西藏東部嘉黎斷裂帶熱歷史之核飛跡定年證據及其大地構造之隱示

Fission Track Ages as Evidence for the Thermal History of Jiala Fault (Eastern Tibet) and its Tectonic Implications

鍾靈(Ling Chung)

指導教授 ： 楊燦堯

國立臺灣大學/理學院/地質科學研究所/碩士(2006年)

https://doi.org/10.6342/NTU.2006.01822

摘要

喀拉崑崙－嘉黎斷裂帶是由數個右移的錯動帶所組成的巨大斷裂帶，也是向東脫逸之北部青藏高原塊體的南界。嘉黎斷層位於此東西橫貫斷裂帶的最東端，並且是新生代以來構造活動劇烈的東喜馬拉雅山結的北界，其活動不只與向東脫逸的青藏高原塊體有關，更與至今構造活動仍強烈的南迦巴瓦山結息息相關。嘉黎斷裂帶經過通麥後分成兩個分支斷層，帕隆以及布曲斷裂帶，向東南方發育通過察隅地區。本研究地點位於南迦巴瓦山結北方的通麥地區以及東南方的察隅地區。樣本則是採集於斷裂帶中變形或是未變形的岩體，利用核飛跡定年法的分析，以探討藏東地區嘉黎斷裂帶的活動歷史與熱歷史。
分析結果顯示察隅地區之帕隆斷裂帶樣本的鋯石與磷灰石核飛跡年代範圍為ca. 23－19 Ma；布曲斷裂帶之鋯石結果為ca. 10－9 Ma，磷灰石為ca. 6 Ma；通麥地區的定年結果較察隅地區年輕許多，鋯石與磷灰石核飛跡年代皆小於3 Ma。
根據本研究之核飛跡定年數據，嘉黎斷裂帶自開始活動以來，主要活動帶有向南轉移的趨勢。約23－19 Ma時嘉黎斷裂帶的北分支帕隆斷裂帶有一次快速抬升的時期，此次的抬升應與整個嘉黎斷裂帶與其兩分支斷層的錯移有關；18 Ma之後帕隆斷裂帶的活動減緩，印度板塊擠壓的能量轉由藏北塊體順時鐘旋轉所吸收，此時期活動斷層剩下嘉黎－布曲斷層並持續活動至∼11 Ma。本研究於察隅以及通麥地區10 Ma以來不同的核飛跡記錄顯示10－6 Ma應為一次大規模的抬升，影響區域可能廣及整個喜馬拉雅山及西藏東部的許多地區；而3 Ma左右在通麥發生的快速抬升事件（∼2.6 mm/yr）應為區域性事件，導因於印度板塊在東喜馬拉雅山結集中的嵌入式擠壓歐亞大陸板塊，活化了北方的嘉黎斷裂帶所致。察隅與通麥地區異時的抬升順序可能進一步暗示了藏東河川的襲奪順序。

關鍵字

西藏 ； 嘉黎斷裂帶 ； 核飛跡定年

並列摘要

Jiali Fault in eastern Tibet bounds the Karakorum-Jiali Fault Zone (KJFZ) in the east and cuts the Namche Barwa Syntaxis northerly. Its movement is not only closely related to the clockwise rotation and extruded body of eastern Tibet, but also strongly correlated to the northeastward indentation of India plate. Representative samples have been collected for fission-track (FT) dating from Jiali fault zone (Tungmai, north of Namche Barwa Syntaxis) and its two easternmost branches, the Parlung and Puqu Faults (near Chayu).
FT ages are analyzed using external detector method. In Chayu region, zircon and apatite FT ages from undeformed granites in Parlung Fault are ca. 23-19 Ma; in the southern branch, Puqu Fault, zircon and apatite FT ages (from both deformed and undeformed rocks) are 10-9 Ma and ca. 6 Ma respectively. In Tungmai area, FT results yield younger ranges than Chayu area (both zircon and apatite ages < 3 Ma from deformed samples).
Based on the FT dates in this study, we can conclude that the stress/strain of Jiali Shearing Zone may have shifted from northern branch to southern branch since its initial movement. During 23-19 Ma, the northern branch, Parlung Fault, had undergone an uplifting event which is considered to be related to the shearing of the fault. Consequently, the shearing stress may transfer to the southern branch and had lasted until ~11 Ma. The different ages younger than ~10 Ma obtained from Chayu and Tungmai suggest that the 10-6 Ma uplifting was a large scale event that occurred in Himalayas region and eastern Tibet. However, the uplifting after 3 Ma is believed to be a regional event that resulted from the indentation of India into Eurasia Plate and focusing erosion in Eastern Himalaya Syntaxis. Moreover, the diachronous uplifting in eastern Tibet might provide possible time series constraint for the river capture hypothesis of the unusual drainage system in eastern Tibet.

並列關鍵字

Tibet ； Jiali Fault ； Fission track dating

參考文獻

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