This paper report paleomagnetic data from late Cretaceous diorite dykes that sub-vertically intrude granodiorites in the eastern Gangdese belt near the city of Lhasa.Our research goals are to provide further constrain...This paper report paleomagnetic data from late Cretaceous diorite dykes that sub-vertically intrude granodiorites in the eastern Gangdese belt near the city of Lhasa.Our research goals are to provide further constraints on pre-collisional structure of the southern margin of Asia and the onset of the India-Asia collision.Magnetite is identified as the main magnetic carrier in our study.The magnetite shows no evidence of metamorphism or alteration as determined from optical and scanning electron microscope observations.A strong mineral orientation is revealed by anisotropy of magnetic susceptibility analysis both for the intruded dykes and the country rocks.The authors interpret this AMS fabric to have formed during intrusion rather than deformation.Fifteen of 23 sites yield acceptable site mean characteristic remanences with dual polarities.A scatter analysis of the virtual geomagnetic poles suggests that the mean result adequately averaged paleosecular variation.The paleomagnetic pole from the Gangdese dykes yields a paleolatitude of 14.3°N±5.8°N for the southern margin of Asia near Lhasa.The paleolatitude corresponds to an in-between position of the Lhasa terrane during about 130‒60 Ma.Furthermore,the mean declination of the characteristic remanent magnetization reveals a significant counterclockwise rotation of 18°±9°for the sampling location since about 83 Ma.In the light of tectonic setting of the dykes,the strike of the southern margin of Asia near Lhasa is restored to trend approximately about 310°,which is compatible with the hypothesis that the southern margin of Eurasia had a quasi-linear structure prior to its collision with India.展开更多
We performed on paleomagnetic investigation of the Upper Cretaceous red sandstones collected from Fujiau and Guangdong provinces. Significant characteristic directions were isolated by principal comPonent analysis fro...We performed on paleomagnetic investigation of the Upper Cretaceous red sandstones collected from Fujiau and Guangdong provinces. Significant characteristic directions were isolated by principal comPonent analysis from 22 of 25 and 9 of 14 sampling sites iu Fujian and Guangdong,respectively. Maximum concentration of global mean directions every province is achieved at 70 %and complete (100 % ) untilting for Fujian and Guangdong, respectively. We regarded these mean directions as the Late Cretaceous paleomagnetic directions and calculated virtual geomagnetic poles (VGPs); Fujian, Lat. /Lon. = 79. 4°N/210. 3°E (α95= 5. 1°) and Guangdong, Lat. /Lon. = 80. 1°N/193. 4°E (α95=8. 0°). These two VGPs are nearly equal to each other and to a mean VGP from Sichuan Province reported previously. This observation suggests no relative movement among three regions, Fujian, Guangdong and Sichuan, since the Late Cretaceous. Two VGPs from this study are significantly different from previously reported VGPs from the same regions. Further systematic paleomagnetic works are needed to clarify this difference of VGP Positions.展开更多
The amalgamation of Pangea formed the contorted Variscan-Alleghanian orogen,suturing Gondwana and Laurussia during the Carboniferous.From all swirls of this orogen,a double curve in Iberia stands out,the coupled Canta...The amalgamation of Pangea formed the contorted Variscan-Alleghanian orogen,suturing Gondwana and Laurussia during the Carboniferous.From all swirls of this orogen,a double curve in Iberia stands out,the coupled Cantabrian Orocline and Central Iberian curve.The Cantabrian Orocline formed at ca.315–290 Ma subsequent to the Variscan orogeny.The formation mechanism of the Cantabrian Orocline is disputed,the most commonly proposed mechanisms include either(1)that south-westernmost Iberia would be an Avalonian(Laurussian)indenter or(2)that the stress field changed,buckling the orogen.In contrast,the geometry and kinematics of the Central Iberian curve are largely unknown.Whereas some authors defend both curvatures are genetically linked,others support they are distinct and formed at different times.Such uncertainty adds an extra layer of complexity to our understanding of the final stages of Pangea’s amalgamation.To solve these issues,we study the late Carboniferous–early Permian vertical-axis rotations of SW Iberia with paleomagnetism.Our results show up to 70counterclockwise vertical-axis rotations during late Carboniferous times,concurring