錐狀岩板

錐狀岩板（英語：cone sheet）是一種淺成岩的火成岩侵入體，常出露在部分被侵蝕的火山雜岩中心。錐狀岩板是由較薄的傾斜岩板構成，通常只有幾米厚，形狀如同向下指向的圓錐體。 從空中看，它們通常是圓形到橢圓形。 最初被命名是在英國第三紀火山省 Ardnamurchan、Mull 和其他在中央的複合體。

錐狀岩板地點 Mingary, Ardnamurchan， Scotland

上圖錐狀岩板近觀

分佈

錐狀岩板分佈很廣，各大洲都有，分佈的地質年代從晚古生代到第三紀。岩性以淺成岩最多，深成岩亦有，包括輝綠岩 ^[1] ， 粗面岩^[2], 響岩^[3], 輝長岩^[4], 流紋岩^[5], 二長岩^[6], 鹼性玄武岩^[7],，花崗岩^[8]。

形成

錐狀岩板常與放射狀岩脈共存，兩者均屬板狀侵入岩。若在同一火山系統在，大都共享同一岩漿來源。兩者都由於岩漿的向上拱壓而造成。放射狀岩脈是侵入岩充填由張力造成的裂縫。而錐狀岩板是侵入岩充填由剪切力造成的裂縫^[9]。

圍岩結構和和區域應力場也控制侵入岩的幾何形狀^[10]。且區域應力場是隨時間變化，也受岩漿房的形狀、深度和內部壓力的控制^[11]。一些錐狀岩板（例如Ardnamurchan）是多次侵入岩形成的，每層錐狀岩板的構造形狀不同，表明來自不同的岩漿房。岩漿侵入時，先形成岩床再膨脹成岩蓋，導致上覆岩層被迫向上隆起，並引起錐形張裂。引入岩漿侵入^[12][13]。

參考文獻

1. Geldmacher, Jörg; Haase, Karsten M.; Devey, Colin W.; Garbe-Schönberg, C. Dieter (1998). "The petrogenesis of Tertiary cone-sheets in Ardnamurchan, NW Scotland: petrological and geochemical constraints on crustal contamination and partial melting". Contributions to Mineralogy and Petrology. 131 (2–3): 196–209. doi:10.1007/s004100050388.
2. Donoghue, Eleanor; Troll, Valentin R.; Harris, Chris (2010). "Fluid–Rock Interaction in the Miocene, Post-Caldera, Tejeda Intrusive Complex, Gran Canaria (Canary Islands): Insights from Mineralogy, and O- and H-Isotope Geochemistry". Journal of Petrology. 51 (10): 2149–2176. doi:10.1093/petrology/egq052.
3. Ancochea, Eumenio; Huertas, María José; Hernán, Francisco; Brändle, José Luis (2014). "A new felsic cone-sheet swarm in the Central Atlantic Islands: The cone-sheet swarm of Boa Vista (Cape Verde)". Journal of Volcanology and Geothermal Research. 274: 1–15. doi:10.1016/j.jvolgeores.2014.01.010.
4. Johnson, S. E.; Paterson, S. R.; Tate, M. C. (1999). "Structure and emplacement history of a multiple-center, cone-sheet–bearing ring complex: The Zarza Intrusive Complex, Baja California, Mexico". Geological Society of America Bulletin. 111 (4): 607–619. doi:10.1130/0016-7606(1999)111<0607:SAEHOA>2.3.CO;2.
5. Branch, C.D. (1959). Progress Report on Upper Palaeozoic Intrusions Controlled by Ring Fractures near Kidston, North Queensland (PDF). Bureau of Mineral Resources Geology and Geophysics, Department of National Development, Commonwealth of Australia.
6. Rodriguez-Losada, J.A.; Martinez-Frias, J. (2004). "The felsic complex of the Vallehermoso Caldera: interior of an ancient volcanic system (La Gomera, Canary Islands)". Journal of Volcanology and Geothermal Research. 137 (4): 261–284. doi:10.1016/j.jvolgeores.2004.05.021.
7. Geshi, N. (2005). "Structural development of dike swarms controlled by the change of magma supply rate: the cone sheets and parallel dike swarms of the Miocene Otoge igneous complex, Central Japan". Journal of Volcanology and Geothermal Research. 141 (3–4): 267–281. doi:10.1016/j.jvolgeores.2004.11.002.
8. Ahmed, F. (1977). "Petrology and Evolution of the Tehilla Igneous Complex, Sudan". Journal of Geology. 85 (3): 331–343. doi:10.1086/628303
9. Phillips, W.J.（1974）The dynamic emplacement of cone sheets, Tectonophysics,Volume 24, Issues 1–2,Pages 69-84, ISSN 0040-1951,https://doi.org/10.1016/0040-1951(74)90130-9. (https://www.sciencedirect.com/science/article/pii/0040195174901309)
10. Macdonald J.G. (1989) Cone sheets. In: Petrology. Encyclopedia of Earth Science. Springer, Boston, MA. https://doi.org/10.1007/0-387-30845-8_41
11. Galland, O., Burchardt, S., Hallot, E., Mourgues, R., and Bulois, C. (2014), Dynamics of dikes versus cone sheets in volcanic systems, J. Geophys. Res. Solid Earth, 119, 6178– 6192, doi:10.1002/2014JB011059.
12. Walter, Thomas R.; Troll, Valentin R. (2001-06-01). "Formation of caldera periphery faults: an experimental study". Bulletin of Volcanology. 63 (2): 191. doi:10.1007/s004450100135. ISSN 1432-0819.
13. Magee C.; Stevenson C.; O'Driscoll B.; Schofield N.; McDermott K. (2012). "An alternative emplacement model for the classic Ardnamurchan cone sheet swarm, NW Scotland, involving lateral magma supply via regional dykes" (PDF). Journal of Structural Geology. 44: 73–91. doi:10.1016/j.jsg.2012.08.004.