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171.
WANG Deming 《《地质学报》英文版》2007,81(4):525-538
Zosterophyllum longa sp.nov.is reported from the Lower Devonian Pingyipu Formation, Jiangyou District,northern Sichuan of China.This new plant has vertically elongate sporangia differing from all known species of Zosterophyllum,demonstrating morphological variations in Zosterophyllophytina.New materials of Zosterophyllum yunnanicum from the Lower Devonian Xujiachong Formation,Qujing District,eastern Yunnan of China show that fertile axes of this species are anisotomous or pseudomonopodial or K-shaped in branching.Sometimes fertile lateral axes are very short and bear an axUlary axis at the dividing point.Distinct thickening occurs along the whole margin of a sporangium,with sporangial lobes undeveloped.The evolution of Zosterophyllum is tentatively discussed.A biostratigraphic method of Gerrienne and Streel is introduced and applied to dating of the Lower Devonian Xujiachong Formation,which is considered as of the late Pragian-early Emsian. 相似文献
172.
南极冰盖自形成以来就一直是全球环境体系最重要的组成部分 ,其扩展和消融的动态演化过程不仅是南极大陆最重要的地质过程 ,而且也是全球气候和环境变化最直接的反映和体现。因此 ,有关这一课题的研究一直是国际地质学界所关注的热点。本文回顾了南极冰川和气候演化研究的历史 ,总结了当前这方面研究的成果以及所存在的问题 ,探讨了其未来的发展趋势 ,在此基础上 ,对我国南极考察队发现格罗夫山 (GroveMountains)地区新生代沉积岩的意义进行了阐述 相似文献
174.
中、新生代天山隆升过程及其与准噶尔、阿尔泰山比较研究 总被引：49，自引：4，他引：45
根据穿越天山地质剖面观察、系统裂变径迹(FT)测年年龄与热演化模拟结果分析,并综合前人研究结果,天山陆内造山带中、新生代主要经历2次明显的隆升事件,分别为晚侏罗世—早白垩世和中新世以来(25~0Ma)。从天山地区磷灰石FT年龄结果来看,主要记录了早期隆升年龄,但热演化模拟结果显示普遍经历了中新世以来的快速隆升。在天山北缘从盆山边缘的近25Ma开始隆升到前缘带的现今活动,表明天山陆内造山带在隆升的同时还逐渐“增生”扩展。系统研究和分析表明,东西准噶尔和阿尔泰地区则主要记录了晚中生代以来的持续隆升过程,新生代构造活动不明显或强度相对天山要弱。上述事实表明,天山及其中亚地区新生代的陆内活动是受喜马拉雅碰撞与青藏高原隆升的影响,具有向北渐弱的特征。 相似文献
175.
西秦岭关家沟组物源分析 总被引：5，自引：0，他引：5
西南秦岭摩天岭地区关家沟组的时代、沉积环境及构造背景一直是争论的焦点。对关家沟组粉砂岩、板岩进行了常量、微量及稀土元素地球化学分析表明关家沟组物源主要来自活动大陆边缘的岛弧环境。以本区地层斜层理产状及砾石优选方位为依据,对关家沟组岩层古水流方向综合分析,推测其古水流方向为230°~356°,以北西向为主;砾石的优选方位在228°~338°之间,以北北西向为主;砾石分布特征由南向北颗粒由大逐渐变小、磨圆度由差至较好、优选方位由杂乱到较好的变化趋势。结合前人成果,关家沟组应属于碧口弧前盆地系统内,推测关家沟组内的沉积物主要来自南东向的岛弧。 相似文献
176.
The Maximum Effective Moment Criterion （MEMC） and Its Implications in Structural Geology 总被引：4，自引：0，他引：4
ZHENG Yadong WANG Tao WANG Xinshe The Key Laboratory of Orogenic Belts Crustal Evolution School of Earth Space Sciences Peking University Beijing Institute of Geology Chinese Academy of Geological Sciences Beijing 《《地质学报》英文版》2006,80(1):70-78
1 Introduction A high-level generalization of structures in the earth crust has been given by Ramsay (1980): low-angle thrusts in the brittle upper crust and high-angle reverse shear zones in the ductile middle-lower crust are formed in contractional regimes; high-angle normal faults in the brittle upper crust and low-angle normal shear zones in the ductile middle- lower crust are formed in extensional regimes. The formation of low-angle thrusts and high-angle normal faults in brittle domains … 相似文献
177.
