EMRP3.1 | Paleomagnetism, micromagnetism and magnetic fabrics: Recent advances and geological applications

EMRP3.1

Paleomagnetism, micromagnetism and magnetic fabrics: Recent advances and geological applications

The recent methodological and instrumental advances in paleomagnetism, micromagnetic modelling, and magnetic fabric research further increased their already high potential in solving geological, geophysical, and tectonic problems. Integrated paleomagnetic and magnetic fabric studies, together with structural geology and petrology, are very efficient tools in increasing our knowledge about sedimentological, tectonic or volcanic processes, both on regional and global scales. This session is intended to give an opportunity to present innovative theoretical or methodological works and their direct applications in various geological settings. Especially welcome are contributions combining paleomagnetic and magnetic fabric data, integrating various magnetic fabric techniques, combining magnetic fabric with other means of fabric analysis, or showing novel approaches in data evaluation and modelling. We also highly solicit contributions showing all aspects of paleomagnetic reconstructions, acquisition of characteristic remanence and remagnetisations applied to solving geotectonic problems. We also solicit contributions that (i) take advantage of recent advances in imaging magnetic behaviour at the grain-scale; (ii) present paleomagnetic challenges that could be solved using newly available methods; and/or (iii) use micromagnetic modelling to characterize the behaviour of magnetic carriers.

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Co-organized by SSP1/TS1

Convener: Martin Chadima | Co-conveners: Lennart de Groot, Sara Satolli, Marco Maffione

Orals

| Wed, 26 Apr, 14:00–15:45 (CEST)

Room -2.21

Posters on site

| Attendance Wed, 26 Apr, 08:30–10:15 (CEST)

Hall X2

Posters virtual

| Attendance Wed, 26 Apr, 08:30–10:15 (CEST)

vHall TS/EMRP

Orals: Wed, 26 Apr | Room -2.21

The oral presentations are given in a hybrid format supported by a Zoom meeting featuring on-site and virtual presentations. The button to access the Zoom meeting appears just before the time block starts.

Chairpersons: Martin Chadima, Lennart de Groot

14:00–14:05

5-minute convener introduction

14:05–14:15

EGU23-10000

ECS

solicited

On-site presentation

Toward finer resolution APWPs

Leandro Gallo, Mat Domeier, Facundo Sapienza, Nicholas Swanson-Hysell, Bram Vaes, Yiming Zang, Maëlis Arnould, Boris Robert, Tobias Rolf, and Annique van der Boon

Our understanding of paleogeography through Earth history relies heavily on apparent polar wander paths (APWPs), which represent the time-dependent position of Earth’s spin axis relative to a given tectonic plate. However, there are a number of limitations associated with conventional approaches to APWP construction. First, the paleomagnetic record contains significant uncertainty in individual pole positions that is not propagated into APWPs. This traditional approach makes it difficult to incorporate age and positional uncertainty into synthesized paths and assigns equal weight to paleomagnetic poles with vastly different numbers of underlying sites. Second, the effective propagation of site-level uncertainties into the APWP requires a transformation that renders traditional parametric assumptions (i.e., Fisher statistics) on the pole level ineffective. Here, we overcome these limitations with a bottom-up Monte Carlo uncertainty propagation scheme that operates on site-level paleomagnetic data. To demonstrate our methodology, we present a large compilation of site-level Cenozoic paleomagnetic data from North America, which we use to generate a high-resolution APWP. We show that even in the presence of significant noise, polar wandering can be assessed with unprecedented temporal and spatial resolution.

How to cite: Gallo, L., Domeier, M., Sapienza, F., Swanson-Hysell, N., Vaes, B., Zang, Y., Arnould, M., Robert, B., Rolf, T., and van der Boon, A.: Toward finer resolution APWPs, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10000, https://doi.org/10.5194/egusphere-egu23-10000, 2023.

14:15–14:25

EGU23-10221

On-site presentation

Cenozoic and Late Cretaceous Apparent Polar Wander of the Pacific Plate: Implications for True Polar Wander and Global Plate Motion Circuits

Richard Gordon, Daniel Woodworth, and Kevin Gaastra

The apparent polar wander (APW) path of the Pacific plate during Cenozoic and Late Cretaceous time has important paleogeographic, global tectonic, geodynamic, and paleoclimatic implications. Here we present recent progress on our assessment of Pacific plate APW with a focus on new poles determined from analysis of the skewness of marine magnetic anomalies due to seafloor spreading, which produces high precision paleomagnetic poles.

Our recent and new results include paleomagnetic poles for chron C24r (57–54 Ma; Woodworth et al. 2023), chron 21n (48−46 Ma; Woodworth et al. in preparation), chron 27r (63−62 Ma; Gaastra et al., in preparation), and chron 30n−31n (69−66 Ma; Ritchey et al., in preparation). The new chron 24r pole extends the northward progression of the 69–58 Ma track in the previously determined Pacific plate apparent polar wander path beyond the southern end of the 46–10 Ma track, which is now extended by our chron 21n pole. That the two tracks overshoot one another implies either a brief interval during which the Pacific plate moved substantially and rapidly southward relative to a mantle reference frame or to an episode of true polar wander (TPW, the re-orientation of the solid Earth relative to the spin axis). The reconstructed plate geometry and relative plate motions are inconsistent with ancient plate driving forces having been capable of driving the plate southward. Considering our results together with drill-core paleomagnetic paleolatitudes, we find that the most likely explanation is a ≈7° episode of TPW between ≈54 Ma and ≈50 Ma.

The new high precision paleomagnetic poles for the Pacific plate, when compared with continental paleomagnetic results from Torsvik et al. (2012) reconstructed to a common frame of reference, allow an updated test of two plate motion circuits relating the Pacific plate to the circum-Pacific continents. Analysis of the plate-motion circuit through Antarctica (or through Australia) continues to indicate a significant paleomagnetic misfit that increases with age during Cenozoic time up to a maximum of ≈7−8° at ≈50 Ma. Analysis of the fixed hotspot circuit indicates a smaller insignificant misfit of up to ≈5° that also increases with age.

If the plate circuit through Antarctica is flawed, as indicated by the paleomagnetic results, any or all of the following may have contributed to the flaw: (1) intraplate deformation (cf., Kreemer & Gordon, 2014), (2) unrecognized diffuse oceanic plate boundaries (e.g., Gordon & Stein, 1992), (3) motion between East and West Antarctica not localized across mid-ocean ridge segments, and (4) horizontal extension across large expanses of submerged continental area in the south Pacific (e.g., Sutherland et al., 2020).

