松潘—阿坝地块三叠系古地磁结果及运动学意义     

何登发  庄忠海  马永生 《现代地质》2007,21(3):556-563

迄今为止,位于扬子地块的西北缘,夹持于扬子、华北、塔里木和羌塘—昌都地块之间呈倒三角形构造区块的巴颜喀拉褶皱带尚未有构造古地磁研究成果报导。为配合该区油气勘查与油气资源评价,并对构造区块定位提供定量数据,开展了松潘—阿坝地块的古地磁研究。采样区集中在西秦岭构造区南亚带(摩天岭和若尔盖)、中亚带(洮河)和巴颜喀拉构造区的马尔康复向斜带(巴颜喀拉褶皱区)4个微地块。采样地层单元主要为三叠系。共采集57个采点,376块岩心标本。通过对岩石样品测试数据的分析和计算,获得洮河、巴颜喀拉、摩天岭和若尔盖(后两者夹于前两者之间)4个微地块古地磁极极点位置:经度为191.4°E~202.9°E,纬度为49.5°N~58.5°N。洮河和巴颜喀拉两微地块在晚三叠世的古纬度同为26.2°N,表明晚三叠世这4个被断裂相隔的微地块已构成一个统一的较大的地块。洮河和巴颜喀拉地块在三叠纪时的古纬度变化分别从早三叠世的13.4°N和11.3°N向北移动到晚三叠世的26.2°N,同时在北向移动过程中从早三叠世至晚三叠世分别发生了约40°和16°的逆时针旋转。  相似文献   

华北与西伯利亚地块碰撞时代的古地磁分析——兼论苏鲁-大别超高压变质作用的构造起因   总被引：4，自引：2，他引：4  

李朋武  高锐  管烨  李秋生 《地球学报》2007,28(3):234-252

对华北和西伯利亚地块进行了古纬度和纬度运移量的对比分析,结合古生物地理、同位素年代学等地质数据,确定了两地块的运动特征,相应地,确定了位于两地块间中亚洋盆最终闭合时代,并与苏鲁-大别山地区的超高压变质岩的峰期变质时代进行了对比.结果表明:①西伯利亚地块于晚泥盆世开始快速向北漂移,分隔华北和西伯利亚地块的中亚洋在晚泥盆世至晚石炭世期间已经存在;②早二叠世西伯利亚地块开始快速向南漂移,并于二叠纪末期(～250 Ma)和华北地块发生碰撞;③早二叠世,中亚洋纬度宽度约39°;④苏鲁-大别山地区的超高压变质岩的形成  相似文献   

Paleomagnetism of traps of the Franz Josef Land Archipelago     

V.V. Abashev  D.V. Metelkin  N.E. Mikhaltsov  V.A. Vernikovsky  V.Yu. Bragin 《Russian Geology and Geophysics》2018,59(9):1161-1181

The paper presents results of paleomagnetic studies of traps of the Franz Josef Land (FJL) Archipelago. This area is considered to be part of the Barents Sea Large Igneous Province (LIP) and is usually associated with the Early Cretaceous stage of plume activity, by analogy with other manifestations of late Mesozoic trap magmatism in the High Arctic. Recent isotope-geochemical studies, however, suggest a much longer history of basaltoid magmatism in the FJL area, from Early Jurassic through Early Cretaceous, with three pulses at 190, 155, and ≈ 125 Ma. Given a significant difference in age, paleomagnetic directions and corresponding virtual geomagnetic poles are supposed to form discrete groups near the Jurassic-Early Cretaceous paleomagnetic poles of Eastern Europe. However, the calculated virtual geomagnetic poles, on the contrary, show a single “cloud” distribution, with its center being shifted to the Early Cretaceous paleomagnetic poles of Siberia. The performed analysis demonstrates that the significant variance is caused mostly by the high-latitude position of the FJL and secular variations of the geomagnetic field during the formation of the traps. Products of the Early Cretaceous magmatism evidently prevail in the data sample. The coincidence of the average paleomagnetic pole of the FJL traps with the Early Cretaceous (145-125 Ma) interval of the apparent polar wander path of Siberia rather than Eastern Europe confirms the hypothesis of the Mesozoic strike-slip activity within the Eurasian continent. This activity might be a natural result of the evolution of the Arctic Ocean.  相似文献   

