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Science China Earth Sciences 2004年第12期47卷 1102-1112页

作者： zhang jianxin meng fancong yang jingsui Institute of Geology Chinese Academy of Geological Sciences Beijing 100037 China Institute of Geology Chinese Academy of Geological Sciences Beijing 100037 China Institute of Geology Chinese Academy of Geological Sciences Beijing 100037 China

In Yuka-Luofengpo area of the north Qaidam Mountains, eclogitic metapelites are recognized. The metapelites enclosed lenses of eclogites, and locally intercalated with eclogites. Their typical mineral assemblages are garnet+kyanite+chloritoid+phengite+quartz+rutile. Strong growth zoning is preserved in garnets of metapelites, and phengite contains up to 3.4 Si per formula units. The petrographic observations and textural relations testify to the following sequence of mineral assemblages connected to three metamorphic stage: (1) Grt+ChlI+CldI +PheI ± StI+Qtz; (2) Grt+Ky+PheII±CldII+Qtz; and (3) Grt+CldIII+ChlII+PheIII+StII ± ky+ Qtz. Applying THERMOCALC Program, Grt-Phe thermometer and Grt-Ky-Phe-Qtz barometry, P-T conditions for three metamorphic stages were obtained: P=1.07±0.31GPa, T=564±22? (prograde stage); P=2.3–3.1GPa, T=615–700°C-(peak stage); and P =1.22 ± 0.26GPa, T=581±20°C (retrograde stage). A hairpin shape P-T path similar to that of adjacent eclogite is inferred. In combination with eclogitic mineral relics in marbles and orthogneisses enclosing eclogites, we thought that the relationship between eclogites and country rocks is “in situ” rather than “tectonic emplacement”.

关键词： eclogitic metapelites, in situ, tectonic emplacement.

Evidence for UHP metamor-phism of eclogites from the Altun Mountains

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Chinese Science Bulletin 2002年第9期47卷 751-755页

作者： jianxin zhang jingsui yang Zhiqin Xu fancong meng Haibing Li Rendeng Shi Chinese Acad Geol Sci Inst Geol Beijing 100037 Peoples R China

Ultrahigh pressure (UHP) metamorphism refers to metamorphism that has occurred at pressures for the stability of coesite. The polycrystalline quartz inclusions showing the characteristic texture within garnets of eclogites indicates the pre-existence of coesites under the peak meta-morphic condition. The unusual exsolution textures in om-pacites and apatites, and the pressure estimations of phengite-bearing eclogites have been taken to provide further proof of eclogite formation under the UHP conditions. Combined with the fact that coesites have been observed in country rocks of eclogites in North Qaidam Mountains, another UHP metamorphic belt cut by the large-scale strike-slip fault in the Altun-North Qaidam area of China is confirmed.

关键词： Altun Mountains eclogite UHP metamorphism.

Lawsonite-bearing eclogites in the north Qilian and north Altyn Tagh:Evidence for cold subduction of oceanic crust

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Chinese Science Bulletin 2006年第10期51卷 1238-1244页

作者： zhang jianxin meng fancong Institute of Geology Chinese Academy of Geological Sciences Beijing100037 China

Lawsonite-bearing eclogites are recog-nized respectively in the north Qilian (NQL) and north Altyn Tagh (NAT), based on petrography and mineral chemistry. Lawsonite coexists with omphacite and phengite as inclusions in garnet, indicating ec-logite-facies metamorphism. Peak metamorphic con-ditions for equilibrium lawsonite-omphacite-phengite- garnet peak assemblages are estimated to be 2.1―2.4 GPa and 420―500℃, which is in the stability field of lawsonite eclogite-facies. A low geotherm of 6―8℃/km is referred, which is in consistent with a cold subduction. The occurrences of lawsonite-bearing eclogites in both NQL and NAT provide further evi-dence that the NAT HP/LT metamorphic belt is pos-sibly the northwestward extension of the NQL HP/LT metamorphic belt offset by the Altyn Tagh left-lateral slip fault. The NQL and NAT lawsonite-bearing ec-logites are formed by subduction of oceanic crust before collision of the Alashan and Qilian blocks in early Paleozoic.