How to cite: Gordon, R., Woodworth, D., and Gaastra, K.: Cenozoic and Late Cretaceous Apparent Polar Wander of the Pacific Plate: Implications for True Polar Wander and Global Plate Motion Circuits, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10221, https://doi.org/10.5194/egusphere-egu23-10221, 2023.

14:25–14:35

EGU23-1736

ECS

On-site presentation

Locating the Lhasa Block within the Neo-Tethys Ocean at ~268 Ma: Paleomagnetism and Its Paleogeographic Implications

Longyun Xing, Xin Cheng, and Hanning Wu

The origin and drift history of the Lhasa block in South Tibet is crucial towards unraveling the evolution of the Neo-Tethys Ocean, which has not yet been well constrained by the paucity of paleomagnetic data, especially for the late Paleozoic. Hence, a systematic paleomagnetic investigation of 50 sandstone samples (6 sites), 166 volcanic samples (21 sites) and 76 limestone samples (9 sites) from the middle Permian (267.8 ± 5.0 Ma) Luobadui Formation was conducted in the Lhunzhub area. The results reveal an Eocene re-magnetization component in the sandstone samples, but stable high temperature (field) components obtained from most volcanic and limestone samples can successfully pass the fold, reversal and paleosecular variation tests, which likely represents primary magnetization. On this basis, the middle Permian paleomagnetic pole position (P_lat= 40.9°N, P_long=324.5°E, N=27 sites (dp/dm=3.3/6)) and paleolatitude (~15.9°S) of the Lhasa block are presented. Combined with published paleomagnetic data from other Tethyan continental blocks, this new constraint reveals that the Lhasa block was located in the interior of the Neo-Tethys Ocean at about 268 Ma. In further considering the geological records of the Lhasa block, we propose that the block rifted from the northwestern margin of the Gondwana-Australian plate prior to the middle Permian, and the Neo-Tethys Ocean represented by the Bangong Co-Nujiang and Yarlung-Zangbo Suture Zones coexisted during the middle Permian.

How to cite: Xing, L., Cheng, X., and Wu, H.: Locating the Lhasa Block within the Neo-Tethys Ocean at ~268 Ma: Paleomagnetism and Its Paleogeographic Implications, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1736, https://doi.org/10.5194/egusphere-egu23-1736, 2023.

14:35–14:45

EGU23-1701

ECS

On-site presentation

Paleomagnetism of Late Triassic Volcanic Rocks From the Southern Qiangtang Block, Tibet: Constrains on the Closure of the Paleo-Tethys Ocean

Bitian Wei, Xin Cheng, Mathew Domeier, and Hanning Wu

14:45–14:55

EGU23-10068

On-site presentation

A (new?) ~50 Kyr geomagnetic event recorded in a stalagmite from the Bat Cave, Portugal

Eric Font, Elisa M. Sánchez-Moreno, Eduardo Lima, Ana Raquel Brás, Jorge, E. Spangenberg, Larry Edwards, Ricardo Trindade, Luca Dimuccio, Altug Hasözbek, Josep Parés, Fernando Jiménez Barredo, Janine Araujo de Carmo, and Joshua Feinberg

Stalagmites are potential candidates for high-resolution reconstruction of the Earth’s magnetic field and paleoclimatic variations. Here we provided a pristine record of a geomagnetic event recorded in two stalagmites from the Bat Cave, Central Region of Portugal. SQUID microscopy reveals a high concentration of magnetic particles. FORC diagrams and hysteresis parameters point to non-interacting single-domain magnetite as the main magnetic carrier. Carbon and oxygen isotope compositions are interpreted as primary and provide the record of a Greenland interstadial. Paleomagnetic data show a gradual variation of the magnetic declination and inclination from the normal component to an antipodal reverse component. Return to the normal component is abrupt and is not apparently associated with visible hiatus in the precipitation rate of the stalagmite. Preliminary U-Th dating point to an age of ~50-55 Kyr for the geomagnetic event recorded in both stalagmites. However, owing to the speleothem’s high detrital content and low U concentration, alternative techniques are being explored to improve the uncertainty in radiometric dating. This geomagnetic event can possibly correspond to the Laschamp geomagnetic excursion dated at ~41 Kyr or to a newly discovered ~50 kyr short-lived geomagnetic reversal.

Acknowledgments: This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020- IDL, MIT-EXPL/ACC/0023/2021, and PTDC/CTA-GEO/0125/2021).

How to cite: Font, E., M. Sánchez-Moreno, E., Lima, E., Brás, A. R., Spangenberg, J. E., Edwards, L., Trindade, R., Dimuccio, L., Hasözbek, A., Parés, J., Jiménez Barredo, F., Araujo de Carmo, J., and Feinberg, J.: A (new?) ~50 Kyr geomagnetic event recorded in a stalagmite from the Bat Cave, Portugal, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10068, https://doi.org/10.5194/egusphere-egu23-10068, 2023.

14:55–15:05

EGU23-2234

On-site presentation

Anisotropy of out-of-phase magnetic susceptibility in titanomagnetite-bearing rocks due to weak field hysteresis

Frantisek Hrouda, Josef Jezek, and Martin Chadima

Magnetic susceptibility (both in-phase, ipMS, and out-of-phase, opMS, components) and its anisotropy were investigated in artificial specimens with pure synthetic magnetite and in rocks with titanomagnetite with variable Ti-content reaching X_Usp = 0.6 of ulvospinel end member. The opMS of pure magnetite is in its absolute values three orders lower than the ipMS. The phase angle is then lower than 0.2° in absolute values, which is mostly lower than the sensitivity of phase angle determination. Consequently, the opMS can be considered effective zero. In low-Ti titanomagnetite (X_Usp~0.2), the intensity of the ipMS variation with field is very low, hardly reaching 1% of the initial value. In high-Ti titanomagnetite (X_Usp~0.6), the intensity of ipMS variation is relatively strong reaching 50% of the initial value and that of opMS variation is even much stronger reaching multiples of the initial value.

In artificial specimens with magnetite, the opMS is isotropic from the statistical point of view as indicated by the values of the F-statistics and by confidence angles. In titanomagnetite-bearing rocks, the opAMS ellipsoids resemble the ipAMS ellipsoids, the degree of opAMS being significantly higher than that of ipAMS. The principal directions of ipAMS and opAMS are related closely in specimens with high-Ti titanomagnetites and only poorly in specimens with low-Ti titanomagnetites. In specimens with high-Ti titanomagnetites, there is a linear and very strong (R² = 0.9433) correlation between the degree of ipAMS and root squared degree of opAMS.

