Secondary remanent magnetization carried by magnetite inclusions in silicates: a comparative study of unremagnetized and remagnetized granites     

Yo-ichiro Otofuji  Koji Uno  Takahiro Higashi  Tomomichi Ichikawa  Tsuyoshi Ueno  Toshiaki Mishima  Takaaki Matsuda 《Earth and Planetary Science Letters》2000,180(3-4):271-285

Magnetic carriers in remagnetized Cretaceous granitic rocks of northeast Japan were studied using paleomagnetism, rock magnetism, optical microscopy and scanning electron microscopy (SEM) by comparison with unremagnetized granitic rocks. The natural remanent magnetization (NRM) of the remagnetized rocks is strong (0.3–1.7 A/m) and shows a northwesterly direction with moderate inclination (NW remanence), whereas the unremagnetized rocks preserve weak NRM (<0.5 A/m) with westerly and shallow direction (W remanence). Although thermal demagnetization shows that both NRMs are carried by magnetite, the remagnetized rocks reveal a higher coercivity with respect to alternating field demagnetization (20 mT相似文献   

中国东部晚元古代—三叠纪古板块的运动学研究   总被引：1，自引：1，他引：1  

朱鸿  万天丰 《地球科学》1991,(5)

本文在认真选择现有的、比较可靠的古地磁资料基础之上,综合构造变形、沉积古地理、岩浆活动与变质作用的资料,再造了中国东部各板块自晚元古代(晨旦纪)到三叠纪的古构造图。晋宁事件以后直到古生代的整个时期,华南各板块与中朝板块张裂分离,保持相当的距离并在中、低纬度地带不断迁移,形成各具特色的构造演化史。三叠世末期,临沧、保山地体拼合到扬子板块的西侧,湘桂板块可能插入南华板块;中三叠世末期南华板块与扬子板块拼合,并使它们发生普遍的褶皱;晚三叠世末期,扬子板块才与中朝板块拼合,中国东部各板块联成一体,使构造格架基本定型。  相似文献   

晚白垩世后青藏高原和塔里木地块的整体北移     

翟永健  谭承泽 《现代地质》1990,4(4):27-34

本文根据塔里木地块及其以南的昆仑、羌塘和拉萨地块晚中生代特别是晚白垩世古地磁数据,提出青藏高原自晚白垩世后北向移动两千余公里,主要并不是通过它本身的大规模地壳缩短来完成,而是与塔里木地块一起作大规模整体北移的结果。一种可能的解释是,在欧亚大陆北部稳定区和塔里木地块之间广大的中亚构造带,自晚白垩世后发生了大规模的地壳缩短。  相似文献   

碰撞前印度大陆北缘古地理轮廓——藏南晚白垩世堆拉灰岩古地磁研究     

易治宇  梁雅伦  赵杰  闫永刚  陈力为  唐祥德 《地质学报》2016,90(11):3282-3292

堆拉灰岩的古地磁数据为重建碰撞前印度大陆北缘轮廓提供了重要制约,但也留下了一些疑点,为此,本文对该地区晚白垩世海相沉积开展了进一步的古地磁研究。通过对10个采点样品的系统退磁及统计分析,得到宗山组最下段经地层校正后的特征剩磁分量为D=168.2°,I=-7.3°,α95=7.5°。该分量与前人从该地区宗山组中、上段得到的古地磁结果无显著区别,并在95%的置信水平上通过褶皱检验,表明剩磁是褶皱前获得的。尽管如此,堆拉晚白垩世灰岩统一的负极性特征与其沉积期间(Turonian-Maastrichtian)对应的古地磁标准极性柱不符,表明该地区宗山组不同层位可能普遍遭遇了重磁化,不能用来约束喜马拉雅地体的古地理位置。基于以上考虑,本文仅用前人从岗巴宗山地区获得的古地磁结果对晚白垩世期间特提斯喜马拉雅地体的古地理位置进行了计算和修正,结果显示该地体在宗山组上段沉积期间(约71~65Ma)的古纬度约为9°S,计算得到当时大印度的北向延伸量为1500km,与前人从宗浦组得到的古地磁结果一致。  相似文献   

贵德盆地黄河出现的古地磁年代及其意义   总被引：2，自引：0，他引：2  

聂军胜  宋春晖  方小敏  徐先海  孙东 《海洋地质与第四纪地质》2003,23(2):59-64

发源于青藏高原的黄河,其形成与青藏高原隆起有密切关系,因此,黄河上游的形成演化,对于研究青藏高原的隆升以及黄河水利的开发利用等均有重要的实际意义和科学价值。青藏高原东北部的贵德盆地发育巨厚的新生代地层,其最上部的一套湖相沉积代表了黄河出现之前的最后沉积。古地磁测年表明这套地层的结束时代约为1．8Ma,指示黄河在本区大约同时出现,是青藏运动C幕的产物,此后至今黄河已净下切了约940m,指示本区高原的快速隆起,不支持青藏高原在中新世达到最大高度然后垮塌的观点。  相似文献   

