The Ediacaran apparent polar wander path for the Rio de la Plata Craton was analyzed and a new alternative path is presented. This revised path was constructed considering an opposite polarity for poles older than ca. 590 Ma. This path is more consistent with that recently proposed for West Africa, whose large oscillations were attributed to two events of inertial interchange true polar wander (IITPW). A compilation and selection of Ediacaran paleomagnetic data from the main cratons were analyzed leading to a set of global paleogeographic reconstructions throughout the Ediacaran. This model assumes that a “Clymene Ocean” existed between Central Gondwana and West Africa – Amazonia along this period. All cratons with reliable paleomagnetic information, share similar motions during two time-intervals. The first one (615-590 Ma) can be described by rotation around an Euler pole located in the equator, while the second one (575-565 Ma) by another around an Euler pole on the tropics. Whether these apparent large and fast displacements can be assigned to IITPW events is discussed along with the consistency of considering a large Clymene Ocean during this time.

How to cite: Cukjati, A., Franceschinis, P., Arrouy, M. J., Gómez-Peral, L., Poiré, D., Trindade, R., and Rapalini, A.: The Ediacaran Apparent Polar Wander Path of the Río de la Plata craton revisited: Paleogeographic implications., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-463, https://doi.org/10.5194/egusphere-egu24-463, 2024.

The Central High Atlas is the Moroccan segment of the Atlas System, which is the largest intraplate mountain range in North Africa. The Mesozoic evolution of the High Atlas is related with extensional tectonics, magmatic activity, and salt tectonics. It primarily consists of basins developed during the Triassic and Jurassic that underwent inversion during the Cenozoic. The region exhibits dominant NE-SW and ENE-WSW trending folds, intertwined with smaller-scale oblique or perpendicular folds.

Previous paleomagnetic investigations have revealed that sedimentary Jurassic rocks (both carbonates and red beds) in the Central High Atlas are affected by a Cretaceous regional remagnetization. This interfolding remagnetization, occurred after the syn-sedimentary tectonic extensional stage but before the Cenozoic basin inversion linked to the convergence between the African and European plates. The reference of remagnetization direction has been determined using the Small Circle Intersection (SCI) technique and, by comparing it with the African Aparent Polar Wander Path (APWP), has been dated to approximately 100 million years (Ma), representing a synchronous phenomenon across the entire High Atlas. Once the reference is stablished, paleomagnetic data can be used to calculate the paleobedding of each site at the remagnetization time (i.e. between extension and compressional stages) and to restore the structure at 100 Ma. This procedure allows to quantitatively separate the compressional imprint from the extensional one in the present-day structure.

This work presents a high-resolution paleomagnetic study in the Anemzi syncline area, encompassing 91 sites within the paradigmatic structures of the Central High Atlas, covering an area of 35 km². The Anemzi syncline features a southern limb bounding with a vertical set of Jurassic intrusive bodies and Triassic shales and basalts, while the northern limb exhibits Lower Jurassic carbonates overthrusting northwards Middle Jurassic rocks.

By applying Small Circle analysis to remagnetization directions, 91 paleobeddings corresponding to the age of remagnetization (i.e., 100 Ma) were determined. These paleobeddings were employed to construct seriated geological cross-sections, depicting the structural architecture 100 Ma ago. These cross-sections were then compared with their present-day counterparts. Both series of cross-sections were the base to develop two 3D geological models, showcasing the present-day and restored structures at 100 Ma, integrating both paleomagnetic results and structural data.

Comparisons between palinspastic and present-day cross-sections and 3D models provide insights into the evolution of the Central High Atlas, spanning both the basinal stage and subsequent inversion. This comparative analysis offers valuable clues for understanding the significance of inherited extensional structures (such as normal faults, gabbro intrusion, diapirism, etc.) in the context of compressional structuring.

How to cite: Yenes, L., Calvín, P., Santolaria, P., Villalaín, J. J., and Marcén, M.: A 3D Cretaceous palinspastic model from paleomagnetic data in the Central High Atlas (Morocco), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16117, https://doi.org/10.5194/egusphere-egu24-16117, 2024.

