發(fā)布時(shí)間：2018-06-02 04:30

  本文選題：揚(yáng)子克拉通 + 崆嶺地體　； 參考：《中國地質(zhì)大學(xué)》2017年碩士論文

【摘要】：新太古代是早期地殼的形成與演化過程中的一個(gè)重要階段,期間地球內(nèi)部動(dòng)力學(xué)機(jī)制可能發(fā)生重大改變,一直是前寒武紀(jì)研究的熱點(diǎn)。目前,~2.7-2.6的巖漿和變質(zhì)事件在全球各克拉通已有廣泛報(bào)道和記錄。然而,由于揚(yáng)子克拉通內(nèi)植被覆蓋嚴(yán)重以及較少的太古宙露頭,~2.7-2.6 Ga巖漿事件在揚(yáng)子克拉通的分布與性質(zhì)仍未得到很好地限定。近年來,鋯石U-Pb和Lu-Hf同位素分析技術(shù)的成熟和應(yīng)用,為揚(yáng)子克拉通前寒武紀(jì)研究提供了大量資料。此外,崆嶺地體作為揚(yáng)子克拉通的太古宙陸核,其內(nèi)保留有一系列古太古代-元古代巖石,最老可達(dá)3.45 Ga。本文對(duì)崆嶺地區(qū)北部現(xiàn)代河流(龔家河,霧渡河和鳊魚池溪)河沙中的碎屑鋯石進(jìn)行了原位微區(qū)U-Pb定年和Lu-Hf同位素分析。在三件樣品中共獲得323顆諧和鋯石年齡和190個(gè)鋯石Lu-Hf同位素?cái)?shù)據(jù),各樣品的年齡組成類似。總體而言,可劃分為以下年齡峰:3.3-3.1 Ga,3.0-2.8 Ga,2.7-2.6 Ga,2.6-2.2 Ga,2.0-1.9 Ga,1.9-1.7 Ga,1.7-1.5 Ga,和1.0-0.8 Ga,所占比例分別為5%,18%,30%,15%,27%,1%,2%和1%。在鋯石的陰極發(fā)光(CL)圖像顯示大多鋯石具有振蕩環(huán)帶,且Th/U比值多大于0.3,表明巖漿成因。然而部分2.0-1.9 Ga鋯石無巖漿振蕩環(huán)帶,Th/U比值小于0.1,以及與2.7-2.6 Ga鋯石近似一致的初始176Hf/177Hf(t)組成,表明其可能是由2.7-2.6 Ga鋯石經(jīng)后期變質(zhì)重結(jié)晶作用形成。另外鋯石的U-Pb和Lu-Hf同位素特征與當(dāng)?shù)貛r漿巖的鋯石記錄相似,由此該結(jié)果可以有效反映崆嶺地體的形成和演化階段。根據(jù)以上結(jié)果,崆嶺地區(qū)主體形成于中-新太古代(3.0-2.6 Ga)。Lu-Hf同位素結(jié)果顯示3.0-2.8 Ga鋯石εHf(t)值在-11.3和0之間,表明相應(yīng)母巖漿中含有大量古老陸殼物質(zhì)。而2.7-2.6 Ga鋯石的εHf(t)值高達(dá)+7.4,且其中約有43%鋯石εHf(t)值位于同期球粒隕石演化線上,表明巖漿活動(dòng)期間有較多新生陸殼物質(zhì)加入。根據(jù)2.7-2.6 Ga碎屑鋯石在本文樣品中所占比例,并與崆嶺內(nèi)變沉積巖和周邊古老沉積地層中的鋯石年齡結(jié)果進(jìn)行對(duì)比,筆者提出2.7-2.6 Ga巖漿活動(dòng)在當(dāng)?shù)靥胖鎺r石的形成過程中占主導(dǎo)地位。另外結(jié)合前人對(duì)揚(yáng)子克拉通內(nèi)零星2.7-2.6 Ga太古宙巖石露頭,火山巖中鋯石捕擄晶以及沉積地層中碎屑鋯石的研究,2.7-2.6 Ga構(gòu)造-熱事件可能廣泛影響了整個(gè)揚(yáng)子克拉通,與同時(shí)期世界范圍內(nèi)其他克拉通保持一致,該過程可能對(duì)應(yīng)早期揚(yáng)子克拉通的穩(wěn)定。自此以后,揚(yáng)子克拉通又經(jīng)歷了一系列新太古代-古元古代的構(gòu)造-熱事件,其可能與Sclavia/Nunavutia超級(jí)克拉通(2.6-2.2Ga)和Columbia超大陸(2.1-1.5 Ga)的聚合與裂解過程有關(guān)。
[Abstract]:NeoArchean is an important stage in the formation and evolution of the early crust, during which the dynamic mechanism of the earth's interior may change greatly, and it has always been a hot spot in the Precambrian study. The magmatic and metamorphic events of 2.7-2.6 have been widely reported and recorded in various cratons around the world. However, the distribution and properties of the Archean outcrop 2.7-2.6 Ga magma events in the Yangtze craton have not been well limited due to the serious vegetation coverage in the Yangtze craton. In recent years, the maturity and application of zircon U-Pb and Lu-Hf isotopic analysis techniques have provided a lot of data for the study of the Yangtze Craton Precambrian. In addition, as the Archean continental nucleus of the Yangtze craton, the Kongling terrane contains a series of ancient Archean and Proterozoic rocks, the oldest of which is 3.45Ga. In this paper, in situ U-Pb dating and Lu-Hf isotopic analysis of zircons from sediments of modern rivers (Gonjiahe, Wudu River and bream fish pond stream) in the northern part of the Kongling area have been carried out. A