【作者】 陈文；

【导师】 崔彬； 刘敦一；

【作者基本信息】 中国地质大学（北京） ， 矿物学、岩石学、矿床学， 2003， 博士

【摘要】 青藏高原倍受世界各国地质学家的关注。在青藏高原地质研究中，其演化的时间格架是重要内容之一。长期以来，科学家们在年代学方面做了大量工作，但因为缺乏系统性，致使多期地质事件的同位素年代制约精度很差。本文首先从常规⁴⁰Ar／³⁹Ar阶段升温定年实验室的改进入手，进而建立了激光⁴⁰Ar／³⁹Ar定年实验室，利用这两种先进同位素地质定年方法，结合其他手段，对青藏高原腹地和北缘的阿尔金断裂系多期地质事件进行了详细的同位素年代学研究： 一、参照国际先进实验室的流程，对我们的常规⁴⁰Ar／³⁹Ar阶段升温实验室在样品的预处理、样品的照射条件和系统空白测量及校正等方面进行了改进，使之产出的同位素年代数据更可靠并为国际同行所承认。 二、通过实验设备配制、样品对激光吸收能力试验、高真空熔样室设计加工、样品加工、样品照射及J值研究、干扰核反应校正、系统空白测定和实验流程的探索利优化等工作，建立起激光⁴⁰Ar／³⁹Ar定年实验室。用该方法可做如下工作：1．实现了微量样品乃至于单颗粒矿物测年和在岩石光片上寻找待测矿物直接进行微区（几十微米—几百微米）⁴⁰Ar／³⁹Ar测年。2．进行年轻样的⁴⁰Ar／³⁹Ar年龄分析。3．利用连续激光能量连续可调之特性进行矿物阶段升温测年。 三、在花岗岩类岩石成因判别的基础上，应用多种同位素测年手段，较为精确地测定了青藏高原腹地中生代以来板块俯冲、地体拼合碰撞及后期陆内演化等多期地质事件的时代及确定了阿尔金断裂形成时代和后期三次大规模活化的时代，初步建立起青藏高原中生代以来地质演化的同位素年代格架（把青藏高原腹地及其北缘中生代以来发生的板块俯冲、会聚、地体磁撞造山及后期陆内演化等大、中、小各期地质事件分成以下四大期十二小期）： Ⅰ期：240-212Ma，板块俯冲；地体碰撞；岩浆侵位；阿尔金断裂形成。 Ⅰ₁：240-（＞）220Ma，巴颜喀拉洋壳向昆仑地体俯冲，以昆仑岩带和阿尼玛卿岩带中CAG型岩浆侵位为标志；阿尔金剪切作用发生。 Ⅰ₂：227-218Ma，巴颜喀拉和羌塘之间洋壳俯冲，以金沙江岩带IAG型岩浆侵位为标志。 Ⅰ₃：217-212Ma，造山后期岩浆侵位。以POG型花岗岩在巴颜喀拉地体内大量生成、在阿尼玛卿岩带中较多出现、在昆仑岩带利金沙江岩带少量出现为标志。 Ⅱ期：160-140Ma，断裂系活动；金沙江、东昆仑剪切作用发生；部分岩体动力变质变形。动力来源于拉萨地体和羌塘地体的碰撞。 Ⅱ₁：160-155Ma，金沙江岩带发生剪切变形，岩体局部糜棱岩化。 Ⅱ₂：150-145Ma，昆仑岩带、阿尼玛卿岩带岩石发生动力变质变形，岩体局部糜棱岩化。 Ⅲ₃：157-140Ma 阿尔金断裂系活化；大范围碱性岩浆侵位 中国地质大学（北京）博士论文 Ill期：120习0 Ma，强度不高但范围广泛的动、热构造事件发生。 断裂系、剪切带再活动。动力来源于北部。Ill：120－100Ma，昆仑岩带、阿尼玛卿岩带部分岩体中矿物氟同位素体系重设。Illa：119－90Ma 阿尔金断裂再次活动。Illa：110－90 Ma 金沙江断裂再次活动。 IV期：45 Ma以来，高原快速抬升；断裂系活化，产生大规模走滑活动； 岩体或被断层切割、迁移，或抬升剥蚀。IVI：45－25MI，岩体和整个青藏高原一起呈周期性的、脉动式抬升。IVZ：～25M2，岩体揭顶。IVs：25Ma以来，岩体剥蚀。更多还原

