【作者】 吴锁平；

【导师】 吴才来；

【作者基本信息】 中国地质科学院 ， 矿物学、岩石学及矿床学， 2008， 博士

【摘要】 花岗岩作为壳幔相互作用的产物,承载着丰富的地质过程信息。然而,目前柴北缘古生代花岗岩类研究程度不高,极大地影响了地学工作者对该区古生代花岗岩质岩浆作用与造山响应的认识。同时。被广泛应用的Sr-Nd同位素初始比值和Nd同位素模式年龄的精度(误差)估算,一直未能引起地学界足够的重视,更缺乏可供利用的误差计算公式。基于上述存在的问题,本项研究的目的是:建立研究区古生代花岗岩类精确的年代学格架,判别其成因类型和构造环境,分析其造山响应:推演出一套适用于Sr、Nd同位素初始比值和Nd同位素模式年龄等重要示踪参数误差计算的公式;确定柴北缘地区大地构造属性(华北板块还是扬子板块?)。为达到上述目的,本项研究采用野外地质调查、实验室分析测试和综合分析相结合的研究方法。通过研究,得出如下认识及结论:1)柴北缘古生代花岗质岩浆活动可以划分为五期,由早到晚依次为:第Ⅰ期为早奥陶世末～中奥陶世(475Ma～460Ma),第Ⅱ期为晚奥陶世末～早志留世(450Ma～425Ma)、第Ⅲ期为早泥盆世(410Ma～395Ma)、第Ⅳ期为晚泥盆世晚期(380Ma～370Ma)和第Ⅴ期为中二叠世(275Ma～260Ma)。2)嗷唠山、大头羊沟、赛什腾山和团鱼山岩体属于准铝质钙碱性系列;大柴旦西北小岩体、野马滩岩体、锡铁山岩体、三岔沟岩体和柴达木山岩体都属于过铝质系列和高钾钙碱性系列;绿梁山岩体为强过铝质钙碱性～高钾钙碱性。3)嗷唠山和团鱼山岩体的源岩为基性岩(玄武岩);锡铁山和野马滩岩体的源区主要是中元古代沙柳河岩群;柴达木山和绿梁山岩体的源岩主要为古元古代达肯大坂岩群:大柴旦西北及大头羊沟小岩体的源区以达肯大坂岩群为主,但其中含有相当多的基性岩源岩;三岔沟和赛什腾山岩体的源岩是变质基性岩与变质沉积岩的混合物。模式年龄显示柴北缘具有扬子陆块基底的属性。4)柴达木山岩体和锡铁山岩体为S-型,绿梁山岩体为后碰撞SP型,大柴旦西北小岩体和野马滩岩体为I-S-过渡类型,其余岩体均为I-型。同一时期可以形成不同成因类型的花岗岩。5)各期花岗质岩浆活动的造山响应是:第Ⅰ期,洋壳深俯冲并发生榴辉岩相高压变质作用,地表形成火山弧(滩间山群)和洋壳发生部分熔融;第Ⅱ期,大洋闭合后,柴达木陆块向欧龙布鲁克陆块之下俯冲,俯冲的陆壳发生高压麻粒岩相变质作用(形成绿梁山高压基性麻粒岩),地幔物质上涌带动地壳物质部分熔融;第Ⅲ期,柴北缘地区进入后碰撞阶段,地壳加厚已经到最大状态即将开始减薄、加厚的地壳在深部发生部分熔融:第Ⅳ期,地壳不断减薄,山间盆地和陆内裂陷盆地形成,磨拉石～陆相火山岩建造,地幔上隆热流升高导致地壳部分熔融;第Ⅴ期,古特提斯洋封闭,柴北缘的二次俯冲引发又一期I-型花岗岩活动。6)Sr、Nd同位素初始比值和Nd同位素模式年龄等误差计算公式,在理论上是可靠的,在本目研究中的应用也是成功的。应用结果表明,Nd同位素参数的误差普遍小于Sr同位素参数的误差;同时,金红石饱和温度计比锆石饱和温度计更适合花岗岩类的岩浆结晶温度估算。更多还原

