2008年4月天山北坡一次强寒潮天气成因分析   总被引：2，自引：0，他引：2       下载免费PDF全文

赵俊荣  郭金强  田惠萍 《气象与环境学报》2010,26(1):54-58

利用T213 0场预报资料对2008年4月18日新疆天山北坡带中部石河子垦区发生的50 a不遇强寒潮天气过程的环流背景、影响系统及物理量场进行了综合分析。结果表明：“2008.04.18”强寒潮天气主要成因是：里黑海脊发展东移与东欧脊同位相叠加并顺转, 脊前东北风带建立并加强,诱导泰米尔半岛冷空气沿脊前东北气流西南下到横槽中, 迫使横槽转向强烈发展东南压,并形成高空急流,强锋区和强冷高压;由于高压脊部分东南垮,导致中高纬度强冷空气大举东南下,造成强寒潮天气过程;西南急流与冷空气的交汇产生了较强的动力辐合和水汽辐合,对大暴雪的形成起到了重要作用;大暴雪发生在较强的能量锋区、高湿区和水汽通量辐合区内。  相似文献   

核磁共振测井T_2cutoff确定方法及适用性分析   总被引：4，自引：1，他引：3       下载免费PDF全文

肖亮  肖忠祥 《地球物理学进展》2008,23(1):167-172

T2cutoff是核磁共振测井中的一个重要参数,它决定了核磁共振测井测量的有效孔隙度、渗透率、自由流体饱和度、束缚水饱和度等参数的精确程度.目前国内外普遍选取的T2cutoff为:砂泥岩储层取33ms,碳酸盐岩储层取92ms.实际研究发现T2cutoff应是变化的量而并非单一值.简单的运用单一的T2cutoff来计算各种地层参数势必会产生误差甚至得出错误的解释结论.叙述了33ms作为T2cutoff的由来及其不合理性,同时分析了目前国内外确定T2cutoff的各种方法及其适用性.  相似文献   

3．0T磁共振的临床应用特点研究   总被引：6，自引：1，他引：5  

昌仁民  刘广保  张玉忠  胡罢生  陈斌  曲华丽  许乙凯  邱士军  张雪林 《CT理论与应用研究》2008,17(4):76-81

本文对3．0T磁共振信噪比、磁敏感性效应、电介质效应、化学位移效应、驰豫时间和特殊吸收率5方面的特点、优势与不足进行分析和研究,帮助了解3．0T的一些基本物理知识,正确认识3．0T的临床应用价值,扬长避短,充分发挥其在临床和科研方面的优势。  相似文献   

High-resolution cyclostratigraphy of geochemical records from Permo-Triassic boundary section of Dongpan, southwestern Guangxi, South China     

Peng XingFang  Feng QingLai  Li ZhouBo  Meng YouYan 《中国科学D辑(英文版)》2008,51(2):187-193

Spectral analysis is applied to geochemical data from a deep-water Permian-Triassic Boundary (PTB) section across PTB in Dongpan, Guangxi for high-resolution cyclostratigraphic research. The characteristics of the Milankovitch Cycles have been well recorded in the strata of the Dongpan section. Spectrum on Ce/La records shows especially that the ratios among its three preponderant cycles in the section are 5:2:1, which well displays the phenomenon of the sedimentary cycles driven by orbital force. The Milankovitch theory is further confirmed by the Paleozoic records.  相似文献   

基于T/P卫星海面测高的黄东海海面地形变化探讨     

钟鹤翔  谢志仁  崔树红  信忠保 《海洋通报》2005,24(5):1-7

利用Topex/Posedion卫星的SSHA数据对黄、东海1993-2001年期间的平均海面地形的空间形态特征、变化速率的空间分布特征及年内变化特征等3个方面进行了分析.研究结果表明,该海区9a平均海面地形的基本特征为：东南高、西北低,由东南向西北倾斜,最大高差超过90 cm;1993-2001年期间全海区均呈现海面上升趋势,上升速率值在5～8.6 mm/a之间,海面上升的空间分异表现为南快北慢,东快西慢.海面地形的年内变化在时间上呈正弦波动,空间上中、北部区域变化速度快,年较差大;南部区域变化速度慢,年较差小;变化空间特征复杂.  相似文献   

Chloritoid–glaucophane schist in the north Qilian orogen, NW China: phase equilibria and P–T path from garnet zonation     