【Abstract】 1. To improve the classic 40Ar/39 Ar dating techniqueThe 40Ar/39Ar dating technique is developed from the conventional K-Ar method. Several studies display that geological events sometimes result in excess Ar component within the minerals and often result in radiogenic Ar loss. In the two cases, the wrong ages obtained from the classical K-Ar method are higher than the true age (excess Ar present) or lower than the true age (radiogenic Ar loss). However, in the 40Ar/39Ar stepwise incremental heating method, the calculation technique of plateau age can avoid this error. Therefore, this method is especially useful for dating rocks that have undergone complex thermo-tectonic history in polymetamorphic areas. By improving the technique of sample preparing, sample irradiation in the nuclear reactor and correction of blanks, our laboratory has ability to produce more and more high precision ages of 40Ar/39Ar.2. Fundamental of laser 40Ar/39Ar dating method:Our Laboratory has successfully set up the laser microprobe 40Ar/39Ar geological dating method. Our works include adjustment of the high-gain electron multiplier in mass spectrometer and correction of mass discrimination, adjustment of the Laser, test for absorption ability of minerals to laser, designing and manufacturing high-vacuum sample chamber, sample preparation and irradiation, research on the variability of J values on the surface of rock chips, measuring atmospheric argon, determination and correction of blanks and ages, etc.The laser microprobe technique is particularly effective for some geological samples. It can be used, for example, for research of distribution of the components in extremely small samples that are very difficult to be separated and purified and those which contain excess argon. If samples contain different generation of mineral fragments of same mineralogical species, then it is possible to analyze the different generation of minerals and receive information about their ages and migration of Ar isotopes during mineral grains were fully or partly recrystallized.3. Isotope geochronology study in the central part of the Tibetan plateauThe central part of the Tibetan Plateau is consists of the Kunlun Terrane, Bayanhar Terrane, Qiantang Terrane and Lhasa Terrane . On the north of it is the Qaidam Basin. This area was controlled by four large-scale faults: South Kunlun suture, Jinsshajiang suture, Bangonghu Suture and Yaluzangbu suture.This area has undergone polymetamorphism and deformation and at least three periods of magmatism. Continuous activities of magmatism, metamorphism were mainly controlled by collision of the Terranes. Combining the isotope geochronological results with the fieldwork observations, we could draw some conclusions as follows:The Kunlun-Bayan Har terranes experienced the subduction of oceanic crust and collision somewhat earlier than the Bayan Har-Qiangtang terranes, with only a very short interval in between and even the collisions overlapped partially in time.In the northern part, the oceanic crust occurring between the Bayan Har and Kunlun terranes started subduction from south to north at about 243 Ma, and did not stop until the development of post-orogenic POG-type granite in the Bayan Har terrane at 220 Ma, thus illustrating the orogeny in the form of subduction and collision kept active for over 20 Ma. But it remains to be identified whether the Bayan Har terrane collided with the Kunlun immediately after the termination of the subduction. Although the layers uplifted nearly 2 km prior to the emplacement of POG type granite in Xidatan and Xiaonanchuan, it can not be confirmed that there occurred large scale collision within the Kunlun terrane, since no continent-continent collision-related granites (CCG type) were found in the East Kunlun rock belt.In the Jinshajiang suture zone, it lasted only a span of 9 Ma from the start of subduction (marked by the eruption of andesitic magmas and intrusion of intermediate rock of IAG type at about 227 Ma) to the end of subduction, con更多还原