The validity of the dipole model of geomagnetic field according to inclination distribution

The magnetic field of the Earth is 99 % of the internal origin and generated in the outer liquid core by the dynamo principle. In the 19th century, Carl Friedrich Gauss proved that the field can be described by a sum of spherical harmonic terms. Presently, this theory is the basis of e.g. IGRF models (International Geomagnetic Reference Field), which are the most accurate description available for the geomagnetic field. In average, dipole forms 3/4 and non-dipolar terms 1/4 of the instantaneous field, but the temporal mean of the field is assumed to be a pure geocentric axial dipolar field. The validity of this GAD (Geocentric Axial Dipole) hypothesis has been estimated by using several methods. In this work, the testing rests on the frequency dependence of inclination with respect to latitude. Each combination of dipole (GAD), quadrupole (G2) and octupole (G3) produces a distinct inclination distribution. These theoretical distributions have been compared with those calculated from empirical observations from different continents, and last, from the entire globe. Only data from Precambrian rocks (over 542 million years old) has been used in this work. The basic assumption is that during the long-term course of drifting continents, the globe is sampled adequately. There were 2823 observations altogether in the paleomagnetic database of the University of Helsinki. The effect of the quality of observations, as well as the age and rocktype, has been tested. For comparison between theoretical and empirical distributions, chi-square testing has been applied. In addition, spatiotemporal binning has effectively been used to remove the errors caused by multiple observations. The modelling from igneous rock data tells that the average magnetic field of the Earth is best described by a combination of a geocentric dipole and a very weak octupole (less than 10 % of GAD). Filtering and binning gave distributions a more GAD-like appearance, but deviation from GAD increased as a function of the age of rocks. The distribution calculated from so called keypoles, the most reliable determinations, behaves almost like GAD, having a zero quadrupole and an octupole 1 % of GAD. In no earlier study, past-400-Ma rocks have given a result so close to GAD, but low inclinations have been prominent especially in the sedimentary data. Despite these results, a greater deal of high-quality data and a proof of the long-term randomness of the Earth's continental motions are needed to make sure the dipole model holds true.Maan magneettikenttä on 99-prosenttisesti sisäsyntyistä alkuperää ja muodostuu dynamoperiaatteen mukaan Maan ulkoytimessä. Carl Friedrich Gauss osoitti 1800-luvulla, että kenttää voidaan kuvata palloharmonisten termien summalla. Nykyisin tähän teoriaan perustuvat mm. IGRF-mallit (International Geomagnetic Reference Field), jotka ovat tarkin saatavilla oleva kuvaus Maan magneettikentästä. Keskimäärin hetkellisen kentän voimakkuudesta dipolin osuus on 3/4 ja ei-dipolaaristen termien 1/4, mutta kentän aikakeskiarvon on oletettu olevan puhdas pyörimisakselin suuntainen dipolikenttä. Tämän ns. GAD-hypoteesin (Geocentric Axial Dipole) pätevyyttä on arvioitu useilla menetelmillä. Tässä työssä testaus on perustunut kentän inklinaation vaihteluun leveysasteen funktiona. Jokainen dipolin (GAD), kvadrupolin (G2) ja oktupolin (G3) yhdistelmä tuottaa tietyn inklinaatiojakauman. Näitä teoreettisia jakaumia on verrattu eri mannerten sekä lopuksi koko maailman havainnoista laskettuihin kokeellisiin jakaumiin. Työssä on käytetty vain prekambrista dataa (yli 542 miljoonan vuoden ikäisistä kivistä). Perusoletuksena on, että kun mantereet liikkuvat riittävän pitkään, niiden vaelluskäyrät kattavat koko maapallon. Helsingin yliopiston paleomagneettisessa tietokannassa oli yhteensä 2823 mittaustulosta. Havaintojen laadun, iän ja kivityypin vaikutusta jakaumiin on testattu. Teoreettisten ja kokeellisten jakaumien vertailuun on käytetty khiin neliötestausta. Myös ajallis-alueellista keskiarvoistusta on käytetty päällekkäisyyksien karsimiseksi. Magmakivihavainnoista tehdyn mallinnuksen perusteella Maan keskimääräistä magneettikenttää kuvaa parhaiten keskeisdipolin ja hyvin heikon oktupolin (10 % GAD:ista) yhdistelmä. Luotettavimmista paleomagneettisista tuloksista, ns. avainnavoista, laskettu jakauma noudattaa GAD:ia lähes täydellisesti, sillä sen kvadrupoli on nolla ja oktupolikin vain 1 % GAD:ista. Missään aiemmassa tutkimuksessa ei ole saatu näin hyvin dipolimalliin sopivaa jakaumaa yli 400 vuosimiljoonan takaiselle aineistolle, vaan matalat inklinaatiot ovat yleensä korostuneet etenkin sedimenttikivissä. Saaduista tuloksista huolimatta dipolimallin toimivuuden varmistamiseksi tarvitaan edelleen lisää laadukasta havaintoaineistoa ja osoitus Maan mannerliikkeiden pitkän aikavälin satunnaisuudesta

