Ar/Ar thermochronology of the Kampa Dome, southern Tibet: Implications for tectonic evolution of the North Himalayan gneiss domes

Structural and thermochronological studies of the Kampa Dome provide constraints on timing and mechanisms of gneiss dome formation in southern Tibet. The core of Kampa Dome contains the Kampa Granite, a Cambrian orthogneiss that was deformed under high temperature (sub-solidus) conditions during Himalayan orogenesis. The Kampa Granite is intruded by syn-tectonic leucogranite dikes and sills of probable Oligocene to Miocene age. Overlying Paleozoic to Mesozoic metasedimentary rocks decrease in peak metamorphic grade from kyanite + staurolite grade at the base of the sequence to unmetamorphosed at the top. The Kampa Shear Zone traverses the Kampa Granite — metasediment contact and contains evidence for high-temperature to low-temperature ductile deformation and brittle faulting. The shear zone is interpreted to represent an exhumed portion of the South Tibetan Detachment System. Biotite and muscovite ⁴⁰Ar/³⁹Ar thermochronology from the metasedimentary sequence yields disturbed spectra with 14.22 ± 0.18 to 15.54 ± 0.39 Ma cooling ages and concordant spectra with 14.64 ± 0.15 to 14.68 ± 0.07 Ma cooling ages. Petrographic investigations suggest disturbed samples are associated with excess argon, intracrystalline deformation, mineral and fluid inclusions and/or chloritization that led to variations in argon systematics. We conclude that the entire metasedimentary sequence cooled rapidly through mica closure temperatures at  14.6 Ma. The Kampa Granite yields the youngest biotite ⁴⁰Ar/³⁹Ar ages of  13.7 Ma immediately below the granite–metasediment contact. We suggest that this age variation reflects either varying mica closure temperatures, re-heating of the Kampa Granite biotites above closure temperatures between 14.6 Ma and 13.7 Ma, or juxtaposition of rocks with different thermal histories. Our data do not corroborate the “inverse” mica cooling gradient observed in adjacent North Himalayan gneiss domes. Instead, we infer that mica cooling occurred in response to exhumation and conduction related to top-to-north normal faulting in the overlying sequence, top-to-south thrusting at depth, and coeval surface denudation.     

近4万年渤海西岸海侵时古海面的现代标高对比研究*

近4万年以来,相应于两次高太阳辐射暖湿期渤海西岸曾经两次海水泛陆事件,即40~28kaB.P.与10~4kaB.P.海侵事件。文章基于众多钻孔海相层中有孔虫、介形类等海相微体生物化石的组合特征恢复海水深度,重建了海侵最大时的古海面的现代标高。结果显示: 40~28kaB.P.海侵,海面的现代标高最高可达-11~-5m;10~4kaB.P.海侵则为2~3m。后者同众多研究所认为的中全新世存在高海面,海面高度为2~3m的结论大致吻合,前者则与全球气候尚处在间冰阶,冰川部分消融,世界洋面处在-50m的大背景不协调。而辽东与山东半岛沿海众多钻孔揭示,40~28kaB.P.渤海地区并没有高于-50~-20m海面存在的证据。通过区域环境的综合分析,认为40~28kaB.P.渤海西岸的海侵,是早玉木冰期持续4~5万年之久的冰期低海面环境,这种特殊的环境使现代渤海西岸的大部分区域远离沉积环境,成为冲刷侵蚀区,这种效应叠加在冰期边缘海式构造下沉与弧后盆地性质的构造下沉背景之上造成区域性异常地面低洼;渤海西岸异常地面低洼在间冰阶全球趋暖,冰川型海侵的过程中形成的区域性强烈"视"海侵(指示当时海侵时海水深度很大,而不是海水的陆泛范围大)。     

Unstable kinetic Alfvén wave in partially ionized plasma

The stability of kinetic Alfven waves is discussed for a partially ionized plasma with a flux of ionizing electrons which balance the plasma particle losses. Accidental electromagnetic perturbations are shown to be unstable due to the energy change of ionizing electrons.     

利用ADS40立体影像建立一体化数字线划图生产体系

为提高数字线划图生产的效率,本文基于ADS40立体影像测图技术,综合利用遥感技术、摄影测量技术、GIS技术及数据库系统,提出了一种一体化数字线划图生产方案。该方案通过嫁接航天远景MapMatrix以及清华山维EPS两个平台,实现针对ADS40相机L1级影像从数据读取、立体模型构建、立体采集、DLG处理以及最终形成GIS入库数据的整个处理流程。实验证明,本文提出的工作方案是利用遥感技术提升城市大比例尺地形图生产、缩短更新周期的有效方案。     

基于ADS 40数据的现状图测绘

新疆伊犁河谷土地开发整理现状图测绘由于其作业范围广,精度要求高,采用了ADS 40数字航空摄影数据。本文主要阐述了基于ADS 40数据进行航测外业和内业完成伊犁河谷4 000 km2的现状图测绘的生产过程。     

The Antarctic oscillation-East Asian summer monsoon connections in NCEP-1 and ERA-40

Connections between the spring Antarctic Oscillation(AAO)and the East Asian summer monsoon (EASM)in two reanalysis datasets—NCEP-1(NCEP/NCAR Reanalysis 1)and ERA-40(ECMWF 40- year Reanalysis)—are investigated in this study.Both show significant correlation between AAO and EASM rainfall over the Yangtze River valley,especially after about 1985.Though ERA-40 shows weaker anomalous signals connecting AAO and EASM over southern high latitudes than NCEP-1,both datasets reveal similar connecting patterns between ...     

