Global Paleomagnetic Database Research Articles

New Early Neoproterozoic Paleomagnetic Constraints of the Northwestern China Blocks on the Periphery of Rodinia

AbstractRecent studies highlight the debates about the role of the northwestern China blocks, for example, north Tarim block, south Tarim block (STB), Altyn Tagh block (ATB) and Qaidam‐Qilian block (QQB) during the assembly of Rodinia. We herein present a combined paleomagnetic, geochronological, and geochemical study on 16 mafic dikes in the northern ATB. After removing a recent viscous remanent magnetization, three characteristic remanent magnetization components (CHs) were isolated. CH1 was identified in eight NW‐trending diabase dikes, one of which was newly dated at 895.3 ± 7.7 Ma through use of SHRIMP baddeleyite U‐Pb methodology. It yields a mean direction (D/I) of 123.3°/−42.2° (α95 = 12.1°). The paleopole (40.9°S/184.6°E, A95 = 11.7°) was calculated by averaging eight virtual geomagnetic poles (VGPs) from each dike. A partial baked‐contact test supports the primary origin of CH1. CH2 was isolated from three E‐W trending diabase dikes, pointing northwest with considerably shallower downward inclinations. CH3 was obtained from five lamprophyre dikes, directing southeast with moderate to shallow upward inclinations. However, the VGPs of either CH2 or CH3 are insufficient to average a precise mean pole. Geochemical analyses also reveal petrogenetic discrepancy among the dikes with distinct CHs. Combining the new ∼895 Ma pole of CH1 with the global paleomagnetic database and being aided by geological evidence, we propose that the STB‐ATB‐QQB and the north China craton were located along the northwestern side of Laurentia in Rodinia at ∼895 Ma, and suggest the connection might have been intact until ∼780 Ma.

New paleomagnetic results from the ca. 1.0 Ga Jiayuan Formation of the Huaibei Group in the North China craton, and their paleogeographic implications

The Rodinia supercontinent formed in the transition between Mesoproterozoic and Neoproterozoic. The high-quality paleomagnetic poles around 1000 Ma, however, are rather scarce in the global paleomagnetic database, hindering a well-calibrated paleogeographic reconstruction for when and how Rodinia assembled. The late Mesoproterozoic to early Neoproterozoic Huaibei Group strata (ca. 1120–890 Ma) exposed at the southeastern margin of the North China craton (NCC) provide great promise for paleomagnetism. In this study, we mainly report a new paleopole (54.2 °S, 111.4 °E, A95 = 5.1°) obtained from the upper Jiayuan Formation in the middle Huaibei Group by incorporating our new data with the previously published virtual geomagnetic poles. That average pole passed a positive fold test and a positive reversal test, along with the pole’s distinctiveness from younger poles of the NCC, support the interpretation that the remanence is primary. New detrital zircon U–Pb age analyses of a sandstone sample of the Jiayuan Formation and the mafic sills intruding the overlying strata dated previously together constrain the depositional age of the Jiayuan Formation to be between ca. 1089 and ca. 945 Ma. Our new data, incorporated with other poles previously reported from the Huaibei Group and the mafic sills intruding the strata, reveal that the NCC underwent large-scale paleolatitudinal shifts from the polar region to low latitudes across the transition between Mesoproterozoic and Neoproterozoic. Matching the apparent polar wander paths of the NCC and Laurentia suggests that they together drifted from the polar region in the northern hemisphere at ca. 1110 Ma to moderate latitudes in the southern hemisphere around 1000 Ma during the assembly of Rodinia.

New Paleomagnetic Insights Into the Neoproterozoic Connection Between South China and India and Their Position in Rodinia

AbstractA paleogeographic affinity of the south China craton (SCC) with India in the Neoproterozoic has long been advocated based on lines of geological evidence. However, the lack of coeval paleomagnetic data renders the putative connection ambiguous. Here we report new paleomagnetic results obtained from seven ca. 770 Ma mafic sills in SCC that provide new critical constraints on the issue. The data quality is assured by a positive regional tilt test, a reversal test, and by adequately averaging‐out paleosecular variation. Our data, together with coeval poles from the global paleomagnetic database, support a reconstruction in which the SCC was connected with India at ca. 770 Ma via linkages with smaller continental blocks. The SCC‐India landmass was located at high‐to‐mid latitudes and far from Laurentia and Australia, which were located at low latitudes at ca. 770 Ma.