南沙群岛海域沉积物古地磁参数对米兰科维奇周期的响应     

侯红明  汤贤赞  王保贵  袁友仁 《热带海洋学报》1995,(3)

对南沙群岛海域８７－１１柱样天然剩余磁化强度（ＮＲＭ）及９０－１０３柱样ＮＲＭ、磁化率（ｘ）、剩磁倾角（Ⅰ）等的功率谱分析表明：晚更新世以来该区沉积物的古地磁参数较好地反映了古气候、古环境的变化，响应着古气候变化的米兰科维奇天文学周期；在周期成分中，以地球轨道偏心率周期（ｅ）及岁差周期（ｐ）为主，地轴倾斜度周期（ε）无明显表现，同时获得了与特殊地球位置相关联的岁差半周期成分。研究还表明，古地磁参数存在着明显的对古气候变化的非线性响应，明显不同于开阔大洋；同时，不同的沉积单元，沉积物古地磁参数对古气候变化响应的灵敏度各不相同。  相似文献   

湖北省郧县恐龙化石分布地区古地磁学初步研究   总被引：2，自引：0，他引：2  

林文姣  徐世球  任有福  周修高  李正琦 《地质科技情报》2001,20(2):35-36

湖北郧县梅铺－带晚白垩世地层以盛产恐龙化石闻名于国内外，在大量地质工作研究的基础上进行了古地磁学研究，给出了该区的古应力方向，为该区建立国家地质公园和地质科学考察研究中心、地学科普教育基地提供了基础参考数据。  相似文献   

Morphological aspects of a new type of counter electrojet event     

R. G. Rastogi 《Annales Geophysicae》1999,17(2):210-219

The study describes the time and space morphologies of a rather new type of counter electrojet event on the basis of data from the excellent chain of magnetic and ionospheric observatories along the Indo-Russian longitude sector. Abnormally large westward currents are observed during almost the whole of the daytime hours on a series of days. These events do not form any vortices in the current system and do not apparently seem to be associated with tidal effects or any solar magnetosphere events or geomagnetic disturbances. The existence of a westward electric field over the equatorial ionosphere has been confirmed by the absence of an equatorial type of sporadic E in the ionograms at Thumba precisely during the periods when H at Trivandrum minus H at Alibag is negative. The equatorial F region anomaly was also absent on the counter electrojet day. Such counter electrojet events during the northern winter months of low solar activity years are suggested to be the result of the modified wind system in the ionosphere associated with stratospheric warming events.  相似文献   

Paleomagnetic study on the Early Triassic red beds from Jiaocheng,Shanxi Province     

Ruiping?ShiEmail author  Baochun?Huang  Rixiang?Zhu  Shoumai?Ren 《中国科学D辑(英文版)》2004,47(2):108-114

Paleomagnetic and rock magnetic study has been conducted on the Early Triassic red beds of Liujiagou Formation from Jiaocheng, Shanxi Province. Hematite was shown as the main magnetic mineral. After eradicating an initial viscous component at room temperature to ~100°C–200°C, thermal demagnetization shows that most samples contain two remanence components, intermediate-temperature remanence component at 250°C–500°C and high-temperature component at 500°C–680°C. The intermediate-temperature component has a negative fold test at the 95% confidence level. And the pole position of the intermediate-temperature component in geographic coordinates is correlated with the Middle Jurassic reference pole of the North China Block (NCB) within the 95% confidence, suggesting that it might be a remagnetization component acquired during the Yanshanian period. The high-temperature component contains both reversal and normal polarities with positive fold test and C-level positive reversal test at the 95% confidence level, which suggests that this high-temperature component can be regarded as primary magnetization. Comparison of this newly obtained Early Triassic paleopole with the coeval mean pole of the Ordos Basin suggests that a locally relative rotation may have happened between the Ordos and the Jiaocheng area of Shanxi Province. This rotation may be related with two faults: one is Lishi big fault separating Ordos from Shanxi and the other is Jiaocheng big fault, which is situated in the southeast of sampling locality and was still in motion during the Cenozoic.  相似文献   

Paleomagnetic age and palaeobiological significance of hominoid fossil strata of Yuanmou Basin in Yunnan   总被引：4，自引：0，他引：4  

Friedrich A. Heller 《中国科学D辑(英文版)》2004,47(5)

The Yuanmou area in Yunnan Province is a fa-mous place for origin of mankind. Qian Fang et al. found tooth fossils of Yuanmou man in Shangnabang Village of Yuanmou in 1965. Jiang Nengren et al. identified the hominoid teeth from animal fossils un-earthed near Zhupeng Village in the Xiaohe Basin which were delivered by the local peasants. Hominoid fossils were also found in Leilao Village of Yuanmou afterward. These great discoveries have aroused ex-tensive concern in academic circle[1,2…  相似文献