with the anticipated kinematics if SW Iberia was part of the southern limb of the Cantabrian Orocline.Our results do not allow the necessary penecontemporaneous clockwise rotations in Central Iberia to support a concomitant formation of both Cantabrian and Central Iberian curvature.The coherent rotation of both Gondwanan and Avalonian pieces of SW Iberia discards the Laurussian indenter hypothesis as a formation mechanism of the Cantabrian Orocline and confirms the Greater Cantabrian Orocline hypothesis.The Greater Cantabrian Orocline likely formed as a consequence of a change in the stress field during the late Carboniferous and extended beyond the Rheic Ocean suture affecting the margins of both Laurussia and Gondwana.展开更多
The Mesozoic magmatism in Southern Brazil is represented mainly by the basaltic flows of the Serra Geral Formation,the tholeiitic dikes swarms from the Ponta Grossa Arch,Florianópolis,and along the coast
A precise U-Pb baddeleyite age of 1999±2 Ma has been obtained for the NNW trending Lac Shpogan dyke swarm of the James Bay area of the eastern Superior craton.Previously the age of the swarm was
The 1.235 Ga ESE-trending Sudbury dyke swarm cuts Paleoproterozoic to Archean rocks,but at its SE end becomes deformed and metamorphosed by the^1 Ga Grenville orogen,a result of collision between
This paper conducts systematic test research on the 2920 paleomagnetic directional samples taken from Ordovician-Paleogene sedimentary formation in the north slope of Qomolangma in south of Tibet and obtains the prima...This paper conducts systematic test research on the 2920 paleomagnetic directional samples taken from Ordovician-Paleogene sedimentary formation in the north slope of Qomolangma in south of Tibet and obtains the primary remanent magnetization component and counts the new data of paleomagnetism the times. Based on the characteristic remanent magnetization component, it calculates the geomagnetic pole position and latitude value of Himalaya block in Ordovician-Paleogene. According to the new data of paleomagnetism, it draws the palaeomagnetic polar wander curve and palaeolatitude change curve of the north slope of Qomolangma in Ordovician-Paleogene. It also makes a preliminary discussion to the structure evolution history and relative movement of Himalaya bloc. The research results show that many clockwise rotation movements had occurred to the Himalaya block in northern slope of Qomolangmain the process of northward drifting in the phanerozoic eon. In Ordovician-late Cretaceous, there the movement of about 20.0° clockwise rotation occurred in the process of northward drifting. However, 0.4° counterclockwise rotation occurred from the end of late Devonian epoch to the beginning of early carboniferous epoch; 6.0° and 8.0° counterclockwise rotation occurred in carboniferous period and early Triassic epoch respectively, which might be related with the tension crack of continental rift valley from late Devonian period to the beginning of early carboniferous epoch, carboniferous period and early Triassic epoch. From the Eocene epoch to Pliocene epoch, the Himalaya block generated about 28.0° clockwise while drifting northward with a relatively rapid speed. This was the result that since the Eocene epoch, due to the continuous expansion of mid-ocean ridge of the India Ocean, the neo-Tethys with the Yarlung Zangbo River as the main ocean basin closed to form orogenic movement and the strong continent-continent collision orogenic movement of the east and west Himalayas generated clockwise movement in the mid-Himalaya area. According to the calculation of palaeolatitude data, the Himalaya continent-continent collusion orogenic movement since the Eocene epoch caused the crustal structure in Indian Plate-Himalaya folded structural belt-Lhasa block to shorten by at least 1000 km. The systematic research on the paleomagnetism of Qomolangma area in the phanerozoic eon provides a scientific basis to further research the evolution of Gondwanaland, formation and extinction history of paleo-Tethys Ocean and uplift mechanism of the Qinghai-Tibet Plateau.展开更多