The magnificent seven: A proposal for modest revision of the quality index

Thirty years ago, Rob Van der Voo proposed an elegant and simple system for evaluating the quality of paleomagnetic data. As a second-year Ph.D. student, the lead author remembers Rob waxing philosophical about the need to have an appropriate, but not overly rigid evaluation system. The end result was a 7-point system that assigned a (1) or (0) for any paleomagnetic result based on objective criteria. The goal was never to reject or blindly accept any particular result, but merely to indicate the degree of quality for any paleomagnetic pole. At the time, the global paleomagnetic database was burgeoning and it was deemed useful to rank older paleomagnetic results with the newer data being developed in modern laboratories. Van der Voo's, 1990 paper launched a silent revolution in paleomagnetism. Researchers began to evaluate their data against those seven criteria with the anticipation that reviewers would be similarly critical.Today, paleomagnetism is a mature science. Our methods, analyses, and results are more sophisticated than they were 30 years ago. Therefore, we feel it is appropriate to revisit the Van der Voo (1990) criteria in light of those developments. We hope to honor the intention of the original paper by keeping the criteria simple and easy to evaluate while also acknowledging the advances in science. This paper aims to update the criteria and modernize the process. We base our changes on advances in paleomagnetism and geochronology with a faithful adherence to the simplicity of the original publication. We offer the “Reliability” or “R” index as the next generation of the Van der Voo “Quality” or “Q” index. The new R-criteria evaluate seven different information items for each paleomagnetic pole including age, statistical requirements, identification of magnetic carriers, field tests, structural integrity, presence of reversals and an evaluation for possible remagnetization.

A combined geochronological and paleomagnetic study on ∼1220 Ma mafic dikes in the North China Craton and the implications for the breakup of Nuna and assembly of Rodinia

A new combined geochronological and paleomagnetic study was carried out on the late Mesoproterozoic mafic dikes in the northeastern and central North China Craton (NCC). Three dikes were dated at 1224.2 ± 5.1 Ma, 1219.9 ± 6.0 Ma and 1215.2 ± 7.7 Ma through use of the secondary ion mass spectrometry (SIMS) zircon dating method and one dike was dated at 1219.1 ± 4.3 Ma by using SIMS baddeleyite dating method, indicating that these dikes emplaced at ∼1220 Ma. A total of 286 paleomagnetic core samples were collected from seven ∼1220 Ma dikes and their host rocks, as well as two ∼775 Ma dikes for field tests. All the samples were subjected to stepwise thermal demagnetization. Rock magnetic experiments of representative samples demonstrate that the dominant magnetic carriers of the ∼1220 Ma dikes are single-domain and pseudo-single domain magnetite grains. Two paleomagnetic components were identified from the ∼1220 Ma dikes. The low temperature component is a viscous magnetic remanence acquired in the recent geomagnetic field. The high temperature component (HTC) was isolated between 500 and 580°C, which directs east and down with moderate inclination. A paleomagnetic pole (11.3°N, 175.8°E, A95 = 7.6°) was determined by averaging seven virtual geomagnetic poles (VGPs), each VGP corresponding to the mean HTC direction of an individual dike. The ∼1220 Ma pole passed a baked-contact test and appeared to adequately average out secular variation. It differs from any younger poles of the NCC, and is thus considered as a reliable pole for the NCC. While our new results place the NCC at intermediate paleolatitudes (∼28.8°N for site located at 36.8°N, 113.4°E) at ∼1220 Ma, the coeval high-quality poles in the global paleomagnetic database, however, indicate that the Australian cratons were positioned near the pole and Laurentia was located around the Equator, depicting a dispersed paleogeographic pattern of the three continents at ∼1220 Ma. The updated paleomagnetic data together with geological evidence may suggest that the NCC separated from northern Australia between ∼1320 and ∼1220 Ma, and later joined northwestern Laurentia between ∼1220 and ∼1110 Ma.

