共查询到20条相似文献，搜索用时 296 毫秒
1.
碳酸盐岩是记录古地磁场信息的重要载体,然而,广泛存在的重磁化现象制约了碳酸盐岩在古地磁研究中的应用,其重磁化机制亟待解决.本文对采自贵州羊蹬地区的319块奥陶系碳酸盐岩定向样品作了详细的古地磁学和岩石磁学研究,其结果表明,94%样品(A类)记录了单一剩磁分量A,其解阻温度低于450℃;在地理坐标系下的平均方向为Dg/Ig=3.1°/48.1°(α95=2.9°),对应的古地磁极(87.0°N,2.8°E,A95=3.0°)与扬子地块古近纪-第四纪的古地磁极重合.6%样品(B类)记录了两个磁化分量,其高温分量(450℃~585℃)与A分量显著不同,但明显远离扬子块体早古生代古地磁极;低温分量(< 450℃)与A分量类似.说明羊蹬剖面奥陶系碳酸盐岩记录了两期重磁化.A分量和B低温分量的主要载磁矿物为磁黄铁矿(胶黄铁矿),B高温分量的主要载磁矿物为磁铁矿.这些磁性矿物都是成岩后的次生矿物.其中,解阻温度高于450℃的磁铁矿可能受晚燕山期造山运动影响生成;磁黄铁矿(胶黄铁矿)等矿物可能与印度板块与欧亚大陆碰撞引起的喜马拉雅造山运动所产生的流体作用有关,以后一期重磁化为主.新生代早期青藏高原隆升产生的流体在流经东南缘的碳酸盐岩等沉积岩层时,与原岩发生相互作用,使磁黄铁矿、胶黄铁矿、磁铁矿等磁性矿物生长并获得化学剩磁,造成了广泛重磁化. 相似文献
2.
R. V. Veselovskiy A. A. Arzamastsev L. I. Demina A. V. Travin S. B. Botsyun 《Izvestiya Physics of the Solid Earth》2013,49(4):526-547
The new paleomagnetic data on forty dikes and two intrusive plutons of Devonian age located in different parts of the Kola Peninsula, which have not been previously covered by systematic paleomagnetic studies, are reported. We describe the results of the rock magnetic, petrographic, and microprobe investigations of the Devonian dikes and present their isotopic ages (40Ar/39Ar, stepwise heating). Within the studied area, almost all the Devonian dikes, metamorphic Archaean-Proterozoic complexes of the Fennoscandian Shield, and Proterozoic dikes have undergone low-temperature hydrothermal-metasomatic alteration, which resulted in the formation of new magnetic minerals with a secondary (chemical) component of magnetization. The comparison of the paleomagnetic poles indicates the Early Jurassic age of the secondary component. We suggest that regional remagnetization event was caused by endogenic activity genetically related to the formation of the Barents Sea trap province 200–170 Ma ago. On the basis of the obtained data, the preliminary Devonian paleomagnetic pole of the East European Platform is determined. 相似文献
3.
4.
Belén Oliva-Urcia Emilio L. Pueyo Juan C. Larrasoaña 《Earth and Planetary Science Letters》2008,265(3-4):525-534
New paleomagnetic analyses of Triassic, Cretaceous and Eocene strata in the south-central Pyrenees show evidence for a widespread remagnetization, located along the southern border of the Axial Zone, the Internal Sierras, and the northern part of the Jaca-Pamplona basin. This remagnetization, always reversed in polarity, was acquired after an extensive period of Late Eocene–Early Oligocene folding and tilting in the area, and affects limestones, sandstones, marls and red beds. In addition, a characteristic prefolding component was identified in 30% of Upper Cretaceous and Triassic red beds. These results, together with a revaluation of previously published paleomagnetic data from the central Pyrenees, indicate that the spatial distribution of the postfolding remagnetization coincides with that of a domain of pressure solution cleavage. A relationship between the intensity of the remagnetization and the characteristic (prefolding component) with respect to the density of cleavage surfaces, leads us to propose a mechanism for the remagnetization related to the development of pressure solution cleavage that is framed within the tectonic evolution of the central Pyrenees. Partial dissolution of rock under tectonic compression leads to the liberation and subsequent accumulation of insoluble minerals in cleavage planes. Magnetic grains are part of the relatively insoluble residue, and they reorient in the presence of the ambient field after they are freed during dissolution of the rock matrix. Chemical reequilibrium (dissolution and/or neoformation of magnetic carriers) during this process cannot be excluded. The remagnetization mechanism we propose can help to explain widespread remagnetizations in low to moderately deformed rocks without the need of large-scale migration of orogenic fluids. 相似文献
5.
