Fluid inclusion evidence for basement decompression during Permo-Triassic extension, SE New England, USA     

K. O'HARA 《Journal of Metamorphic Geology》1991,9(5):567-579

Abstract CO₂-bearing fluid inclusions in strongly lineated but weakly foliated late Precambrian gneisses within the Hope Valley Shear zone of Connecticut and Rhode Island are of mixed composition ( X _co2± 0.1; 7 wt% NaCl equivalent) and variable density (0.59–0.86 g/ml) and occur mainly as isolated inclusions. Also present are dilute (3 wt% NaCl equivalent) aqueous inclusions which occur on healed fractures related to greenschist facies retrograde metamorphism. Isochores for dense isolated CO₂-bearing inclusions indicate pressures of 7.5–9 kbar at 500–600° C, the estimated temperature conditions of peak metamorphism. Published ⁴⁰Ar/³⁹Ar hornblende plateau age spectra indicate cooling through about 500° C at 265 ± 5 Ma. Isochores for low-density CO₂-bearing inclusions and aqueous inclusions intersect at the conditions of retrograde metamorphism (325–400° C) and indicate pressures of 3–4 kbar. Published ⁴⁰Ar/³⁹Ar biotite plateau ages indicate cooling through about 300° C at 250 ± 5 Ma. These data define a P–T uplift curve for the region which is convex towards the temperature axis and indicate uplift rates between 0.4 and 3.3 mm/year in Permian time. Exhumation of basement gneisses was coeval with normal (west-down) motion along the regional basement–cover contact (Honey Hill–Lake Char–Willimantic fault system), and is interpreted as due to post-orogenic extensional collapse of the Alleghanian orogeny.  相似文献   

致密星的X射线辐射时延现象     

屈进禄  宋黎明  吴枚  李年福 《天文学进展》2002,20(2):144-157

能谱仅反映了高能天体辐射的部分性质，而高能X射线辐射的时变可以反映致密天体的动态性质。因此，在构造高能辐射的理论模型时，既要考虑X辐射的能谱性质，也要考虑其时变性质。特别对高能天体X辐射的快速光变，一般认为其发生在致密天体附近，致密天体快速光变的研究可以揭示出致密天体附近的物理性质，因此，时变可以对X辐射模型给以很强的限制。X射线源不同能量光子到达观测者的时间差称为X射线辐射的时延。介绍了高能X辐射时变中的时延分析方法及其最新发展，综述了致密双星系统中黑洞侯选林和中子星的时延现象，并简单介绍了为解释这些现象所发展的模型，以及时延对模型的限制。  相似文献   

WIYN Open Cluster Study – XVI. Optical/infrared photometry and comparisons with theoretical isochrones     

Aaron J. Grocholski  Ata Sarajedini 《Monthly notices of the Royal Astronomical Society》2003,345(3):1015-1029

We present combined optical/near-infrared photometry ( BVIK ) for six open clusters – M35, M37, NGC 1817, NGC 2477, NGC 2420 and M67. The open clusters span an age range from 150 Myr to 4 Gyr and have metal abundances from  [Fe/H]=−0.27  to +0.09 dex. We have utilized these data to test the robustness of theoretical main sequences constructed by several groups as denoted by the following designations – Padova, Baraffe, Y², Geneva and Siess. The comparisons of the models with the observations have been performed in the  [ M_V , ( B − V )₀], [ M_V , ( V − I )₀]  and  [ M_V , ( V − K )₀]  colour–magnitude diagrams as well as the distance-independent  [( V − K )₀, ( B − V )₀]  and  [( V − K )₀, ( V − I )₀]  two-colour diagrams. We conclude that none of the theoretical models reproduces the observational data in a consistent manner over the magnitude and colour range of the unevolved main sequence. In particular, there are significant zero-point and shape differences between the models and the observations. We speculate that the crux of the problem lies in the precise mismatch between theoretical and observational colour–temperature relations. These results underscore the importance of pursuing the study of stellar structure and stellar modelling with even greater intensity.  相似文献   

Palaeoecology of a late Allerød peat bed at Godøy,western Norway     

Hilary H. Birks  Geoffrey Lemdahl  John Inge Svendsen  Jon Y. Landvik 《第四纪科学杂志》1993,8(2):147-159

