發(fā)布時間：2018-04-16 10:07

  本文選題：深部碳循環(huán) + 碳酸巖質(zhì)包體��； 參考：《中國地質(zhì)大學》2016年博士論文

【摘要】：古亞洲洋的俯沖閉合形成了顯生宙最大的增生造山帶。在此過程中大量的地殼物質(zhì)伴隨著洋殼俯沖返回到地幔,引發(fā)大規(guī)模的殼-幔作用。由此引起的熔體-橄欖巖反應可能也是誘發(fā)華北克拉通破壞的重要因素。另外,俯沖板塊上的沉積碳酸鹽巖也可隨著俯沖的進行返回地幔。作為地球表層碳返回地球深部的唯一方式,沉積碳酸鹽巖的俯沖再循環(huán)在深部碳循環(huán)研究中起著不可替代的作用。本論文通過興蒙造山帶南緣達里湖地區(qū)玄武巖中的碳酸巖質(zhì)包體及華北克拉通北緣漢諾壩地區(qū)玄武巖中的單斜輝石巨晶的系統(tǒng)研究,揭示了古亞洲洋俯沖引起的熔體-橄欖巖反應及沉積碳酸鹽巖深部地幔再循環(huán)。古亞洲洋俯沖引起的沉積碳酸鹽巖地幔再循環(huán)作用被興蒙造山帶南部達里湖玄武巖中的碳酸巖質(zhì)包體所記錄。達里湖碳酸巖質(zhì)包體主要由碳酸鈣組成,其稀土元素配分模式及微量元素類型均和沉積碳酸鹽巖非常相似,都具有明顯的Ce負異常和Sr正異常。而且其亦具有演化的Sr同位素組成(87Sr/86Sr=0.70893-0.71054),表明此碳酸巖質(zhì)包體為沉積碳酸鹽巖通過俯沖作用深部地幔再循環(huán)的產(chǎn)物。達里湖碳酸巖質(zhì)包體內(nèi)存在著原位金剛石,證明沉積碳酸鹽巖曾俯沖到至少120 km的深度。沉積碳酸鹽巖通過底劈作用脫離俯沖板塊,進入熱的地幔楔。其后通過脫氣過程快速上升到淺部巖石圈地幔。達里湖碳酸巖質(zhì)包體的Ni和Fe的含量遠遠超過沉積碳酸鹽巖,暗示了碳酸巖質(zhì)包體從俯沖板塊脫離入地幔后可能受到了地幔物質(zhì)的影響。達里湖碳酸巖質(zhì)包體中上地幔礦物斑晶可能為碳酸巖質(zhì)熔體侵入到上地幔輝石巖中而成。達里湖碳酸巖質(zhì)包體中存在著一個以SiC為主的超還原礦物組合,包括SiC、TiC、自然金屬(Si、Fe、Ni)和硅化物。SiC大小為20-50 gm,藍色到無色透明,常發(fā)現(xiàn)于碳酸巖質(zhì)包體的微空洞中。SiC有四種多型,以β-SiC (3C)和4H型為主,其后為15R型和6H型。達里湖SiC具有明顯’3C虧損的碳同位素組成(813C=-13.2‰～-22.8‰,平均值為-17.7‰),而且具有明顯的空間變化。數(shù)值模擬結(jié)果表明達里湖SiC的低δ13C值及碳同位素的空間變化可由石墨與硅酸鹽礦物的脫氣反應形成。達里湖SiC主要產(chǎn)出于微空洞中,其中充填的CO或CO2可有效的維持局部超還原環(huán)境,將SiC和外部氧化環(huán)境分開。寄主巖石的快速冷卻在一定程度上也有利于SiC的保存。古亞洲洋的南向俯沖可能引發(fā)華北克拉通北緣廣泛的熔體-橄欖巖反應。這一過程被華北克拉通北部漢諾壩玄武巖中的單斜輝石巨晶所記錄。漢諾壩玄武巖中產(chǎn)出大量單斜輝石巨晶,根據(jù)其物理化學特征,可將其分為兩類。類型一單斜輝石巨晶比類型二擁有更高的Cr、Nb含量和Mg#(82.9)以及更演化的Sr-Nd同位素組成(87Sr/86Sr=0.704520,143N/144Nd=0.512350).這些特點表明類型一單斜輝石可能由熔體-橄欖巖反應生成,而且熔體可能來自于俯沖古亞洲洋殼于金紅石不穩(wěn)定域的熔融。類型二單斜輝石巨晶的Mg#和主微量元素間具有很好的相關性,而且其Sr-Nd同位素組成落在了寄主玄武巖的最不演化端元。這些數(shù)據(jù)表明類型二單斜輝石巨晶由寄主巖漿于高壓下結(jié)晶而成。類型一單斜輝石巨晶中含有大量平行的不透光條帶及斜方輝石出溶體。不透光條帶由微晶斜長石、橄欖石組成。其總體化學成分和石榴子石非常相似,而且和寄主單斜輝石具有相同的Sr同位素組成。表明不透光條帶是類型一單斜輝石巨晶中石榴子石出溶體裂解的產(chǎn)物。石榴子石出溶的溫壓條件為2.75 GPa、1290℃。實驗結(jié)果表明單斜輝石在增壓或者降溫的條件下可以出溶石榴子石。雖然在玄武巖噴發(fā)過程溫度會降低,但是急劇的降壓過程會抑制石榴子石的出溶。因此,類型一單斜輝石巨晶中的石榴子石出溶體可能形成于古亞洲洋俯沖造成的華北克拉通北緣巖石圈加厚過程中。
[Abstract]:The closure of the paleo Asian Ocean subduction formed the largest Phanerozoic accretionary orogenic belt. A large number of crustal material in the process with the subduction of oceanic crust returned to the mantle, causing massive crust mantle interaction. The important factors of peridotite melt reaction may be caused by the destruction of the North China Craton is induced. In addition, the deposition of carbonate rocks in subduction the plate can also be with the subduction of the mantle. The only way to return to the earth's surface as carbon return in deep earth, recirculation subduction of the carbonate rock plays an irreplaceable role in the carbon cycle of the deep. This paper through the system research and the North China Craton basalts from Hannuoba in monoclinic pyroxene megacrysts carbonate rock basalt pack up in the lake area of xing'anling-mongolian orogenic belt on the southern margin of the peridotite melt reaction reveals subduction of the paleo Asian Ocean caused by carbonate rocks and sedimentary The deep mantle recycling. Recycling effect caused by the subduction of the paleo Asian Ocean sedimentary carbonate mantle is xing'anling-mongolian orogenic belt of Southern Dali Lake basalt in carbonate enclaves recorded. Up in the lake carbonate rock xenoliths mainly composed of calcium carbonate, the REE patterns and trace elements and types the deposition of carbonate rocks is very similar, have obvious Ce negative anomaly and Sr positive anomaly. But it is also composed of Sr isotope evolution (87Sr/86Sr=0.70893-0.71054), showed that the product of the carbonate rock inclusions for carbonate rocks by the subduction of the deep mantle recycling. Up in the lake carbonate rock package exists in vivo in situ diamond, proof of sedimentary carbonate rocks have subducted to at least 120 km. The depth of sedimentary carbonate rocks from the subducting plate through the diapir action, into the mantle wedge. Then through the heat degassing process quickly rose to the shallow 宀╃煶鍦堝湴騫，

本文編號：1758409