類別:http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/602026-03-06T20:12:56Z2026-03-06T20:12:56Z龜山島高鎂安山岩之岩漿成因Chiu-Hong Chu朱秋紅http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/367422021-06-13T08:13:44Z2005-01-01T00:00:00Z標題: 龜山島高鎂安山岩之岩漿成因; Generation of high-Mg andesites in the Kueishantao volcano, the southernmost part of the Okinawa Trough
作者: Chiu-Hong Chu; 朱秋紅
摘要: 菲律賓海板塊以每年大約七公分的速度向西北方隱沒至歐亞大陸板塊下方，形成了琉球島弧及沖繩海槽弧後盆地，根據Chung et al. (2000) 的研究，沖繩海槽最南部分 (Southernmost Part of Okinawa Trough, SPOT) 不是一般認定的單純的弧後盆地，因此有島弧火山噴發所造成的龜山島座落其中。過去傳統上將龜山島火山岩歸類為典型的島弧鈣鹼系列安山岩 (SiO2 ≈ 60 wt.%) ，但本研究顯示若干岩樣的鎂含量較高 (MgO ≥ 5 wt.%) ，可視為高鎂安山岩，本研究中擬利用詳細的地球化學資料結合地球物理證據，探討此種岩石的成因。在微量元素組成上，龜山島高鎂安山岩具有富集的大離子岩石圈 (Cs,Rb,Ba) 、釷、鈾及鉛等元素，以及虧損的高場力鍵結元素 (Nb,Ta,Ti) ，與世界其他地區的島弧岩漿顯示相似的特性；此外，它們的主量和微量元素成份和Rudnick and Fountain (1995) 所提出的平均大陸地殼的組成近乎相同。在同位素組成上，龜山島高鎂安山岩具有低的釹同位素 (εNd ≈ –4.3 〜 –5.0)、高的鍶同位素 (87Sr/86Sr ≈ 0.706) 及鉛同位素比值 (206Pb/204Pb ≈ 18.76, 207Pb/204Pb ≈ 15.69, 208Pb/204Pb ≈ 39.06)，似乎反映了明顯的大陸地殼訊號。然而，歸納以上所有地球化學資料，本研究發現龜山島高鎂安山岩無法利用傳統上認為的基性岩漿的結晶分異加上地殼混染 (AFC) 模式解釋，而更可能是由隱沒的菲律賓海洋板塊加上沉積物熔融所形成。地球化學模擬計算結果顯示的岩漿成因過程為：隱沒的沉積物及海板塊分別發生部份熔融，這兩種岩漿以大約1：1的比率混合後，再與地幔楔以9：1的比率發生岩漿─地幔楔交互作用，即可造成龜山島高鎂安山岩。這樣的岩漿成因模式需要一個特殊的熱源，可能與SPOT的地體環境有關；而地震層析成像研究報導，在本地區隱沒帶的四十公里深處有一個明顯的低速區，與本研究所推測的部份熔融作用吻合。; Kueishantao is an emerged volcanic islet located at the western end of the Southernmost Part of Okinawa Trough (SPOT). The Okinawa Trough, extending from SW Kyushu, Japan to NE Taiwan, is widely regarded as a backarc basin that is built behind the Ryukyu arc-trench system owing to subduction of the Philippine Sea plate underneath the Eurasian plate. The SPOT, however, is not a simple backarc basin but an embryonic rift zone in which early arc volcanism occurs as a result of the Ryukyu subduction. The Kueishantao is one of such volcanoes thus formed in the SPOT and consists mainly of andesitic lava flows dated to be ~7000 yr old. In this study, we report whole rock major and trace element, and Sr-Nd-Pb isotope compositions of the Kueishantao andesites. The results indicate that some of the samples have unexpectedly high magnesium, with MgO ≥ 5 wt.% and Mg# > 0.5, relative to their silica contents (SiO2 ≈ 60 wt.%), which allow them to be coined as high-Mg andesites (HMAs). In the incompatible element variation diagram, these Kueishantao HMAs exhibit enrichments in the large ion lithophile elements and Th, U and Pb, and depletions in the high field strength elements, features typical of arc lavas from the Ryukyu subduction zone as well as convergent margins worldwide. More interestingly, their overall geochemical compositions are very similar to those of the mean continental crust proposed by Rudnick and Fountain (1995). The Kueishantao HMAs have uniform isotope compositions, with low εNd (–4.3 to –5.0), high Sr (87Sr/86Sr ≈ 0.706) and Pb (18.76, 15.69 and 39.06 of 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb, respectively) ratios. Such “continental” isotopic signatures have led previous workers to argue significant crustal contamination during magma ascent as a major petrogenetic process, but our evaluation shows that this simple binary mixing model fails to explain their geochemical and Pb isotope systematics. We propose, instead, that the Kueishantao HMAs result from partial melting of the altered Philippime sea crust and overlying subducting sediments, followed by a melt-mantle wedge interaction. This interpretation is in consistency with seismic tomographic data beneath the SPOT area characterized by a complex collision/extension/subduction tectonic context off NE Taiwan.2005-01-01T00:00:00Z龜山島火山岩之岩漿演化及其構造上的隱示Ching-Lung Chiu邱清龍http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/305772021-06-13T02:09:17Z2007-01-01T00:00:00Z標題: 龜山島火山岩之岩漿演化及其構造上的隱示; Magmatic Evolution of Volcanic Rocks in Kueishantao and
Its Tectonic Implication
作者: Ching-Lung Chiu; 邱清龍
摘要: 龜山島位於沖繩海槽最西南端，是北台灣最年輕的火山，其最後一次噴發年代約為7 ka (Chen et al., 2001)。朱秋紅（2005）將MgO＞5 wt.%的龜山島火山岩視為高鎂安山岩。然而，典型的高鎂安山岩（Crawford et al.,1989; Tatsumi and Maruyama,1989; Tatsumi and Hanyu, 2003），如：玻安岩（Boninites）及瀨戶內海高鎂安山岩（Setouchi HMAs），兩者的氧化鎂、鎳和鉻含量均較龜山島高鎂安山岩高，且龜山島火山所處的地體環境是否能提供高鎂安山岩的形成，仍有待商榷，故將龜山島含鎂量較高的火山岩歸類為高鎂安山岩可能較不適當。因此，筆者根據氧化鎂的含量，將龜山島火山岩可劃分成兩群：I型安山岩（MgO＜4.5wt.%）及II型安山岩（MgO＞4.5wt.%）。I型安山岩分布於岩層的下半部，II型安山岩則分布在岩層的上半部，顯示龜山島的岩漿性質由早期的正常島弧岩漿轉變為後期具有較高MgO含量的岩漿。從微量元素分析結果顯示，除了II型安山岩具有較高之鎳（Ni）、鉻（Cr）含量外，其餘微量元素含量大致皆與I型安山岩相近。I型安山岩和II型安山岩的隕石標準化稀土元素分布圖（REE Pattern）和整體不相容元素分布圖（Spidergram）均具有極相似的型態，均呈現銪(Eu)元素負異常、富集的輕稀土元素(LREE) 和大離子岩石圈元素(LILE)，以及虧損的高場力元素(Ti, Nb, Ta)。另外，從龜山島鑽井岩芯觀察結果顯示，上半部岩層具有較多的上部地殼之捕獲岩，而下半部岩層則含有較少之捕獲岩，意味著II型安山岩可能受到相當程度的地殼混染作用，而I型安山岩則可能僅受輕微地殼混染作用的影響。本研究利用地殼混染（crustal contamination）及結晶分化（fractional crystallization）的觀念，配合龜山島地區的大地構造資料，建立龜山島火山岩的岩漿演化模式： 1. I型安山岩可能由玄武岩質岩漿經歷約45%的結晶分化作用而成； 2. II型安山岩則因受到南沖繩海槽擴張的影響，玄武岩質岩漿可快速上升，岩漿因而僅受輕微的結晶分化作用，並且在上升的過程捕獲上部地殼物質，受到約15∼25%的地殼混染作用，如此可形成II型安山岩。; Kueishantao (KST) is a young volcanic island located at the southernmost part of the Okinawa Trough. It is mainly composed of andesitic lava flows and pyroclastic flows. Based on major-element geochemistry, KST andesites can be divided into two subgroups, in which Type I Andesites are defined as possessing lower MgO and SiO2, and Type II Andesites possessing higher MgO and SiO2. In general, both of them reveal similar trace-element compositions except that Type II Andesites exhibit high Ni and Cr contents. In primitive-mantle-normalized incompatible element diagram and chondrite-normalized REE pattern, Type I and II Andesites have highly similar patterns. They are characterized by enrichment of large ion lithophile elements (LILEs) and Th, U and Pb, and depletion of high field strength elements (HFSEs). Type I Andesites are in the lower part of core, and Type II Andesites are distributed in the topper part, indicating that KST magmatic evolution from low MgO magmas transferring into high MgO magmas.
