本文選題：金伯利巖 + 霞石巖　； 參考：《中國地質(zhì)大學(北京)》2016年博士論文

【摘要】：二疊紀塔里木大火成巖省不同于其他大火成巖省,以復(fù)雜的巖石組合為特征。本文在前人研究的基礎(chǔ)上,選取塔里木大火成巖省瓦吉里塔格雜巖體中的金伯利質(zhì)巖石、碳酸巖和霞石巖為研究對象,對其巖石成因進行研究并對塔里木大火成巖省深部地質(zhì)過程進行初步的探討,取得的主要研究成果和新認識如下:1、通過金紅石SIMS U-Pb定年及詳細地野外觀察,基本厘定了霞石巖的噴發(fā)時間為270Ma,證明其是代表了塔里木大火成巖省晚期的巖漿活動。結(jié)合前人的年代學成果,說明塔里木大火成巖省的活動時限較長,持續(xù)了約30Ma。2、對金伯利質(zhì)巖石中發(fā)現(xiàn)的碳酸質(zhì)和硅酸質(zhì)球粒展開詳細研究,其中,碳酸質(zhì)球粒幾乎由純的方解石組成,硅酸質(zhì)球粒除了含有方解石外,還含有大量鈣鐵榴石、金云母和輝石。研究表明,這些球粒的地球化學特征與實驗巖石學得到的液態(tài)不混溶熔體并不相符,因此它們不能代表由液態(tài)不混溶作用形成的熔體。碳酸質(zhì)球粒的出現(xiàn),說明巖漿本身富含CO2組分,指示著金伯利質(zhì)巖漿起源于一個發(fā)生了碳酸鹽化的地幔源區(qū)。3、本論文報道了金伯利質(zhì)巖石、碳酸巖、霞石巖的鎂同位素特征,δ26Mg值變化范圍分別為-0.36‰~-0.75‰,-1.09‰~-0.68‰,-0.35‰~-0.55‰,它們均低于正常地幔的δ26Mg值(-0.25‰),指示它們的源區(qū)很可能受到早-中古生代俯沖的沉積碳酸鹽巖交代的影響。霞石巖具有幔源的Sr-Nd同位素和殼源的Mg-O同位素特征,而碳酸巖也具有幔源的Sr-Nd-O和殼源的Mg-C同位素特征,這種同位素解耦現(xiàn)象對俯沖過程中碳酸鹽礦物的相轉(zhuǎn)變提供了非常重要的約束:隨著俯沖深度的增加,碳酸鹽礦物可由白云石經(jīng)菱鎂礦向方鎂石、鈣鈦礦轉(zhuǎn)變,且其俯沖深度可達900km甚至地球核幔邊界。研究表明,霞石巖源區(qū)的碳酸鹽礦物主要以菱鎂礦的形式存在,而碳酸巖源區(qū)多以方鎂石的相態(tài)存在。4、霞石巖在野外呈熔巖狀直接覆蓋在泥盆紀地層之上,二者之間缺少石炭紀地層,說明在霞石巖噴出之前存在公里級的地殼隆升造成石炭系的剝蝕丟失。菱鎂礦分解需要相對于正常地幔絕熱線的一個高的熱異常。高的熱異常和大規(guī)模的地殼隆升為塔里木大火成巖省的地幔柱成因提供了更多的支持。5.提出地幔柱-巖石圈相互作用的模型來解釋塔里木大火成巖省的重要特征,論證了在地幔柱作用的晚期,塔里木巖石圈地幔發(fā)生了一定程度的減薄。塔里木大火成巖省所具有的豐富的巖石系列可歸因于地幔柱-巖石圈相互作用的不同階段的產(chǎn)物。
[Abstract]:The Permian Tarim igneous province is different from other major igneous provinces and is characterized by complex rock assemblages.On the basis of previous studies, the kimberlite, carbonatite and hayite in the Wagiritag complex of Tarim great igneous rock province are selected as the research objects in this paper.The petrogenesis and the deep geological process in Tarim great igneous province are studied. The main research results and new understandings are as follows: 1. Through the age determination and detailed field observation of rutile SIMS U-Pb,The eruption time of the igneous rocks is determined to be 270 Ma, which indicates that it represents the magmatic activity in the late stage of Tarim igneous province.Combined with previous geochronological results, it is shown that the activity time of Tarim great igneous province is relatively long, which lasted about 30 Ma.2.The carbonated and silicic acid spherulites found in kimberlite rocks are studied in detail, among which,The carbonated spheroids are almost composed of pure calcite, and the silicic acid spherulite contains not only calcite, but also a large amount of calcium ferrite, phlogopite and pyroxene.It is shown that the geochemical characteristics of these spherulites are not consistent with the liquid immiscible melts obtained from experimental petrology, so they cannot represent the melts formed by liquid immiscibility.The appearance of carbonaceous spherulites indicates that the magma itself is rich in CO2 components, indicating that the kimberlite magma originated from a carbonated mantle source region .3.This paper reports kimberlite, carbonatite, and kimberlite.The 未 26Mg values vary from -0.36 鈥，

本文編號：1766502