青藏高原拉萨地块西段三叠纪古地磁结果及其构造意义   总被引：1，自引：0，他引：1  

程鑫  周亚楠  郭强  侯宝宁  吴汉宁 《地质通报》2015,34(203):306-317

报道拉萨地块西段三叠纪古地磁研究的初步结果。古地磁样品来自措勤县敌布错北缘新发现的海相三叠纪地层,共采集6个采点67块独立定向样品。岩石磁学实验表明,样品中含有大量中低矫顽力中等阻挡温度的磁性矿物和一定量的磁铁矿。于4个采点的47块样品中分离出现代地磁场的低温粘滞剩磁（分量A）,在6个采点66块样品中获得白垩纪的次生剩磁分量（分量B）,5个采点28块样品获得高温特征剩磁分量（分量C）。分量C仅可在少数以磁铁矿为主要载磁矿物的样品高温区间（525~585℃）获得,可通过标准褶皱检验,为岩石形成时期的原生剩磁信息。计算得出拉萨地块三叠纪的古地磁极位置：φρ=17.4°N、λρ=205.9°E、（dp=6.7,dm=3.7）,该结果表明拉萨地块三叠纪处于南纬中低纬度地区。结合羌塘古地磁结果推测,羌北地块与拉萨地块之间班公湖—怒江缝合带所代表的特提斯洋盆可能在早三叠世打开,早三叠世—晚三叠世期间快速扩张并推动羌北地块快速北移,促使了羌北地块与欧亚大陆南缘的拼合。  相似文献   

广东南雄盆地晚白垩系古地磁研究     

王保贵  汤贤赞  侯红明  方大钧 《热带海洋学报》1994,(3)

对广东南雄盆地大凤一河南街剖面和古城一坪岭剖面上白垩统南雄组（Ｋ２ｎ）２５个采点、古新统上湖组（Ｅ１ｓ）２个采点的古地磁研究，经系统热退磁及倒转检验，分析出南雄组的特征剩磁方向为Ｄ＝３２．７°，Ｉ＝２７．４°，Ｋ＝１６．１，α９５＝８．４°，Ｎ＝２０；显示晚白垩世时期华南大陆位于１４．５°Ｎ的位置，同时晚白垩世以后华南大陆可能曾发生较大规模的顺时针旋转。  相似文献   

大同火山活动在区域沉积中的记录和阶段性历史研究     

胡小猛  周天航  蔡顺  陈硕  刘毓阳  陈美君 《地理学报》2017,72(9):1669-1679

大同火山活动的阶段性历史是一个尚未被揭示清楚的地学问题。野外实地考察及室内磁化率、化学成分、粒度和古地磁的测定结果显示：古湖滨处水平层理发育的火山碎屑层存在4个不同倾角的倾斜;古湖近岸处的湖相沉积层中含有4层火山碎屑层;古湖深处的湖相沉积层中出现4个磁化率显著正异常的层位,且这些层位粒度都较粗;古湖岸上的黄土沉积中出现3个磁化率为峰值、Rb/Sr比值为谷值的层位;古湖深处湖相沉积剖面中存在B/M和Jaramillo磁极性界限。据此进一步分析后认为：① 湖相沉积剖面中的磁化率显著正异常层位、黄土沉积中的高磁化率—低Rb/Sr比值层位可能是混入了大量火山灰物质;它们是区域火山活跃期的记录。② 系列沉积剖面特征指示区域火山活动曾经历4个活跃期,每个活跃期期间有多次密集的火山喷发。③ 4个活跃期的年代大约为早于0.90 Ma BP（第一活跃期）、~0.47 Ma BP（第二活跃期）、~0.31 Ma BP（第三活跃期）和~0.09 Ma BP（第四活跃期）;黄土沉积中还记录了区域北部有一个发生于~0.19 Ma BP的活跃期。此外,区域湖相沉积中所记录的4个火山活跃期都出现在湖退时期,平静期出现在湖侵时期。  相似文献   

How far between Iran and Eurasia was the Turan plate during Triassic–Jurassic times?     