PALEOMAGIA: A PHP/MYSQL database of the Precambrian paleomagnetic data

Most paleomagnetic applications require a precise, rationally organized and up-todate catalogue or database of paleomagnetic results worldwide. These include reconstructions of continents, calculations of the Apparent Polar Wander Paths (APWPs) or paleolatitude drift curves, testing the Geocentric Axial Dipole (GAD) model, studies of geomagnetic paleosecular variation or reversal asymmetries, comparison of coeval results obtained from different types of rocks, estimation of inclination shallowing in sedimentary rocks and understanding the delay in remanence acquisition caused by slow cooling in large intrusions. For this purpose, various databases, such as the Global Paleomagnetic Database (GPMDB), and the Magnetics Information Consortium Database (MagIC) have been generated. This paper presents a new relational database (PALEOMAGIA) where 3278 entries of Precambrian data have been split geographically, sorted according to age and rock types and ranked using a revised version of the Van der Voo grading scheme. The latest geochronologic information is included wherever available. Significant effort has been put to the retrieval and archiving of data published in the last decade, which are virtually nonexistent in GPMDB. Here we present the database and its browser-based user interface from a scientific and a technical point of view.

Asymmetry of geomagnetic polarity: Equatorial dipole, Pangaea, and the Earth’s core

The paper presents the results of analyzing the set of dual-polarity paleomagnetic results the Global Paleomagnetic Database (GPMDB). The dataset was expanded by the results from the Paleomagnetic Data Catalogue for the USSR and with new data published after 2005. Some results were rejected to avoid the influence of overprints of ancient and recent magnetization. Overall, 59 dual-polarity results for the lithospheric plates of Baltica, Laurentia, and Siberia with their immediate framing were selected for the analysis in the interval of ages 207–359 Ma. The new data confirmed the model of the paleomagnetic field, according to which the field contains a long-lived component corresponding to the equatorial dipole which is responsible for the non-antipodal paleomagnetic directions in the zones of normal and reverse polarity in sedimentary and volcanic rock sequences. Retaining its value of 5–8% of the central axial dipole, the equatorial dipole changed its polarity a few times during the interval 359–207 Ma. The northern poles of the dipole formed two antipodal groups on the Earth’s surface, which lie within or near the subduction zones on the periphery of the Pangaea Supercontinent. Such localization of the equatorial dipole is suggested to be related to the ascending branches of the mantle convection and to the topography of both boundaries of the outer Earth’s core.

Paleosecular variation models for ancient times: Clues from Keweenawan lava flows

Statistical paleosecular variation models predict distributions of paleomagnetic vectors as a function of geographic position. Such models have been used in a variety of applications that test whether a given data set fairly represents the variability and average properties of the geomagnetic field. The simple relationship between inclination of the geomagnetic field and latitude predicted by geocentric axial dipole (GAD) models has been a cornerstone for plate reconstructions for decades, yet many data sets exhibit a tendency to be shallower than expected for a dominantly axial geocentric magnetic field. Too shallow inclinations have variously been interpreted as plate motion, permanent non-dipole field components or bias in inclination from sedimentary processes. Statistical PSV models could in principle be used to resolve the cause of inclination anomalies because there is a simple relationship between the elongation of the distribution of directions in the vertical plane and the average inclination. Shallowing of inclinations from sedimentary processes results in a progressive transformation of the elongation direction in the vertical plane containing the average direction into a pronounced elongation in the plane perpendicular to that. However, the applicability of statistical models based on the last 5 million years for more ancient times is an open question. Here we present new data from the Keeweenawan North Shore Volcanics ( ∼ 1.1 Ga). These data are consistent with statistical PSV model predictions and are less well fit by models that include a 20% axial octupole component. We also find evidence for a pervasive overprinting by hematite in a shallower direction and find support for the contention that the asymmetric reversal(s) observed in Keweenawan aged rocks along the North shore of Lake Superior can be explained as an age progression, with the reverse directions being older than the normal directions. Finally, we re-consider implications from an analysis of inclinations from the Global Paleomagnetic Database for the Paleozoic and Pre-Cambrian. We find that the data are inconsistent with a random sampling of any simple geomagnetic field model and conclude that the data set under-samples the field in a spatial sense.

