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291.
青龙村群及其地质时代 总被引:5,自引:2,他引:5
青龙村群在延边地体中具有重要地质意义。笔者通过对该群的工作和所获得的微古化石,认为青龙村群在层序上仅包含该区1:5万区调青龙村剖面中的中、下段,其上段不属于青龙村群范畴;青龙村群的形成地质时代应为晚震旦─早寒武世。 相似文献
292.
Ge Tongming Liu Jian Fan Limin Zhong Shuixian Wu Nengyou Hsu Vindell A. Baksi 《《地质学报》英文版》1995,8(2):221-233
Abstract This paper discusses the Cretaceous-Tertiary magnetic polarity sequence of the the Hengyang Basin on the basis of magnetostratigraphic study. The age of each stratigraphic unit has been determined with the magnetic polarity time scale combined with <sup>39</sup>Ar/<sup>40</sup>Ar dating, thus providing evidence for determining the geological ages of different formations. The authors assign the age of the Dongjing Formation of the Hengyang Basin to Early Cretaceous, the Shenhuangshan Formation to Early-Late Cretaceous, the Daijiaping Formation to Late Cretaceous, and the Dongtang and Xialiushi formations to Palaeocene. 相似文献
293.
Using the lAP two-level general circulation model,the ice age July climate was simulated through the surface conditions of 18 000 years before present assembled by the CLIMAP Project.Comparing with the present July simulation results,the ice age atmosphere is found to have a substantially lower temperature,precipitation,and cloudiness,higher sea-level pressure,especially in the high latitude land region of the Northern Hemisphere and Antarctica.When the CO2 content is set as the modern value the climatic response is very small,which shows that the problems of CO2 sensitivity should be studied by means of coupled models.It is also pointed out that there are some common characteristics between CO2-induced climatic changes and the ice age surface condition-induced climatic changes,which may give us some insight into how climate responds to external forcings. 相似文献
294.
大庙斜长岩的40Ar/39Ar年龄测定呈现出一条典型的马鞍型年龄谱,在中温阶段有二个明显的坪年龄1656±15 Ma和1029±7 Ma,结合其构造位置和全球斜长岩分布来看,它们分别代表了侵位年龄和后期热扰动的时代。密云奥长环斑花岗岩中角闪石的40Ar/39Ar坪年龄为1716±21 Ma。两者时空上密切相关,代表了裂谷作用初期非造山环境中双模式岩浆作用产物。斜长岩类和苏长岩之间稀土配分模式的相似性表明,它们明显为同一成因的岩浆分异系列的产物。 相似文献
295.
Chronology of Sanbagawa metamorphism 总被引:5,自引:0,他引:5
By collating age data based on the fossil age of the protoliths, radiometric dating of the metamorphic minerals, and sedimentary records of erosion at the earth's surface, the history of the Sanbagawa metamorphism can be summarized as follows. (1) The pre-metamorphic sedimentary rocks (Carboniferous-Jurassic + Early Cretaceous?) became mixed and formed a thickened packet in the vicinity of an ancient trench through a variety of subduction-related tectono-sedimentary processes, probably in Early Cretaceous time (c., 130-120 Ma). (2) The subducted protoliths underwent progressive metamorphism reaching a maximum depth of c. 30 km in late Early Cretaceous time (c. 116 ± 10 Ma). (3) The high-P/T metamorphic rocks began to rise toward the surface (during the interval 110-50 Ma) with minimum estimates for the average cooling rate around 9-12°C/Ma and an average uplift rate around 0.4-0.5 mm/year. (4) Finally, at some stage after reaching the erosional surface, the high-P/T metamorphic rocks were covered unconformably by the middle Eocene (c. 50-42 Ma) Kuma Group. On the basis of the present chronological summary of the Sanbagawa metamorphism, the areal extent of the Sanbagawa metamorphism is also discussed with respect to the weakly metamorphosed subduction-accretion complex of the next tectonic belt to the south, the Northern Chichibu belt. 相似文献
296.
根据新疆及苏联天山地区的地震目录和古地震研究成果,将整个天山地区的地震韵律划分为地震世、地震亚世、地震期、地震幕、地震阶五级,探讨了各级韵律的特征。估计了我国天山地区未来地震活动趋势。 相似文献
297.
298.
本文主要论述吉林省延边地区屯田营组时代。通过对屯田营组研究历史的回顾,从火山岩喷发—沉积序列和生物地层资料指出屯田营组时代为晚侏罗世,屯田营组与金沟岭组同是晚侏罗世两个火山旋回。 相似文献
299.
300.
G. Franz D. Pudlo G. Urlacher U. Haussmann A. Boven K. Wemmer 《International Journal of Earth Sciences》1994,83(3):614-623
Field investigations, K-Ar age determinations and chemical data were used to describe the development of an intraplate volcanic province, the Darfur Dome, Sudan. Magmatism started 36 Ma ago at a small subvolcanic complex (Jebel Kussa) in the center of the dome and was active in the same area between 26 and 23 Ma. Two major volcanic fields (Marra Mountains and Tagabo Hills) developed between 16 and 10 Ma. Volcanism started again at 6.8 Ma with a third volcanic field (Meidob Hills) and at 4.3 Ma in the Marra Mountains and with the reactivation of the center. Activity then continued until the late Quaternary. Having started in the center of the Darfur Dome, volcanism moved in 36 Ma 200 km towards the NNE and 100 km SSW No essential difference in the alkaline magma types (basanitic to phonolitic-trachytic, with different amounts of assimilation of crustal material) in the different fields, was observed. Magmatism is thought to have been produced by a rising mantle plume and volcanism was triggered by stress resolution along the Central African Fault Zone. 相似文献