The paleomagnetis m of 109 oriented samples collected from drill cores through 5 rock units of Late Cretaceous and Early Tertiary on Fildes Peninsula were systematically studied. According to the study, the paleomagne...The paleomagnetis m of 109 oriented samples collected from drill cores through 5 rock units of Late Cretaceous and Early Tertiary on Fildes Peninsula were systematically studied. According to the study, the paleomagnetic pole position of this area is different from the position of Australia during the 55-45 Ma period. This means that when the break-up of the Gondwanaland at 55-45 Ma ago, Australia was separated from the Gondwanaland, drifting southward 20°-30°Lat. and rotating 70°-80°westward and then gradually arriving at recent position. The paleolatitudinal data indicate that it is not impossible that the area studied was covered with land glacier at that time. The apparent polar wander path of Antarctica through the geological time are also roughly worked out.展开更多
A preliminary study of paleomagnetism and rock magnetism has been done on 55 eclogite samples collected from the Chinese Continental Scientific Drilling (CCSD) site at the Maobei (毛北) area, Donghai (东海) County, Ji...A preliminary study of paleomagnetism and rock magnetism has been done on 55 eclogite samples collected from the Chinese Continental Scientific Drilling (CCSD) site at the Maobei (毛北) area, Donghai (东海) County, Jiangsu (江苏) Province. Also the isothermal remanence, hysteresis loop, magnetic fabric, thermal susceptibility were measured, and analyses were made by electron-probe and scanning electric microscope on some samples synchronously. The result indicates that there are two groups of stable remanence, the normal and reversed magnetization. The remanence orientations are: D=94.3o, I=-29.1o and D=273.7o, I=15.4o, respectively. The magnetization intensity and the density of the samples which carry the normal magnetization are very different from those bearing reversed magnetization. The magnetic anisotropy is weak, and the minimum axis is hardly determined. The isothermal remanence and the hysteresis loop show that the magnetic carriers of the eclogite are likely SD (single domain) and PSD (pseudo-single domain) magnetite. According to the magnetic property, the cause of formation of magnetic carriers, the mechanism of the remanence, and the significance for the tectonics are discussed.展开更多
We report rock magnetic and paleomagnetic results for Middle Silurian Gongpoquan and Middle Ordo-vician Huaniushan volcanic samples collected from the Ma-zongshan and Hongliuyuan areas of Gansu Province, northwest Chi...We report rock magnetic and paleomagnetic results for Middle Silurian Gongpoquan and Middle Ordo-vician Huaniushan volcanic samples collected from the Ma-zongshan and Hongliuyuan areas of Gansu Province, northwest China. The results indicate that the main magnetic mineral of the Gongpoquan and Huaniushan volcanic rock is magnetite, and it may remain characteristic remanent magnetization acquired at the time of formation of the rocks. However, with the exception of samples from site go20, most of Middle Ordovician Huaniushan volcanic samples have a very weak nature remanent magnetization, and generally show an erratic demagnetization behavior, which does not allow isolation of characteristic remanent magnetizations from these samples. Comparison of paleomagnetic results obtained from the Beishan area of Gansu with Paleozoic apparent polar wander paths for Tarim and Siberia suggests that the Beishan tarrane, the southern part of the Beishan area of Gansu beyond the Mingshui-Shipanjin-Xiaohuang-shan zone,展开更多
The Mesoproterozoic mafic dyke swarms are extensively distributedin the central North China Craton(NCC) including North Shanxi, Wutai and Lüliang areas, which are not deformed and metamorphic but high magnetic, s...The Mesoproterozoic mafic dyke swarms are extensively distributedin the central North China Craton(NCC) including North Shanxi, Wutai and Lüliang areas, which are not deformed and metamorphic but high magnetic, so the dyke swarms become the mark to compare the high meta-morphic rock areas in magnetism. Based on the analysis of paleomagnetism of mafic dyke swarms in North Shanxi, Wutai and Lüliang areas, NCC inclined southward about 18° so that North Shanxi lifted up and rotated 10° left to Wutai area. The dyke swarms in Lüliang developed later than in North Shanxi and Wutai area. The NNW-trending and WNW-trending dyke swarms developed in Lüliang while the North China Plate moved northward consistently so that the paleomagnetism of dyke swarms in Lüliang is greatly different from North Shanxi and Wutai area.展开更多