The opinions vary on the secondary remagnetization mechanisms of carbonate rocks. The prevalent interpretations of magnetic remanences are either chemical in origin that invoked the large-scale migration of orogenic fluids. or thermoviscous magnetization involved burial diagenetic processes. The paleomagnetic study carried out in northwestern part of Henan Province (north of the Qinling orogenic belt) reveals that 90% of carbonate rocks have suffered from the secondary remagnetization. On the basis of rock magnetic experiments, the assemblage of the magnetic minerals, remanent carriers and its formation process, and the possible mechanisms of remagnetization in these carbonate rocks are discussed. 相似文献
6.
A. G. Iosifidi V. A. Mikhailova V. V. Popov E. S. Sergienko A. V. Danilova N. M. Otmas 《Izvestiya Physics of the Solid Earth》2018,54(1):163-177
New data for the Early and Late Carboniferous sections of the Russian platform (Moscow syneclise and Donbass) are presented. Magneto-mineralogical studies are carried out to identify the magnetic minerals—carriers of natural remanent magnetization. Extensive Late Paleozoic remagnetization of Carboniferous rocks is revealed. The obtained paleomagnetic data allowed us to determine the average paleomagnetic poles for the Gzhelian, Serpukhovian, and Visean stages of Carboniferous deposits of the Moscow syneclise. 相似文献
7.
R. V. Veselovskiy A. A. Arzamastsev V. A. Tselmovich A. M. Fetisova E. P. Kulakova 《Izvestiya Physics of the Solid Earth》2017,53(6):898-907
Based on the results of the preliminary paleomagnetic investigation of 57 Precambrian dikes of the Kola Peninsula, in 31 of them a stable monopolar component of natural remanent magnetization (NRM) is revealed (D = 353.2°, I = 53.0°, K = 58, and α95 = 3.4°). The peculiarities of the distribution of this magnetization component within the Kola Peninsula and the rock magnetic characteristics of the dikes in which this component is isolated suggest its secondary nature and relate the mechanism and formation time to the remagnetization processes which took place in the northwest of Fennoscandia about 1.8 billion years ago during the Svecofennian orogeny. The corresponding geomagnetic pole of Fennoscandia has the coordinates Plat = 54.5°, Plong = 224.0°, and A95 = 3.9° and is located in the immediate vicinity of the known Paleoproterozoic (1.9–1.7 Ga) poles of Baltica (Khramov et al., 1997; Veikkolainen et al., 2014). 相似文献
8.
Henry C. Halls 《Earth and Planetary Science Letters》1991,105(1-3)
Consistent age relationships between oppositely magnetized dykes of the 2.45 Ga Matachewan dyke swarm suggest that only a single magnetic field reversal occurred during the period of igneous activity. The magnetic field throughout most of this time was characterized by a SSW declination and shallow negative inclination but reversed toward the waning stages of magmatism. The new paleomagnetic data provide the oldest known magnetic reversal for which the relative reversal sense is known. 相似文献
9.
Yong-Hee Park Seong-Jae Doh Dongwoo Suk 《Physics of the Earth and Planetary Interiors》2007,160(3-4):269-284
The Bakjisan Syncline is located in the northwestern part of the Taebaeksan Basin, Korea. New paleomagnetic data for the Upper Carboniferous–Lower Triassic Pyeongan Supergroup from the Pyeongchang area on the west limb of the Bakjisan Syncline have been obtained, and synthesized and compared with previous data from the Jeongseon area on the east limb of the syncline. A total of 350 specimens were collected from 21 sites to clarify the relationship between the spatial distribution of remagnetized areas and the thrust system in the Taebaeksan Basin. The characteristic remanent magnetization (ChRM) isolated from all samples was a remagnetized component acquired after tilting of the strata and carried by various magnetic minerals (magnetite, hematite and pyrrhotite). From rock magnetic studies, electron microscope observations and XRD analyses, the pervasive remagnetization is interpreted to be associated mainly with a fluid-mediated chemical remanent magnetization (CRM). This is consistent with the results of previous work in adjacent areas. The paleomagnetic pole position (88.3°E, 83.9°N, A95 = 4.9°) from the Pyeongan Supergroup in the Bakjisan Syncline indicates that the timing of the remagnetization event is Early Tertiary times (i.e. Paleocene to Eocene) by comparison with reliable paleopoles from the Korean Peninsula. Early Tertiary CRMs are also reported from previous studies of an adjacent region within the northwestern part of the Taebaeksan Basin. In contrast, a primary remanent magnetization was reported in the southeastern part of the Taebaeksan Basin. This implies that the major thrust system (the Gakdong thrust) which separates the two regions has caused them to experience substantially different geologic histories since deposition of the strata. Since many thrusts with NS trend are observed in the northwestern part of the Taebaeksan Basin compared with the southeastern region, it appears that the remagnetizing fluids pervasively penetrated the northwestern part of the basin by utilizing the already well-developed thrust system. 相似文献
10.