C. J. WEI  S. G. SONG 《Journal of Metamorphic Geology》2008,26(3):301-316

Chloritoid–glaucophane‐bearing rocks are widespread in the high‐pressure belt of the north Qilian orogen, NW China. They are interbedded and cofacial with felsic schists originated from greywackes, mafic garnet blueschists and low‐T eclogites. Two representative chloritoid–glaucophane‐bearing assemblages are chloritoid + glaucophane + garnet + talc + quartz (sample Q5‐49) and chloritoid + glaucophane + garnet + phengite + epidote + quartz (sample Q5‐12). Garnet in sample Q5‐49 is coarse‐, medium‐ and fine‐grained and shows two types of zonation patterns. In pattern I, X_grs is constant as X_py rises, and in pattern II X_grs decreases as X_py rises. Phase equilibrium modelling in the NC(K)MnFMASH system with Thermocalc 3.25 indicates that pattern I can be formed during progressive metamorphism in lawsonite‐stable assemblages, while pattern II zonation can be formed with further heating after lawsonite has been consumed. Garnet growth in Q5‐49 is consistent with a continuous progressive metamorphic process from ～14.5 kbar at 470 °C to ～22.5 kbar at 560 °C. Garnet in sample Q5‐12 develops with pattern I zonation, which is consistent with a progressive metamorphic process from ～21 kbar at 540 °C to ～23.5 kbar at 580 °C with lawsonite present in the whole garnet growth. The latter sample shows the highest P–T conditions of the reported chloritoid–glaucophane‐bearing assemblages. Phase equilibrium calculation in the NCKFMASH system with a recent mixing model of amphibole indicates that chloritoid + glaucophane paragenesis does not have a low‐pressure limit of 18–19 kbar as previously suggested, but has a much larger pressure range from 7–8 to 27–30 kbar, with the low‐pressure part being within the stability field of albite.  相似文献   

P–T conditions for the Arendal granulites, southern Norway: implications for the roles of P, T and CO₂ in deep crustal LILE-depletion     

R. C. LAMB  P. C. SMALLEY  D. FIELD 《Journal of Metamorphic Geology》1986,4(2):143-160

Abstract The orthopyroxene-clinopyroxene, garnet-orthopyroxene and garnet-clinopyroxene geothermometers, and the garnet-orthopyroxene-plagioclase, garnet-clinopyroxene-plagioclase and anorthite-ferrosilite-grossular-almandine-quartz geobarometers are applied to metabasites and the garnetplagioclase-sillimanite-quartz geobarometer is applied to a metapelite from the Proterozoic Arendal granulite terrain, Bamble sector, Norway. P–T conditions of metamorphism were 7.3 ± 0.5 kbar and 800 ± 60°C.
This terrain shows a regional gradation from the amphibolite facies, into normal LILE content granulite facies rocks and finally strongly LILE deficient granulite facies gneisses. Neither P nor T vary significantly across the entire transition zone. The change in 'grade'parallels the increasing dominance of CO₂ over H₂O in the fluid phase.
LILE-depletion is not a pre-condition of granulite facies metamorphism: granulites may have either 'depleted'or 'normal'chemistries. The results presented herein show that LILE-deficiency in granulite facies orthogneisses is not necessarily related to variations in either P or T . The important mechanisms in the Arendal terrain were (a) direct synmetamorphic crystallization from magma, with primary LILE-poor mineralogies imposed by the prevailing fluid regime, and (b) metamorphic depletion, involving scavenging of LILEs during flushing by mantle-derived CO₂-rich fluids. The latter process is constrained by U–Pb and Rb–Sr isotopic work to have occurred no later than 50 Ma after intrusion of the acid-intermediate gneisses, and was probably associated with contemporary basic magmatism in a tectonic environment similar to a present day cordilleran continental margin.  相似文献   

Age and early metamorphic history of the Sanbagawa belt: Lu–Hf and P–T constraints from the Western Iratsu eclogite     

S. ENDO  S.WALLIS  T. HIRATA  R. ANCZKIEWICZ  J. PLATT  M. THIRLWALL  Y. ASAHARA 《Journal of Metamorphic Geology》2009,27(5):371-384