Studies have been done of the secondary chemico-viscous remanent magnetization (CVRM) produced in the oxidization and decomposition of high-purity crystal siderite specimens collected from Dalizi Deposit, Jilin Provin...Studies have been done of the secondary chemico-viscous remanent magnetization (CVRM) produced in the oxidization and decomposition of high-purity crystal siderite specimens collected from Dalizi Deposit, Jilin Province. The CVRM intensity increases to a peak value at an annealing temperature of 490℃. The direction of CVRM is always parallel to the applied field, and no self-reversal behavior has been observed in the transformation of maghemite to hematite. It is suggested that the phase transition of magnetic minerals can make great contribution to secondary magnetization. Results of successive heating at low temperature indicate that the crystal mineral siderite is basically stable. Finally, the paleomagnetic significance of CVRM is discussed.展开更多
THE Early Ordovician Baiyungang Formation limestone in Tarim is characterized by multiplemagnetic components including primary remanent magnetism (PRM) and late remagnetiza-tion. Considerable attention should be paid ...THE Early Ordovician Baiyungang Formation limestone in Tarim is characterized by multiplemagnetic components including primary remanent magnetism (PRM) and late remagnetiza-tion. Considerable attention should be paid to its petromagnetic significance. Investigatingthe relationship between these components and the magnetic carriers is important to distin-展开更多
The new paleomagnetic data of the early Triassic Daye Formation from Hubei Province are reported. The ChRM passes consistency test and reversal test. Two magnetic components were isolated with principal component anal...The new paleomagnetic data of the early Triassic Daye Formation from Hubei Province are reported. The ChRM passes consistency test and reversal test. Two magnetic components were isolated with principal component analysis （PCA）. Component B is a ChRM and component A was acquired by remagnetization during lndosinian cycle. Rock magnetic study shows that the carrier is dominantly detrital magnetite. According to the data, in conjunction with recently published Triassic paleornagnetic results, mean paleopole of the Triassic Yangtze Block is calculated as 30.3°N, 198.4°E, α<sub>95</sub> = 9.2°.Distribution of all Triassic declinations indicates obviously local rotation in the mid-Yangtze areas,which results in consistence of the declinations with fold axes. By comparison with Triassic paleomagnetic data in the South China Block and some of geological evidence, it is inferred that the timing of the suture between the Yangtze Block and the South China Block is earlier in western part than in eastern part in the展开更多
Ⅰ. INTRODUCTIONThe Permian-Triassic section in Guangyuan County of Sichuan Province was chosen for a magnetostratigraphic study. Previously, the section has been studied in detail palaeontologically and an iridium an...Ⅰ. INTRODUCTIONThe Permian-Triassic section in Guangyuan County of Sichuan Province was chosen for a magnetostratigraphic study. Previously, the section has been studied in detail palaeontologically and an iridium anomaly has been detected at the Permian-Triassic boundary. Field work and paleomagnetic sampling were carried out in October 1984. All measurements and experiments were done in the paleomagnetic laboratory of the Institute of Geophysics, ETH Zürich in 1985.展开更多
It has been debated whether there was southward movement of the South China Block (SCB) during the Cretaceous. In this study, a paleomagnetic investigation was carried out on the Late Cretaceous volcanic rocks (~88 Ma...It has been debated whether there was southward movement of the South China Block (SCB) during the Cretaceous. In this study, a paleomagnetic investigation was carried out on the Late Cretaceous volcanic rocks (~88 Ma) of the Shimaoshan Group in Yongtai County, Fujian Province. Rock magnetic experiments showed that magnetite in pseudo-single-domain and multi-domain grain and hematite were predominant magnetic phases. Stepwise thermal demagnetization successfully isolated characteristic directional components at high-temperature interval (>500°C) from 383 specimens in 19 sites, which yielded a paleomagnetic pole for the studied section at 83.1°N, 152.6°E (N=19, A 95=3.9°), and the scatter S B=9.0. The Fisher distribution of virtual geomagnetic poles (VGPs) and the consistence of S B with the expected value at the 95% confidence level indicate that the yielded paleomagnetic pole is free of paleomagnetic secular variation influence. The new pole, which is well consistent with that from the Eurasian apparent polar wander path (APWP) curve, suggests no obvious southward movement of the sampling site during the Cretaceous.展开更多
基金financially supported by the National Science Foundation of China(92055205,41672223)the start-up funding from Sun Yat-sen University(74110-18841244).
