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Petrological analysis for high-grade metamorphic rocks in the Kontum Massif, central Vietnam
BUI THI MEN
High-grade metamorphic rocks
|Abstract:||越南中部的Kontum地塊主要由高品位變質岩（閃石到粒狀岩相）組成，傳統上被認為是印度支那地塊的“前寒武紀基底”。最近的地質年代學研究報告了奧陶紀-西陸紀和二疊紀-三疊紀兩個明顯的超高溫變質事件。但是，在這些研究中表明超高溫的支持證據文獻很少。當前的研究進行了詳細的岩石學分析，以重建Kontum斷塊的構造演化和構造演化。從露頭可以觀察到黑雲母±白雲母片麻岩夾有角閃石的三個岩性單元，後來被未變形的花崗閃長岩侵入。岩石學分析表明，片麻岩和閃石均在閃石相下變質變形。石榴石±黑雲母±鉀長石±微晶線±鎳鐵礦±白雲母±亞氯酸鹽±斜長石±石英±閃石，黑雲母±白雲母±藍晶石±石英礦物組合物見於黑雲母±白雲母片麻岩樣品。觀察到角閃石，黑雲母，斜長石，輝石，綠泥石，白雲母，角閃石的石英礦物組合。礦物百分比顯示出石英長石岩（片麻岩）和基岩（閃石岩）的大體化學組成，分別代表了大陸殼和海洋殼。 Kontum斷層中的岩石可能經歷了兩次變質事件，其中最高的變質條件取決於石榴石或藍晶石的存在以及Kfs±Pl±Bt±Grt（Ma）的平衡礦物。由亞氯酸鹽和白雲母（Mb）的存在定義的較低條件。 Kontum地塊中的高級變質岩顯示出順時針P-T路徑，其中Ma和Mb的峰值變質條件為逆變質，被認為分別比三疊紀和晚三疊紀發生。因此，孔通地塊的構造演化很可能與印度支那和華南地塊之間的碰撞造山作用有關。|
The Kontum Massif, central Vietnam composed mainly of high-grade metamorphic rocks (amphibolite to granulite facies) and has been traditionally regarded as the ‘Precambrian basement’ of Indochina Block. Recent geochronology studies reported two distinct ultra-high temperature metamorphic events during Ordovician-Silurian and Permian-Triassic. However, the supporting evidence to indicate for ultra-high temperatures within those studies were poorly documented. The current study conducts detail petrological analysis to reconstruct the metamorphic evolution along with the tectonic evolution of the Kontum Massif. Three lithology units of biotite ± muscovite gneiss interlayered with amphibolite that was later intruded by undeformed granodiorite can be observed from the outcrop. Petrological analysis indicated both gneiss and amphibolite were metamorphosed and deformed under amphibolite facies. Characteristic garnet ± biotite ± K-feldspar ± microline ± myrmekite ± muscovite ± chlorite ± plagioclase ± quartz ± amphibole, biotite ± muscovite ± kyanite ± quartz mineral assemblages are observed for biotite ± muscovite gneiss samples. Hornblende ± biotite ± plagioclase ± pyroxene ± chlorite ± muscovite ± quartz mineral assemblages are observed for amphibolite. The mineral percentages revealed bulk chemical composition of quartzo-feldspathic rocks (for gneiss) and basic rocks (for amphibolite), which are represented for the continental crust and oceanic crust, respectively. Rocks in the Kontum Massif might be experienced two metamorphic episodes with the highest peak metamorphic conditions is determined by the presence of garnet or kyanite and equilibrium minerals of Kfs ± Pl ± Bt ± Grt (Ma). The lower condition defined by the occurrence of chlorite and muscovite (Mb). High-grade metamorphic rocks in the Kontum Massif show a clockwise P-T path with peak metamorphic conditions of Ma and Mb as retrograde metamorphism which is considered to be occurred ealier than Triassic and Late Triassic, respectively. Therefore, the tectonic evolution for Kontum Massif is most likely related to a collisional orogeny between the Indochina and South China blocks.
|Appears in Collections:||學位論文|
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