Two distinct age estimates for eclogite-facies metamorphism in the Sanbagawa belt have been proposed: (i) c.  120–110 Ma based on a zircon SHRIMP age for the Western Iratsu unit and (ii) c.  88–89 Ma based on a garnet–omphacite Lu–Hf isochron age from the Seba and Kotsu eclogite units. Despite the contrasting estimates of formation ages, petrological studies suggest the formation conditions of the Western Iratsu unit are indistinguishable from those of the other two units—all ∼20 kbar and 600–650 °C. Studies of the associated geological structures suggest the Seba and Western Iratsu units are parts of a larger semi-continuous eclogite unit. A combination of geochronological and petrological studies for the Western Iratsu eclogite offers a resolution to this discrepancy in age estimates. New Lu–Hf dating for the Western Iratsu eclogite yields an age of 115.9 ± 0.5 Ma that is compatible with the zircon SHRIMP age. However, petrological studies show that there was significant garnet growth in the Western Iratsu eclogite before eclogite facies metamorphism, and the early core growth is associated with a strong concentration of Lu. Pre-eclogite facies garnet (Grt1) includes epidote–amphibolite facies parageneses equilibrated at 550–650 °C and ∼10 kbar, and this is overgrown by prograde eclogite facies garnet (Grt2). The Lu–Hf age of c.  116 Ma is strongly skewed to the isotopic composition of Grt1 and is interpreted to reflect the age of the pre-eclogite phase. The considerable time gap ( c.  27 Myr) between the two Lu–Hf ages suggests they may be related to separate tectonic events or distinct phases in the evolution of the Sanbagawa subduction zone.  相似文献   

Metamorphic phase relations in orthopyroxene-bearing granitoids: implication for high-pressure metamorphism and prograde melting in the continental crust     

S. K. BHOWMIK  L. SAHA  S. DASGUPTA  M. FUKUOKA 《Journal of Metamorphic Geology》2009,27(4):295-315

In this work, the factors controlling the formation and preservation of high-pressure mineral assemblages in the metamorphosed orthopyroxene-bearing metagranitoids of the Sandmata Complex, Aravalli-Delhi Mobile Belt (ADMB), northwestern India have been modelled. The rocks range in composition from farsundite through quartz mangerite to opdalite, and with varying K₂O, Ca/(Ca + Na)_rock and FeO_tot + MgO contents. A two stage metamorphic evolution has been recorded in these rocks.
An early hydration event stabilized biotite with or without epidote at the expense of magmatic orthopyroxene and plagioclase. Subsequent high-pressure granulite facies metamorphism (∼15 kbar, ∼800 °C) of these hydrated rocks produced two rock types with contrasting mineralogy and textures. In the non-migmatitic metagranitoids, spectacular garnet ± K-feldspar ± quartz corona was formed around reacting biotite, plagioclase, quartz and/or pyroxene. In contrast, biotite ± epidote melting produced migmatites, containing porphyroblastic garnet incongruent solids and leucosomes.
Applying NCKFMASHTO T–M (H₂O) and P–T pseudosection modelling techniques, it is demonstrated that the differential response of these magmatic rocks to high-pressure metamorphism is primarily controlled by the scale of initial hydration. Rocks, which were pervasively hydrated, produced garnetiferous migmatites, while for limited hydration, the same metamorphism formed sub-solidus garnet-bearing coronae. Based on the sequence of mineral assemblage evolution and the mineral compositional zoning features in the two metagranitoids, a clockwise metamorphic P–T path is constrained for the high-pressure metamorphic event. The finding has major implications in formulating geodynamic model of crustal amalgamation in the ADMB.  相似文献   

Reproductive Biology of Yeilowfin Tuna T. albacares in the West-Central Indian Ocean     

ZHU Guoping  XU Liuxiong  ZHOU Yingqi  SONG Liming 《中国海洋大学学报(英文版)》2008,7(3)

Survey of yellowfin tuna in the west-central Indian Ocean was conducted on board of Chinese Iongliners during 2003, 2004 and 2005, which is a part of Chinese Tuna Fishery Scientific Observer Program (CTFSOP). The reproductive biology has been investigated. A total of 1023 samples are collected including 417 ovaries and 606 testes. Spawning activities of yellowfin tuna have been studied for both male and female from January to June. The data showed that the average monthly sex ratio is 0.59, and the minimum length at sexual maturity is 101 cm for female and 110 cm for male respectively. Length at 50% sexual maturity is esti- mated at 113.77 cm for female and 120.20 cm for male, whereas maturation rate is 0.066 cm-1 for female and 0.091 cm-1 for male. Sex ratio by length class indicates that the proportion of male is higher than female's along with size increasing; for instance, in the group of the body length longer than 145 cm, some females have their body length from 145 to 160 cm and males have their body length at 160 cm and even longer. Statistically, yellowfin tuna has a significant seasonal reproduction.  相似文献