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| 題名: | 臺灣金門太武山近期閃電熔岩之礦物、微觀構造及化學特徵;The mineralogical, microstructural, and chemical characteristics of Recently Formed Fulgurite in Kinmen, Taiwan |
| 作者: | 孟婷茹;Meng, Ting-Ju |
| 貢獻者: | 地球科學學系 |
| 關鍵詞: | 閃電熔岩;花崗片麻岩;金門;太武山;閃電 |
| 日期: | 2020-07-24 |
| 上傳時間: | 2020-09-02 15:36:56 (UTC+8) |
| 出版者: | 國立中央大學 |
| 摘要: | 雲對地閃電(簡稱對地雷)是常見的自然現象，其所夾帶的高能電流及高壓的衝擊波多會對鑿擊地面造成影響。現有文獻說明，對地雷鑿擊到地表，會產生高溫並形成閃電熔岩。對地雷鑿擊之地點(材料)不同，會產生不同型態的閃電熔岩。目前相關的文獻報導，多以鬆散物質(泥或沙)為源之閃電熔岩，以岩石為源之閃電熔岩報導非常稀少。本研究將提供花崗片麻岩質的閃電熔岩特徵，闡述閃電作用對岩石產生之作用。天氣風險公司的觀測資料顯示於民國107年5月7日發生對地雷事件，其閃電的電流峰值高達162 kA，落點位置在金門縣太武山地區，該區為太武山花崗片麻岩。在野外有兩個明顯的雷擊點，推測為此次閃電事件造成，並看到表面有類似燒灼過的痕跡。我們對閃電熔岩使用傳統及同步輻射X光繞射儀、偏光顯微鏡、拉曼光譜儀、場發射掃描式電子顯微鏡、穿透式電子顯微鏡進行分析，以及建立閃電能量模型。結果顯示，閃電熔岩具有一層具孔隙的深黑至棕黑薄玻璃層蓋在原岩之上或是充填裂隙中，且熔岩的表面有些尖角(不利保存)，成分也非常不均質，這說明閃電熔岩是近期形成的高溫瞬時事件(時間太久會產生風化而消失)。本研究也發現長石有平面狀特徵，表示該熔岩在具高壓的衝擊波下形成。此外，玻璃層中有發現碳及還原態的鐵，暗示閃電在燒融的過程成造成還原反應，與前述文獻相符合。另外，在閃電熔岩上有硫氧化物的存在，例如：黃鉀鐵礬類、石膏及重晶石等，說明形成後富含鐵及硫的玻璃層提供其所需元素，並與水(降雨)產生反應並藉其分布可知雨水當時的分布。在能量模型中，本研究依據此次的閃電事件的能量計算約會產生3.40至376.30平方米面積（形成厚度50微米的玻璃層），而在野外的燒灼總面積（約為9.5平方米）若是以閃電總能量消散1%來看，其理論值遠大於觀察所得，這暗示許多能量可能藉由閃電通道影響到更遠或是更深的地方。本研究獲得之岩石閃電熔岩特徵(花崗片麻岩與花崗岩)，可供日後岩石閃電熔岩之相關研究參考。;Cloud-to-ground lightning (CG lightning) is a common natural phenomenon which comes up with high energetic current and high pressure shock wave, and will form the associated geological evidence including melting and shock lamella on rocks, termed fulgurites. Because lightning strikes on different protolith. Our CG lightning event took place on granitic gneiss in Kimen county, Taiwan, on May. 7th, 2018. In the field, we found two strike points which are done by one lightning event. In our research, we used microanalytical methods including optical microscope, Field-Emission Scanning Electron Microscope (FESEM), Transmission Electron Microscope (TEM), regular and synchrotron X-ray Diffraction (XRD), and Raman spectroscope, and built an energetic model of lightning. Our results show the fulgurites were characterized with a black-to-brown, roughly thin, and heterogeneous glassy crust with some vesicles covering on the host rock or injecting to cracks. Planar fractures derived from high pressures (up to several GPa) were found in k-feldspars suggesting the presence of shock waves. Also, we found some carbon and high reduced-state iron indicate that lightning made some reduction during the melting. Jarosite groups, were recognized to locally deposit on fulgurites, likely suggesting the presence of hydrothermal condition in near-surface exposures after the cessation of the CG lightning. These features which are easier to be weathered and disappear implies the fulgurites are formed recently by a high temperature and transient event. In addition, comparing the modelling result with the field observation (~9.5 m2 in area with the thickness of 50 μm), latter is much less than the former. Our study establishes a reference rock fulgurites data originated from CG lighting on granitic rocks set for future on-site drilling and presents an application of these data for studies of ancient rock fulgurite relicts. |
| 顯示於類別: | [地球物理研究所] 博碩士論文
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