Paleomagnetic studies and estimation of geomagnetic paleointensity at the early/middle Riphean boundary in rocks of the Salmi Formation (North Ladoga area)

The territory of Karelia (Baltic Shield) is virtually not represented in the global paleomagnetic database for the Lower Riphean time interval (1650—1350 Ma). As regards the paleointensity Han, the huge interval 1–2 Ga in length is represented in the global paleointensity database by only eight determinations concentrated in the interval 1–1.35 Ga. The paper presents results of paleomagnetic studies of volcanic and subvolcanic rocks composing the Early Riphean Salmi Formation, which outcrops in the valley of the lower Tulemaioki River in the northern coast area of Lake Ladoga. Results of the study indicate that, in the Early Riphean time, the East European craton was located in the tropical region of the Southern Hemisphere between 15° S and 40° S. The inferred value of Han is close to the lower boundary of the interval (1.36–11.56) × 1022 A m2, encompassing previously published intensity values of the paleofield 1–1.35 Ga; this supports the hypothesis on the existence of long intervals of a lower field in the period in question [Maquoin et al., 2003].

Apparent polar wander paths for the major continents (200 Ma to the present day): a palaeomagnetic reference frame for global plate tectonic reconstructions

SUMMARY Synthetic apparent polar wander (APW) paths for North America, South America, Eurasia, India, Central Africa, Australia and Antarctica for the last 200 Myr are proposed. Computation of these APW paths is based upon the latest version (4.5a) of the Global Paleomagnetic Database (GPMDB), a revised global plate tectonic model since the Early Jurassic, and a new technique for generating smoothed APW paths. The smoothing technique includes the following steps: (1) pre-selection of palaeopoles, including pre-filtering parameters (number of sites, number of samples per site, 95 per cent confidence circle about mean direction, cleaning procedure, and time uncertainty); (2) generation of palaeolatitude and declination plots for a reference site on each continent that combines palaeopoles via a global plate tectonic circuit; (3) independent spline regression analyses of the palaeolatitude and declination plots; (4) removal of palaeolatitude or declination data that deviate by more than 10 ◦ from the regression curves (post-filtering process); (5) generation of synthetic APW paths from the resulting palaeolatitude and declination plots. These synthetic APW paths are then rotated into African coordinates to determine the best-fit APW path and a global palaeomagnetic reference frame. Four representative plate tectonic reconstructions and global plate velocity fields are presented for the three time intervals that correspond to globally synchronous changes in plate motion.

New edition of the Global Paleomagnetic Database

A new version of the Global Paleomagnetic Database—GPMDB V 4.6—is available now at the Tectonics Special Research Centre of the University of Western Australia Web site (http://www.tsrc.uwa.edu.au/). This version contains 9259 paleomagnetic poles from 7513 rock units published in 3673 articles up to December 2004 inclusive.This version has also been completely updated using the latest International Stratigraphic Chart published by the International Commission on Stratigraphy (ICS) on its Web site (www.stratigraphy.org). This new timescale is significantly different from the timescale which has been used in the database for the past decade. All entries in the database based on biostratigraphic ages have had their absolute minimum and maximum age limits revised according to this new scale. Therefore, users of the database who have compiled their own files based on the old database should be aware that the assigned absolute ages have now changed.

Global Paleomagnetic Data Base developed into its visual form

The Global Paleomagnetic Database (GPMDB) created and developed by M.W. McElhinny and J. Lock is used by researchers all over the world. The well‐known version of this data base is in Microsoft Access format, a user‐friendly interface that requires no programming skills. The next step in developing these data bases lies in the visualization of data and the integration of the paleomagnetic data with Geographical Information Systems (GIS). One of the most popular GIS software applications among Earth scientists is Arc View, which was developed by the Environmental Systems Research Institute (ESRI). A new Arc View 3.1 application visualizes the GPMDB and provides a range of new possibilities for interactive search, analysis, and plate tectonic applications of paleomagnetic data.

New paleomagnetic result from the Ethiopian flood basalts in the Abbay (Blue Nile) and Kessem gorges

