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研究生:王珮玲
研究生(外文):Wang, Pei-Ling
論文名稱:鉀長石氬40╱氬39同位素熱年代學之研究與應用
論文名稱(外文):K-feldspar 40Ar/39Ar Thermochronology and its Applications
指導教授:羅清華羅清華引用關係
指導教授(外文):Lo Ching-Hua
學位類別:博士
校院名稱:國立臺灣大學
系所名稱:地質學系
學門:自然科學學門
學類:地球科學學類
論文種類:學術論文
論文出版年:1998
畢業學年度:86
語文別:中文
論文頁數:198
中文關鍵詞:氬40/氬39定年熱年代學鉀長石大南澳片岩紅河斷裂帶平潭東山變質帶
外文關鍵詞:40Ar/39Ar DatingThermochronologyK-feldsparTananao SchistRed River Shear ZonePingTan-DongShan Metamorphic Belt
相關次數:
  • 被引用被引用:6
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運用於鉀長石之 40Ar/39Ar 定年的多重擴散區間理論,是解析岩體經歷
之熱歷史演化的良好工具,本研究以此為主軸,探討來自(一)受控於板
內舒張作用而緩慢剝蝕的平潭─東山變質帶中晉江半島之片麻岩、(二)
導因於大型橫移斷層活動而快速冷卻的紅河斷裂帶之變質岩,以及(三)
歷經多次變質作用的大南澳片岩之熱歷史演化,以了解多重擴散區間理論
運用在鉀長石之 40Ar/39Ar 定年時,在解析不同地體架構下之岩體熱歷
史的適用情形,並對各研究區域之地體構造演化提出更進一步見解。在區
域地體構造方面的研究結果顯示:一、平潭-東山變質帶中晉江半島之片
麻岩中的鉀長石樣品,經由 40Ar/39Ar 定年的各種基本作圖法,或是多
重擴散區間理論,均可解析出對冷卻速率之變化有較為良好控制之岩體冷
卻歷史,首先快速降溫,隨後緩慢冷卻,最後冷卻速率有些微增加的趨勢
,其結果與區域性的年代資料一致,顯示平潭-東山變質帶於晚中生代發
生快速抬升作用。二、出露於越南北部的達紐康渥 (Day Nui Con Voi)
變質岩體,記錄哀牢山-紅河斷裂帶左移的活動歷史,表現出從 27 Ma
至 21 Ma 左右,由東南向西北方向逐一快速冷卻剝蝕的過程,綜合關於
此一斷裂帶活動可得的剝蝕記錄,並配合附近區域的已有地質資料可知,
哀牢山-紅河斷裂帶的活動稍晚於青藏高原東部發生層脫作用 (約 40-30
Ma) 和南海海盆開始發育的時間 (約為 30 Ma) ,隱示哀牢山-紅河斷裂
帶的活動是發生在兩個已經存在的岩石圈薄弱處之間。三、台灣大南澳片
岩記錄了台灣弧陸碰撞由壓縮應力之增積狀態,轉變為舒張應力之快速剝
蝕階段的完整歷史,藉由不同大地應力架構下所產出的礦物所記錄的事件
年代,以及歷經完整地體演化的片麻岩之熱歷史,可知處於台灣弧陸碰撞
之背地部份的高度變質岩體之快速冷卻剝蝕 (<2 Ma) ,與區域應力狀態
轉為舒張階段的時間相一致 (約在 3.0 至 1.5Ma 間) ,此一地體演化歷
史首次由同位素定年方法揭露絕對年代方面的良好控制。經由上述不同地
體架構岩體的熱歷史分析,可以瞭解多重擴散區間理論的適用性和限制:
對於經歷單純冷卻歷史的鉀長石樣品,使用適當的循環式加熱程序,便可
經由 40Ar/39Ar 定年的各種基本作圖法推估岩體的冷卻歷史,而在運用
多重擴散區間理論上,必須確認年代譜不受非放射源氬氣影響,才能解析
出正確的岩體熱歷史演化,而確認樣品之氬同位素成分來源的最佳即是同
位素對比圖;另一方面,對於經歷單一快速冷卻歷史的鉀長石樣品,多重
擴散區間理論模擬所得之冷卻曲線,必須經過反複測試模擬,以確知冷卻
曲線的準確性和延伸性,在實驗操作上,則可以使用進階式的加熱程序,
由較低的溫度起始加熱,便能符合取得擴散參數需要,解析岩體的熱歷史
;相反地,對於經歷多次熱事件作用之鉀長石樣品,多重擴散區間理論在
其熱歷史解析上,在實際運用的困難,除了受限於相關地質資料的缺乏,
而無法判斷模擬結果正確與否外,經由多重擴散區間理論模擬求得之樣品
擴散參數,很可能在多次變質作用的影響下,與其生成時的結構相異,自
然無法今日之礦物結構所表現的擴散性質,推測岩體所經歷的熱歷史。
K-feldspar 40Ar/39Ar thermochronology is demonstrated to provide
a powerful tool to unravel the cooling history of a terrane.