关键词：祁连山阿尔泰山硬柱石榴辉岩洋底壳

Genesis of the mega-crystal zircons in the dunite veins of North Qaidam Mountains,northwestern China

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Chinese Science Bulletin 2009年第16期54卷 4688-4696页

作者： meng fancong zhang jianxin Institute of Geology Chinese Academy of Geological Sciences Beijing 100037 China

A megacrystal zircon occurs in serpentinized dunite veins from North Qaidam, northwestern China. It is red-brown and 3―4 mm long and 2 mm wide in size. BSE imaging shows the presence of micro-grains (30―50 μm) of zircon between olivine and serpentine, part of them gathering into clusters (100―300 μm). Thus we infer that these zircon crystals were precipitated from hydrothermal fluid. Inclusions of baddeleyite (white) in the shape of isolated island locally occur in the large zircon (grey), implying that the former formed earlier than the latter. The mirco-baddeleyite (50―100 μm) aggregate consists of baddeleyite (3―5 μm) and olivine (<5 μm), indicating the zircon formation through interaction between baddeleyite and silica-bearing fluid. Therefore, we consider a genetic link between the formation of the large zircon and the serpentinization of dunite. SHIRIMP U-Pb dating of the large zircon gave two groups of concordant ages at 414 ± 13 Ma and 371 ± 9 Ma, respectively. This might reflect two episodes of zircon growth in response to two episodes of fluid action.

关键词：柴达木锆石中国晶体西北岩脉山区巨型

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Determination of the Altyn Tagh strike-slip fault basin and its relationship with mountains

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Chinese Science Bulletin 2002年第7期47卷 572-577页

作者： Li Haibing yang jingsui Shi Rendeng Wu Cailai P.Tapponnier Wan Yusheng zhang jianxin meng Fanchong Institute of Geology Chinese Academy of Geological Sciences100037BeijingChina Institut de Physique du Globe 4 Place Jussieu75252ParisCedex 05France

A special extended basin topography is developed in the middle segment of the Altyn Tagh Fault Zone. The ratio of its length to width is over 50. The long boundaries at the two sides of the basin are controlled by the straight normal faults with strike-slip component. Within the basin, the Cenozoic strata are spread. The Altyn Tagh main fault goes through the basin, and a series of strike-slip topography was formed within the basin. The reverse thrust structures were formed at the two sides of the center of the basin, thus making the geological bodies composed of old metamorphic rocks at the two sides of the basin extrude vertically, and forming the extended massif (mountain) at the sides of the basin and parallel to the basin. This special topography was called the strike-slip fault basin. The giant extended strike-slip fault basin began to form during Pliocene, and its topography was basically formed during the late Pleistocene. It is the special topography formed during the strike-slip deformation

关键词： strike-slip fault basin transpression uplifting Altyn Tagh Fault Zone.

柴北缘锡铁山早古生代HP/UHP变质作用后的构造热事件——花岗岩和片麻岩的同位素与岩石地球化学证据

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岩石学报 2005年第1期21卷 45-56页

作者：孟繁聪张建新杨经绥中国地质科学院地质研究所北京100037

对柴达木盆地北缘锡铁山地区花岗岩中的结石采用单颗粒锆石U-Pb法(TIMS)测年,谐合线上数据点给出的结果为428±1Ma,代表了花岗质岩浆的形成(上侵)时代,在锆石岩相学研究的基础上对围岩片麻岩中的锆石采用SHRIMP进行测年,10个点的Th/U比... 详细信息