We present a quantitative relationship between blocking temperature and time that, in principle, provides a calibration of thermal remagnetization in nature. For a given metamorphic temperature-time regime, one can decide whether a given laboratory blocking temperature (or for paleointensity work, a range of blocking temperatures) is consistent with primary natural remanence (NRM) or with a metamorphic overprint. Independent of the domain structure or the chemical composition of the magnetic minerals, two general types of behaviour are predicted. If the primary NRM possesses laboratory (or primary cooling) blocking temperatures within 100°C or so of the Curie temperature, thermal remagnetization at lower temperatures, even over times as long as 106 years, is improbable. If the blocking temperatures are lower, viscous remagnetization is pronounced at temperatures well below those indicated by laboratory thermal demagnetization. An approximate scale of the “survival potential” of primary NRM in rocks of different metamorphic grades indicates that primary paleointensities are unlikely to be recovered from rocks metamorphosed above high-greenschist facies if the predominant magnetic mineral is nearly pure magnetite, or above middle-amphibolite facies if nearly pure hematite is predominant. Evidence from laboratory experiments and paleomagnetic field studies in metamorphic regions suggests, however, that these survival estimates are unduly optimistic. Chemical remagnetization through the destruction of primary magnetic minerals, and not thermal remagnetization, probably sets an effective upper temperature for the survival of primary NRM. 相似文献
11.
An intensive paleomagnetic investigation has been conducted on the Middle Triassic Leikoupo Formation on the Wangcang section (32.14°N, 103. 17°E). The results indicate the magnetic minerals are dominant by multidomain magnetite or maghemite, and the characteristic remnant magnetization revealed by stepwise thermal/alternating field demagnetization is close to the present-day geomagnetic direction of the sampling site. This suggests that dolomitization/thermal viscous magnetization is responsible for the remagnetization of this kind of rocks. 相似文献
12.
V. E. Pavlov A. M. Pasenko A. V. Shatsillo V. I. Powerman V. V. Shcherbakova S. V. Malyshev 《Izvestiya Physics of the Solid Earth》2018,54(5):782-805
Representative paleomagnetic collections of Lower Cambrian rocks from the northern and eastern regions of the Siberian platform are studied. New evidence demonstrating the anomalous character of the paleomagnetic record in these rocks is obtained. These data confidently support the hypothesis (Pavlov et al., 2004) that in the substantial part of the Lower Cambrian section of the Siberian platform there are two stable high-temperature magnetization components having significantly different directions, each of which is eligible for being a primary component that was formed, at the latest, in the Early Cambrian. The analysis of the world’s paleomagnetic data for this interval of the geological history shows that the peculiarities observed in Siberia in the paleomagnetic record for the Precambrian–Phanerozoic boundary are global, inconsistent with the traditional notion of a paleomagnetic record as reflecting the predominant axial dipole component of the geomagnetic field, and necessitates the assumption that the geomagnetic field at the Proterozoic–Phanerozoic boundary (Ediacaran–Lower Cambrian) substantially differed from the field of most of the other geological epochs. In order to explain the observed paleomagnetic record, we propose a hypothesis suggesting that the geomagnetic field at the Precambrian–Cambrian boundary had an anomalous character. This field was characterized by the presence of two alternating quasi-stable generation regimes. According to our hypothesis, the magnetic field at the Precambrian–Cambrian boundary can be described by the alternation of long periods dominated by an axial, mainly monopolar dipole field and relatively short epochs, lasting a few hundred kA, with the prevalence of the near-equatorial or midlatitude dipole. The proposed hypothesis agrees with the data obtained from studies of the transitional fields of Paleozoic reversals (Khramov and Iosifidi, 2012) and with the results of geodynamo numerical simulations (Aubert and Wicht, 2004; Glatzmayer and Olson, 2005; Gissinger et al., 2012). 相似文献
13.