The amount of xenoliths in the drill cores increases from the bottom to the top, inferring that the degree of crustal contamination increases progressively. Base on the combination of results of chemical analyses, isotopic compositions and petrographic observation, we propose that magmatic evolution of KST is as follows. Firstly, Type I Andesites were produced by about 45% fractional crystallization of basaltic magmas, which were derived from melting of the mantle wedge induced by hydrous fluids released during dehydration reactions in the subducting Philippine oceanic lithosphere, prior to the opening of the southern Okinawa Trough. Secondly, as a result of the opening of the Okinawa Trough, quick ascending of magma may shorten its storage time in magma chamber and experienced less fractional crystallization. Finally, magma assimilated the continental crust materials (about 15-25%) during it ascended through the upper continental crust and then produced Type II Andesites.2007-01-01T00:00:00Z龍門山斷層帶南段天全河沿岸河階的活動構造特性研究Yuan-Min Cai蔡原閔http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/37622021-05-13T08:36:32Z2016-01-01T00:00:00Z標題: 龍門山斷層帶南段天全河沿岸河階的活動構造特性研究; Active tectonic characteristics of river terraces along the Tianquan River, southern Longmenshan fault zone, China
作者: Yuan-Min Cai; 蔡原閔
摘要: 龍門山斷層帶位於中國青藏高原與四川盆地之間，這個交界帶一直以來都被地質學家認為是構造活躍的區域，並且在近年來發生了兩起重大的地震。首先是2008年發生在龍門山斷層帶北段的汶川地震，此次的地震在地表上有大規模的破裂帶與錯移。五年後，發生在龍門山斷層帶南段的蘆山地震，卻沒有明顯的地表破裂。蘆山地震發生前，地質學家對這個區域的活動構造研究較少，所以到目前為止，蘆山地震究竟是由哪一條斷層所造成，還是有其爭議。
本研究利用構造地形學的方法，研究龍門山斷層帶南段河階之特性、年代與成因，來推測此地區的構造發育與其影響因素。首先藉由數值地形模型，調查蘆山地震區域的河階分布狀況，在天全河沿岸的天全及始陽兩個城市，發現有大規模階地群的分布。經由野外調查及測量之後發現，兩地的河階均僅有約1-3公尺厚的沉積層蓋在砂頁岩互層的底岩之上，沉積層中主要為與現今河道中大小及來源相似的礫石。透過利用RTK-GPS測量階地與河道之坡度，發現兩者的坡度相似。這些證據均顯示兩地的河階可能屬於被構造所抬升的底岩型河階。此外，RTK-GPS的河階測量數據搭配DEM的分析，可以更有效判斷兩地的河階邊界與階面，結果顯示天全縣河階數約有4階，而始陽鎮則多達11階。本研究並利用天全縣河階的定年結果，計算Terrace 1形成後區域的下切速率約為介於1-2 mm/year，這個速率相似於龍門山斷層北段汶川區域的構造活動速率，顯示龍門山斷層帶南北段近期的構造活動速率可能沒有太大的差異。此外由定年結果也發現近期天全縣構造速率變化有由慢轉快的趨勢，與前人青衣江河階之研究相似，因此可能表示著整個龍門山斷層帶南段近期的構造速率皆有由慢轉快的趨勢。
根據本研究的結果，顯示這個區域的構造活動對人類社會具有潛在的未來威脅，因此本研究成果將有助於該區域未來進一步的新構造研究，並且用於預防地震及相關地質災害，以保護該區域高達百萬人的生命及財產安全。; The Longmenshan fault zone at the western edge of the Sichuan Basin has long been identified as an active tectonic belt. This has been clearly illustrated by the disastrous Wenchuan and Lushan earthquakes in the recent decade. The two earthquakes, however, have distinctive characters. In the north, the Wenchuan event occurred on major fault zones identified previously. But in the south, the Lushan event was not accompanied by surface ruptures. Before the Lushan event, there were not many active tectonic studies in this area, either. As a result, the seismogenic structure of the Lushan event is still under debate.