Database-wide studies on the validity of the Geocentric Axial Dipole hypothesis in the Precambrian

A branch of science concentrated on studying the evolution of the Earth's magnetic field has emerged in the last half century. This is called paleomagnetism, and its applications include calculations of field directions and intensity in the past, plate tectonic reconstructions, variations in the conditions in the Earth s deep interior and the climatic history. With the increasing quantity and quality of observations, it has been even possible to construct models of conterminous continent blocks, or supercontinents, of the Pre-Pangaea time. These are crucial for the understanding of the evolution of our planet from the Archean to today. Paleomagnetists have traditionally heavily relied on the theory that when averaged over a period long enough, the Earth s magnetic field can be approximated as being equivalent to that generated by a magnetic dipole located at the center of the Earth and aligned with the axis of rotation. The credibility of this GAD (Geocentric Axial Dipole) hypothesis is strongest in the geologically most recent eras, such as most of the Phanerozoic and notably in the last 400 million years. Attempts to get an adequate view of the magnetic field in the Earth's earlier history have for a long time been challenged by the reliability limitations of Precambrian paleomagnetic data. With the absence of marine magnetic anomalies, observational data need to be gathered from terrestrial rocks, notably those formed within cratonic nuclei, the oldest and most stable parts of continents. To answer the call for a concise and comprehensive compilation of paleomagnetic data from the early history of the Earth, this dissertation introduces a unique database of over 3300 Precambrian paleomagnetic observations worldwide. The data are freely available at the server of the University of Helsinki (http://h175.it.helsinki.fi/database) and can be accessed via an online query form. All database entries have been coded according to their terranes, rock formation names, ages, rock types and paleomagnetic reliabilities. A new modified version of the commonly applied Van der Voo (MV) classification criteria for filtering the paleomagnetic data is also presented, along with a novel method for binning the entries cratonically to revise the previously employed way of applying binning via a simple evenly spaced geographic grid. Besides compiling data, tests of the validity of the GAD hypothesis in the Precambrian have been conducted using inclination frequency analysis and asymmetries of magnetic field reversals. Results from two self-contained tests of the GAD hypothesis suggest that the time-averaged Precambrian geomagnetic field may include the geocentric axial quadrupole and the geocentric axial octupole, but both with strengths less than 10% of the geocentric axial dipole, with the quadrupole perhaps being smaller than the octupole. In no other study a model so close to GAD has been reasonably fitted to the Precambrian paleomagnetic data. The weakness of the non-dipolar coefficients required also implies that no substantial adjustments need to be made to the novel models of Precambrian continental assemblies (supercontinents), such as the Paleo-Mesoproterozoic Columbia (Nuna) or the