The results of the present research are mainly applicable to the rocks whose magnetism is dominantly carried by titanomagnetite and pure magnetite. The opAMS indicates solely the titanomagnetite fabric unaffected by magnetite whose fabric may often originate in different conditions or in different time.

How to cite: Hrouda, F., Jezek, J., and Chadima, M.: Anisotropy of out-of-phase magnetic susceptibility in titanomagnetite-bearing rocks due to weak field hysteresis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2234, https://doi.org/10.5194/egusphere-egu23-2234, 2023.

15:05–15:15

EGU23-4479

ECS

On-site presentation

Full vector inversion of magnetic microscopy data using Euler deconvolution as a priori information

Gelson Ferreira de Souza Junior, Ricardo Ivan Ferreira da Trindade, Leonardo Uieda, Roger Fu, and Janine Araujo do Carmo

Classically, paleomagnetic data is obtained from bulk samples, where the signal is obtained from the sum of all magnetic moments within the sample volume. This typically includes stable and unstable remanence carriers. With the advance of microscope imaging techniques (e.g., SQUID microscopes, Quantum Diamond Microscopes) it is now possible to spatially isolate the contribution of single grains or clusters of grains. Yet, despite recent advances in the inversion techniques to derive full vector information from the magnetic microscopy data, there is still no inversion protocol capable of obtaining the magnetization directions of each magnetic particle without using a priori information or physically separating the spatial position of each anomaly. Here we present an algorithm capable of automatically identifying the position of each magnetic anomaly source by combining signal processing and tridimensional Euler deconvolution. Subsequently, we recover both the direction and the intensity of the magnetic moment of each magnetic source with no need for any kind of additional information. The method presented here is a potential technique that may help increase the statistical accuracy of data obtained in paleomagnetic studies from magnetic microscopy data, especially in the case of complex characteristic remanent magnetization.

How to cite: Ferreira de Souza Junior, G., Ivan Ferreira da Trindade, R., Uieda, L., Fu, R., and Araujo do Carmo, J.: Full vector inversion of magnetic microscopy data using Euler deconvolution as a priori information, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4479, https://doi.org/10.5194/egusphere-egu23-4479, 2023.

15:15–15:25

EGU23-5045

ECS

On-site presentation

Building Physical Models of the Distribution of Iron-oxides in Basalts: ‘How MMT deals with MicroCT resolution limitations’

Frenk Out, Rosa de Boer, John Walmsley, and Lennart de Groot

Micromagnetic tomography (MMT) is a new promising paleomagnetic technique that obtains magnetic moments for individual iron-oxides. These magnetic moments are inferred from surface magnetometry data obtained with quantum diamond microscopy (QDM), and iron-oxide positions determined with micro X-Ray computed tomography (MicroCT). Different to classical techniques, MMT does not depend on bulk measurements of samples. This makes it possible to only select the most reliable magnetic recorders. To make this improvement possible, MMT first has to deal with the presence of undetected magnetic carriers in basaltic rock samples used in previous MMT studies. Although particles smaller than 1 µm are good recorders of the magnetic field and may be visible in surface magnetometry, they are not detected by MicroCT. This violates one of the foundations of MMT and may disturb magnetic moments of other detected grains. However, it is currently unknown how many of these small disturbing particles are present in Hawaiian basaltic samples. We know that the smallest disturbing grains have a diameter of around 40 nm, since particles smaller than this threshold become superparamagnetic and cannot store magnetic signals. For this reason we want to obtain a grain-size distribution for iron-oxides from 20 nm to 10 µm to cover the complete range of grains that are capable of storing Earth’s magnetic field. This requires a combination of FIBSEM slice-and-view and MicroCT techniques; FIBSEM detects single and pseudo-single domain grains with sizes between 20 nm and 1 µm and MicroCT detects multi-domain grains with sizes larger than 1 µm. Subsequently, FIBSEM and MicroCT data are combined to obtain the full spectrum of grain sizes. Unfortunately, grains are not uniformly distributed in the samples, so a scaling by volume would not produce a realistic spectrum. Therefore, based on observations that iron-oxides grains cluster on the interfaces of other minerals, we calculated how many times FIBSEM mineral interfaces from FIBSEM data fit the mineral interfaces from MicroCT data. Then, this factor is used to scale the FIBSEM iron-oxides to MicroCT iron-oxides and to obtain a complete distribution of all grain sizes. Interestingly, this distribution shows a clear peak in grain size at 70-80 nm. Furthermore, the smallest grain fraction is fitted a lognormal trend, but the fraction larger than 0.18 µm are fitted an exponential decay trend. With these trendlines in place we have finally acquired a realistic set of boundary conditions for the distribution of iron-oxide particles in basaltic rocks. This enables us to populate models with a realistic distribution of particles, which ultimately may shed light on the disturbing presence of small iron-oxides in MMT results. If we know the effect of these disturbances, we will understand which grains MMT can solve with highest certainty, ultimately leading to paleomagnetic interpretations on grain scale.

How to cite: Out, F., de Boer, R., Walmsley, J., and de Groot, L.: Building Physical Models of the Distribution of Iron-oxides in Basalts: ‘How MMT deals with MicroCT resolution limitations’, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5045, https://doi.org/10.5194/egusphere-egu23-5045, 2023.

15:25–15:35

EGU23-10086

ECS

On-site presentation

Micromagnetic Modeling of Thermoremanent Magnetization in Small Natural Pseudo-Single Domain Magnetite Particles

Annemarieke Beguin, Even Nikolaisen, and Karl Fabian

Earth and planetary rocks record magnetic variations and are crucial recorders to further our understanding of the formation and evolution of the Earth’s magnetic field. The acquisition and stability of remanent magnetization in rocks are controlled by the magnetization state of magnetic particles. Where the thermoremanent magnetization (TRM) of pseudo-single domain (PSD) magnetite particles probably dominates the natural remanence of many igneous rocks. These PSD particles are therefore important carriers of paleomagnetic information. Nevertheless, the extension of Néel's (1955) elegant analytical theory of single domain (SD) particles to larger PSD particles meets with substantial technical challenges. Understanding the unblocking of energy barriers between energetically favorable domain states is important when predicting the TRM behavior of natural particles. While categorizing different magnetization states is manageable for simple SD particles, it will become increasingly difficult with increasing particle size. Mapping the full energy landscape for PSD particles can be challenging and time-consuming.