In order to further understand the neotectonic characteristics of the Lushan earthquake region, we analyzed fluvial terraces first by satellite images, in the hope that such geomorphic features would provide information of active structures of the area. Along the Tianquan River, river terraces are particularly well developed near two cities, Tianquan and Shiyang. After detailed field investigations, we found that underneath these terraces, early Tertiary bedrocks crop out below river sediments that are only 1-3 m thick. This indicates that the Tianquan River has incised into bedrocks. The slope of the terrace surfaces is similar to that of the present-day riverbed, and the river sediments in the terrace outcrops have similar grain size distribution as current riverbed sediments. Therefore, we suggest that the terraces along the Tianquan River were result of tectonic uplift. Using the Real Time Kinematic-Global Positioning System (RTK-GPS) and Digital Elevation Model (DEM) results, we defined Tianquan terraces with 4 levels, and Shiyang terraces with 11 levels. With the ages of the terraces and the amount of incision, we obtained the incision rate of the Tianquan River. The incision rate of the Tianquan River is about 1-2 mm/year, very similar to the structural activity rate of the northern Longmenshan fault zone. We also found the structural activity rate in Tianquan area increased recently, and this trend is very similar to the results obtained from studies of Qingyi River terraces, in the southern region Longmenshan fault zone. Therefore, we speculated that the structures became more active recently in the entire southern Longmenshan fault zone.
Based on our results, the tectonic activity poses potential threatening to this area. Therefore, we hope the results of this study would provide more information of neotectonic characteristics of the southwestern Sichuan Basin, as well as future earthquake hazards in this densely populated region.2016-01-01T00:00:00Z黑潮上游區全新世古海洋學研究Yu-Shih Lin林玉詩http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/244482021-06-08T05:26:24Z2005-01-01T00:00:00Z標題: 黑潮上游區全新世古海洋學研究; Holocene Paleoceanography in the Upper Reach of the Kuroshio
作者: Yu-Shih Lin; 林玉詩
摘要: 過去對於黑潮全新世古海洋學的探討，岩心材料多半侷限於沖繩海槽內，且研究方法上倚賴傳統的浮游有孔蟲轉換函數與氧碳同位素，使得過去對於全新世一些古生態與古海洋記錄的解釋有所爭議。本研究分析、比對黑潮上游區（菲律賓海至台灣東部外海）與南沖繩海槽的海洋岩芯記錄，並同時利用傳統（浮游有孔蟲群聚、多種類浮游有孔蟲氧碳同位素）與新近（鎂鈣比）的古海洋指標，企圖釐清沖繩海槽內古海洋訊號的意義，進而從中探索黑潮的歷史。首先透過對全新世中期「普林蟲銳減事件」的研究，了解浮游有孔蟲古生態在黑潮上游區的變化。結果顯示「普林蟲銳減事件」的地理範圍並不限於邊緣海內，而是遍及西北太平洋地區；但是各項古海洋指標均顯示，在此ㄧ大範圍古生態事件發生的同時，並無對應的古水文變化。本研究推測該事件發源於赤道太平洋地區，並對該事件提出族群生態學的可能解釋。此外，浮游有孔蟲群聚組合深受沖繩海槽內複雜的水文作用影響，不適合作為黑潮的指標。本研究進一步利用化學指標分析古海表溫與古海表鹽度的變化，結果顯示南沖繩海槽全新世時期海表溫並無顯著變化，但海表鹽度逐漸降低。此一表水變淡的趨勢與東亞季風的消長趨勢不符，卻與西赤道太平洋的表水鹽度變化一致。因此，本研究推測北赤道洋流—黑潮系統的表層水鹽度在全新世以來逐漸變淡，但不排除太平洋海盆在全新世以來海水逐漸變淡的可能性。總結前文，全新世時期南沖繩海槽內的古海洋變化與赤道太平洋有著海洋遙相關。; I have studied a suite of deep-sea cores (MD01-2403, OR715-21 and MD98-2188) located in the upper reach of the Kuroshio (from the Philippine Sea to off eastern coast of Taiwan) and the Southern Okinawa Trough (SOT) using both traditional methods (foraminiferal assemblages and stable isotopes) and a newly developed paleothermometer (Mg/Ca ratio). The goal of this research is to investigate paleoceanographic relationships among the East Asian monsoon (EAM), Equatorial Pacific (EP) and SOT during the Holocene, and to further unravel the Holocene history of the Kuroshio.