Three components of magnetization have been observed in ninety-six samples (twelve sites) of amygdaloidal basalts and “sedimentary greenstones” of the Unicoi Formation in the Blue Ridge Province of northeast Tennessee and southwest Virginia. These components could be isolated by alternating field as well as thermal demagnetization. One component, with a direction close to that of the present-day geomagnetic field is ascribed to recent viscous remanent magnetizations; another component, with intermediate blocking temperatures and coercivities, gives a mean direction of D = 132°, I = +43°,α95 = 9° for N = 10 sites before correction for tilt of the strata. This direction and the corresponding pole position are close to Ordovician/Silurian data from the North American craton and we infer this magnetization to be due to a thermal(?) remagnetization during or after the Taconic orogeny. This magnetization is of post-folding origin, which indicates that the Blue Ridge in our area was structurally affected by the Taconic deformation. The third component, with the highest blocking temperatures and coercivities, appears to reside in hematite. Its mean direction, D = 276°, I = ?17°,α95 = 13.8° for N = 6 sites (after tilt correction) corresponds to a pole close to Latest Precambrian and Cambrian poles for North America. The fold test is inconclusive for this magnetization at the 95% confidence level because of the near-coincidence of the strike and the declinations. We infer this direction to be due to early high-temperature oxidation of the basalts, and argue that its magnetization may have survived the later thermal events because of its intrinsic high blocking temperatures. A detailed examination of the paleomagnetic directions from this study reveals that the Blue Ridge in this area may have undergone a small counterclockwise rotation of about 15°. 相似文献
14.
15.
An intensive paleomagnetic investigation has been conducted on the Middle Triassic Leikoupo Formation on the Wangcang section (32.14°N, 103. 17°E). The results indicate the magnetic minerals are dominant by multidomain magnetite or maghemite, and the characteristic remnant magnetization revealed by stepwise thermal/alternating field demagnetization is close to the present-day geomagnetic direction of the sampling site. This suggests that dolomitization/thermal viscous magnetization is responsible for the remagnetization of this kind of rocks.
相似文献16.
The depth to the top of magnetic dykes can be estimated from total field aeromagnetic data using the relation between the depth to magnetic sources and the autocorrelation function of magnetic data. By using synthetic anomalies we show that in the ideal case, depth can be determined to an accuracy of 10% or better, when the anomaly sources are two-dimensional dykes. However, the estimated depths depend on the width of the dykes. The estimated depth is about 0.6 times the actual depth to the top of thin dykes, and around the true depth for thick dykes having width-to-depth ratio around 3. The depth is considerably overestimated for very thick dykes (e.g., contacts, which is a special case of the thick dyke). Thus, the autocorrelation method requires that the width-to-depth ratio of the dyke is estimated independently to correctly estimate the depths. Alternatively, it must be assumed that the width-to-depth ratio for the two-dimensional source body is between 1.5 and 4. 相似文献
17.
The Caribou Lake gabbro, part of the Blachford Lake Intrusive Suite accurately dated at –2186±10 mA, has a predominantNW–/SE+ magnetization with a mean, irrespective of sign, ofD=119°,I=50°, 95=5° and a palaeopole 14°N, 064°W,A
95=5°; it has not proved possible to determine if the magnetization is primary. The Easter Island dyke, less well-dated in the range –2200 to –2500 Ma, has a predominantWNW+ magnetization, whose mean, when corrected for an 8° tilt, isD=288°,I=46°, 95=5 and palaeopole is 32°S, 2°W,A
95=5°; the magnetization is probably primary. A vertical magnetization (D), not significantly different from the present field, occurs sporadically in both units and is considered to be Late Phanerozoic in age. Palaeopoles from the Caribou Lake gabbro and the Easter Island dyke, together with those already known from Early Proterozoic intrusives of the Archaean Slave Structural Province, roughly define a swath (the Slave Track) which maps the motion of the Slave Province relative to the geomagnetic axis during this interval. The corresponding array of palaeopoles (the Superior Track) from the Superior Structural Province does not fall in the same place. Hence it would appear that Slave and Superior were not in their present relative positions in the Early Proterozoic in disagreement with arguments that have been made for a fixed supercontinent during much of the Proterozoic. Mid-Proterozoic paleomagnetic signatures indicate that Slave and Superior had assumed their present relative position by about –1750 mA. These Early Proterozoic relative motions are the earliest for which there is palaeomagnetic evidence.Earth Physics Branch Contribution No. 1111. 相似文献
18.