【Abstract】 As the product of crust-mantle interaction, granites contain abundant information about geological processes. So, it’s not easy to discuss Paleozoic granites and their orogenic response without detailed study in North Margin of Qaidam Basin. Meanwhile , the initial Sr ,Nd isotope ratios and Nd isotopic model age are used to trace the source rock of granites, but the precision estimation of these parameters have not been attached enough importance to. Also, there is no formula can be used to calculate errors of these parameters.Based on above reasons, the purposes of the research are to build a reliable geochronological framework of Paleozoic granitoid in study area, to distinguish their genetic types and tectonic settings, and to analyses their orogenic response; to derive a set of formulas for calculating errors of the paramers mentioned above; to ascertain if North Qaidam belongs to North China Block or Yangtze Block (South China). In order to achieve these goals, field geological surveying, laboratory testing, comprehensive analysis and research are adopted as a way for the studying.Research results and conclusions are as follows:1) Granitic magmatic activities during Paleozoic in North Margin of Qaidam Basin can be divided into five stages, from early to late , the first stage is from 475Ma to 460Ma, or from the end of Early Ordovician to Middle Ordovician; the second stage from 450Ma to 425Ma, or from the end of late Ordovician to Early Silurian; the third stage from 410Ma to 395Ma, equivalent to Early Devonian; the fouth stage from 380Ma to 370Ma, equals to Late Devonian; the last stage from 275Ma to 260Ma, equivalent to Middle Permian.2) Aolaoshan, Datouyanggou, Saishitengshan and Tuanyushan plutons belong to metaluminous calc alkaline series; Northwest Daqaidan, Yematan, Xitieshan, Sanchagou and Qaidamshan plutons attributed to peraluminous high-k calc-alkaline series; Luliangshan pluton belongs to strongly peraluminous calc-alkaline and high-k calc-alkaline series.3) The source rock of these plutons: basic rock (basalt ) for Aolaoshan and Tuanyushan plutons; Middle-Proterozoic Shaliuhe Group for Xitieshan and Yematan plutons; Early-Proterozoic Dakendaban Group for Chaidamushan and Lvliangshan plutons; mainly Dakendaban Group and a part of basic rock for Northwest Dachaidan and Datouyanggou plutons; the intermixture of metamorphic basic rock and sedimentary for Sanchagou and Saishitengshan plutons.4) Nd isotopic model ages show that the basement of North Qaidam is similar to that of Yangtz Block, Genetic types of granites in the area: Qaidamshan pluton and Xitieshan pluton are S-type granites; Lvliangshan pluton is post-collision SP type; Daqaidamxibei and Yematan plutons are I-S-type granites, the other plutons belong to I-type granite. Additionally, different genetic type granites can occur in the same stage of magmatasm.5) The orogenic responses of granitic magma activities during Paleozoic in North Margin of Qaidam Basin are: deep subduction and ecologite-facies metamorphism of the oceanic crust, and volcanic arc (Tanjianshan Group) formed at the first stage; Qaidam Block was subducted beneath Oulongbuluke Block and undergone a high-pressure granulite facies metamorphism to form Lvliangshan high-pressure basic granulite, upwelling mantel material caused the partial melting of crust material at the second stage; post-collision stage, crustal thickening reached to the top and ready to thinning, partial melting produced within thickened lower crust at the third stage; continuous crustal thinning , intramontane basins , rift basins and molasses - continengtal volcanic rock formations, upwelling mantel thermal flow lead to partial melting of the crust at the fourth stage; Paleo-Tethys Ocean was closed, the second subduction in North Qaidam Basin resuled in the activity of I-type granitic magma again.6) Formulas for error calculating about the initial Sr, Nd isotope ratios and Nd isotopic model age are theoretically reliable, and the application of these formulas in this research are also successful. The result of the application indicates that the error of Nd isotopic trace parameters is less than that of Sr isotopic trace parameters. By the way, the crystallization thermometer of rutile is more suitable than that of zircon.更多还原