This study investigates the thermal evolution of rocks (1) in
Pingtan-Dongshan metamorphic belt (2) in Ailaoshan-Red River
shear zone, north Vietnam (3) in Tananao metamorphic complex and
tries to figure out the applicability of multi-domain diffusion
theory for K-feldspar 40Ar/39Ar thermochronology in different
tectonic settings. Several conclusions are provided as age
constraints for further interpretation of kinematic evolutions
in various areas:(1) 40Ar/39Ar thermochronological study of a K-
feldspar sample extracted from a granitic gneiss in the Pingtan-
Dongshan metamorphic belt of SE China, yields many valuable T-t
(temperature-time) data allowing to construct a cooling curve
for the metamorphic terrain. The K-feldspar sample has been
treated by non-conventional (including cycling and isothermal
steps) heating schedule to extract argon during the experiments.
Through a combination analysis of age spectrum, Arrhenius plot
and correlation diagram, several dates and their corresponding
diffusion can successfully be derived. Consequently, with
considering their respective closure temperatures, the
analytical data for a single K-feldspar sample allow the
derivation of cooling path for rock body. Although a continuous
segement of cooling curve is not possible to be conducted, it
still broadly extends the capability of 40Ar/39Ar K-feldspar
dating in elucidating the thermal history. The obtained cooling
curve is perfectly in agreement with that obtained from other
isotopic systems, reflecting a two-stage cooling history for the
metamorphic complex during the exhumation of the complex due to
the Cretaceous extension tectonism in the region. Although
there are still a number of uncertainties about the retention
sites and the release mechanisms for argon in the K-feldspar,
the results of present study have clearly implied that argon may
have resided in different sites within the mineral grains, which
exhibit their own activation energy and closure temperature. If
the multi-domain diffusion theory is applied, it is shown that
the cooling paths strongly depend on the shape of age
spectra.(2) In order to explore the timing of strike-slip
movement along the Ailao Shan-Red River (ASRR) shear zone, an
40Ar/39Ar thermochronological study of the Day Nui Con Voi
metamorphic complex in northern Vietnam was undertaken. The
complex, exposed in the southeastern segment of the ASRR shear
zone, reveals a rapid cooling during the late Oligocene to early
Miocene (27-21 Ma) after a very slow cooling during ~34-27 Ma.
The slow cooling period most likely resulted from a geothermal
perturbation in the lithosphere owing to the late Paleogene
(40-30 Ma) extension in eastern Tibet and western Yunnan, China.