Doyle R. Watts 《Earth and Planetary Science Letters》1982,61(1):190-198
Palaeomagnetic remanence may be reset by orogeny in a manner analogous to isotopic systems. The heavy mineral seams and associated psammite in the deformed and metamorphosed Lower Morar Division of the Moine Assemblage of northwest Scotland have a palaeomagnetic signature that is characteristic over a wide area. The various components of the magnetization are resolved by detailed thermal demagnetization. These components are post-tectonic, as they are not affected by any structural fabric. They may be classified according to blocking temperature and, when statistically distinguishable, show a systematic change of direction from high to lower temperature possibly associated with apparent polar wander. Comparison to the European palaeomagnetic record suggests a late Silurian to early Devonian age of magnetization for the localities south of the Strath Conon Fault. The distribution of remanance directions and blocking temperatures is not consistent with the pattern of potassium-argon ages in this part of the British Caledonides. If the magnetization is purely of thermal origin, the palaeomagnetic record indicates higher temperatures at later time than does the potassium-argon record. This remagnetization event is related to the closing stages of the Caledonian orogeny. 相似文献
19.
Results of paleomagnetic study of Early Proterozoic rocks in the Baikal Range of the Siberian craton
V. Yu. Vodovozov A. N. Didenko D. P. Gladkochub A. M. Mazukabzov T. V. Donskaya 《Izvestiya Physics of the Solid Earth》2007,43(10):855-867
This paper presents paleomagnetic results obtained from the study of Early Proterozoic rocks in the Baikal Range of the Siberian craton, namely, the 1850–1880-Ma volcanicalstic rocks of the Akitkanskian series of the North Baikal volcanic-plutonic belt) and 1674-Ma basic dikes of the Chaya complex within the massif. The data of this work are used to reconstruct the development of the Siberian craton structure in the Early Precambrian. The projections of the inferred paleomagnetic directions onto a sphere form S (southern) and W (western) groups of vectors of characteristic magnetization components. The S group consists of three clusters representing primary magnetization components belonging to different time levels of the end of the Early Proterozoic. The W group is represented by directions associated with a metachronous magnetization probably acquired during the Riphean. Four paleomagnetic poles are obtained. Two of them that can be regarded as key poles correspond to time levels of 1875 and 1670 Ma (the Early Proterozoic). The two other poles can be used for a detailed reconstruction of the Proterozoic segment of the Siberian apparent polar wander path. The data presented in the paper indicate that the formation of the southern Siberian craton structure was accomplished at the end of the Early Proterozoic, which resulted in a synchronous motion of different blocks composing the southern flank of the craton (in particular, the Sharyzhalgai and Baikal Ranges). 相似文献
20.
I. V. Golovanova K. N. Danukalov V. I. Kozlov V. N. Puchkov V. E. Pavlov Y. Gallet N. M. Levashova G. S. Sirota R. R. Khairullin M. L. Bazhenov 《Izvestiya Physics of the Solid Earth》2011,47(7):623-635
We have carried out paleomagnetic studies of the Upper Vendian sedimentary rocks from the Bashkirian Meganticlinorium (Southern
Ural). The rocks were sampled at three localities spread over more than 100 km. Totally, more than 300 samples were collected
from about 40 sampling sites. Stepwise thermal demagnetization up to 700°C revealed a stable component of magnetization of
either polarity in 25 sites. The fold test and the reversal test for this component are positive, which is usually regarded
as a sound argument in favor of the primary origin of magnetization. However, the Basu paleomagnetic pole (longitude 187.3°E,
latitude 1.1°N) is located near the Late Ordovician-Early Silurian segment of the apparent polar wander path for Baltica,
which might indicate a Paleozoic remagnetization of Vendian rocks. In this work we analyze different interpretations of the
obtained results and evaluate the reliability of the Late Riphean and Vendian paleomagnetic data for Baltica. 相似文献