Here we present an automated process that can categorize all possible local energy minima (LEM) from micromagnetic modeling results. The automated process determines if magnetic states with approximately equal total energy are in the same reversible region. We incorporate calculations of energy barriers between LEMs for an assemblage of natural magnetite particles obtained by focused-ion-beam (FIB) nano-tomography. The technique was tested for a suite of PSD particles from single-vortex to multi-vortex states, where we systematically studied the energy landscape and relaxation time as a function of temperature. To map the energy landscape, LEM and energy barriers between all possible LEM were calculated for temperatures between room temperature and Curie temperature. Combining these results in a statistical model allows for predicting the TRM acquisition of individual particles and isotropic ensembles of equal particles. The results are discussed in terms of the TRM behavior of natural PSD magnetite, magnetic stability, and the implications for paleomagnetic research.

How to cite: Beguin, A., Nikolaisen, E., and Fabian, K.: Micromagnetic Modeling of Thermoremanent Magnetization in Small Natural Pseudo-Single Domain Magnetite Particles, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10086, https://doi.org/10.5194/egusphere-egu23-10086, 2023.

15:35–15:45

EGU23-14336

On-site presentation

Temporal constraints on Fe mobility in Jack Hills zircon

Steven Reddy, Richard Taylor, Richard Harrison, David Saxey, William Rickard, Fengzai Tang, Cauê Borlina, Roger Fu, Benjamin Weiss, Paul Bagot, and Helen Williams

Ancient detrital zircon grains containing magnetite inclusions have the potential to record the Earth’s magnetic field as far back as the Hadean. However, this requires magnetite to be either a primary inclusion or to be a secondary inclusion that forms shortly after zircon crystallization. Microstructural and TEM analysis of Jack Hills zircon show that magnetite, the magnetic recorder in these zircon crystals, is secondary in nature and is associated with the mobility of Fe. However, the timing of Fe mobility within Jack Hills zircon is poorly constrained. Here we undertake nanoscale characterization of highly magnetic zones of zircon, identified by quantum diamond microscopy (QDM), using atom probe tomography (APT). The APT data show the presence of Pb-bearing nanoclusters and these record isotopic compositions consistent with formation during two discrete thermal events at 3.4 Ga and < 2 Ga. The older population of clusters contain no detectable Fe. However, the younger population of clusters are Fe-bearing. This result shows that the Fe required to form secondary magnetite was not present in the zircon prior to 3.4 Ga and that remobilization of Pb and Fe, the latter associated with magnetite formation, took place after 2 Ga, during an annealing event that took place more than one billion years after deposition of the Jack Hills sediment at 3 Ga. This use of APT to date Fe mobility provides a novel approach to temporally constrain the formation of intragranular secondary magnetite inclusions in highly magnetic areas of zircon grains.

How to cite: Reddy, S., Taylor, R., Harrison, R., Saxey, D., Rickard, W., Tang, F., Borlina, C., Fu, R., Weiss, B., Bagot, P., and Williams, H.: Temporal constraints on Fe mobility in Jack Hills zircon, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14336, https://doi.org/10.5194/egusphere-egu23-14336, 2023.

Posters on site: Wed, 26 Apr, 08:30–10:15 | Hall X2

The posters scheduled for on-site presentation are only visible in the poster hall in Vienna. If authors uploaded their presentation files, these files are linked from the abstracts below, but only on the day of the poster session.

Chairpersons: Martin Chadima, Lennart de Groot

X2.285

EGU23-1885

ECS

On-site presentation

Paleomagnetic and micromagnetic measurements of Middle Devonian pillow lavas from Germany

Rosa de Boer, Annique van der Boon, Peter Königshof, and Lennart de Groot

Paleomagnetic data from the Middle Devonian are typically difficult to interpret. Directions and paleointensities often do not fit with dipolar field behavior or expected paleogeography. The reason why the geomagnetic field cannot be reconstructed with traditional methods has been topic of debate, but no consensus has been reached. We would like to understand what happened to the geomagnetic field during the Middle Devonian and why the configuration of the field was potentially unusual.

We aim to expand the existing paleomagnetic record for the Middle Devonian by sampling a site in Braunfels, Germany. This site consists of relatively unaltered pillow lavas. Petrographic and rockmagnetic analyses indicate the presence of magnetite and minor maghemite in the samples. We obtained paleomagnetic directions using alternating field (AF) and thermal demagnetization experiments. The directions are scattered and do not cluster around paleomagnetic directions that are expected for Germany in the Devonian.

Paleointensity data were acquired using the ZIIZP-Thellier method, resulting in a field intensity of approximately 6 µT, which equals a VADM of 8-15 ZAm². The latter is in line with very low field intensities generally reported for the Devonian.

Various mechanisms have been suggested to explain the typically scattered and ambiguous Devonian paleomagnetic data, such as significant overprinting, tectonic rotations and a non-dipolar field configuration. Our results confirm an extremely weak magnetic field, but this alone does not explain the scattered directions. To exclude the possibility that the scattered directions are related to (partial) overprinting we use Quantum Diamond Microscope imaging to assess the magnetizations of individual magnetic grains instead of the bulk magnetic signal of the sample. With this method, a distinction can be made between e.g., different generations of magnetizations, revealing information on the Middle Devonian geomagnetic field that was previously inaccessible by considering the magnetic moments of bulk samples alone.

How to cite: de Boer, R., van der Boon, A., Königshof, P., and de Groot, L.: Paleomagnetic and micromagnetic measurements of Middle Devonian pillow lavas from Germany, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1885, https://doi.org/10.5194/egusphere-egu23-1885, 2023.

X2.286

EGU23-6373

ECS

On-site presentation

Magnetic analysis of individual iron oxide grains; application of Micromagnetic Tomography to a natural sample.