The Xigaze forearc basin was formed along the southern margin of Asia as the Neo-Tethys Ocean subducted beneath Asia. Among the strata within the Xigaze forearc basin, the Padana Formation (Fm) comprises purple-red and gray shale interbedded with sandstone, and likely holds crucial evolution information of the southern Asian margin during the Late Cretaceous prior to the India-Asia collision. However, the chronology of the Padana Fm has not been well constrained. To refine the chronology of the Padana Fm and better constrain the paleopositions of the southern margin of Asia, we conducted a paleomagnetic study of the strata in the Xigaze forearc basin, with a particular focus on the Padana Fm. A total of 263 paleomagnetic samples were collected and subjected to stepwise thermal demagnetization, revealing two-component magnetizations. The low temperature component (LTC) was removed by ~300℃, representing overprints of the present geomagnetic field. The high-temperature component (HTC) was typically unblocked at 580∼680 °C, indicating magnetite and hematite as major remanence carriers. A total of 110 reliable HTCs were isolated from the sandstones in the Padana Fm and passed reversal tests, representing primary remanence. Changes in polarities of the HTCs with stratigraphic heights define four polarity zones, which, together with results of previous detrital zircon U-Pb ages and biostratigraphic zones, allow to constrain the chronology of the Padana Fm to 83.6 Ma-69.2 Ma. With the significantly refined chronology, the paleomagnetic data of the Padana Fm can be used to constrain the tectonic evolution of the Xigaze forearc basin in the Late Cretaceous. Tentative interpretations of the coeval paleogeography of the southern Asian margin prior to the India-Asia collision will be discussed.

How to cite: Xu, S., Li, Y.-X., Liu, X., Li, B., and Li, X.: Paleomagnetism of the Late Cretaceous Padana Fm in Xigaze forearc basin and its paleogeographic constraints on the southern margin of Asia prior to the India-Asia Collision, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17916, https://doi.org/10.5194/egusphere-egu24-17916, 2024.

Abstract:

The Deccan Continental flood basalts (DCFB) are associated with three major dyke swarms: the Narmada-Satpura-Tapi (N-S-T), the Western Coastal and the Nasik-Pune dyke swarm. The DCFB around Pachmarhi is characterized by a lower Magnesium number (Mg#) and higher TiO₂ content, suggesting more evolved Deccan basalts compared to others. Approximately 244 mappable doleritic and basaltic dykes around Pachmarhi, located in the eastern part of the N-S-T dykes within the DCFB, have lengths ranging from 140 m to 22 km, with a mean of ~5.15 km. The Pachmarhi dyke swarms exhibit emplacement within preexisting fractures, with a discernible preferred orientation aligning at ~N82°E, roughly following an ~E-W trending trajectory. This alignment corresponds to the general trend of the Narmada-Son lineament (NSL) and is perpendicular to the direction of the minimum horizontal stress (σ₃). This σ₃ direction aligns with the ~N-S trending paleoextension during the period of dyke emplacement. Selected dykes in Pachmarhi have been studied using the Anisotropy of Magnetic Susceptibility (AMS) technique. The primary aim is to determine the direction and sense of magma flow within the dykes, providing insights into the depth, number, and spatial distribution of magma chambers and their potential association with the mantle plume. The Rock magnetic studies on the Pachmarhi dykes have unveiled the presence of high-titanium magnetite particles, predominantly of Pseudo-Single Domain (PSD) nature, with a lesser proportion of Multi-Domain (MD) grains.

To ascertain the direction and sense of magma flow in dyke margins with oblate fabric, the imbrication of the magnetic foliation plane (dip and strike of the K₁-K₂ plane) has been employed. For dyke margins exhibiting prolate fabric, the imbrication of the magnetic lineation (plunge of the K₁ axis) has been utilized. However, in cases where one dyke margin features an oblate ellipsoid and the other a prolate ellipsoid, the imbrication of the magnetic foliation is used for the former, while the imbrication of the magnetic lineation is used for the latter. This thorough analysis has revealed multiple trends of magma flow ranging from vertical/sub-vertical to inclined suggesting that most of the dykes were close to the magma sources, with just a single dyke exhibiting a sub-horizontal flow pattern, based on the angle measurements from the horizontal.

