發(fā)布時(shí)間：2018-06-06 04:24

  本文選題：祁連地塊 + 中新元古代　； 參考：《中國(guó)地質(zhì)大學(xué)(北京)》2015年碩士論文

【摘要】：長(zhǎng)期以來(lái),人們對(duì)祁連地塊基底物質(zhì)組成和時(shí)代歸屬一直存在著不同的認(rèn)識(shí),對(duì)其大地構(gòu)造屬性及演化歷史也存在有較大的分歧。筆者通過(guò)青海省1:5萬(wàn)上日木策爾等5幅區(qū)域地質(zhì)調(diào)查發(fā)現(xiàn),前人認(rèn)為的“古元古代托賴巖群”實(shí)際是囊括了不同時(shí)代、性質(zhì)和變質(zhì)程度的巖石和地質(zhì)體,因此,筆者,通過(guò)大比例尺填圖、露頭解剖和鋯石U-Pb測(cè)年,將原“托賴巖群”解體成了托賴巖群、元古代片麻狀花崗巖和變形的古生代侵入體三部分。其中重新厘定的托賴巖群,包括下巖組和上巖組兩部分;侵入其中的元古代片麻狀花崗巖主要為中粗粒黑云二長(zhǎng)花崗片麻巖。為精確限定新厘定的托賴巖群的形成時(shí)代,本次工作分別在該巖群下巖組片麻巖、上巖組石英巖、含矽線石榴二云石英片巖和侵入其中的新元古代中粗粒黑云二長(zhǎng)花崗片麻巖采集樣品,進(jìn)行了系統(tǒng)的LA-MC-ICP-MS鋯石U-Pb測(cè)年。結(jié)果顯示,下巖組片麻巖樣品中最年輕的碎屑鋯石年齡為1058Ma,上巖組石英巖樣品最年輕的碎屑鋯石為1149 Ma,含矽線石榴二云石英片巖中最年輕的碎屑鋯石年齡為1178Ma,侵入該巖群的中粗粒黑云二長(zhǎng)花崗片麻巖侵位年齡為897±4 Ma。這表明厘定后的托賴巖群的沉積時(shí)代至少應(yīng)該晚于1178Ma、早于897Ma。值得注意的是,當(dāng)前碎屑鋯石樣品的年齡譜其最大峰值在1700Ma附近,同時(shí)1200Ma和1400Ma左右有弱的峰值,2500~1900Ma則為明顯的低頻區(qū)。這表明當(dāng)時(shí)源區(qū)存在多期強(qiáng)烈的古元古代及中元古代巖漿活動(dòng)記錄,且以古-中元古代之交的巖漿活動(dòng)為主。同時(shí)其年齡譜系特征與華北克拉通有關(guān)研究結(jié)果具有較高的相似性,暗示中祁連地塊可能與華北克拉通更具親緣性,并可能共同見(jiàn)證了Columbia超大陸的聚合與離散;而該地塊后期又被897±4Ma的晉寧期(格林威爾期)黑云二長(zhǎng)花崗巖侵入,則表明新元古代時(shí)期的中祁連地塊很可能參與了Rodinia超大陸的聚合;區(qū)內(nèi)更晚的早中奧陶世巖漿侵入活動(dòng),則屬于早古生代祁連洋消減-閉合階段的相關(guān)記錄。
[Abstract]:For a long time, people have different understanding of the material composition and age attribution of the basement of Qilian block, as well as the tectonic attributes and evolution history of Qilian block. According to the 5 regional geological surveys of 15: 50, 000 in Qinghai Province, it is found that the "Gu Yuan ancient Tolaiyan group" actually includes rocks and geological bodies of different ages, properties and degrees of metamorphism. Based on large scale mapping, outcrop anatomy and zircon U-Pb dating, the original "Torailite Group" was disintegrated into three parts: Tolaiyan Group, Proterozoic granitic granites and deformed Paleozoic intrusions. The newly determined Toraili group includes two parts: the lower rock formation and the upper rock formation, and the major intrusive granitic granites. In order to accurately define the formation time of the newly determined Torai rock group, the present work has been carried out in the lower part of the rock group, the gneiss of the rock formation, and the quartzite of the upper rock formation, respectively. LA-MC-ICP-MS zircon U-Pb dating was carried out on the samples collected from silicon-bearing pomegranate quartz schist and Neoproterozoic middle-coarse black cloud granitic gneiss. The results show that The youngest clastic zircon age of the gneiss samples of the lower formation is 1058Ma. the youngest of the quartzite samples of the upper rock formation is 1149 Ma. the youngest of the quartzite schist with silicon-line pomegranate is 1178Ma. it intruded into the rock group. The emplacement age of the granitic gneiss is 897 鹵4 Ma. This indicates that the sedimentary age of the determined Torai rock group should be at least later than 1178 Maand 897Ma. It is worth noting that the maximum peak value of the current age spectrum of the clastic zircon samples is near 1700Ma, while the weak peak value of 1200Ma and 1400Ma is about 25000 ~ 1900 Ma, which is an obvious low-frequency region. This indicates that there were many strong records of Paleoproterozoic and Mesoproterozoic magmatism in the source area at that time, and the magmatic activity between Paleoproterozoic and Mesoproterozoic was dominant. At the same time, its age pedigree features are similar to those of the North China Craton, suggesting that the Central Qilian block may be more related to the North China Craton, and may witness the aggregation and dispersion of the Columbia supercontinent. The late stage of the block was invaded by the Jinning (Greenwell) bifeldite of 897 鹵4Ma, indicating that the Neoproterozoic Middle Qilian massif was probably involved in the aggregation of the Rodinia supercontinent, and that the late early Middle Ordovician magmatic intrusion occurred in the area. It belongs to the early Paleozoic Qilian ocean subduction-closure stage.
【學(xué)位授予單位】：中國(guó)地質(zhì)大學(xué)(北京)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2015
【分類號(hào)】：P588

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本文編號(hào)：1985074