Martha Kosters, Rosa de Boer, Frenk Out, David Cortes Ortuno, Michael Volk, and Lennart V. de Groot

The magnetic information stored in volcanic rocks is a valuable archive of the history of the behavior of the Earth’s magnetic field. Micromagnetic Tomography (MMT) allows to determine magnetic moments of individual iron-oxide grains in rocks. Theoretically this enables us to separate contributions from non-ideal recorders and ideal recorders, overcoming the difficulties arising from bulk measurements. Here we present results from two sister specimens from the 1907-flow from Hawaii’s Kilauea volcano to which MMT was applied. One specimen was imaged both by the Quantum Diamond Microscope in Harvard and by the MicroCT scanner Nanoscope–S in Delft, producing magnetic moments of 1,646 individual grains. The sister sample underwent stepwise AF-demagnetization: a step toward classic paleomagnetic analysis, from which we present (preliminary) results. In MMT, individual grains are allocated a magnetization through a least-squares inversion. For the first sample, we produced more than one magnetization for each grain, because each grain was present in multiple unique inversion ‘tiles’ (smaller sub-areas due to computational constraints). This enabled a statistical analysis of the (robustness of) results, presented here. For the second sample (preliminary) demagnetization results per grain are presented. We also present results of an investigation into a parameter for selecting grains that can be reliably resolved from the statistical analysis. For both samples only relatively large iron-oxide grains (diameter > 1.5 - 2 µm) were resolved, as the resolution of the MicroCT was limited. However, any analysis of magnetism at grain level is a step in understanding how magnetizations are stored in individual grains, and is of importance for those specimens that only contain large iron-oxides.

How to cite: Kosters, M., de Boer, R., Out, F., Cortes Ortuno, D., Volk, M., and de Groot, L. V.: Magnetic analysis of individual iron oxide grains; application of Micromagnetic Tomography to a natural sample., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6373, https://doi.org/10.5194/egusphere-egu23-6373, 2023.

X2.287

EGU23-8391

On-site presentation

State-of-the-art of the Pyrenean Paleomagnetic Database

(withdrawn)

Emilio L. Pueyo, Roi Silva-Casal, Cristina García-Lasanta, Berta López-Mir, Kirsten Elger, Antonio Pedrera, and Jesus García-Senz

X2.288

EGU23-6247

ECS

On-site presentation

Structural analysis by anisotropy of magnetic susceptibility and U-Pb geochronology of the Gamaye pluton (Kédougou-Kéniéba Inlier, West Africa)

Aliou Dembele, Olivier Bolle, Marc Poujol, Moussa Dabo, and Mamadou Lamine Bouaré

The Gamaye pluton (Kedougou-Kenieba Inlier, West African Craton) is elongated along a N-S direction, over about 20 km, to the east of the sinistral, transcurrent Senegal-Mali Shear Zone (SMSZ). It is assumed to have been emplaced at around 2045±27 Ma (Rb-Sr whole-rock and feldspar age; Bassot & Caen-Vachette, 1984) and, as other granitoids from the Kedougou-Kenieba Inlier, it displays a spatio-temporal relationship with world-class gold mineralization (Lawrence et al., 2013a, b). The pluton is made of a leucocratic, coarse-grained, locally porphyritic granite, associated with a subordinate, mesocratic, fine-grained facies, mostly found in a small (1.5 x 4 km) body along the western border of the pluton. Preliminary apatite LA-ICP-MS U-Pb dating yield ages with quite large uncertainties, which highlight, however, magmatic pulses with distinct emplacement ages: 2294.6±68.3 Ma (western mesocratic body), 2160±34.8Ma (main leucocratic facies) and 1922.7±53.1 Ma (a tiny mesocratic body in the east of the pluton). The western part, particularly the democratic body, and the southern part of the pluton, close to the SMSZ, are mylonitized, displaying a S-C fabric, whereas the northern, central and eastern parts are almost isotropic. However, a study of the microstructures shows that these parts of the Gamaye pluton have also undergone solid-state deformation and dynamic recrystallization. Measurements of the anisotropy of magnetic susceptibility, conducted on about 50 samples, reveal paramagnetic signatures, with bulk susceptibilities lower than 0.5×10^-3SI. The shape of the magnetic fabric ranges from oblate to prolate, and the degree of anisotropy increases towards the western limit of the pluton and the SMSZ, together with the rock strain intensity. There is also a deflection of the magnetic foliation and lineation in that direction: in particular, when approaching the western border, the magnetic fabric is dominated by NNW-SSE-trending, steeply-dipping foliations (parallel to the C plane of the S-C fabrics) and gently-plunging lineations (concordant with the strike-slip movement of the SMSZ). It is concluded that the Gamaye pluton has been emplaced along the SMSZ and/or has been deformed by this transcurrent regional discontinuity.

Reference

Bassot, J.P., Caen-Vachette, M., 1984. Données géochronologiques et géochimiques nouvelles sur les granitoïdes de l’Est du Sénégal: implications sur l’histoire géologique du Birimien de cette région. In: Klerkx, J., Michot, J. (Eds.), African Geology, Belgium, Tervuren, pp. 196–209.

Lawrence, D.M., Treloar, P.J., Rankin, A.H., Harbidge, P., Holliday, J., 2013a. The geology and mineralogy of the Loulo mining District, Mali, West Africa: evidence for two distinct styles of orogenic gold mineralization. Econ. Geol. 108, 199–227.

Lawrence, D.M., Treloar, P.J., Rankin, A.H., Boyce, A., Harbidge, P., 2013b. A fluid inclusion and stable isotope study at the Loulo mining District, Mali, West Africa: implications for multifluid sources in the generation of orogenic gold deposits. Econ. Geol. 108, 229–257.

How to cite: Dembele, A., Bolle, O., Poujol, M., Dabo, M., and Bouaré, M. L.: Structural analysis by anisotropy of magnetic susceptibility and U-Pb geochronology of the Gamaye pluton (Kédougou-Kéniéba Inlier, West Africa), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6247, https://doi.org/10.5194/egusphere-egu23-6247, 2023.

X2.289

EGU23-608

ECS

On-site presentation

Systematic reorientation of diamagnetic fabrics of Taunus quartzite due to experimental impact cratering

Sonal Tiwari, Amar Agarwal, Thomas Kenkmann, and Michael H. Poelchau

Systematic reorientation of diamagnetic fabrics of Taunus quartzite due to experimental impact cratering

Sonal Tiwari¹, Amar Agarwal¹, Thomas Kenkmann², Michael H. Poelchau²

¹Department of Earth Sciences, Indian Institute of Technology-Kanpur, Kanpur – 208016, India.

