| 摘要: | 地調所規劃的「臺灣東北部礦產地質調查」4年期計畫，是以台灣東北部海域的火山島及海底火山區域為調查重點。本團隊工作是使用多音束水深、底拖聲納與磁力資料，並確認水層噴氣柱位置，用以調查該區地質構造、火成岩體、噴氣現象、其他熱液換質現象等相關研究。 在海底地形成果方面，109年度我們已完成高解析的1米解析度的海底地形圖資，也完成作業區域周圍的海底地形圖資整編。地形調查成果顯示基隆海底火山及其東側地形凹陷區，以及野柳線形為較明顯的地貌特徵。磁力結果顯示有一東北-西南向的磁力高區沿著可能火山位置分布，從北邊彭佳嶼、花瓶嶼到台灣本島北部高磁力異常區之間。底拖聲納調查結果顯示，區域內具有相當明顯的火成作用與熱液活動相關特徵，包含海底火山、強反射面、噴氣柱、流體通道等近海床的構造特徵。在淺部地層中，流體通道分布廣泛，水層中噴氣柱分佈密集，顯示基隆海底火山區域的熱液活動相當活躍。且根據近海床地層資料的分析結果，基隆海底火山周圍及其東側地形凹陷區可能具有熱液硫化礦物的潛能。 在110年度水深資料蒐集區域周圍的主要海底地形架構，包含有棉花峽谷、基隆海谷、基隆陸棚以及東海陸棚等。噴氣柱相當廣泛的分佈在作業區內，但是彭佳嶼、棉花嶼周邊以及棉花峽谷上卻沒有噴氣柱的分布。海底火山SV1的火山頂上有幾處噴氣柱沿著火山軸出露，軸邊兩側的坡上則都有明顯崩塌地貌，在花瓶嶼及其周圍則多為侵蝕地形，其西側及南側有SV3-SV6等4座新發現海底火山。底拖聲納結果也發現此區域具有相當明顯的火成作用與熱液活動的相關特徵，除了明顯的海底火山特徵外，且地層中具有疑似熱液作用沿地層滲入形成礦脈所出現的強反射面震測相以及疑似火成岩性質的聲波基盤。另外，噴氣柱、流體通道與斷層也出現在作業區的近海床構造特徵中。磁力異常顯示作業區的西側為磁力異常低區、東側則為相對高區。其海底火山SV1、花瓶嶼、與其他海底火山（SV3-SV6）都位於磁力異常高區，最高值則位於SV3西南處。磁化強度則呈現北低南高的趨勢，花瓶嶼、SV1和SV6位處在磁化強度中間值區域，而SV4和SV5則位在磁化強度高值處。 為了延續過去兩個年度的調查成果與此4年期計畫的目標，本（111）年度計畫將持續在花瓶嶼及其北側區域的海底火山SV2、SV7進行調查研究。預期藉由研究區域所收集的高解析聲納資料、磁力探測資料與多音束水深資料，提供詳細的海床地貌特徵、淺部地層構造，及建立磁化強度分布概況，並辨識熱液噴口的位置。且將持續進行海底地形圖資的整編，作為相關研究所需之精密海底地形圖，幫助建立東北海域基礎地質資料。綜合這些地球物理研究相關資料，可以瞭解調查區域內的火成岩體、噴氣現象、其他熱液換質現象與海床淺部地層沉積物之地質構造特徵，並推論熱液硫化礦床在地層中可能的通道。 ;The four-year project of " Geological investigation of mineral deposits off northeast Taiwan " planned by the Central Geological Survey (CGS) is to survey the volcanic features of the offshore area of northeast Taiwan. By analyzing multi-beam echo sounder, high-resolution deep-tow sonar system, magnetometer and water column signals, we will investigate the geological structures that are related to the potential areas of hydrothermal ore deposits. In 2020, we have created a 1 m grid bathymetric map. We have also compiled the bathymetric data around the investigation area. The main bathymetric features include the Keelung Submarine Volcano, a bathymetric depression area in the east and the linear structure to the east of the Yehliu Cape. Our magnetic analysis shows that there is a NE-SW trending high magnetization zone from Pengjia Islet to Mianhua Islet and northern Taiwan. According to our deep-tow sonar survey results, the volcanic and hydrothermal activities are still remarkable, including gas plumes, fluid channels and other high acoustic reflectance features in the shallow seabed. Fluid channels and gas plumes (or gas flares) in the seawater are widely distributed in our investigation area, indicating hydrothermal activity is active. Particularly, some near-surface fluid channels and strong reflectance layers are exposed to the seafloor. In 2021, the main topographic structures around the bathymetry map, collection area include Mianhua Canyon, Keelung Sea Valley, Keelung Shelf, and East China Sea continental shelf, The gas plume widely distributed in the investigation area, but there haven't been gas plume on Pengjia Islet, Mianhua Islet and the Mianhua Canyon. We observed gas plumes exposed along the axis of the volcano on the top of the submarine volcano SV1, and slump structure on the slopes both sides of the axis. There observed mostly erosional landform around Huaping Islet. The SV3-SV6 newly discovered submarine volcanoes in the west and south side area. The deep-tow sonar survey results have quite obvious characteristics related to igneous and hydrothermal activities. They are submarine volcanoes, basement（apparently igneous intrusion）, strong reflectors, gas plumes, faults and other near-surface structural features. The magnetic data shows that an obvious high magnetic anomaly in the east and low anomaly in the west is displayed in the study area. Among them, the submarine volcano SV1, Huaping Islet, and other submarine volcanoes (SV3-SV6) are all located in the anomalously high magnetic area, and the highest value is located in the southwest of SV3. However, the highest magnetic anomaly is slightly offset to the location of submarine volcanoes. The distribution of magnetization in this area shows a decreasing trend from the south to the north. Most of the submarine volcanoes and HV are located in the middle and slightly high magnitude magnetization zone. In order to follow the survey results over the past two years , the project will investigate and study the area around Huaping Islet and the submarine volcanoes SV2 and SV7 in 2022. It is expected that the high-resolution sonar data, magnetic data, and multibeam data to provide detailed seafloor morphology features, stratigraphic structure, and establish the magnetization distribution that identify the location of the hydrothermal vents. We will continue to compile the bathymetric map data that can be used to establish the basic geological data off northeast Taiwan. The integration of all the geophysical and chemical results can provide a more comprehensive information on the sedimentary features of the strata and better understand the distribution of the hydrothermal deposits and the possible fluid pathways. |