Lemaire  M.M.  Westphal  M.  Gurevitch  E.L.  Nazarov  K.  Feinberg  H.  Pozzi  J.P. 《Geologie en Mijnbouw》1997,76(1-2):73-82

Calc-alkaline volcanic deposits from the south-west of the Turan plate, near the city of Turkmenbasi (40°00N, 52°58&\prime;E) in Turkmenistan, were studied paleomagnetically. These rocks have been affected by a greenschist-facies metamorphism, possibly of regional extent, that has been K/Ar-dated as 200 to 227 Ma old. A low-blocking-temperature component (D = 349°, I = 64°), close to the present field direction and probably of viscous or recent chemical origin, was isolated by a negative fold test at three sites. The mean direction of a high-blocking-temperature component isolated at 15 sites, mainly carried by magnetite, is scattered before and after tectonic correction and is therefore difficult to interpret. A group of seven sites with low inclinations before and after tectonic correction was isolated. The mean inclination of these sites (31 ± 8°), syn-folding or post-folding, corresponds to a paleolatitude of 17 ± 8° which is lower than the conventional Eurasian paleolatitudes for post-Permian times. The paleomagnetic data from the Turan and Iran plates constrain this low paleolatitude to the Late Triassic and Jurassic period. This requires a shortening of at least 7° between the Turan plate and Eurasia during this time.  相似文献   

山西保德-静乐地区新近纪地层时代讨论     

朱大岗  孟宪刚  邵兆刚  雷伟志  王津  韩建恩  余佳  吕荣平  王艳 《中国区域地质》2008,(4):510-516

通过对山西保德-静乐地区新近纪地层的野外地质调查和实测剖面,对分布于该区的新近纪地层进行了详细的研究和划分,获得了新的ESR和古地磁测年数据,并结合生物地层序列确定了该区新近系地层的顺序为：新近系上新统静乐组（N2j）、新近系中新统上部保德组（N1^26）和中新统下部芦子沟组（N1^1l）。  相似文献   

Paleomagnetic results of Paleozoic and Mesozoic rocks from Xingshan-Zigui section in Hubei Province, South China     

Hanning Wu  Rixiang Zhu  Vincent Courtillot  Lixin Bai  Jianxiao Xing  Yongxin Zhao  Gelian Yang 《中国科学D辑(英文版)》1999,42(2):182-194

The paleomagnetic reconnaissance study of the Paleozoic and Mesozoic sedimentary rocks from the Yangtze Block (YZB) was made to conduct the Apparent Polar Wander Path (APWP) of the YZB during the Phanerozoic. A total of 825 samples from 84 sites were collected from a continuous section along the Xiangxi River valley in Xingshan and Zigui counties in Hubei Province, northern margin of the YZB. Stepwise thermal/alternating demagnetization isolated well defined characteristic magnetization (ChRM) at a higher temperature in most of the samples, and relatively thermal stability and high coercivity were revealed from these samples. All the ChRMs can pass the fold and/or reversal tests, suggesting that they are probably primary. Therefore, new pole positions are presented for the YZB. Project supported by the National Natural Science Foundation of China (Grant No. 49334050).  相似文献   

新疆及周边古地磁研究与构造演化   总被引：20，自引：3，他引：17  

李永安  孙东江  郑洁 《新疆地质》1999,(3)

新疆古地磁研究始于1979年,20年来通过对塔里木、准噶尔、昆仑山等地区的古地磁研究,获得了古生代—新生代塔里木板块、准噶尔板块和青藏板块古地磁极移曲线和古纬度资料。震旦纪以前塔里木板块尚未形成,晚震旦世在赤道附近各地块才联合成塔里木板块的主体部分。后经历了两次快速北移,一次快速南移。准噶尔板块早古生代为一个独立的微板块,在晚古生代与哈萨克斯坦板块联合成一体,组成了哈萨克斯坦-准噶尔板块;塔里木板块震旦纪时还属冈瓦纳大陆的一个组成部分,早古生代逐渐脱离了冈瓦纳大陆,快速向北漂移,晚古生代早期与准噶尔板块首次在东部碰撞,成为劳亚大陆南缘的一个增生体。将介于劳亚大陆和冈瓦纳大陆之间的古陆体,称之谓华夏古陆群。晚古生代末—中生代早期,华夏古陆群先后增生到劳亚大陆南缘;早古生代早期古特提斯洋尚未形成,诸地块处于冈瓦纳大陆范围内,位于南半球的赤道附近。在中-晚志留世,这些地(板)块才快速向北漂移,由于洋扩张,形成了古特提斯洋,构成了三大陆块群夹两个大洋的古地理格局;二叠纪是特提斯构造演化关键时期,晚侏罗-早白垩世昆仑地块与柴达木地块和塔里木地块发生碰撞,联合成一体。早侏罗世早期柴达木地块等与塔里木地块发生碰撞联合,造成了古特提斯洋消亡。早侏罗世中期,开  相似文献