The rapid cooling, consistent with a rapid cooling span in 27-17
Ma compiled from the entire ASRR shear zone, constrains the
duration of the left-lateral shearing which eventually offset
Indochina from South China by about 600 km. The time constraints
we have established reinforce the argument that the onset of the
ASRR shear zone postdates the opening of the South China Sea
that began ~30 Ma. This result highlights the urgent necessity
for re-evaluating the Cenozoic tectonic models of Southeast
Asia.(3) As a typical example of arc-continent collision, the
hinterland of the Taiwan Mountain Belt has experienced a
complicated deformation history from ductile compression/
shearing during the accretion stage to a syn-tectonic extension
during the later stage. In order to further constrain the
kinematic processes of deformation, a detailed
thermochronological analysis on the hinterland of the Taiwan
Mountain Belt was conducted in the present study. The results
show that biotites collected from the mylonization zones yield
dates of 3.0 to 4.1 Ma, which could represent the age of the
ductile deformation within the hinterland. On the other hand,
40Ar/39Ar dates of two adularias collected from joint planes of
granitic gneisses yield ages of 1.5 to 1.1 Ma, which would
depict the younger age limit for brittle deformation during the
syn-tectonic extension. These 40Ar/39Ar mineral dates,
therefore, clearly demonstrate that the deformation of the
hinterland changed its style from ductile deformation to brittle
deformation in between 3.0 to 1.5 Ma. Moreover, the results of
multi-domain diffusion modeling for two K-feldspars collected
from granitic gneisses reveal a rapid cooling/uplifting of the
hinterland during the last 2 Ma. These data would suggest that
the on-lapping of syn-tectonic extension may have occurred since
~2Ma. It is also interesting to note that the sedimentation
rates in basins along both sides of the Taiwan Mountain Belt
started to increase significantly at around 2 Ma. This is in
perfect agreement with the rapid cooling/uplifting of the
hinterland in terms of time. From these results, it can be
concluded that the rapid cooling/uplifting of the hinterland or
the exhumation of the basement complex in Taiwan may have
resulted from syn-tectonic extension, rather than from
compression tectonism. In other words, extension tectonism may
have played an important role in the mountain building processes
and in the exhumation of basement complexes in collision zones.
The present study presents a good example that the kinematic
processes of deformation within the hinterland of a mountain
belt can be revealed by 40Ar/39Ar dating.
封面
目錄
中文摘要
英文摘要
目錄
圖目
表目
第一章 緒論
1.1 研究動機與目的
1.2 研究題材
第二章 多重擴散區間理論在鉀長石40Ar/39Ar定年學上的運用
2.1 多重擴散區間的理論基礎
2.2 多重擴散區間理論的分析方法
2.3 多重擴散區間理論的運用實例
2.4 多重擴散區間理論的限制與問題
2.5 多重擴散區間理論的前瞻性
第三章 運用實例一;福建晉江半島變質岩
基本作圖解析和多重擴散區間理論運用在受超氬影響之樣本
3.1 地質背景與前人研究
3.2 40Ar/39Ar定年分析結果
3.3 討論
3.3.1 由單一鉀長石樣本之基本作圖比對求完整冷卻曲線的可能性
3.3.2 循環式加熱程序的優越性
3.3.3 與多重擴散區間理論比較
3.3.4 氬儲存體的特性
3.3.5 綜合討論
3.4 小結
第四章 運用實例二:越南紅河斷裂帶
4.1 地質背景與前人研究
4.2 40Ar/39Ar定年分析結果
4.2.1 角閃石
4.2.2 雲母
4.2.3 鉀長石
4.3 討論
4.3.1 越南連紐康渥變質岩的熱歷史
4.3.2 哀牢山-紅河斷裂帶的活動歷史
4.3.3 哀牢山-紅河斷裂帶的活動與鄰近地區大地構造活動的關係
4.3.4 多重作擴散區間理論在快速冷郤樣本之熱歷史研究的適用性
4.4 小結
第五章 運用實例三:台灣大南澳片岩
5.1 地質背景與前人研究
5.2 40Ar/39Ar定年分析結果
5.2.1 糜嶺岩中的黑雲母樣本
5.2.2 節理面上熱液礦脈中的冰長石
5.2.3 片麻岩和偉晶岩中的鉀長石
5.3 討論
5.3.1 來自糜嶺岩中的黑雲母樣本年代意義
5.3.2 大南澳片岩之大地應力狀改變的絕對年代控制
5.3.3 鉀長石之多重作擴散區間理論在多次變質作用影響下的適用性
5.4 小結
第六章 結論
致謝
參考文獻
附錄
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