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題名 | 澎湖火山頸中玄武岩柱狀節理多樣性之成因探討=The Origin of Diverse Columnar Joints in the Volcanic Necks on the Penghu Islands, Taiwan |
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作者 | 莊文星; 陳汝勤; 林長興; 洪清林; | 書刊名 | 經濟部中央地質調查所彙刊 |
卷期 | 20 2007.07[民96.07] |
頁次 | 頁71-99 |
分類號 | 354.1 |
關鍵詞 | 澎湖; 玄武岩; 火山頸; 柱狀節理; 多樣性; 地景; 成因探討; Volcanic neck; Basalt; Columnar jointing; Genesis; Penghu; Taiwan; |
語文 | 中文(Chinese) |
中文摘要 | 臺灣及鄰近區域依火山活動之先後順序、地體構造與地理區可劃分成西部、東部和北部三大火山區。從兩千多萬年前之中新世時代以來,中國南海之擴張方興未艾,此時在陸緣地區,形成了許多由正斷層所構成的半地塹構造。由於南海擴張所引發的熱力與裂隙作用在臺灣西部麓山帶及澎湖列島引發了一系列的火山活動。澎湖玄武岩之分布十分廣泛,除花嶼外,遍及澎湖全縣諸島嶼,保留相當完整,可說是臺灣西部火山區之代表。 柱狀節理是火山岩區所特有的地質景觀,岩漿噴出地表或貫入岩層後,溫度逐漸降低,岩體因冷卻收縮而形成柱狀節理。火山爆發時岩漿經由裂隙孔道傳輸至地表,這些通道常由岩漿凝固而成,質堅硬抗風化,故可留存甚久。澎湖員貝嶼、鳥嶼、小白沙嶼、金嶼、錠鉤嶼、頭巾嶼、貓嶼、北雞籠嶼、風櫃、虎頭山和西嶼大池--池西等地,均有典型火山頸構造之柱狀節理存在。火山頸底部基座常以一圓形小火口為中心,呈水平輻射之柱狀節理排列;而火山頸主體之柱狀節理型態,常取決於岩漿通道之口徑、溢出熔岩流厚度、岩漿組成與原始地貌等因素。 本文重點在於闡述澎湖玄武岩火山頸八大柱狀節理系統:(1)「線形岩脈狀」呈水平或微傾斜之柱狀節理(以頭巾嶼為代表);(2)「圓錐體A字形」柱狀節理(以北雞籠嶼、員貝嶼為代表);(3)「梯形塔狀」柱狀節理(以虎頭山、風櫃為代表);(4)「羽狀」柱狀節理(以鳥嶼和貓嶼為代表);(5)「百褶裙式」柱狀節理(以員貝嶼為代表);(6)「瓜皮式」柱狀節理(以西嶼池西為代表);(7)「葵花式輻射狀」柱狀節理(以金嶼和東吉嶼為代表);(8)「V字扇形」柱狀節理(以七美、員貝嶼為代表)。 構成澎湖基性熔岩火山頸地質構造之三大要件--火山頸主體、基座與低平火山口,其系列組織架構十分完整,如員貝嶼「百褶裙式」柱狀節理;鳥嶼、貓嶼「羽狀」之柱狀節理;西嶼池西「瓜皮式」柱狀節理和東吉嶼、金嶼「葵花式輻射狀」柱狀節理;這些火山頸規模雖不大,但搭配其基座所呈現於海蝕平臺上,以小火山口為中心而呈放射狀排列之水平柱狀節理,其結構與形貌之美,不但可媲美美國俄明州魔鬼塔,更可說是大自然鬼斧神工塑造火山頸之傑作。 建議內政部、澎湖縣政府與澎湖國家風景區管理處...等主管單位加快地景保育工作,早日建立完整的地景登錄,免遭人為破壞,使之成為國家級之觀光景點。亦可規劃「澎湖玄武岩」成為全國地景旅遊地標,邁向設置國家級之地質公園;「澎湖玄武岩」若結合七美島之史前古石器工廠文化遺址,與澎湖全縣的石滬漁業文化,亦可爭取列入聯合國科教文組織(UNESCO)的世界遺產(文化與自然之複合式世界遺產)名錄。 |
英文摘要 | Taiwan is located at the eastern margin of the Eurasian Plate. Formation of this island was closely related to the subduction of the Philippines Sea plate into the Eurasian plate in the north and the collistion between the Luzon are and the Asian continent to the east. Since the Cenozoic Era, intra-plate volcanism related to continental rifting has prevailed in the passive continental margin. The western foothills of Taiwan and the neighboring islets of the Penghu Islands (Penghu) were inevitably affected by such tectonic event. Therefore, volcanic eruptions of Taiwan region can be classified in northern, eastern and western provinces. Miocene volcanism prevailed in Penghu Islands, thus belonging to the Western volcanic province. The hot magma was transmitted through a conduit system or fractures to the surface during volcanic eruption. These volcanic conduits are mostly formed through the consolidation of the magma. Generally speaking, they are quite resistant to weathering processes and the well-preserved. At Ginyu (Gold isle), Liaoyu (Bird isle) and Yuanpeiyu (Scallop isle) there are either horizontal or clino to pleated-skirt geological structures specific to volcanic conduits present in the volcanic necks. A typical volcanic neck structure contains three portions: the main body, craterlet (maars) and basement in a horizontal plane with columnar jointing in a radial arrangement. The columnar joints found among the Penghu Islands are either horizontal or clino to pleated-skirts formed specific to volcanic conduits. The shapes of the columnar jointing in the volcanic necks depend upon the diameter of the passage conduit, the thickness of the emitted lava, the composition of the magma, and the topographic features of the strata underlying the site of eruption. The occurrence of volcanic necks in the Penghu Islands, is highly diversified and these volcanic necks are worthy of permanent preservation simply for tourism and educational purposes. We report eight (8) typical examples of volcanic conduits among the Penghu Islands. (1) Touchinyu: basaltic dike with horizontal to clino-columnar jointing in a tuffaceous agglomerate wall. (2) The Yuanpeiyu. Hsiyu-Taichi, Peichilongyu A-form cone shaped topographic feature with straight columnar jointing. (3) The Hutoushan and Fengkuei trapezoid tower landform also has straight columnar jointing. (4) The Niaoyu and Maoyu (Cat Isle) conduits denote the feather pinna type showing the remains of the upwelling lava flow. (5) The Yuanpeiyu conduit is a pleated-skirt configuration of columnar jointing. (6) The Chihsi-Hsiyu conduit exhibits a watermelon-peel shaped columnar jointing. (7) The Cinyu and Tungchiyu conduits present a Helianthus annuus configuration and (8) The Chimeiyu and Yuanpeiyu conduits display a radial fan shape columnar jointing basalt configuration. We suggest that they may be used as the Logos for each community of the Penghu volcanic scenic area. There outcrops wellillustrate the mechanism and genesis of such highly diverse volcanic necks and columnar jointing system in the basaltic area provide a good example for discussing the classification and genesis of volcanic conduits or volcanic necks. |
本系統之摘要資訊系依該期刊論文摘要之資訊為主。