Magnetostratigraphy Research Articles

Applications of paleomagnetism and rock magnetism in understanding volcanic processes and timescales: perspectives to Korean volcanological research

Applications of paleomagnetism and rock magnetism in understanding volcanic processes and timescales: perspectives to Korean volcanological research

Volcanomagnetic signals related to the 2021 Tajogaite volcanic eruption in the Cumbre Vieja rift (La Palma, Canary Islands)

After almost 50 years of quiescence, the Cumbre Vieja rift in La Palma underwent a reactivation process that culminated in the eruption of the Tajogaite volcano from September 19 to December 13, 2021. In July 2021, a magnetic station (CFU) was deployed in the western flank of the Cumbre Vieja rift, 2 km away from the site where the eruptive vents would open two months later. In September 2021, a second magnetic station (SAN) was installed near the southern end of the rift. In this paper we study two months of geomagnetic data at CFU before the eruption and three months of geomagnetic data at SAN during the eruption. The analysis of these time series revealed a magnetic signal at the CFU station with an amplitude of 10 nT and a duration of 10 days by mid-August, one month before the eruption onset. We studied possible correlations with other physical parameters (ground deformation, long-period and very-long-period seismic activity) and concluded that this signal could be related to changes in the magnetization of rocks beneath the volcanic edifice caused by magma intrusion and volcanic/hydrothermal fluids circulation preceding the eruption. At the SAN magnetic station, the time series suggests that a slight decrease in the geomagnetic field could reflect the end of the eruptive process.

Imaging and modelling the subsurface structure of the Rungwe Volcanic Province in SW Tanzania with aeromagnetic data: An improved structural map to support geothermal exploration

The Rungwe Volcanic Province (RVP) in the East African Rift System, SW Tanzania, provides a unique opportunity to investigate geothermal resources in the context of particularly complex continental rifting processes. To support geothermal resource targeting in the RVP, we present a revised neotectonic structural map based on an interpretation of aeromagnetic data constrained by 2D-forward modelling of magnetic anomalies integrated with the distribution of previously reported faults, seismic epicentre locations, 3D magnetotelluric resistivity models and surface geothermal manifestations. Magnetic anomalies in the RVP, including the nationally prominent Mbeya anomaly, are related to the high magnetic susceptibility or remanent magnetism of Precambrian rocks and Cretaceous carbonatite intrusions buried in the rift under a varying thickness of non-magnetic sediments and volcanic rocks. Magnetic lineaments are related to structures controlling the geometry of the Precambrian rocks and concealed dikes and the thickness of the sediments and volcanics. The recent Ngozi and Rungwe trachyte volcanics have relatively low magnetic susceptibility comparable to the low susceptibility of the sediments in the rift basins. The revised neotectonic structural map shows prominent NW, NE and NS-trending magnetic lineaments that correlate with previously reported faults and alignments of seismic epicentres in the study area and with the regional trend of the rift segments. The NE-trending magnetic lineaments are consistent with interpretations of the current stress field in the RVP. The main volcanoes in the RVP, Ngozi, Rungwe and Kiejo (also known as Kyejo and Kieyo), are aligned with the NW-trending linear magnetic feature joining the Lupa and Livingstone rift border faults. This lineament is intersected and frequently displaced by the NE and NS-trending lineaments, suggesting that the NE to NS-striking structures are younger. The Rungwe and Ngozi volcanoes as well as numerous ‘’monogenetic’’ eruption centres and the Mwakaleli caldera, which originated ca. 2 Ma ago (Ebinger et al., 1989) following a large explosive eruption emplacing widespread ignimbrite deposits, are located within a zone of low-intermediate magnitude magnetic features forming a basin-like structure surrounded by magnetic high anomalies of the Precambrian basement structures. We interpret the intersections between the NW-trending intra-rift faults and the NS and NE-trending faults as favourable locations for wells to target high permeability within the geothermal resource conceptual models previously constructed using 3D MT resistivity imaging integrated with supporting geoscientific data. The intersections provide a focus area for follow-up ground mapping of subtle features that may be associated with very recent fault movement.

