本文選題：藏北　切入點(diǎn)：奧陶紀(jì)不整合面　出處：《中國(guó)地質(zhì)大學(xué)(北京)》2015年碩士論文

【摘要】：西藏自治區(qū)北部那曲地區(qū)榮瑪鄉(xiāng)位于南羌塘地塊的北部,在榮瑪鄉(xiāng)西約3km的溫泉發(fā)育有一典型的不整合面,由中、上奧陶統(tǒng)塔石山組平行不整合于一套淺變質(zhì)中厚層石英砂巖夾薄層泥灰?guī)r之上。200余粒碎屑鋯石測(cè)年結(jié)果顯示塔石山組底部碎屑巖的最大沉積年齡為471±6Ma,近600粒碎屑鋯石測(cè)年結(jié)果顯示淺變質(zhì)石英砂巖的最大沉積年齡則為527±7Ma。溫泉不整合面上、下碎屑巖最大沉積年齡之差達(dá)56Ma,表明這兩套地層之間存在明顯的沉積間斷,且該平行不整合面的形成時(shí)代應(yīng)為奧陶紀(jì)早期。最近在鄰區(qū)發(fā)現(xiàn)了侵位于該套淺變質(zhì)石英砂巖中的早奧陶世花崗巖類(lèi)巖石(471—477Ma),因此將不整合面之下的淺變質(zhì)石英砂巖時(shí)代歸入寒武紀(jì)。對(duì)碎屑鋯石原位稀土元素和氧逸度計(jì)算研究未能顯示較好的結(jié)果。不整合面之上的塔石山組碎屑鋯石主要來(lái)源于“泛非運(yùn)動(dòng)”晚期形成的結(jié)晶巖,且為近源鋯石,表明了“泛非運(yùn)動(dòng)”晚期形成的結(jié)晶巖在奧陶紀(jì)早期就已隆升至地表遭受剝蝕,為區(qū)內(nèi)中、上奧陶統(tǒng)塔石山組的形成提供物質(zhì)來(lái)源。該奧陶紀(jì)平行不整合面的發(fā)現(xiàn),表明南羌塘地塊與喜馬拉雅地塊、拉薩地塊等相類(lèi)似,同屬岡瓦納大陸體系。南、北羌塘早古生代地層系統(tǒng)之間的顯著差異表明在寒武—奧陶紀(jì)之交,南、北羌塘地塊就已被古大洋盆分隔開(kāi),開(kāi)始各自獨(dú)立演化。
[Abstract]:Rongma Township of Naqu region in the north of Tibet Autonomous region is located in the northern part of the Qiangtang block in the south. There is a typical unconformities in the hot springs of 3km in Rongma Township. The parallel unconformity of the Upper Ordovician Tashishan formation on a set of shallow metamorphic quartz sandstone intercalated with thin layer marl shows that the maximum sedimentary age of detrital rocks at the bottom of the Tashishan formation is 471 鹵6Maand nearly 600 clastic rocks. The results of zircon dating show that the maximum sedimentary age of the shallow metamorphic quartz sandstone is 527 鹵7 Ma. The difference of the maximum sedimentary age of the lower clastic rocks is 56 Ma, which indicates that there are obvious sedimentary discontinuities between the two sets of strata. The formation age of the parallel unconformity plane should be early Ordovician. The early Ordovician granitic rocks transgressive in this set of shallow metamorphic quartz sandstone were recently discovered in the adjacent area, so the shallow metamorphic quartzite sand below the unconformity surface was found. The study of in situ rare earth elements and oxygen fugacity of clastic zircons has not shown good results. The detrital zircons of the Tashishan formation above the unconformable surface are mainly derived from the crystalline rocks formed in the late stage of the "Pan-African Movement". The near source zircon indicates that the crystalline rocks formed in the late Pan-African Movement have been uplifted to the surface and denudated in the early Ordovician. The formation of the Upper Ordovician Tashishan formation provides a material source. The discovery of the parallel unconformities in the Ordovician indicates that the southern Qiangtang block is similar to the Himalayan and Lhasa blocks and belongs to the Gondwana continental system. The significant differences between the early Paleozoic stratigraphic systems in the northern Qiangtang indicate that at the turn of Cambrian-Ordovician the southern and northern Qiangtang blocks were separated by the paleo-oceanic basin and began to evolve independently.
【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(lèi)號(hào)】：P588.21;P534.4

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