Neoproterozoic Rodinia. Although the supercontinent science still has plenty of uncertainty, it is more plausibly caused by the geological incoherence of the data and the lack of precise age information rather than by long-lived non-dipolar geomagnetic fields.Paleomagnetismi on viimeisen puolen vuosisadan aikana kehittynyt Maan muinaisen magneettikentän tutkimukseen keskittynyt tieteenala. Sitä voidaan soveltaa paitsi magneettikentän suuntien ja voimakkuuden laskentaan, myös mannerliikkeiden mallintamiseen, Maan syvärakenteen analysointiin ja jopa ilmastohistorian tutkimiseen. Paleomagneettisten havaintojen määrän ja laadun kasvun myötä on tullut myös mahdolliseksi koostaa malleja useiden mannerten muodostamista kokonaisuuksista eli ns. supermantereista. Niistä tunnetuimmat ovat Pangaea sekä sitä edeltävän ajan Rodinia ja Columbia. Paleomagneettinen menetelmä on pitkään nojannut oletukseen, jonka mukaisesti Maan magneettikentän pitkän aikavälin keskiarvoa voidaan riittävällä tarkkuudella kuvata pyörimisakselin suuntaisella dipolikentällä, jonka keskipiste yhtyy Maan keskipisteeseen. Tämän ns.keskeisdipolihypoteesin (GAD = Geocentric Axial Dipole) pätevyys on varmimmin kyetty osoittamaan viimeisten 400 vuosimiljoonan ajalle. Sitä varhaisemman ajan magneettikentän analysointia on pitkään haitannut havaintojen keskimääräisen laadun heikkeneminen geologisen ajan funktiona. Koska merenpohjan magneettiset anomaliat antavat tietoa geomagneettisesta kentästä vain noin 200 vuosimiljoonan taakse, yli 540 vuosimiljoonan takaisen prekambriajan paleomagneettinen data rajoittuu maanpäällisiin kiviin. Näistä erityisen käyttökelpoisia ovat mannerten sisäosissa sijaitsevien geologisesti stabiilien kratonien kivet. Tarve kattavalle ja helposti saatavilla olevalle Maan prekambrisen magneettikentän havaintotietokannalle johti Globaalin paleomagneettisen tietokannan (GPMDB = Global Paleomagnetic Database) kehittämiseen. Tässä väitöskirjassa on laadittu uusi yli 3300 havaintoa sisältävä PALEOMAGIA-niminen tietokanta, joka Globaalista paleomagneettisesta tietokannasta poiketen sisältää runsaasti vuoden 2004 jälkeen julkaistua aineistoa ja antaa käyttäjälle mahdollisuuden suodattaa havaintodataa laatukriteerien perusteella. Tietokannan aineisto on vapaasti saatavilla osoitteessa http://h175.it.helsinki.fi/database. PALEOMAGIA-tietokantaa on tässä väitöskirjassa sovellettu Maan magneettikentän keskeisdipolihypoteesin tutkimiseen kentän inklinaatiokomponentin tiheysjakaumaa ja kentän napaisuuskäännösten epäsymmetriaa hyödyntäen. Lisäksi väitöstyössä on esitetty uusi Maan muinaiseen geologiaan perustuva menetelmä prekambriajan havaintoaineiston alueellisen keskiarvoistuksen tekemistä varten. Saatujen tulosten nojalla on myös arvioitu tavallisimpien supermannermallien pätevyyttä. Väitöstyön tärkein johtopäätös kumoaa aiemmin esitetyt epäilykset Maan magneettikentän keskeisdipolimallin pätemättömyydestä prekambriaikana. Keskeisdipolin ohella kentän aikakeskiarvon kuvaamiseen tarvittavat kvadrupoli- ja oktupolikomponentit ovat voimakkuudeltaan alle 10 % keskeisdipolin voimakkuudesta, eivätkä ne vaikuta merkittävästi mannerten keskinäisiin sijainteihin supermannermalleissa. Mallien koostamista kuitenkin vaikeuttavat edelleen suuresti havaintoaineiston geologiset rajoitteet ja täsmällisen ikäinformaation puute