Application of remote sensing and electrical resistivity technique for delineating groundwater potential in North Western Nigeria

Improving the living condition of residents of Palladan and Basawa community requires access to drinking water. The main objectives of this paper are to identify suitable groundwater zones for productive drilling and to assess groundwater mineralization in the coastal aquifers of the study area. Geographic Information Systems (GIS) and Analytical Hierarchy Process (AHP) were used in the methodology to generate the groundwater potential map. Slope, landcover/land use, lineament density, rainfall, soil cover and drainage density were taken into account to characterize the groundwater potential zones. Weights were assigned to the various parameters and their characteristics according to their impact on groundwater recharge. The groundwater potential map was classified into five zones namely: poor, fair, moderate, good, excellent. Based on the lineament density map, the distribution of these lineaments reveals the degree of porosity or permeability in each area and, consequently, its groundwater potential. Aeromagnetic data filtering permits the construction of a structural map that illustrates various geophysical lineaments that are known to be fault systems in the research area. These faults are the main routes via which groundwater seeps into the subsurface and granitoid-type magnetic rocks intrude into the basement. The research region is badly fractured/failed and made up of four lithologic units, including the aquifer layer (clayey sands in the cracked basement) with thicknesses varying from 12–55 m, according to the vertical electrical sounding (VES) applications. According to geoelectric cross-sections, the subsurface structures are made of granitic rocks that are surrounded by normal faults that trend both NW and NE. It is believed that groundwater flows into the hard rock aquifers in the studied locations through these notable geological features, such as faults and fractures. Two phenomena are responsible for the mineralization of water: a process of interaction between water and rock; and a process of salinization resulting from natural phenomena or anthropic activities. The present study could guide hydrogeological investigations and groundwater resource management planning in the study area.

Anisotropy of magnetic susceptibility and rock magnetism of high-grade rocks from Eastern Ghats Mobile Belt, India: Constraints to tectonics

Anisotropy of magnetic susceptibility and rock magnetism of high-grade rocks from Eastern Ghats Mobile Belt, India: Constraints to tectonics

Role of coal ash morphology and composition in delivery and transport of trace metals in the aquatic environment

Fly ash is predominately the inorganic byproduct of coal combustion for electrical power generation. It is composed of aluminosilicates with Fe, Mg, K, and Ca forming submicron to 100 μm spheres and amorphous particles. During combustion trace elements are incorporated into the heterogenous fine particles that can pose risks to the environment and human health. This study combines optical, rock magnetic, and geochemical analyses of fly ash originating from Appalachian coal to develop an integrated suite of environmental coal ash tracers. The non-magnetic portion of power plant fly ash has higher abundance of clear spheres and clear amorphous particles, combined with enrichment of As, B, Th, Ba, Li, Se, Cd, Pb, and Tl. The magnetic fraction is enriched in opaque and orange spheres and Cu, U, V, Mo, Cr, Ni, and Co. Plerospheres occur in either fraction. We investigated ash-bearing fluvial sediment from Emory-Clinch River system that was impacted by the instantaneous TVA spill in 2008 and Hyco Lake in North Carolina that was contaminated by chronic releases of fly ash since 1964. Five years after the TVA spill, most ash in the riverbed reflects one population with trace element concentrations proportional to percent total ash. This relationship does not hold for As and Se, volatile elements associated with the outer surface of clear spheres, which are affected by river transport. At Hyco Lake, small clear and opaque spheres correlate with trace elements released from storage ponds. The combination of trace elements, fly ash morphology and rock magnetism provides a powerful set of tools to assess the distribution of ash and potential impact on the environment. We conclude that dispersal of fly ash to the aquatic environment, especially small clear and opaque spheres, should be avoided in favor of dry landfills.

