their compositions and pressure-temperature regimes based on experimental, field, and petrographic evidence". Tectonophysics. Elsevier. 43 (1–2): 127–144. Bibcode:1977Tectp..43..127S. doi:10.1016/0040-1951(77)90009-9.

[”7”-7] John, T.; Schenk V.; Mezger K.; Tembo F. (2004). "Timing and PT evolution of whiteschist metamorphism in the Lufilian Arc-Zambezi Belt orogen (Zambia): Implications for the assembly of Gondwana". The Journal of Geology. 112 (1): 71–90. Bibcode:2004JG....112...71J. doi:10.1086/379693. S2CID 73549945. Retrieved 21 December 2011.

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