New paleomagnetic investigations on the Ethiopian trap series have been undertaken at the Abbay and Kessem gorges in an attempt to better constrain the 30 Ma paleomagnetic pole of Africa. We sampled six thick massive basaltic lava flows, totaling 230 m, from Abbay Gorge and 10 lava flows, 180 m in thickness, from Kessem Gorge. Detailed paleomagnetic analyses disclosed that the carriers of the characteristic remanent magnetization (ChRM) are different in different lava flows. These are mostly titanomagnetites, titanomaghemites, and magnetite minerals with a broad range of coercive force and blocking temperatures. The heating and cooling susceptibility vs. temperature curves, many of which are irreversible, may indicate chemical remagnetization, notably low temperature maghemitization. Only one flow (KS04) with a clear 580°C Curie temperature was apparently unaffected by chemical remagnetization. The ChRM direction of this flow is identical to that in other flows, which suggests that if and when remagnetization occurred, this was shortly after emplacement of the lava flows. All of the flows sampled have normal polarity. However, a reversed component of low to medium coercive force and low to medium unblocking temperature occurs in flow KS01 at Kessem Gorge. The ChRM directions for the 16 sites are D=3.1°, I=5.8° (α95=12.7°). The paleomagnetic pole obtained from these is at λ=83.0°N, φ=193.3°E (A95=9.0°). Comparison with three previous studies of the traps shows remarkable consistency and a number of means are derived and discussed. Two final preferred poles for the traps are at λ=79.0°N, φ=196.9°E (A95=2.8°) when all 112 published flows are used, and λ=78.7°N, φ=209.4°E (A95=3.4°) when only the 76 flows from the four more recently analyzed sections are included. Both are compatible with the recent reference synthetic pole for Africa of Courtillot and Besse [J. Geophys. Res. (2002) in press]. In that sense, the Ethiopian trap pole is not anomalous and does not require more of a non-dipolar contribution than indicated by analyses of the global paleomagnetic data base covering the last few million years.

The global paleomagnetic database: Current status

The Global Paleomagnetic Database (GPMDB) is a data base for paleomagnetic directions and pole positions. It was first compiled by Lock and McElhinny [1991] and made use of the PC version of the Oracle Database Management System, which at the time was the only PC system available that used SQL, the internationally recognized language for use with database management systems. Subsequently, the Oracle PC system became far too large and complex for the GPMDB, so the data base was transferred to Microsoft Access, which had just become available and also used SQL [McElhinny and Lock, 1996].

Six New Paleomagnetic Databases released

The annual update of the International Association of Geomagnetism and Aeronomy (IAGA)‐sponsored paleomagnetic databases has now been completed. The databases are available as files for use with Access 2.0 (for Windows 3.1) or Access 97 (for Windows 95) as described by McElhinny and Lock “ 1996”. The new package (Version 3.3 of the databases) now includes six databases as follows: Global Paleomagnetic Database (gpmdb2. mdb orgpmdb97.mdb); Magnetostratigraphy Database (magst2.mdb or magst97.mdb); Paleointensity Database (pint2.mdb orpint97.mdb); Polarity Transitions Database (trans2.mdb or trans97.mdb); Secular Variations Database (secvr2.mdb or secvr97.mdb); and Paleosecular Variation from Lavas Database (psvrl2.mdb or psvrl97.mdb).

Shallow bias of paleomagnetic inclinations in the Paleozoic and Precambrian

An updated analysis of the global paleomagnetic database shows that the frequency distributions of paleomagnetic inclinations for the Cenozoic and Mesozoic eras (younger than 250 Ma) are compatible with a random geographical sampling of a time-averaged geomagnetic field that closely resembles that of a geocentric axial dipole. In contrast, the frequency distributions of paleomagnetic inclinations for the Paleozoic and Precambrian eras (prior to 250 Ma) are over-represented by shallow inclinations. After discounting obvious secondary causes for the bias, such as from data averaging, sedimentary inclination error, inhomogeneous lithological distributions, and tropical remagnetization, we show that the anomalous inclination distributions for the Paleozoic and Precambrian can be explained by a geomagnetic field source model which includes a relatively modest (∼25%) contribution to the axial dipole from a zonal octupole field and an arbitrary zonal quadrupolar contribution. The apparent change by around 250 Ma to a much more axial dipolar field geometry might be due to the stabilization of the geodynamo from growth of the inner core to some critical threshold size, a gross speculation which would imply that either the threshold size was rather large or the inner core nucleated rather late in Earth history. Alternatively, if a geocentric axial dipole model is assumed or can eventually be demonstrated independently, the anomalous inclination distributions for the Paleozoic and Precambrian may reflect a tendency of continental lithosphere to be cycled into the equatorial belt, perhaps because geoid highs associated with long-term continental aggregates influence true polar wander.