文摘This paper report paleomagnetic data from late Cretaceous diorite dykes that sub-vertically intrude granodiorites in the eastern Gangdese belt near the city of Lhasa.Our research goals are to provide further constraints on pre-collisional structure of the southern margin of Asia and the onset of the India-Asia collision.Magnetite is identified as the main magnetic carrier in our study.The magnetite shows no evidence of metamorphism or alteration as determined from optical and scanning electron microscope observations.A strong mineral orientation is revealed by anisotropy of magnetic susceptibility analysis both for the intruded dykes and the country rocks.The authors interpret this AMS fabric to have formed during intrusion rather than deformation.Fifteen of 23 sites yield acceptable site mean characteristic remanences with dual polarities.A scatter analysis of the virtual geomagnetic poles suggests that the mean result adequately averaged paleosecular variation.The paleomagnetic pole from the Gangdese dykes yields a paleolatitude of 14.3°N±5.8°N for the southern margin of Asia near Lhasa.The paleolatitude corresponds to an in-between position of the Lhasa terrane during about 130‒60 Ma.Furthermore,the mean declination of the characteristic remanent magnetization reveals a significant counterclockwise rotation of 18°±9°for the sampling location since about 83 Ma.In the light of tectonic setting of the dykes,the strike of the southern margin of Asia near Lhasa is restored to trend approximately about 310°,which is compatible with the hypothesis that the southern margin of Eurasia had a quasi-linear structure prior to its collision with India.
文摘We performed on paleomagnetic investigation of the Upper Cretaceous red sandstones collected from Fujiau and Guangdong provinces. Significant characteristic directions were isolated by principal comPonent analysis from 22 of 25 and 9 of 14 sampling sites iu Fujian and Guangdong,respectively. Maximum concentration of global mean directions every province is achieved at 70 %and complete (100 % ) untilting for Fujian and Guangdong, respectively. We regarded these mean directions as the Late Cretaceous paleomagnetic directions and calculated virtual geomagnetic poles (VGPs); Fujian, Lat. /Lon. = 79. 4°N/210. 3°E (α95= 5. 1°) and Guangdong, Lat. /Lon. = 80. 1°N/193. 4°E (α95=8. 0°). These two VGPs are nearly equal to each other and to a mean VGP from Sichuan Province reported previously. This observation suggests no relative movement among three regions, Fujian, Guangdong and Sichuan, since the Late Cretaceous. Two VGPs from this study are significantly different from previously reported VGPs from the same regions. Further systematic paleomagnetic works are needed to clarify this difference of VGP Positions.
基金the ISES post-doctoral grant to DPG(Project No.WA.146101.2.656).