Heat flow, seismic cutoff depth and thermal modeling of the Fennoscandian Shield

Being far from plate boundaries but covered with seismograph networks, the Fennoscandian Shield features an ideal test laboratory for studies of intraplate seismicity. For this purpose, this study applies 4190 earthquake events from years 2000–2015 with magnitudes ranging from 0.10 to 5.22 in Finnish and Swedish national catalogues. In addition, 223 heat flow determinations from both countries and their immediate vicinity were used to analyze the potential correlation of earthquake focal depths and the spatially interpolated heat flow field. Separate subset analyses were performed for five areas of notable seismic activity: the southern Gulf of Bothnia coast of Sweden (area 1), the northern Gulf of Bothnia coast of Sweden (area 2), the Swedish Norrbotten and western Finnish Lapland (area 3), the Kuusamo region of Finland (area 4) and the southernmost Sweden (area 5). In total, our subsets incorporated 3619 earthquake events. No obvious relation of heat flow and focal depth exists, implying that variations of heat flow are primarily caused by shallow lying heat producing units instead of deeper sources. This allows for construction of generic geotherms for the range of representative palaeoclimatically corrected (steady-state) surface heat flow values (40–60 mWm−2). The one-dimensional geotherms constructed for a three-layer crust and lithospheric upper mantle are based on mantle heat flow constrained with the aid of mantle xenolith thermobarometry (9–15 mWm−2), upper crustal heat production values (3.3–1.1 μWm−3), and the brittle-ductile transition temperature (350 °C) assigned to the cutoff depth of seismicity (28 ± 4 km). For the middle and lower crust heat production values of 0.6 and 0.2 μWm−3 were assigned, respectively. The models suggest a Moho temperature range of 460 to 500 °C.Being far from plate boundaries but covered with seismograph networks, the Fennoscandian Shield features an ideal test laboratory for studies of intraplate seismicity. For this purpose, this study applies 4190 earthquake events from years 2000–2015 with magnitudes ranging from 0.10 to 5.22 in Finnish and Swedish national catalogues. In addition, 223 heat flow determinations from both countries and their immediate vicinity were used to analyse the potential correlation of earthquake focal depths and the spatially interpolated heat flow field. Separate subset analyses were performed for five areas of notable seismic activity: the southern Gulf of Bothnia coast of Sweden (area 1), the northern Gulf of Bothnia coast of Sweden (area 2), the Swedish Norrbotten and western Finnish Lapland (area 3), the Kuusamo region of Finland (area 4) and the southernmost Sweden (area 5). In total, our subsets incorporated 3619 earthquake events. No obvious relation of heat flow and focal depth exists, implying that variations of heat flow are primarily caused by shallow lying heat producing units instead of deeper sources. This allows for construction of generic geotherms for the range of representative palaeoclimatically corrected (steady-state) surface heat flow values (40–60 mW m−2). The 1-D geotherms constructed for a three-layer crust and lithospheric upper mantle are based on mantle heat flow constrained with the aid of mantle xenolith thermobarometry (9–15 mW m−2), upper crustal heat production values (3.3–1.1 μWm−3) and the brittle-ductile transition temperature (350 °C) assigned to the cut-off depth of seismicity (28 ± 4 km). For the middle and lower crust heat production values of 0.6 and 0.2 μWm−3 were assigned, respectively. The models suggest a Moho temperature range of 460–500 °C.Peer reviewe

Radiogenic heat production analysis of Fennoscandian Shield and adjacent areas in Sweden

In northern Europe, radiogenic heat production of surface rocks has been extensively studied in Finland and Norway alike. This paper presents a heat production analysis of Sweden, based on a rock outcrop data compilation obtained from the Geological Survey of Sweden (SGU). The study area comprises Precambrian Shield, Caledonian and platform cover areas. Altogether 39933 samples with uranium, thorium and potassium concentration (C-U, C-Th and C-K) and density () data were available. Heat production (HP) was calculated using raw point data, binning on a regular grid, and averaging by bedrock units in the geological map. Methods based on raw point data and grid-based binning resulted in HP values of 2.5 +/- 4.1 and 2.5 +/- 5.6 Wm(-3), respectively, while averaging by lithology produced a lower value of 2.4 +/- 1.7 Wm(-3). Limiting the lithology-based averaging to Precambrian bedrockareas resulted in heat production of 2.4 +/- 1.6 Wm(-3). Due to the small geographic extent of area covered by sediments, this is similar to the Precambrian-only value. Regardless of the calculation method, heat production in Sweden is considerably higher than the corresponding value for Finland. The Swedish platform cover had apparently the lowestheat production (1.0 +/- 1.8 Wm(-3)) of all units but the presence of Precambrian rocks below the sediments means that this value strongly misleads if used to represent the entire upper crust. Svecokarelian (Svecofennian) and Sveconorwegian rocks, which comprised 94.0 per cent of all individual observations, had heat production values of 2.6 +/- 1.8 and 1.7 +/- 1.4 mu Wm(-3), respectively. Although the Swedish data still have large spatial gaps when compared to Finnish data, most bedrock units in Sweden are covered. It is obvious that the higher heat flow of Sweden compared to that of Finland is caused by near-surface (i.e. upper crustal) heat production, and crustal differentiation in Sweden is also larger.Peer reviewe

Seismic velocity models based on wide-angle refraction and reflection profiles in Finland