Iaga Paleomagnetic Databases with access

Since the release of the Global Paleomagnetic Database (GPMDB) in 1991, there have been successive updates every two years, with the current version being 3.1. The authors have now constructed a set of four databases that have been sponsored by the International Association of Geomagnetism and Aeronomy (IAGA). These include the GPMDB together with the Paleointensity Database (PALIN), the Polarity Transitions Database (TRANS) and the Secular Variation Database (SECVR). Each of these databases is now released to operate under Microsoft Access V2.0 and are specifically designed so as to operate independently of each other. The design and operation of these databases with Access is described in this second supplement to the Global Paleomagnetic Databases.

Anomalous low palaeomagnetic inclinations from Oligocene-Lower Miocene red beds of the south-west Tien Shan, Central Asia

SUMMARY We studied Oligocene to Lower Miocene red beds from the western margins of the South-West Ghissar Range (the westernmost part of the Tien Shan fold belt. Central Asia). A total of 19 sites were sampled on both limbs of a gentle syncline. After removal of an unstable component at 200° to 300°C., the natural remanent magnetization in these red beds from 18 sites is accounted for by one characteristic component, ChRM, which persists up to 680°C. Intermediate directions of the geomagnetic field were recorded at five sites; after tilt correction, the overall mean direction for the remaining 13 sites is D= 3°, I= 30°, k= 19, α95= 8.9°. Both the reversal and the fold tests are positive. Haematite is found to be the main remanence carrier in these red beds. The calculated mean declination fits well with the reference data (Besse & Courtillot 1991), and no rotation with respect to Eurasia is detected, in accord with geological data. In contrast, the mean inclination is about 30° shallower than expected. We argue that this result is not due to large-scale northward transport of the area. Mean inclinations showing a similar amount of shallowing were also reported from the Tadzhik and Fergana basins and Kirghiz Tien Shan from various rock types (Thomas et al. 1993, 1994), and we are of the opinion that neither inclination error nor compaction could have led to such a consistent pattern. The analysis of all reliable Early Tertiary palaeomagnetic results extracted from the Global PaleoMagnetic data base for the northern part of the Eurasian plate reveals that inclination anomalies are very common in this data set, whatever the rock type. The general tendency is a progressive increase in the anomaly amplitude from the Atlantic Ocean to Central Asia. The size and localization of this Tertiary field anomaly is comparable with the present-day non-dipole field anomaly. This suggests that there may have been a long-term standing non-dipole anomaly in the Tertiary Earth magnetic field, perhaps correlated to major features of the contemporaneous plate tectonics, for example the India-Asia collision.

Geomagnetic polarity reversal rate for the Phanerozoic

The recently updated Global Paleomagnetic Database provides an opportunity to construct a preliminary model of long‐term magnetic polarity reversal behavior for the last 570 My. After filtering for quality, a sub‐set of data from this global database is used to estimate relative reversal frequency, and the results show the expected long intervals of low reversal rate during the Cretaceous Normal and Permo‐Carboniferous Reversed Superchrons. In addition to the established superchrons, these new results indicate a long period of very low reversal rate in the Ordovician, which may be a previously unidentified superchron, and an additional short period of anomalously low reversals at the Jurassic/Triassic boundary. If the Ordovician reversal rate anomaly is a single polarity superchron, it represents the third major change in reversal rate within the Phanerozoic, with approximately 200 My between the CNS, the PCRS and the new Ordovician reversed interval.

New updates made to paleomagnetic databases

Version 2.3 of the Global Paleomagnetic Database at March 1994 is now available either as ORACLE Export files or for use with Microsoft ACCESS Version 1.1 (or 2.0) under Windows. The Database for Poles (GPMDB) contains an expanded data set for China and has been completely cross‐checked against the Canadian database for the Laurentian Shield. Several duplicate entries were eliminated (where authors have published the same data in two different journals), and many corrections were made to previous entries.However, Version 2.3 now incorporates the Global Paleointensity Database (PALINT) compiled by H. Tanaka and M. Kono. This database includes all published pre‐archeomagnetic paleointensity results for geological time. The following data sets are now available from World Data Center A in Boulder, Colo. Contact Susan McLean, World Data Center A, National Geophysical Data Center, NOAA, 325 Broadway E/GC1, Boulder CO 80303‐3328; tel. 303497‐6478; fax 303‐497‐6513.