文摘The amalgamation of Pangea formed the contorted Variscan-Alleghanian orogen,suturing Gondwana and Laurussia during the Carboniferous.From all swirls of this orogen,a double curve in Iberia stands out,the coupled Cantabrian Orocline and Central Iberian curve.The Cantabrian Orocline formed at ca.315–290 Ma subsequent to the Variscan orogeny.The formation mechanism of the Cantabrian Orocline is disputed,the most commonly proposed mechanisms include either(1)that south-westernmost Iberia would be an Avalonian(Laurussian)indenter or(2)that the stress field changed,buckling the orogen.In contrast,the geometry and kinematics of the Central Iberian curve are largely unknown.Whereas some authors defend both curvatures are genetically linked,others support they are distinct and formed at different times.Such uncertainty adds an extra layer of complexity to our understanding of the final stages of Pangea’s amalgamation.To solve these issues,we study the late Carboniferous–early Permian vertical-axis rotations of SW Iberia with paleomagnetism.Our results show up to 70counterclockwise vertical-axis rotations during late Carboniferous times,concurring with the anticipated kinematics if SW Iberia was part of the southern limb of the Cantabrian Orocline.Our results do not allow the necessary penecontemporaneous clockwise rotations in Central Iberia to support a concomitant formation of both Cantabrian and Central Iberian curvature.The coherent rotation of both Gondwanan and Avalonian pieces of SW Iberia discards the Laurussian indenter hypothesis as a formation mechanism of the Cantabrian Orocline and confirms the Greater Cantabrian Orocline hypothesis.The Greater Cantabrian Orocline likely formed as a consequence of a change in the stress field during the late Carboniferous and extended beyond the Rheic Ocean suture affecting the margins of both Laurussia and Gondwana.
基金FAPESP Brazilian agency for the financial support
文摘The Mesozoic magmatism in Southern Brazil is represented mainly by the basaltic flows of the Serra Geral Formation,the tholeiitic dikes swarms from the Ponta Grossa Arch,Florianópolis,and along the coast
文摘A precise U-Pb baddeleyite age of 1999±2 Ma has been obtained for the NNW trending Lac Shpogan dyke swarm of the James Bay area of the eastern Superior craton.Previously the age of the swarm was
文摘The 1.235 Ga ESE-trending Sudbury dyke swarm cuts Paleoproterozoic to Archean rocks,but at its SE end becomes deformed and metamorphosed by the^1 Ga Grenville orogen,a result of collision between
基金supported by China Geological Survey(Grant No. H45C004002)the Project of the National Natural Science Foudation of China (Grant No.40272012)
文摘This paper conducts systematic test research on the 2920 paleomagnetic directional samples taken from Ordovician-Paleogene sedimentary formation in the north slope of Qomolangma in south of Tibet and obtains the primary remanent magnetization component and counts the new data of paleomagnetism the times. Based on the characteristic remanent magnetization component, it calculates the geomagnetic pole position and latitude value of Himalaya block in Ordovician-Paleogene. According to the new data of paleomagnetism, it draws the palaeomagnetic polar wander curve and palaeolatitude change curve of the north slope of Qomolangma in Ordovician-Paleogene. It also makes a preliminary discussion to the structure evolution history and relative movement of Himalaya bloc. The research results show that many clockwise rotation movements had occurred to the Himalaya block in northern slope of Qomolangmain the process of northward drifting in the phanerozoic eon. In Ordovician-late Cretaceous, there the movement of about 20.0° clockwise rotation occurred in the process of northward drifting. However, 0.4° counterclockwise rotation occurred from the end of late Devonian epoch to the beginning of early carboniferous epoch; 6.0° and 8.0° counterclockwise rotation occurred in carboniferous period and early Triassic epoch respectively, which might be related with the tension crack of continental rift valley from late Devonian period to the beginning of early carboniferous epoch, carboniferous period and early Triassic epoch. From the Eocene epoch to Pliocene epoch, the Himalaya block generated about 28.0° clockwise while drifting northward with a relatively rapid speed. This was the result that since the Eocene epoch, due to the continuous expansion of mid-ocean ridge of the India Ocean, the neo-Tethys with the Yarlung Zangbo River as the main ocean basin closed to form orogenic movement and the strong continent-continent collision orogenic movement of the east and west Himalayas generated clockwise movement in the mid-Himalaya area. According to the calculation of palaeolatitude data, the Himalaya continent-continent collusion orogenic movement since the Eocene epoch caused the crustal structure in Indian Plate-Himalaya folded structural belt-Lhasa block to shorten by at least 1000 km. The systematic research on the paleomagnetism of Qomolangma area in the phanerozoic eon provides a scientific basis to further research the evolution of Gondwanaland, formation and extinction history of paleo-Tethys Ocean and uplift mechanism of the Qinghai-Tibet Plateau.