New magnetic field measurements of β Cephei stars and slowly pulsating B stars

We present the results of the continuation of our magnetic survey with FORS 1 at the VLT of a sample of B‐type stars consisting of confirmed or candidate β Cephei stars and Slowly Pulsating B (hereafter SPB) stars, along with a small number of normal B‐type stars. A weak mean longitudinal magnetic field of the order of a few hundred Gauss was detected in three β Cephei stars and two stars suspected to be β Cephei stars, in five SPB stars and eight stars suspected to be SPB stars. Additionally, a longitudinal magnetic field at a level larger than 3σ has been diagnosed in two normal B‐type stars, the nitrogen‐rich early B‐type star HD 52089 and in the B5 IV star HD 153716. Roughly one third of β Cephei stars have detected magnetic fields: Out of 13 β Cephei stars studied to date with FORS 1, four stars possess weak magnetic fields, and out of the sample of six suspected β Cephei stars two show a weak magnetic field. The fraction of magnetic SPBs and candidate SPBs is found to be higher: Roughly half of the 34 SPB stars have been found to be magnetic and among the 16 candidate SPBs eight stars possess magnetic fields. In an attempt to understand why only a fraction of pulsating stars exhibit magnetic fields, we studied the position of magnetic and non‐magnetic pulsating stars in the H‐R diagram. We find that their domains in the H‐R diagram largely overlap, and no clear picture emerges as to the possible evolution of the magnetic field across the main sequence. It is possible that stronger fields tend to be found in stars with lower pulsating frequencies and smaller pulsating amplitudes. A somewhat similar trend is found if we consider a correlation between the field strength and the v sin i ‐values, i.e. stronger magnetic fields tend to be found in more slowly rotating stars (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

What is the closest black hole to the Sun?

We examine the distance of the two galactic microquasars GRO J1655–40 and A 0620–00 which are potentially the two closest black holes to the Sun. We aim to provide a picture as wide and complete as possible of the problem of measuring the distance of microquasars in our Galaxy. The purpose of this work is to fairly and critically review in great detail every distance method used for these two microquasars in order to show that the distances of probably all microquasars in our Galaxy are much more uncertain than currently admitted. Moreover, we show that many confirmations of quantitative results are often entangled and rely on very uncertain measurements. We also present a new determination of the maximum distance of GRO J1655–40 using red clump giant stars, and show that it confirms our earlier result of a distance less than 2 kpc instead of 3.2 kpc. Because, it then becomes more likely that GRO J1655–40 could originate from the stellar cluster NGC 6242, located at 1.0 kpc, we review the distance estimations of A 0620–00, which is so far the closest black hole with an average distance of about 1.0 kpc. We show that the distance methods used for A 0620–00 are also problematic. Finally, we present a new analysis of spectroscopic and astrometric archival data on this microquasar, and apply the maximum distance method of Foellmi et al. [Foellmi, C., Depagne, E., Dall, T.H., Mirabel, I.F., 2006b. A&A 457, 249]. It appears that A 0620–00 could indeed be even closer to the Sun than currently estimated, and consequently would be the closest known black hole to the Sun.     

四川省九龙县黑牛洞富铜矿矿床黑云母40Ar-39Ar测年及其地质意义

四川省九龙县黑牛洞铜矿床为近期新发现的一个规模在中型以上,产于江浪变质核杂岩中的富铜矿床。本文测试了黑牛洞铜矿床中与成矿密切相关的黑云母的40Ar/39Ar年龄为136.43±0.77 Ma,说明黑牛洞矿床形成于燕山中期。结合矿区附近李伍富铜床矿床地质特征及成矿年龄,表明黑牛洞铜矿床与李伍铜矿床为同一时期形成的矿床,两者成矿与松潘－甘孜造山带大规模岩浆热事件有关,这对于重新认识李伍铜矿床外围找矿潜力和进一步指导找矿工作具有重要意义。     

川西北花岗岩的冷却过程及其对区域成矿的制约

川西北地区位于松潘-甘孜造山带北部,产出众多的中生代花岗岩和卡林型金矿,金成矿作用与区域构造运动和岩浆活动有密切的内在联系。本文拟从花岗岩的角度分析这种内在联系,故测定了川西北的羊拱海黑云母二长花岗岩、达盖寨黑云母二长花岗岩和可尔因二云母二长花岗岩的黑云母或白云母Ar-Ar年龄,分别得到坪年龄158.7±1.4Ma、185.2±1.4Ma、和157.6±1.2Ma,并参考积累的川西北花岗岩体的年代学数据,绘制了造山带北部、中部、东缘中部几个主要花岗岩体的冷却轨迹。不同构造位置花岗岩体的冷却轨迹表明,从造山带北部到造山带东缘中部,各花岗岩体的侵位年龄依次变新,冷却速率依次变缓,在区域构造运动相对较弱期间,各花岗岩的冷却速率明显降低。由以上特征,本文推断在中生代陆内造山过程中,构造应力自松潘-甘孜造山带北部向造山带东缘中部传递,各区域先后由造山相对活跃期进入造山相对宁静期。在造山宁静期,构造运动较弱,花岗岩体缓慢冷却,地壳较长时间保持低温状态,利于金的成矿作用。因而,川西北的金矿主要形成于区域花岗岩的缓慢冷却阶段,这可能是金矿与花岗岩时空耦合的原因之一。