Laajakulmaiseen taittumis- ja heijastusluotaukseen perustuvat seismiset tutkimukset (WARR) ovat olleet keskeisessä roolissa Fennoskandian kilven rakenteellisessa tutkimuksessa. 1980-luvulta lähtien niissä on kerätty tieteellisesti arvokasta dataa sekä tuotettu seismisiä kuoren nopeusmalleja, jotka eivät ole aiemmin olleet julkisesti saatavilla. Tämän raportin kuvailemassa työssä vanhat nopeusmallit ja laajakulmasektiot muokattiin helpommin käytettäviin formaatteihin ja tallennettiin turvallisesti tutkimusdatan säilytyspalvelu IDAan. IDAssa tutkimusdata on avoimesti saatavilla ja tietokokonaisuuksille on IDAssa pysyvät DOI-tunnisteet. Säilötyn datan käyttö on määritelty Creative Commons By Attribution version 4.0 -lisenssillä. Sama data tulee myös saataville Geologian tutkimuskeskuksen Hakku-palveluun. Saatavilla olevat kaksiulotteiset nopeusmallit on tallennettu muotoon, jossa seisminen nopeus on määritetty koordinaattien pisteissä eri syvyyksillä tekstitiedostoissa. Laajakulmasektiot on tallennettu standard IBM SEG-Y -muotoisina. Tässä raportissa kuvaillaan taittumis- ja heijastusluotaustutkimuksia, saatavilla olevaa dataa sekä sen käyttöä.Seismic wide-angle refraction and reflection (WARR) surveys have been crucial in the study of the structure of the Fennoscandian shield. The valuable data and crustal seismic velocity models of major WARR studies from the 1980s to the present day have not been previously available to the public. In the work described in this report, the velocity models and wide-angle data were re-formatted to more accessible data formats and safely stored in the IDA Research Data Storage service for open access and data identification through Digital Object Identifiers. Data use is allowed under the Creative Commons By Attribution version 4.0 license. The data is also made available through the Hakku service of the Geological Survey of Finland. The velocity models are stored in a universal velocity point format in text files and wide-angle sections are stored in standard IBM SEG-Y format. A general description of WARR studies, available data and data use is given in this report

Seismic velocity models based on wide-angle refraction and reflection profiles in Finland

Laajakulmaiseen taittumis- ja heijastusluotaukseen perustuvat seismiset tutkimukset (WARR) ovat olleet keskeisessä roolissa Fennoskandian kilven rakenteellisessa tutkimuksessa. 1980-luvulta lähtien niissä on kerätty tieteellisesti arvokasta dataa sekä tuotettu seismisiä kuoren nopeusmalleja, jotka eivät ole aiemmin olleet julkisesti saatavilla. Tämän raportin kuvailemassa työssä vanhat nopeusmallit ja laajakulmasektiot muokattiin helpommin käytettäviin formaatteihin ja tallennettiin turvallisesti tutkimusdatan säilytyspalvelu IDAan. IDAssa tutkimusdata on avoimesti saatavilla ja tietokokonaisuuksille on IDAssa pysyvät DOI-tunnisteet. Säilötyn datan käyttö on määritelty Creative Commons By Attribution version 4.0 -lisenssillä. Sama data tulee myös saataville Geologian tutkimuskeskuksen Hakku-palveluun. Saatavilla olevat kaksiulotteiset nopeusmallit on tallennettu muotoon, jossa seisminen nopeus on määritetty koordinaattien pisteissä eri syvyyksillä tekstitiedostoissa. Laajakulmasektiot on tallennettu standard IBM SEG-Y -muotoisina. Tässä raportissa kuvaillaan taittumis- ja heijastusluotaustutkimuksia, saatavilla olevaa dataa sekä sen käyttöä.Seismic wide-angle refraction and reflection (WARR) surveys have been crucial in the study of the structure of the Fennoscandian shield. The valuable data and crustal seismic velocity models of major WARR studies from the 1980s to the present day have not been previously available to the public. In the work described in this report, the velocity models and wide-angle data were re-formatted to more accessible data formats and safely stored in the IDA Research Data Storage service for open access and data identification through Digital Object Identifiers. Data use is allowed under the Creative Commons By Attribution version 4.0 license. The data is also made available through the Hakku service of the Geological Survey of Finland. The velocity models are stored in a universal velocity point format in text files and wide-angle sections are stored in standard IBM SEG-Y format. A general description of WARR studies, available data and data use is given in this report