The intersection of imbrication within the margins of each dyke provides valuable information about the flow geometry of the area, suggesting the presence of multiple shallow subcrustal magma chambers. This finding aligns with earlier confirmations through structural attributes (length and thickness of dykes) by quantifying the magmatic overpressure and the source depth of the magma chamber of the Pachmarhi dykes and Nandurbar-Dhule dykes. The multiple trends of flow indicate a polycentric flow pattern for the Pachmarhi dykes, similar to the Nandurbar-Dhule dyke swarms in the western region of the N-S-T dykes. Consequently, it can be inferred that the emplacement of dykes in the NSL region was primarily facilitated by a "polycentric flow" mechanism through sub-crustal magma chambers, whereby magma was injected through crustal fissures, resulting in a significant volume of magma being generated in the DCFB.

How to cite: Shukla, G., Mallik, J., Krishna, Y., and Banerjee, S.: Fissure-Driven Volcanic Processes in the Deccan Province arising from Shallow Subcrustal Magma Chambers: conclusions derived from the magnetic fabric examination of the Pachmarhi Dyke Swarm, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-283, https://doi.org/10.5194/egusphere-egu24-283, 2024.

New demagnetization results of 53 independently oriented palaeomagnetic samples (145 specimens) of diamictite-rich units from 8 sites collected from the Neoproterozoic sequence of Murchisonfjord, Western Nordaustlandet are presented. The palaeomagnetic samples were obtained from 2 distinct stratigraphical units of Polarisbreen Group: Petrovbreen Member of Elbobreen Formation (2 sites) and Wilsonbreen Formation (6 sites) which represent Marinoan Neoproterozoic glaciation (Halverson et al. 2004). The sequence is a part of Eastern Svalbard Caledonian Terrane/Northeastern Basement Province.

Principal component analyses revealed strong contribution of post-folding high-inclination palaeomagnetic component TILL L/M demagnetized up to 320°C (D = 32.3°, I = 83.6°,  α95=6.6, κ=103.7 recognized in 6 sites, in 35 independently oriented samples and in 77 demagnetized specimens). Calculated paleopole TILL L/M (Φ = 83.24°, Λ = 114.0°; Dp/Dm = 12.7°/13.0°) fall into Late Cretaceous – Paleogene – Neogene sector of Baltica Apparent Polar Wander Path (Torsvik et al. 2012). That suggests a possible relation of TILL L/M remagnetization with Late Cretaceous Svalbard magmatism (e.g. Senger et al. 2014). Great circle analyses point to the additional contribution of low-inclination component, potentially related to Caledonian remagnetization (compare Michalski et al. 2023). At this data processing stage, in investigated tillites no pre-Caledonian paleomagnetic record was recognized. Preliminary rock-magnetic results suggest the presence of maghemite and magnetite. Paleomagnetic, rock-magnetic as well as investigations of Anisotropy of Magnetic Susceptibility (AMS) were conducted at the Laboratory of Palaeomagnetism Department of Magnetism Institute of Geophysics, Polish Academy of Sciences.

All investigated tillites were subjected detailed petrographic and mineralogical observations (reflected /transmitted light microscopy, scanning electron microscopy – SEM, electron microprobe) at the University of Warsaw Inter – Institute Analytical Complex, in the Faculty of Geology and at the Uppsala University in the Department of Earth Sciences. Separated detrital zircons is being subjected to U-Pb dating at the Department of Geological Processes, Czech Academy of Sciences.

This study is part of the NEOMAGRATE project 2022–2025: “Rate of tectonic plates movement in Neoproterozoic – verification of Neoproterozoic True Polar Wander hypothesis”, funded by the Polish National Science Centre (NSC); grant number:2021/41/B/ST10/02390.

References:

Halverson, G.P., Maloof, A.C. and Hoffman, P.F. 2004. The Marinoan glaciations (Neoproterozoic) in northeast Svalbard. Basin Research, 16, 297-324.

Michalski, K., Manby, G.M., Nejbert, K., Domańska-Siuda, J. and Burzyński, M. 2023. Palaeomagnetic investigations across Hinlopenstretet border zone: from Caledonian metamorphosed rocks of Ny Friesland to foreland facies of Nordaustlandet (NE Svalbard). Journal of the Geological Society, 180.

Senger, K., Tveranger, J., Ogata, K., Braathen, A. And Planke, S. 2014. Late Mesozoic magmatism in Svalbard: A revive. Earth-Science Revievs, 139, 123-144.