²Geology, University of Freiburg, 79104 Freiburg, Germany

Corresponding author´s email: sonaljp20@iitk.ac.in

Abstract

Para- and ferromagnetic fabrics are known to provide essential clues for understanding impact cratering processes. However, research on the effects of shock waves on diamagnetic fabrics is lacking. We, therefore, conducted a hypervelocity impact experiment on a block of diamagnetic Taunus quartzite and studied the changes in diamagnetic fabrics. Taunus quartzite was formed by a low-grade Variscan metamorphism that overprinted a 405 Ma old sandstone. It consists of c. 91 vol % quartz and a fine-grained, greenish phyllosilicate-bearing matrix (c. 8 vol %), along with small amounts of rutile, chromite, zircon, monazite, and iron oxides.

The experiment was carried out on a 20 cm Taunus quartzite cube with a two-stage light-gas gun of the Fraunhofer Ernst-Mach Institute for High-Speed Dynamics (EMI) in Freiburg (EMI), Germany. The gun has a 8.5 mm calibre launch tube. The 0.3690 g basalt sphere projectile was accelerated to 5.457 kms^-1, with a target chamber pressure of 1.2 mbar. The projectile diameter (d_p) was 6.18 mm. Later, 14 mm-diameter nonmagnetic diamond bits were used to drill oriented cylindrical cores from unshocked and shocked Taunus quartzite blocks. The AMS of the unshocked and shocked specimens was determined at room temperature in KLY-4S Kappabridge (AGICO). Following the AMS measurements, the cylindrical specimens were cut to make thin sections, which were studied under a Leica DM4 scanning optical microscope.

Hypidiomorphic grain texture, serrated grain boundary, grain boundary migration, ataxial veins, Boehm lamellae, and recrystallized quartz represent the natural microscopic features. Impact-induced microstructures include trans- and intragranular microfractures. Our AMS results demonstrate that in the crater subsurface, the reorientation of the diamagnetic fabrics is concentrated in a zone of ~4 projectile diameters (25 mm) width directly below the point of impact. Higher reorientation in this zone indicates the concentration of damage. The damage is concentrated directly below the point of impact. Another important observation is that weak shock waves have caused an increase in the bulk susceptibility. These results, thus, show that the changes in diamagnetic fabrics can be used as a proxy for plastic deformation caused by shock waves at low peak pressures.

Figure. The images show the specimens' position (black dots), the point source (brown dot), the impact crater (brown arc), and the variation in the orientation of k3.

How to cite: Tiwari, S., Agarwal, A., Kenkmann, T., and Poelchau, M. H.: Systematic reorientation of diamagnetic fabrics of Taunus quartzite due to experimental impact cratering, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-608, https://doi.org/10.5194/egusphere-egu23-608, 2023.

X2.290

EGU23-6126

ECS

On-site presentation

Multi-stage tectonic evolution of the Tatra Mts recorded in the para- and ferromagnetic fabrics

Dorota Staneczek, Rafał Szaniawski, and Leszek Marynowski

Magnetic fabrics analysis is widely applied in reconstructions of the tectonic evolution of orogenic belts. The main advantage of this method is the ability to trace even weak deformation in rocks. The main goal of this work is to shed new light on the Cretaceous-Neogene tectogenesis of the Tatra Mts by investigating the para- and ferromagnetic fabrics of nappe units and post-thrusting sequences. It is worth mentioning, that this study provides the first magnetic fabric data from the thrust nappe system of the High Tatra Mts (the most elevated part of the Tatra Mts). We focused on Cretaceous marly limestones, the youngest part of the Mesozoic nappe system in the Tatra Mts, and Oligocene post-thrusting shales/siltstones. Petromagnetic methods combined with paleotemperature estimations enabled us to identify the magnetic mineralogy and its origin. The subsequent analysis of para- and ferromagnetic fabrics supported by the previously obtained mineralogical results let us recognize and characterize different stages of the tectonic evolution of the Tatra Mts. Even though the paleotemperatures recorded for Oligocene and Cretaceous rocks are higher in the High Tatra Mts than in the Western Tatra Mts, petromagnetic features of rocks sampled in both areas remain similar. Anisotropy of Magnetic Susceptibility (AMS) fabric of post-thrusting cover is governed by phyllosilicates. A consistent, approximately NE-SW-oriented magnetic lineation of tectonic origin is present in most analyzed sites and documents weak deformation presumably related to the Miocene uplift of Tatra Mts. Mean ferromagnetic mineral in Oligocene clastic sediments is magnetite. Origin of the AARM lineation in this unit is presumably related to the crystallization of the secondary magnetite on a preexisting phyllosilicate matrix and/or the stress field present during magnetite formation. The magnetic fabric of the Cretaceous marly limestones is controlled mainly by the orientation of phyllosilicates and differs significantly among the High and Western Tatra Mts. AMS results from The Western Tatra Mts’ sites document consistently the NW direction of alpine nappe thrusting. On the contrary, the AMS fabric in the High Tatra Mts shows no clear evidence of tectonic deformation. Ferromagnetic mineralogy of the Cretaceous nappe unit is complex and combines magnetite, hematite and maghemite in various proportions, with the usual dominance of magnetite. In the High Tatra Mts, the AARM fabric carried by magnetite is characterized by sub-vertical magnetic lineation, which we interpret as the impact of local transpression-related deformation associated with the Miocene uplift.

How to cite: Staneczek, D., Szaniawski, R., and Marynowski, L.: Multi-stage tectonic evolution of the Tatra Mts recorded in the para- and ferromagnetic fabrics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6126, https://doi.org/10.5194/egusphere-egu23-6126, 2023.

X2.291

EGU23-15137

On-site presentation

An integrated structural and AMS study to define the emplacement of the Arbus pluton (SW Sardinia, Italy)

Francesca Cifelli, Francesco Secchi, Leonardo Casini, Stefano Naitza, Enrico Carta, and Giacomo Oggiano

The Arbus igneous complex (SW Sardinia, Italy) represents a good example of a short time lived post-collisional composite pluton emplaced at shallow crustal level in the external zone of the Variscan chain. The pluton almost consists of granodiorite and leucogranite rock-suites emplaced at 304 ± 1 Ma within a main NW trending thrust separating the metamorphic wedge from the fold and thrust belt foreland. The pluton emplaced into a dilatational step over connecting two NW–SE dextral shear zones which belongs to a regional network of post-collisional strike-slip structures marking the transition from col- lision to post-collisional extension. The microstructure observed for quartz and K-feldspar confirms the lack of significant post-emplacement deformation, indicating only limited high-temperature sub-solidus recrystallization. Anisotropy of magnetic susceptivity data and field-structural analysis have been carried out to reconstruct the geometry of the pluton and the trajectories of magmatic flow in relation to regional deformation structures. Overall, the magmatic and the magnetic fabrics are broadly discordant with the metamorphic foliation of the country rocks, defining an EW trending elliptical asymmetric sill rooted in the SW quadrant. The reconstructed architecture combined to petrologic observation indicates that accretion of the pluton involved injection of multiple dykes through a sub-vertical feeder zone, combined to lateral flow of the roof controlled by inherited collisional structure. The duration of magmatic activity and the cooling history of the contact metamorphic aureole have been evaluated through a suite of 2D thermal models. All these observations, together with the available geochronological constraints are suggestive of very rapid construction of the pluton. The proposed emplacement model is fully consistent with the regional phase of strike-slip tectonics and widespread magmatism accommodating the large rotation of the Corsica-Sardinia block during the Carboniferous-Permian transition.

