藏北荣玛乡早古生代碎屑岩地球化学特征及地质意义

发布时间：2018-03-24 09:11

本文选题：藏北　切入点：奥陶纪不整合面　出处：《中国地质大学(北京)》2015年硕士论文

【摘要】：西藏自治区北部那曲地区荣玛乡位于南羌塘地块的北部,在荣玛乡西约3km的温泉发育有一典型的不整合面,由中、上奥陶统塔石山组平行不整合于一套浅变质中厚层石英砂岩夹薄层泥灰岩之上。200余粒碎屑锆石测年结果显示塔石山组底部碎屑岩的最大沉积年龄为471±6Ma,近600粒碎屑锆石测年结果显示浅变质石英砂岩的最大沉积年龄则为527±7Ma。温泉不整合面上、下碎屑岩最大沉积年龄之差达56Ma,表明这两套地层之间存在明显的沉积间断,且该平行不整合面的形成时代应为奥陶纪早期。最近在邻区发现了侵位于该套浅变质石英砂岩中的早奥陶世花岗岩类岩石(471—477Ma),因此将不整合面之下的浅变质石英砂岩时代归入寒武纪。对碎屑锆石原位稀土元素和氧逸度计算研究未能显示较好的结果。不整合面之上的塔石山组碎屑锆石主要来源于“泛非运动”晚期形成的结晶岩,且为近源锆石,表明了“泛非运动”晚期形成的结晶岩在奥陶纪早期就已隆升至地表遭受剥蚀,为区内中、上奥陶统塔石山组的形成提供物质来源。该奥陶纪平行不整合面的发现,表明南羌塘地块与喜马拉雅地块、拉萨地块等相类似,同属冈瓦纳大陆体系。南、北羌塘早古生代地层系统之间的显著差异表明在寒武—奥陶纪之交,南、北羌塘地块就已被古大洋盆分隔开,开始各自独立演化。
[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 卤6Maand nearly 600 clastic rocks. The results of zircon dating show that the maximum sedimentary age of the shallow metamorphic quartz sandstone is 527 卤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.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588.21;P534.4

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