Torsvik, T.H., Van der Voo, R., Preeden, U., Mac Niocaill, C., Steinberger, B., Doubrovine, P.V., van Hinsbergen, D.J.J., Domeier, M., Gaina, C., Tohver, E., Meert, J.G., McCausland, P.J.A. and Cocks, L.R.M. 2012. Phanerozoic polar wander, paleogeography and dynamics. Earth-Science Reviews, 114, 325–368.

How to cite: Bal, S., Michalski, K., Manby, G., Nejbert, K., Majka, J., Domańska-Siuda, J., and Hołda-Michalska, A.: New palaeomagnetic data from tillites of Neoproterozoic Polarisbreen Group, Nordaustlandet, Svalbard, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16032, https://doi.org/10.5194/egusphere-egu24-16032, 2024.

Large volumes of mantle peridotite are exposed at the Earth’s surface in ophiolites, becoming vulnerable to the concurrent chemical alteration processes of serpentinization and carbonation. Serpentinization frequently results in the production of secondary magnetite that records the direction of the Earth’s magnetic field at the time of its formation, allowing paleomagnetism to be used as a tool to investigate this process. 

Many ophiolites also experienced large-scale tectonic rotations during their evolution. In some cases, the timing of these rotations is well-documented paleomagnetically, potentially allowing the timing of different phases of serpentinization to be constrained if the magnetization directions of secondary magnetite assemblages can be determined and compared to known rotation histories. Here we present the first attempt to combine paleomagnetic analysis with Quantum Diamond Microscopy (QDM) observations of individual magnetic grain assemblages to test whether sequential phases of alteration can be dated in serpentinized peridotites in this way. 

We focus on the Late Cretaceous Troodos ophiolite of Cyprus that underwent a ~90 CCW tectonic rotation that began shortly after it formed by seafloor spreading. The timing of this rotation is well-constrained by paleomagnetic analysis of the sedimentary rocks that were deposited continuously while the underlying oceanic crust rotated. In this context, different magnetization directions would be expected to be carried by magnetite assemblages produced by serpentinization during: (i) early exposure on the seafloor or deep fluid circulation during Late Cretaceous seafloor spreading; (ii) subsequent progressive tectonic rotation; and (iii) Plio-Quaternary to Recent tectonic uplift and/or reaction with modern meteoric water.

Magnetization directions within the Troodos serpentinites are shown to be highly variable, and include: (i) samples carrying W-directed, high-coercivity components, inferred to be acquired in the Late Cretaceous, and NNW-N-directed, low-coercivity overprints, inferred to be acquired post-rotation; (ii) samples with single component, NW-directed magnetizations, inferred to have been acquired partway through the rotation; (iii) samples with single component, N-directed magnetizations inferred to have been acquired post-rotation; and (iv) one site where samples exhibit antipodal normal and reversed polarity, N-S-directed magnetizations inferred to have been acquired post-rotation but before the Brunhes-Matuyama reversal (780 ka). Overall, these data demonstrate that serpentinization occurred throughout the entire history of the Troodos Ophiolite, with six sites showing evidence of serpentinization in the Late Cretaceous or partway through the rotation and six sites where serpentinization occurred post-rotation from the Eocene to the present day. QDM data from one site where samples exhibit a W-directed ChRM and a NNW-N-directed overprint confirm that all observed magnetite associated with serpentine veins carries the early ChRM, inferred to be acquired during the Late Cretaceous. The source of the low stability component in these samples was not observed in QDM images and remains elusive, but is interpreted to be a modern magnetic overprint.

How to cite: Hepworth, J., Morris, A., Harris, M., Brenner, A., Fu, R., Harrison, R., and Schwarzenbach, E.: Novel paleomagnetic insights into the timing of serpentinization of peridotites in the Troodos ophiolite, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11793, https://doi.org/10.5194/egusphere-egu24-11793, 2024.