How to cite: Cifelli, F., Secchi, F., Casini, L., Naitza, S., Carta, E., and Oggiano, G.: An integrated structural and AMS study to define the emplacement of the Arbus pluton (SW Sardinia, Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15137, https://doi.org/10.5194/egusphere-egu23-15137, 2023.

X2.292

EGU23-17170

On-site presentation

A simple toolbox for evaluating the combined contributions to the whole-rock magnetic fabric

Martin Chadima

The interpretation of magnetic fabric (studied mainly by means of anisotropy of magnetic susceptibility) has become one of the well-established, fast, and reliable rock fabric proxies used in many branches of the Earth science. In the usual case, the magnetic fabric ellipsoid reflects the crystallographic or shape preferred orientation of the grains of the main rock-constituent mineral. If two (or more) sets of mineral grains are present, their combined contribution towards the whole-rock magnetic fabric is proportional to their relative content, their value of bulk susceptibility and their degree of anisotropy. This can be the case of, for example, combined contribution of differently oriented paramagnetic and ferromagnetic sub-fabrics, normal and inverse magnetic fabric, or anisotropic fabric and isotropic matrix. In order to overcome some misconception on how various magnetic fabrics can contribute to the overall rock fabric, we present a simple toolbox for visualizing a combined contribution of two pre-defined end-member magnetic sub-fabrics. These end-member fabrics are defined by their bulk susceptibility, degree of anisotropy, shape of anisotropy ellipsoid and the orientations of its principal directions. The toolbox is part of Anisoft software which enables the instant visualization how magnetic fabric changes as a function of the relative content of the end-member sub-fabrics.

How to cite: Chadima, M.: A simple toolbox for evaluating the combined contributions to the whole-rock magnetic fabric, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17170, https://doi.org/10.5194/egusphere-egu23-17170, 2023.

Posters virtual: Wed, 26 Apr, 08:30–10:15 | vHall TS/EMRP

The posters scheduled for virtual presentation are visible in Gather.Town. Attendees are asked to meet the authors during the scheduled attendance time for live video chats. If authors uploaded their presentation files, these files are also linked from the abstracts below, but only on the day of the poster session. The button to access Gather.Town appears just before the time block starts.

Chairpersons: Martin Chadima, Lennart de Groot

vTE.15

EGU23-12219

ECS

Virtual presentation

Deciphering the variation of magnetic fabric intensity across the Main Central Thrust in Garhwal Himalayas

Asha Borgohain, Pradeep Gairola, Sandeep Bhatt, Virendra Rana, and Sayandeep Banerjee

One of the key aspects of understanding the rapid exhumation of Himalayan core, is to understand the variation of deformation intensity occurring along the major tectonic unit i.e., the Main Central Thrust (MCT). Quantification of magnetic fabrics, derived from analysis of anisotropy of magnetic susceptibility (AMS), defines the strain path in the form of an ellipsoid and provides a rich source of information on the structural evolution of rocks throughout the MCT. The approach of this study is to integrate field and AMS parameters, where field foliation from 73 planes has orientation trending NW-SE with a moderate dip of about 60⁰(best fit great circle) The magnetic foliation is found to be parallel to the field foliation. Variation in orientation direction of magnetic lineation implies the dominance of superposed folding in the study area. The degree of anisotropy (P_j), which quantifies the intensity of preferred orientation of magnetic minerals show values ranging from 1.1 to 1.8. The AMS study reveals that the shape parameter(T) of susceptibility ellipsoid, in most of the samples are positive representing an oblate ellipsoid. To be more precise, this study reflects the inter-relationship between field structures, superposed folding, magnetic fabric parameters to understand the exhumation of Himalayan core.

How to cite: Borgohain, A., Gairola, P., Bhatt, S., Rana, V., and Banerjee, S.: Deciphering the variation of magnetic fabric intensity across the Main Central Thrust in Garhwal Himalayas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12219, https://doi.org/10.5194/egusphere-egu23-12219, 2023.

vTE.16

EGU23-1000

ECS

Virtual presentation

Lava-water interaction and formation of associated facies: a multidisciplinary study of the San Bartolo lava flow of Stromboli

Rasia Shajahan, Elena Zanella, Andrew J L Harris, Lodovico Drovanti, Claudio Robustelli Test, Sonia Calvari, Lucia Gurioli, Sara Mana, and Benjamin van Wyk de Vries

Detailed rock magnetic, facies and textural analyses were carried out across the San Bartolo lava flow (Stromboli) to understand the flow dynamics of lava channel-fed 'a'a entering the water. Having been emplaced 3 ka, San Bartolo is the most recent lava flow field to have been emplaced beyond the Sciara del Fuoco, and underlies the inhabited area on the north-eastern side of the island. One of the remarkable features of the San Bartolo lava flow is the formation of several lobes due to the interaction with seawater. Field analysis shows three facies: 1. Stalling of flow fronts at the coastal interaction to form a littoral barrier to further flow, 2. Ramping of subsequently emplaced units behind this barrier, and creation of a degassed ponded volume, 3. Creation of tubes through the barrier to feed a seaward bench of pahoehoe. Around 12 lobes were identified. All the lobes show similar facies, but each lobe provides a case-type example of the emplacement history and the associated structures. For example, lobe 1 exhibits tube formation associated through the flow front barrier; while lobe 12 shows the formation of inflated pahoehoe lava. Preliminary AMS results show well-confined flow fabrics with a one-to-one relationship to field structures. The samples collected from ramped flow have vertical flow fabrics, while those from tube structures and inflated pahoehoe have horizontal fabrics. Preliminary palaeomagnetic data have characteristic remanent magnetisation (ChRM) directions for all the sampled lobes, with their a₉₅ overlapping, suggesting rapid emplacement. In addition, the average ChRM direction falls in the geocentric axial dipole (GAD) field for Stromboli.