During the past decade, paleoceanographers have reported the so-called 'Pulleniatina Minimum Event (PME)' at 4.5-3.0 ka from the Okinawa Trough and South China Sea. The paleoenvironmental and ecological hypotheses for the PME were tested using our data in the upper reach area and the SOT. The three cores all witness the PME, implying this event is widespread in the western North Pacific. The results of Mg/Ca-based SSTs and thermocline hydrography reconstructed by multispecies isotopic analyses reveal nothing anomalous in the paleoceanographic proxies associated with the PME. Relative abundance of Neogloboquadrina dutertrei did not shows reciprocal pattern to that of P. obliquiloculata in the upper reach area. We proposed a biological hypothesis (epidemic mass mortality) originating in the EP that resulted in the PME. This new hypothesis may be testable by approaches in population dynamics. This PME study has two implications for paleoceanography. First, the discrepancy between the Mg/Ca-derived SSTs and fauna-based SSTs during the PME period is discussed. Second, P. obilquiloculata is not a faithful indicator for the Kuroshio in the Holocene epoch.
To discuss the Holocene SST front variability in the East China Sea, we present the surface water d18O (d18Osw) record in the SOT (MD01-2403), estimated from d18O of Globigerinoides ruber and Ma/Ca-based SST of Globigerinoides sacculifer. The Mg/Ca-based SSTs are quite stable throughout the Holocene, whereas a long-term decrease in d18Osw of ~0.5 o/oo was found over the past 8,000 yrs, equivalent to a decrease of 1 psu in salinity calculated from the local empirical equation: d18Osw=0.51S-17.28 (R2 = 0.81, n=37). We compare the d18Osw record from the SOT with climatic records of Greenland GISP2 ice core d18O, stalagmite d18O of the Dongge Cave in China, and d18Osw of MD98-2181 in the western terminus of the North Equatorial Current. The decreasing trend in SSS in the SOT is inconsistent with the record of Asian monsoon strength of the South China, but agrees better with the d18Osw record from the western tropical Pacific. Our study indicates that the decrease of d18Osw in the SOT might reflect either the decrease of SSS in the North Equatorial Current-Kuroshio system or to a larger extent, a basin-wide change in salinity of the Pacific Ocean.
By examining various paleoceanographic proxies of the upper reach of the Kuroshio, we evaluated previous interpretations and provided new perspectives on the Holocene paleoceanography of the Kuroshio. The extensive distribution of the PME and the freshening trend in the SOT imply an oceanographic teleconnection between the SOT and the EP.2005-01-01T00:00:00Z