total of 323 harmonic zircon ages and 190 zircon Lu-Hf isotopic data were obtained from the three samples. The age composition of each sample was similar. Overall, the following age peaks can be divided into the following age peaks: 3.3-3.1 Ga1 + 3.0-2.8 GaN 2.7-2.6 Ga + 2.6-2.2 GaN 2.0-1.9 Ga 1.9-1.7 Ga 1.7-1.5 Ga, and 1.0-0.8 Ga, respectively, in 518183030 / 15 / 2727 / 27 / 27 / 27 and 1 / 2% and 1 / 2 / 2 / 2, respectively. The cathodoluminescence (CLL) images of zircon show that most zircons have oscillating ring zones and the Th/U ratio is more than 0.3 which indicates the magma genesis. However, part of the 2.0-1.9 Ga zircon without magmatic oscillation ring has a ratio of Th- / U less than 0.1, and an initial composition of 176Hf / 177Hftwhich is approximately consistent with that of 2.7-2.6 Ga zircon, indicating that it may have been formed by the late metamorphic recrystallization of 2.7-2.6 Ga zircon. In addition, the U-Pb and Lu-Hf isotopic characteristics of zircons are similar to the zircon records of the local magmatic rocks, which can effectively reflect the formation and evolution stages of the Kongling terrane. According to the above results, the main body of the Kongling area was formed in the Meso-Neo-Neo-Archean (3.0-2.6 Ga).Lu-Hf) isotope. The results show that the zircon 蔚 Hft) values of 3.0-2.8 Ga are between -11.3 and 0, indicating that the corresponding mother magma contains a large amount of ancient continental crust material. The 蔚 Hftt value of the 2.7-2.6 Ga zircon is as high as 7.4, and about 43% of the zircon 蔚 Hft) values are located on the evolution line of the chondrites, indicating that more new continental crust materials were added during the magmatic activity. According to the proportion of 2.7-2.6 Ga detrital zircon in the samples in this paper, the results are compared with the zircon ages of the altered sedimentary rocks in the Kongling and the ancient sedimentary strata around them. The authors suggest that the magmatic activity of 2.7-2.6 Ga dominates the formation of Archean rocks. In addition, in combination with previous studies on sporadic 2.7-2.6 Ga Archean outcrops in the Yangtze craton, zircon capture in volcanic rocks and detrital zircon in sedimentary strata, the tectonic and thermal events of 2.7-2.6 Ga may have affected the whole Yangtze craton extensively. This process may correspond to the stability of the early Yangtze craton. Since then, the Yangtze craton has undergone a series of tectonic-thermal events of the NeoArchean-Gu Yuan era, which may be related to the polymerization and pyrolysis of Sclavia/Nunavutia super craton 2.6-2.2 Ga and Columbia supercontinent 2.1-1.5 Ga).
【學(xué)位授予單位】：中國地質(zhì)大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類號(hào)】：P597.3

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本文編號(hào)：1967399