How to cite: Shajahan, R., Zanella, E., Harris, A. J. L., Drovanti, L., Robustelli Test, C., Calvari, S., Gurioli, L., Mana, S., and van Wyk de Vries, B.: Lava-water interaction and formation of associated facies: a multidisciplinary study of the San Bartolo lava flow of Stromboli, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1000, https://doi.org/10.5194/egusphere-egu23-1000, 2023.

vTE.17

EGU23-14498

ECS

Virtual presentation

Deformation model of the Cheka pluton of alkaline granitoids: petromagnetic and geochemical data (Southern Urals)

Petr Shestakov, Alexander Tevelev, Alexey Kazansky, Natalia Pravikova, Egor Koptev, Ekaterina Volodina, and Alexandra Borisenko

Introduction. This study investigates the Cheka block (pluton) of alkaline granitoids (Southern Urals, Chelyabinsk Oblast). The objective of this study was to further investigate its existing deformation model after previous studies though the methods of fracture analysis, petromagnetic studies and geochemical analysis.

The Cheka pluton is composed of the Cheka Mountain and has a meridional strike and dimensions of 6.5 km long and 1-2 km wide. The pluton is composed of alkaline rocks of three intrusion phases: first – monzodiorites, second – alkaline syenites, third – alkaline granites and granosyenites. The pluton is Triassic and intrudes Carboniferous volcanics. The western contact of the Cheka pluton is limited by a dextral fault. The pluton is situated in the Magnitogorsk zone.

During the formation of the pluton, extension changed to compression. This led to formation of a right-lateral transpression setting with a system of meridional strike-slip and near-slip extension zones. These changes were followed by low-grade metamorphism.

This study can be split into two sections: structural analysis and geochemical/isotopes description. The first part was partially conducted previously and presented in 2022.

Materials and methods. To reconstruct structural evolution of the pluton a combination of petromagnetic studies, magnetic mineralogy and fracture analysis were used as well as supporting aerial and satellite imagery. 62 core samples and over 180 fracture measurements from 7 locations were used for each method respectively. Petromagnetic data was collected by drilling procedures, processed using MFK-1 kappabridge at room temperature and after heating to 470 °C and analyzed in Anisoft 5.1.08 software. Magnetic mineralogy lab analyses were performed with interpretation using Max UnMix software. Fracture analysis was conducted in Stereonet v.11.3.0.

As the second part of the study geochemical analyses were conducted – silicate geochemistry and ICP-MS at 6 locations.

Results and discussion. Petromagetic studies showed the magma flow to have an orientation of 036°. Analysis of tectonic fractures points to the Riedel fracture model with main fracture zone orientation (compression) of 039°. Since the magma flow and compression orientation match a deformation model can be constructed. Also based on the magma flow orientation, types of protectonic fractures were identified (S, Q, L).

Geochemical analyses showed that the elemental signature of the pluton matches the upper crust the best and shows signs of subduction. Silicate geochemistry shows a clear trend in Na₂O concentration, while K₂O concentrations do not. This pattern is interpreted as a sign of low-grade metamorphism (prehnite-pumpellyite facies).

A full deformation model was created based on two methods with additional supporting data providing strong evidence for the Riedel based deformation model, which corresponds to previous structural and geochemical findings. The model suggests that the Cheka pluton was formed in a general right-lateral transpression setting with following tectonic developments and related low-grade metamorphism.

Financial support. The reported study was funded by RFBR and Czech Science Foundation according to the research project № 19-55-26009. Centre of collective usage ‘Geoportal’, Lomonosov Moscow State University (MSU), provided access to remote sensing data.

How to cite: Shestakov, P., Tevelev, A., Kazansky, A., Pravikova, N., Koptev, E., Volodina, E., and Borisenko, A.: Deformation model of the Cheka pluton of alkaline granitoids: petromagnetic and geochemical data (Southern Urals), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14498, https://doi.org/10.5194/egusphere-egu23-14498, 2023.

vTE.18

EGU23-17243

Virtual presentation

Preliminary rock magnetic and anisotropy of magnetic susceptibility results from the Reykjanes Ridge basalts, Atlantic Ocean (IODP Expeditions 384 and 395C)

Sara Satolli, Anita Di Chiara, and Sarah Friedman

The Reykjanes Ridge is located in the North Atlantic Ocean, southwest of Iceland. Here, the oceanic crust is characterized by a series of V-shaped ridges (VSRs) and V-shaped troughs (VSTs), the formation of which has been linked to three alternative hypotheses: i) thermal pulsing, ii) propagating rifts, and iii) buoyant mantle upwelling. During International Ocean Discovery Program Expeditions 384 and 395C, a transect of five sites were drilled eastwards of the modern Mid-Atlantic Ridge (between 20-30°W) at a latitude of ~60°N, to investigate VSTs/VSRs formation.

In this preliminary study, we analyze basalt samples from four sites, two from VSRs and two from VSTs, using rock magnetic and anisotropy of magnetic susceptibility (AMS) techniques, to investigate the differences between VSRs and VSTs. We analyzed the samples at the CIMaN-ALP (Peveragno) and INGV (Rome) Laboratories of paleomagnetism through bulk susceptibility, AMS, stepwise demagnetization of natural remanent magnetization through alternating field and temperature, hysteresis loops and FORC diagrams, and susceptibility vs temperature curves. Rock magnetism was used to determine the rock magnetic properties of each sample and investigate its correlation with the degree of alteration observed in the basalts. The AMS was measured to determine the magnetic fabric as a proxy of the magmatic fabric, where, for instance, lava flow-like fabric would be typical of an unaltered basalt.

Preliminary results suggest that basalts from VSTs are generally characterized by higher susceptibility values, while the AMS shows a mixed behavior (well defined or dispersed) independently from the structural position. Further rock magnetic data, integrated with petrological, structural and geochemical data will be correlated to the pervasiveness of alteration in each site, the age of basalts and their distance from the Mid-Atlantic Ridge to test the three hypotheses.

How to cite: Satolli, S., Di Chiara, A., and Friedman, S.: Preliminary rock magnetic and anisotropy of magnetic susceptibility results from the Reykjanes Ridge basalts, Atlantic Ocean (IODP Expeditions 384 and 395C), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17243, https://doi.org/10.5194/egusphere-egu23-17243, 2023.