A paleointensity test of the Geocentric Axial Dipole (GAD) hypothesis

The Geocentric Axial Dipole (GAD) model is central to many aspects of geophysics, including plate tectonics and paleoclimate. But its validity is by no means firmly established, particularly for the Precambrian. One test that has met with some success involves the distribution of paleomagnetic inclination angles. It works because any given field morphology has its own distinct probability distribution function (PDF) against which data compilations can be tested. Here, we investigate a second possible test using published paleointensity data. Once again, any given field morphology has a specific PDF of intensity. Likely field models consist of an underlying GAD on which is superimposed modest zonal quadrupole and octupole components. The corresponding paleointensity PDFs turn out to have more complicated shapes than their inclination counterparts, often having multiple maxima and minima. Given sufficient data, this complexity offers greater discrimination between models. In this paper, the potential of the paleointensity test is assessed using an extension of the PINT paleointensity database. We found it useful to analyze the Phanerozoic and Precambrian intervals separately. Despite the inherent limitations of this kind of analysis, a tripartite geodynamo with small zonal multipoles appears to be a good starting point on a way towards more fine-tuned models.The Geocentric Axial Dipole (GAD) model is central to many aspects of geophysics, including plate tectonics and paleoclimate. But its validity is by no means firmly established, particularly for the Precambrian. One test that has met with some success involves the distribution of paleomagnetic inclination angles. It works because any given field morphology has its own distinct probability distribution function (PDF) against which data compilations can be tested. Here, we investigate a second possible test using published paleointensity data. Once again, any given field morphology has a specific PDF of intensity. Likely field models consist of an underlying GAD on which is superimposed modest zonal quadrupole and octupole components. The corresponding paleointensity PDFs turn out to have more complicated shapes than their inclination counterparts, often having multiple maxima and minima. Given sufficient data, this complexity offers greater discrimination between models. In this paper, the potential of the paleointensity test is assessed using an extension of the PINT paleointensity database. We found it useful to analyze the Phanerozoic and Precambrian intervals separately. Despite the inherent limitations of this kind of analysis, a tripartite geodynamo with small zonal multipoles appears to be a good starting point on a way towards more fine-tuned models.Peer reviewe

How to deliver information on induced seismicity to the authorities and general public?

Non peer reviewe

Mesoproterozoic geomagnetic reversal asymmetry in light of new paleomagnetic and geochronological data for the Häme dyke swarm, Finland : Implications for the Nuna supercontinent

Baltica represents one of the key continents of the Mesoproterozoic supercontinent Nuna forming the core of it together with Laurentia and Siberia. This study presents new geochronological and paleomagnetic data obtained for Häme diabase dyke swarm in southern Finland. New U-Pb (baddeleyite) ages 1642 ± 2 Ma and 1647 ± 14 Ma for two reversely magnetized dykes are acquired. Demagnetization revealed a dual polarity remanent magnetization direction carried by magnetite. The combined normal (N) and reversed (R) polarity direction for 11 dykes (=sites) is D = 355.6°, I = -09.1° (k = 8.6 and α95 = 16.6°) yielding a paleomagnetic pole at 23.6°N, 209.8°E (K = 10.6 and A95 = 14.7°) with Van der Voo value Q = 7. N and R magnetized units for the Häme dyke swarm show asymmetry in declination values, probably caused by an age difference between the dykes. The Geocentric Axial Dipole (GAD) model indicates that all geomagnetic reversals should be symmetric (in inclination), yet it has been noted that this is not always the case (e.g. 1.57 Ga Satakunta and Åland dykes in Baltica). By analyzing global dual polarity paleomagnetic data we show that the GAD model is a valid assumption at 1.7 – 1.4 Ga and that the asymmetry between some normal and reversed polarities in global dual-polarity data sets appears randomly over time, and does not follow a global trend. Further, we show that in the case of Åland and Satakunta dykes an unremoved secondary magnetization component could explain the obtained asymmetry. GAD assumption is used to reconstruct the core of Nuna on equatorial latitudes using new data for Häme dykes. Paleomagnetic evidence suggest that maximum assembly of Nuna occurred at 1.5 Ga and the dispersal of the core is proposed to be associated with coeval 1.38 – 1.27 Ga magmatism in its core continents.Peer reviewe

Advancing Precambrian palaeomagnetism with the PALEOMAGIA and PINT(_QPI) databases.

State-of-the-art measurements of the direction and intensity of Earth's ancient magnetic field have made important contributions to our understanding of the geology and palaeogeography of Precambrian Earth. The PALEOMAGIA and PINT(QPI) databases provide thorough public collections of important palaeomagnetic data of this kind. They comprise more than 4,100 observations in total and have been essential in supporting our international collaborative efforts to understand Earth's magnetic history on a timescale far longer than that of the present Phanerozoic Eon. Here, we provide an overview of the technical structure and applications of both databases, paying particular attention to recent improvements and discoveries