本文選題：鋯石U-Pb定年 + 淺變質(zhì)巖系��； 參考：《巖石學(xué)報(bào)》2017年09期

【摘要】：瀾滄群出露于滇西"三江"地區(qū)的南段,其主要巖石由遭受低級(jí)變質(zhì)作用改造的泥質(zhì)巖和基性火山巖組成。這些巖石普遍經(jīng)歷了古特提斯洋的閉合以及隨后的洋陸俯沖過(guò)程,是研究古特提斯洋俯沖-碰撞過(guò)程的重要窗口。但是有關(guān)瀾滄群的形成時(shí)代、物質(zhì)來(lái)源以及形成的構(gòu)造背景等一系列問(wèn)題長(zhǎng)期以來(lái)存在著多種爭(zhēng)議。本文對(duì)瀾滄群中3件石英巖和1件絹云母變質(zhì)石英砂巖樣品中分選出的碎屑鋯石進(jìn)行了陰極發(fā)光圖像分析和LA-ICP-MS U-Pb年代學(xué)研究。瀾滄群淺變質(zhì)巖系碎屑鋯石具有明顯或弱的振蕩環(huán)帶和較高的Th/U比值,表明巖漿成因。年代學(xué)分析結(jié)果表明,4件淺變質(zhì)巖石樣品均得到了兩組主要年齡峰值,分別為530Ma和930Ma、570Ma和915Ma、540Ma和960Ma、570Ma和910Ma。本次研究中碎屑鋯石U-Pb年齡主要分布在570~530Ma和960~910Ma。其中,最年輕的碎屑鋯石年齡峰值~530Ma,支持了前人認(rèn)為瀾滄群沉積時(shí)代為中奧陶紀(jì)(462~454Ma)的認(rèn)識(shí)。本研究中瀾滄群淺變質(zhì)巖系碎屑鋯石年齡分布特征表明源區(qū)可能主要為泛非期和羅迪尼亞超大陸聚合-裂解過(guò)程中形成的巖漿巖。碎屑鋯石磨圓較好指示其經(jīng)歷了較長(zhǎng)距離的搬運(yùn)。瀾滄群淺變質(zhì)巖系碎屑鋯石與羌塘、特提斯喜馬拉雅和拉薩地體變沉積巖或地層中碎屑鋯石具有相似的年齡分布特征,表明它們可能具有相似的源區(qū)。
[Abstract]:Lancang Group is located in the southern section of Sanjiang area in western Yunnan. Its main rocks are composed of shaly rock and basic volcanic rock which were transformed by low grade metamorphism. These rocks generally experienced the closure of the paleoTethys ocean and the subsequent oceanic subduction process, which is an important window to study the subduction-collision process of the paleoTethys ocean. However, there have been many controversies about the formation age, material source and tectonic background of Lancang Group for a long time. The clastic zircon from three quartzite samples and one sericite metamorphic quartz sandstone from Lancang Group have been studied by cathodoluminescence image analysis and LA-ICP-MS U-Pb chronology. The clastic zircon of the shallow metamorphic rock series of Lancang Group has obvious or weak oscillatory ring zone and high Th- / U ratio, which indicates the magma genesis. The results of geochronological analysis show that the four samples of shallow metamorphic rocks have two main age peaks of 530Ma and 930Ma-570Ma and 915Ma-540Ma and 960Ma-570Ma and 910Marespectively. The U-Pb ages of detrital zircon are mainly distributed at 570 Ma and 910 Ma. The youngest detrital zircon age peak value is 530 Ma, which supports the previous understanding that the Lancang Group sedimentary age is the Middle Ordovician (4622 ~ 454 Ma). The age distribution of zircon in the metamorphic rock series of Lancang group indicates that the source area may be mainly composed of magmatic rocks formed during the Pan-African period and during the process of polymerization-pyrolysis of the Lodinia supercontinent. Zircon grinding is a good indicator of its long distance transport. The clastic zircon of the metamorphic rock series of Lancang group has similar age distribution characteristics with that of terrane metamorphic sedimentary rocks or strata in Qiangtang, Tethys Himalayan and Lhasa terrane, indicating that they may have similar source regions.
【作者單位】： 中國(guó)地質(zhì)科學(xué)院地質(zhì)研究所;
【基金】：國(guó)家重點(diǎn)研發(fā)計(jì)劃項(xiàng)目(2016YFC0600310) 國(guó)家自然科學(xué)基金項(xiàng)目(41372069、41302039)聯(lián)合資助
【分類(lèi)號(hào)】：P588.3;P597.3

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