文摘The paleomagnetis m of 109 oriented samples collected from drill cores through 5 rock units of Late Cretaceous and Early Tertiary on Fildes Peninsula were systematically studied. According to the study, the paleomagnetic pole position of this area is different from the position of Australia during the 55-45 Ma period. This means that when the break-up of the Gondwanaland at 55-45 Ma ago, Australia was separated from the Gondwanaland, drifting southward 20°-30°Lat. and rotating 70°-80°westward and then gradually arriving at recent position. The paleolatitudinal data indicate that it is not impossible that the area studied was covered with land glacier at that time. The apparent polar wander path of Antarctica through the geological time are also roughly worked out.
基金This paper is supported by the Focused Subject Program of Beijing (No. XK104910598).
文摘A preliminary study of paleomagnetism and rock magnetism has been done on 55 eclogite samples collected from the Chinese Continental Scientific Drilling (CCSD) site at the Maobei (毛北) area, Donghai (东海) County, Jiangsu (江苏) Province. Also the isothermal remanence, hysteresis loop, magnetic fabric, thermal susceptibility were measured, and analyses were made by electron-probe and scanning electric microscope on some samples synchronously. The result indicates that there are two groups of stable remanence, the normal and reversed magnetization. The remanence orientations are: D=94.3o, I=-29.1o and D=273.7o, I=15.4o, respectively. The magnetization intensity and the density of the samples which carry the normal magnetization are very different from those bearing reversed magnetization. The magnetic anisotropy is weak, and the minimum axis is hardly determined. The isothermal remanence and the hysteresis loop show that the magnetic carriers of the eclogite are likely SD (single domain) and PSD (pseudo-single domain) magnetite. According to the magnetic property, the cause of formation of magnetic carriers, the mechanism of the remanence, and the significance for the tectonics are discussed.
基金Thiswork was supported by the Chinese Academy of Sciences (Grant No. KZCX2-104) the National Natural Science Foundation of China (Grant No. 49874014).
文摘We report rock magnetic and paleomagnetic results for Middle Silurian Gongpoquan and Middle Ordo-vician Huaniushan volcanic samples collected from the Ma-zongshan and Hongliuyuan areas of Gansu Province, northwest China. The results indicate that the main magnetic mineral of the Gongpoquan and Huaniushan volcanic rock is magnetite, and it may remain characteristic remanent magnetization acquired at the time of formation of the rocks. However, with the exception of samples from site go20, most of Middle Ordovician Huaniushan volcanic samples have a very weak nature remanent magnetization, and generally show an erratic demagnetization behavior, which does not allow isolation of characteristic remanent magnetizations from these samples. Comparison of paleomagnetic results obtained from the Beishan area of Gansu with Paleozoic apparent polar wander paths for Tarim and Siberia suggests that the Beishan tarrane, the southern part of the Beishan area of Gansu beyond the Mingshui-Shipanjin-Xiaohuang-shan zone,
基金the National Natural Science Foundation of China (Grant No. 49832030).
文摘The Mesoproterozoic mafic dyke swarms are extensively distributedin the central North China Craton(NCC) including North Shanxi, Wutai and Lüliang areas, which are not deformed and metamorphic but high magnetic, so the dyke swarms become the mark to compare the high meta-morphic rock areas in magnetism. Based on the analysis of paleomagnetism of mafic dyke swarms in North Shanxi, Wutai and Lüliang areas, NCC inclined southward about 18° so that North Shanxi lifted up and rotated 10° left to Wutai area. The dyke swarms in Lüliang developed later than in North Shanxi and Wutai area. The NNW-trending and WNW-trending dyke swarms developed in Lüliang while the North China Plate moved northward consistently so that the paleomagnetism of dyke swarms in Lüliang is greatly different from North Shanxi and Wutai area.