对柴达木盆地北缘锡铁山地区花岗岩中的结石采用单颗粒锆石U-Pb法(TIMS)测年,谐合线上数据点给出的结果为428±1Ma,代表了花岗质岩浆的形成(上侵)时代,在锆石岩相学研究的基础上对围岩片麻岩中的锆石采用SHRIMP进行测年,10个点的Th/U比变化范围在0.01-0.08,表明锆石为变质成因,10个数据点给出的206Pb/238U表面年龄的加权平均值为435±7Ma,代表变质岩的变质年龄,两类岩石的锆石年龄在误差范围内一致,岩浆作用与变质作用时差很小。花岗岩地球化学特征表明岩体为Ⅰ型花岗岩,它的主量元素、稀土元素和微量元素特征与围岩片麻岩十分类似,表明花岗岩的源岩在成分上与围岩片麻岩相似。花岗岩的Nd模式年龄TDM=1.4-1.5Ga,围岩片麻岩的TDM=1.9-2.2Ga,暗示岩浆形成时有地幔物质的添加或混染。推测是由于地幔上隆使深部地壳岩石发生了部分熔融作用,形成花岗质岩浆时添加了地幔物质。锡铁山花岗岩是早古生代碰撞后伸展环境的产物。

关键词：锆石 U-Pb年龄 Sm—Nd同位素组成地球化学花岗岩片麻岩锡铁山柴北缘

CRETACEOUS (?) VOLCANIC ROCKS ON THE NORTH END OF THE ALTYN TAGH FAULT:CHARACTERISTICS AND TECTONIC IMPLICATIONS

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地学前缘 2000年第S1期7卷 218-220页

作者： meng fancong, yang jingsui, zhang jianxin, Wu Cailai, Shi Rendeng, Li Haibing, Li Tianfu [WT5,5”BX](Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China)

The age and evolutional history of the Altyn Tagh fault and its role in the formation and uplift of the Qinghai—Tibetan plateau have been focused for years. Many geologists believe that the formation of the fault is a result of the collision between India and Asia. Some people thought that it should have formed earlier than Cenozoic but have no critical evidence. Here we report a preliminary result from our recent investigation on the volcanic rocks at the north end of the Altyn Tagh fault.1 The volcanic rocks on the north end of the Altyn Tagh fault The volcanic rocks are located on the north end of the Altyn Tagh fault, northern Qinghai—Tibetan plateau. The investigated volcano occurs in the Jiuxi basin, a Cretaceous and Tertiary depositional basin. It is about 300m×100m in size and form about a 100m high cliff above the folded Cretaceous strata. It likes relic neck of a volcano rather than a kind of widely distributed lava flow commonly seen in the northern Tibet. The country rocks are Cretaceous sandstone, silt and fine\|grained conglomerate. The cliff formed most likely due to the differing erosion between the hard volcanic rocks and soft rocks.

关键词： volcanic rocks Altyn Tagh fault Jiuxi Hoh Xil Tibet Gansh u

柴北缘绿梁山早古生代花岗岩浆作用与高温变质作用的同时性

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岩石学报 2008年第7期24卷 1585-1594页

作者：孟繁聪张建新中国地质科学院地质研究所北京100037

采用 SHRIMP 方法获得绿梁山花岗岩的锆石 U-Pb 年龄为430±8Ma(12个测点平均),所有测点的 Tb/U 比值均大于0.1,该年龄代表花岗岩的形成年龄。同时获得部分具有核-幔结构的继承锆石,其核部年龄为475～460Ma,Th/U 比值为0.01～0.02,为典... 详细信息

采用 SHRIMP 方法获得绿梁山花岗岩的锆石 U-Pb 年龄为430±8Ma(12个测点平均),所有测点的 Tb/U 比值均大于0.1,该年龄代表花岗岩的形成年龄。同时获得部分具有核-幔结构的继承锆石,其核部年龄为475～460Ma,Th/U 比值为0.01～0.02,为典型的变质锆石,与围岩片麻岩中的锆石类似,反映了花岗岩与片麻岩之间的成因联系。绿梁山花岗岩属于钙碱性系列,SiO_2含量为65.63%～74.78%,变化较大,属于过铝质岩石,推测其源岩以沉积岩为主。围岩片麻岩以变质沉积岩为主,可能为花岗岩的主要源岩。花岗岩的(^(87)Sr/^(86)Sr)_■为0.71075(t=430Ma),ε_(Nd(430Ma))为-5.5～-4.6,与围岩片麻岩的 Sr-Nd 同位素组成存在较大差别,可能反映了花岗岩形成于高温缺水的环境或者成岩时有地幔物质/年轻地壳物质的加入。花岗岩形成时代与片麻岩变质时代的一致性(430Ma),反映了它们为同一区域构造热事件的产物,是俯冲陆壳发生热松弛的记录。