A peat bed found under solifluction deposits on Godøya island, western Norway, accumulated during a few decades around 11 000 yr BP, at the end of the Allerød period of the Late Weichselian. Palaeoecological investigations showed a local vegetation succession on wet sand culminating in a mire community dominated by Carex nigra. Periodic flooding brought in sand and silt, which decreased as drainage was impeded sufficiently for standing water to develop. The surrounding terrestrial vegetation was dominated by Salix scrub, with some open heath and alpine habitats nearby. Apart from two aquatic species, the 29 insect taxa recorded are characteristic of alpine heaths, plant litter (under Salix scrub) and stream-sides. Their remains, together with the terrestrial plant macrofossils, were washed into the mire from nearby. Because the fossils are locally derived, the environmental reconstructions are of the actual conditions at Godøy at ca. 11 000 yr BP. Palaeotemperature estimates from beetles and plants are in agreement. The coleopteran estimates (Mutual Climatic Range Method) suggest mean July temperatures of 10–13°C, slightly cooler than today (13.5°), and January temperatures between +1 and ?10°C, similar to or much colder than today. Summer temperature estimates from individual plant taxa indicate that temperatures during the Allerød period were similar to today's, but estimates from the reconstructed vegetation and timber-line positions give estimates up to 3.5° cooler. Temperatures fell 2.5–7.5°C at the Younger Dryas. This abrupt and severe cooling initiated the solifluction processes on Godøya that buried the peat. The Godøy peat bed and its contained fossils provide a rare glimpse of Allerød biota and environments at the local (site) scale.  相似文献   

青藏高原多年冻土概论     

郭鹏飞  王健  边纯玉 《青海国土经略》1995,(2)

本文较系统地阐述了青藏高原多年冻土的地带性规律、冻土构造以及融区的类型和分布特征,详细论述了不同作用下形成的冻土(冰缘)地貌,并对青藏高原的冰缘期进行了初步划分与对比。  相似文献   

构造地质学中的地质思维初探     

魏宽义 《地球科学与环境学报》1989,(3)

地质模型的建立,地质思维的正确运用已成为引导地质学前进的两个关键环节。本文以构造地质学领域中近年来的研究成果为基础,探讨了与空间和时间有关的地质思维问题。指出:一个地质现象的观察,一定要结合高一级尺度和低一级尺度的综合研究,才能得出既有形成机制、又有组合规律的全面结论;一个构造形迹,一定要尽力区分出不同的递进变形阶段,以提供以时间为坐标的演化序列。文末,笔者提供了两个研究实例,一个用小构造分析论证区域构造演化,一个据叠加变形原理,把研究对象区分成不同的区段和亚域。  相似文献   

太阳射电爆发中Spike辐射的准周期振荡     

金声震  李小聪 《中国天文和天体物理学报》1989,(2)

本文介绍了在1981年5月16日微波大爆发中毫秒级时间轮廓Spike辐射中发生的准周期振荡现象。这种准周期振荡可能与日面活动区磁杯中的阿尔芬波运动有关,由此我们可以得到爆发源区一些基本物理条件。最后对于准周期振荡现象对Spike辐射的作用和影响作了简单的讨论。  相似文献   

自由能密度上限及毫秒级射电尖峰的“饱和”机制     

黄光力  徐民健 《中国天文和天体物理学报》1989,(4)

本文首先介绍了热力学自由能上限的普遍公式及其推导思想,然后应用于非热电子束的具体形式,从而估计太阳射电活动中的毫秒级尖峰辐射的“饱和”能量;在此基础上,进一步为饱和时间问题作一般性的讨论;最后,在把尖峰“饱和”的几种机制进行了比较之后提出:由于尖峰能量远未达到非线性饱和的水平,因此,由某种外部因素(例如加速机制等)所导致的高能电子束的非均匀性可能是一种较为合理的模型。  相似文献   

黑子活动区流场精细结构     

张洪起  李京  刘建强 《中国天文和天体物理学报》1989,(3)

本文通过太阳活动区光球和色球速度场和磁场观测资料,讨论了黑子活动区附近流场的精细结构,论述了太阳大气中物质的流动呈纤维结构,以及速度场纤维与磁场,色球纤维和网络结构之间的关系。  相似文献   

1986年2月4日太阳耀斑的演化研究   总被引：1，自引：0，他引：1  

肖速民  丁有济  M.J.Hagyard  J.B.Smith Jr 《中国天文和天体物理学报》1988,(4)

本文根据乌鲁木齐天文站的H_α耀斑及3.2cm射电流量观侧资料、云南天文台的黑子精细结构照相和Marshall Space Flight Center的向量磁场图,对1986年2月4日的六个耀斑的形态相关及演化联系,特别是0736UT 4B/3X大耀斑的发展过程进行了综合分析。主要结果是: 1.4日大耀斑的初始亮点和闪光相的主要形态演化,与活动区中沿中性线新浮现的强大电流/磁环系密切相关。后者的主要标志是沿中性线的长的剪切半影纤维及它两端的偶极旋涡黑子群(1_3F_3)。 2.上述大耀斑与1972年8月4日0624 UT大耀斑爆发的磁场背景及主要形态特征相似,表明两者的储能和触发机制可能相同。 3.大耀斑爆发的H_α初始亮点,双带出现,环系形成,亮物质抛射和吸收冕珥等现象同3.2cm射电流量的变化在时间上有较好的对应关系。 4.重复性的前期小耀斑爆发位置和发展趋势与大耀斑的主要形态及演化特征相似。它们相对于剪切的纵场中性线两侧的位置相近或相同。因而,可以看作上述强大电流/磁环系不稳性发展过程中的前置小爆发。  相似文献