SHRIMP Zircon U-Pb Chronology and Geochemistry of the Henglingguan and Beiyu Granitoids in the Zhongtiao Mountains, Shanxi Province 总被引：3，自引：0，他引：3
YU Shengqiang LIU Shuwen TIAN Wei LI Qiugen FENG Yonggang 《《地质学报》英文版》2006,80(6):912-924
Henglingguan and Beiyu metamorphic granitoids, distributed in the northwest of the Zhongtiaoshan Precambrian complex, comprise trondhjemites and calc-alkaline monzogranites, displaying intrusive contacts with the Archean Zhaizi TTG gneisses. And the Beiyu metamorphic granitoids consist mainly of trondhjemites, distributed at the core of the Hujiayu anticline fold. New SHRIMP zircon U-Pb dating data show that the weighted mean ^207pb/^206pb ages are 2435.9 Ma and 2477 Ma for the Henglingguan metamorphic calc-alkaline monzogranites and Beiyu metamorphic trondhjemites, respectively, and reveal -2600 Ma inherited core in magmatic zircons. Whole-rock geochemical data indicate that all the Henglingguan and Beiyu metamorphic trondhjemites and calc- alkaline monzogranites belong to the metaluminous medium- and high-potassium calc-alkaline series. These rocks are characterized by relatively high total alkali contents （Na2O＋K2O, up to 9.08%）, depleted Nb, Ta, P and Ti, and right-declined REE patterns with moderate to high LREEs/HREEs fractionation （the mean ratio of （La/Yb）n = 25）. The Henglingguan and Beiyu metamorphic trondhjemites display negative Rb, Th and K anomalies in the multi-dement spider diagrams normalized by primitive mantle. Sm-Nd isotopic data reveal that these granitoids have initial εNd（t） =-1.2 to ＋2.4 and Nd depleted mantle model ages of TMD = 2622 Ma-2939 Ma. All these geochemical features indicate that these granitoids were formed in an continent-marginal arc, and the trondhjemites mainly originated from partial melting of juvenile basaltic materials and, howbeit, the Henglingguan metamorphic calc-alkaline monzogranites derived from recycling of materials in the ancient crust under a continent-marginal arc. The granitic magma underwent contamination and fractional crystallization during their formation. 相似文献
178.
TIAN Wei LIU Shuwen ZHANG Huafeng 《《地质学报》英文版》2006,80(6):875-885
1 Introduction The early Precambrian basement of the North China Craton (NCC) consists mainly of the Eastern Continental Block, the Western Continental Block and the Trans-North China Orogen (TNCO, or “the Central Tectonic Zone”), which formed by continental collision between the Eastern and Western Blocks (Zhao et al., 1998). This evolutionary model has now been widely accepted (Wu and Zhong, 1998; Guan et al., 2002; Guo et al., 2002; Liu et al., 2002a, b; Liu et al., 2004a, b;… 相似文献
179.
ZHANG Jinjiang ZHAO Lan LIU Shuwen 《《地质学报》英文版》2006,80(6):864-874
The Longquanguan shear zone is an important structural belt in the North China Craton, separating the underlying Fuping complex from the overlying Wutai complex. This shear zone has experienced three episodes of deformation： the first and main episode is a ductile top-to-ESE shear along the gently northwest-west dipping foliations, while the other two episodes are later collapse sliding. Prolonged granites parallel to the shear foliations make one of the main compositions of the Longquanguan shear zone. These granites experienced deformation to form mylonitic rocks when they emplaced during the first episode of deformation. Structural characters of the granites and their contacts to the country rocks indicate that these granites possibly resulted from in-situ partial remelting by shearing, i.e., they are syn-deformational granites. Monazites in these mylonitic granites are magmatic minerals and their crystallization ages may represent ages of the magmatic events, and also the ages for the main deformation of the Longquanguan shear zone. Monazite electronic microprobe dating were carried on two samples of granite, which gives multiple peak ages, among which 1,846 Ma and 1,877 Ma are the main peak ages for the two samples. These ages represent the main deformation of the Longquanguan shear zone, which is consistent with the main regional geological event at about 1,850 Ma caused by the collision between the Eastern and Western Blocks in North China. The good match between the monazite ages and the corresponding regional tectono-thermal events shows the feasibility and reliability of monazite electronic microprobe dating. 相似文献
180.
归纳了自1975年以后华北地区13次中强以上地震的地壳形变短临前兆异常60例。统计地壳形变短临异常与地震的定性关系，发现距震中较远的台站异常出现较早，较近的台站异常出现较晚，地震的震级与异常的空间展布范围成正比，异常往往倾向震中或背向震中。跨断层的位移型形变异常形态有两大类：一类是趋势性异常变化，另一类是高频波动。本文提出了将连续型形变转化为应变的方法。从1989年10月16日大同－阳高61级地 震和1991年3月26日大同－阳高5．8缓地震的实例可见，地震往往发生在高应变区或其附 近，异常量级可达10－6。 相似文献