关键词：花岗岩 SHRIMP锆石地球化学绿梁山柴北缘

STUDY ON THE SEISMIC SOURCE MECHANISMS OF THE TIBETAN PLATEAU

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地学前缘 2000年第S1期7卷 347-349页

作者： zhang Chunhe, yang jingsui, Xu Zhiqin, Li Haibing, zhang jianxin, Wu Cailai, Shi Rendeng, meng fancong, Song Suguang[WT5,5”BX](Institute of Geology, CAGS, 26 Baiwanzhuang St., Beijing 100037, China, Fax: 86\|10\|68311293, Tel:86\|10\|68329770,E\|mail:

Tibet has often been called the “Roof of the World”. The plateau is probably the largest and highest area ever to exist in Earth history, with an average elevation exceeding 5000m. The uplifting of the Tibetan Plateau is the result of continent\|continent collision. This process is still going on and is significant for us to understand the formation and the evolution of global ***’s generally accepted is act as the northern boundary of the Tibetan Plateau is the Altyn Tagh Fault. The Altyn Tagh Fault is recognized as a large\|scale left\|lateral strike\|slip fault, many studies indicate it is the northern margin of the eastward extruded of crustal blocks and the northern boundary of the Plateau as well. Compared to the knowledge on the southern plateau and the Himalaya, we know much less about the northern plateau and the Altyn Tagh Fault. Some people have already begun to realize the importance of the latter for the revealing the uplifting of the Plateau.

关键词： the Tibetan Plateau seismic source mechanism the Altyn Tagh fault, the Y—D—C. fault zone the B—J. fault zone

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北秦岭造山带的早古生代多期变质作用

岩石学报 2011年第4期27卷 1179-1190页

作者：张建新于胜尧孟繁聪中国地质科学院地质研究所北京100037

北秦岭造山带的秦岭岩群以高级变质岩石为特征,主要包括少量榴辉岩、高压麻粒岩和区域上广泛分布的麻粒岩-角闪岩相变质岩石。年代学研究显示秦岭岩群中不同岩石记录了多期变质作用。已有的定年资料给出北秦岭官坡地区的榴辉岩的年龄为5... 详细信息

北秦岭造山带的秦岭岩群以高级变质岩石为特征,主要包括少量榴辉岩、高压麻粒岩和区域上广泛分布的麻粒岩-角闪岩相变质岩石。年代学研究显示秦岭岩群中不同岩石记录了多期变质作用。已有的定年资料给出北秦岭官坡地区的榴辉岩的年龄为500Ma左右,代表榴辉岩相的变质时代。结合岩相学资料,对两个高压麻粒岩样品的SHRIMP和LA-ICPMSU-Pb测定分别获得504±7Ma和506±3Ma的年龄,应代表高压麻粒岩相变质时代。这表明高压麻粒岩和相邻的榴辉岩有相近的变质时代,但形成在造山带中不同的构热造环境中。西峡地区的角闪二辉麻粒岩的U-Pb定年给出两组早古生代年龄,一组为440±2Ma,可能代表了中低压麻粒岩相的变质时代,另一组为426±1Ma,应代表区域角闪岩相的变质时代。桐柏山北部的石榴二辉麻粒岩的U-Pb定年数据给出436±1Ma的年龄,为中压麻粒岩相的变质时代。这些资料表明北秦岭造山带经历了早奥陶世的俯冲和地壳增厚作用,并在晚志留世遭受了广泛的巴罗式区域变质作用。

关键词：北秦岭榴辉岩高压麻粒岩 U-Pb定年巴罗式变质作用碰撞造山作用