基金Project supported by the National Natural Science Foundation of China (Grant No. 49454005)the Ministry of Science and Technoloy Project.
文摘Studies have been done of the secondary chemico-viscous remanent magnetization (CVRM) produced in the oxidization and decomposition of high-purity crystal siderite specimens collected from Dalizi Deposit, Jilin Province. The CVRM intensity increases to a peak value at an annealing temperature of 490℃. The direction of CVRM is always parallel to the applied field, and no self-reversal behavior has been observed in the transformation of maghemite to hematite. It is suggested that the phase transition of magnetic minerals can make great contribution to secondary magnetization. Results of successive heating at low temperature indicate that the crystal mineral siderite is basically stable. Finally, the paleomagnetic significance of CVRM is discussed.
基金This work was supported by the National Natural Science Foundation of China (Grant No. 49334050).
文摘THE Early Ordovician Baiyungang Formation limestone in Tarim is characterized by multiplemagnetic components including primary remanent magnetism (PRM) and late remagnetiza-tion. Considerable attention should be paid to its petromagnetic significance. Investigatingthe relationship between these components and the magnetic carriers is important to distin-
文摘The new paleomagnetic data of the early Triassic Daye Formation from Hubei Province are reported. The ChRM passes consistency test and reversal test. Two magnetic components were isolated with principal component analysis （PCA）. Component B is a ChRM and component A was acquired by remagnetization during lndosinian cycle. Rock magnetic study shows that the carrier is dominantly detrital magnetite. According to the data, in conjunction with recently published Triassic paleornagnetic results, mean paleopole of the Triassic Yangtze Block is calculated as 30.3°N, 198.4°E, α<sub>95</sub> = 9.2°.Distribution of all Triassic declinations indicates obviously local rotation in the mid-Yangtze areas,which results in consistence of the declinations with fold axes. By comparison with Triassic paleomagnetic data in the South China Block and some of geological evidence, it is inferred that the timing of the suture between the Yangtze Block and the South China Block is earlier in western part than in eastern part in the
文摘Ⅰ. INTRODUCTIONThe Permian-Triassic section in Guangyuan County of Sichuan Province was chosen for a magnetostratigraphic study. Previously, the section has been studied in detail palaeontologically and an iridium anomaly has been detected at the Permian-Triassic boundary. Field work and paleomagnetic sampling were carried out in October 1984. All measurements and experiments were done in the paleomagnetic laboratory of the Institute of Geophysics, ETH Zürich in 1985.
基金supported by National Natural Science Foundation of China (Grant Nos. 40634024 and40821091)
文摘It has been debated whether there was southward movement of the South China Block (SCB) during the Cretaceous. In this study, a paleomagnetic investigation was carried out on the Late Cretaceous volcanic rocks (~88 Ma) of the Shimaoshan Group in Yongtai County, Fujian Province. Rock magnetic experiments showed that magnetite in pseudo-single-domain and multi-domain grain and hematite were predominant magnetic phases. Stepwise thermal demagnetization successfully isolated characteristic directional components at high-temperature interval (>500°C) from 383 specimens in 19 sites, which yielded a paleomagnetic pole for the studied section at 83.1°N, 152.6°E (N=19, A 95=3.9°), and the scatter S B=9.0. The Fisher distribution of virtual geomagnetic poles (VGPs) and the consistence of S B with the expected value at the 95% confidence level indicate that the yielded paleomagnetic pole is free of paleomagnetic secular variation influence. The new pole, which is well consistent with that from the Eurasian apparent polar wander path (APWP) curve, suggests no obvious southward movement of the sampling site during the Cretaceous.