The Qaidam Block, situated in the North Tibetan Plateau, is the nexus of the Tarim and North China Blocks. Since the scarcity of geological records documenting the collision age between the Qaidam and Tarim Blocks, the drift history of the Qaidam Block becomes imperative for gaining insights into the formation of East Eurasia. In this study, rock magnetic and paleomagnetic studies were performed on the early Carboniferous sedimentary rocks in the Huaitoutala area. A stable characteristic remanent magnetization component, carried by magnetite, was isolated from 24 sites (204 samples). This component passed the fold tests at a high level a mean yielding the paleopole position at λ=-24.9°N, φ=123.7°E, A₉₅=3.9°. It corresponds to a paleolatitude of ~22.5°N for the QB about 350 Ma. Combined with paleomagnetic data and geological evidence from Qaidam Block and its adjacent regions, we suggest that a convergence between the Qaidam Block and the North China Block at 430-400 Ma, subsequently merged with the Tarim Block at approximately 260-250 Ma.

How to cite: Chai, R., Zhou, Y., and Wu, H.: New Early Carboniferous paleomagnetic results from the Qaidam Block, Northern Tibetan Plateau, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2358, https://doi.org/10.5194/egusphere-egu24-2358, 2024.

The Leqingla deposit serves as a representative skarn-type Pb-Zn deposit in the Gangdese polymetallic belt, South Tibet, China. Although numerous studies have been conducted on this deposit, there is no consensus about its specific genesis, particularly concerning the timing of mineralization. Recent studies indicate that paleomagnetic dating techniques, employed on newly formed magnetic carrier associated with mineralized fluids, permit precise determination of mineralization timing. Hence, a systematic paleomagnetic and petrologic investigation was conducted on the host rock of the Leqingla deposit, which is characterized by the middle Permian Luobadui Formation sandstone. The results reveal that the dominant magnetic carrier in the host rock is hydrothermal authigenic pyrrhotite. The stable characteristic remanent components display maximum clustering when flattened to -5.5% ± 13.5% after tilt corrected. The obtained paleomagnetic pole (P_lat = 74.5°N, P_long = 222.5°E, at N = 8, A₉₅ = 2.9°) is consistent with that of the Pana Formation volcanic rock in the same area. Further combined with the chronological and geological evidences, we refer that the hydrothermal authigenic pyrrhotite in the host rock may record chemical remagnetization information acquired between 54-47 Ma. The magmatic activity (54-47 Ma) induced by the India-Asia collision is closely related to remagnetization and the formation of the Leqingla deposit.

How to cite: Xing, L., Cheng, X., and Wu, H.: Paleomagnetic Dating Constraints on the Genesis of the Leqingla Pb-Zn Deposit, South Tibet, China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2854, https://doi.org/10.5194/egusphere-egu24-2854, 2024.

We present an analysis of paleomagnetic data from Cenozoic sedimentary rocks of the northern Junggar Block in central Asia to assess if the northern Junggar Block has suffered vertical axis rotations with respect to stable Eurasia. Stepwise thermal demagnetizations isolated a stable high-temperature component of magnetization in most specimens, which we interpret as the primary magnetization from the positive reversal test. Based on high-resolution magnetostratigraphic studies (Zhang et al., 2007, 2012), we calculated the mean direction of each 5 Myrs of 44-30 Ma and 25-17 Ma covered by the sample age and yielded seven mean directions in 45-37.5 Ma, 40-35 Ma, 37.5-32.5 Ma, 35-30 Ma, 25-20 Ma, 22.5-17.5 Ma, respectively. The variation between the observed declination from the study area and the reference declination from Eurasia indicates that a local counterclockwise rotation of 18.8 ± 11.4° took place during 40±2.5 - 35±2.5 Ma. Together with the paleomagnetic data during 23-3.1 Ma in the southern part of the Junggar Basin (Charreau et al., 2005, 2009), it can be concluded that Junggar Block experienced local counterclockwise rotation with respect to the Eurasia in the piedmont of the north and south rim successively due to the strike-slip fault. At a larger scale, the blocks in the Central Asia Right–Slip Fault Zone have experienced tectonic rotation at different times under the far-field effect of India-Eurasia collision, that is, formed an overall counterclockwise vertical axis rotation mode of different stages because of strike-slip faulting.

How to cite: Zhong, M., Kravchinsky, V., Zhang, R., and Cheng, X.: The localized rotations in Junggar Block for the last 50 Myr: new paleomagnetic constraints , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10116, https://doi.org/10.5194/egusphere-egu24-10116, 2024.