The Sierra Madre Oriental Orocline: Paleomagnetism of the Nazas Province in NE Mexico

AbstractCurved mountain belts are spectacular natural features that contain crucial 3D information about the tectonic evolution of orogenic systems in the absence of other kinematic markers. The Mesozoic units exposed in the Mexican Fold and Thrust Belt in northeastern Mexico show a striking curvature, whose kinematic history has not been studied. The existing tectonic models of the region simply assumed the shape of the tectonic units as an inherent feature to the orogen. We investigated the kinematic history of this curvature through paleomagnetism and rock magnetism analyses, coupled with an exhaustive review of available published literature. The studied data sets indicate a protracted history of (re)magnetizations that occurred during the Late Jurassic‐Paleocene times at least during the Late Jurassic, Cretaceous and early Eocene. More significantly, they show significant counterclockwise rotations in the northern flank of the curvature and moderate clockwise vertical axis rotations along its southern flank. This data set suggests that the Sierra Madre Oriental was a linear belt that experienced oroclinal bending or buckling during the Cretaceous to early Eocene period (120–50 Ma).

Remagnetization of Upper Triassic Limestone From the Central Lhasa Terrane (Tibet): Identification, Mechanisms, and Implications for Diagnosing Secondary Remanent Magnetization in Carbonate Rocks

Remagnetization of Upper Triassic Limestone From the Central Lhasa Terrane (Tibet): Identification, Mechanisms, and Implications for Diagnosing Secondary Remanent Magnetization in Carbonate Rocks

Paleomagnetism of mafic dykes in South Rewa Basin, India: Constraints to extension of Deccan volcanism

The magma source for mafic dykes from South Rewa Basin (SRB) in central India is invariably linked to Rajmahal volcanism (117 Ma) for Damodar, Raniganj-Jharia, and Bengal basin (Permian - Quaternary) to the east, and Deccan volcanism (66 Ma) for Satpura Basin to the west of SRB. However, the magmatic events linked to the SRB are not explicit. To ascertain the dyke association with these volcanic events, we performed a comprehensive paleomagnetic study on the exposed dykes and basalts from Shahdol region in SRB. Rock magnetism indicate that magnetite or titano-magnetite is the main remanence carrier mineral in these dykes. The measured directions produce a mean declination (Dm) of 338° and mean inclination (Im) of - 35° (α95= 8.4°, k = 25.3, N = 13), is close to Deccan normal directions. The calculated Pole position (λp) is at 42.02°N, and (Lp) is at 289.33°E, suggesting that the studied dykes are emplaced simultaneously along with Deccan Traps (36.96°N/78.70°W) and not of Rajmahal Traps (11.37°N/297.58°E). These dykes can be the result of multiple Deccan magma intrusions along the Narmada-Tapti lineament and intra-basinal faults in the SRB of central India.

Integration Of 3G Data (Geomagnetic, Gravity And Geology) To Identify Geothermal System Controlled By Geological Structure Of Telomoyo Plateau (Study Case Of Candi Umbul Area)

As the technology development, there are more and more new innovations that utilize existing resources to support the energy needs and to fulfill the consumer needs. The energy source that is being discussed at this time is geothermal energy. Geothermal energy sources are considered effective because they are renewable and environmentally friendly when compared to other energies such as fossil energy. In Indonesia itself, geologically, it has a complex series of volcanoes that can be used as a heat source in this new energy innovation. One area that thought to have geothermal potential is the telomoyo mountain area, which is indicated by the manifestation of hot springs on the surface, precisely around Candi Umbul. However, it is necessary to conduct subsurface studies to identify the presence of subsurface structures such as faults or intrusions as heat sources, where this can be overcome using geophysical methods. This research was conducted using the integration of two geophysical methods, namely the geomagnetic method to determine the direction of the fault continuity and the gravity method to determine the regional heat source, and in the other side geological data as a reference for interpretation. From geomagnetic measurements, 163 rock magnetism data were obtained which indicated the existence of a fault continuity with northeast-southwest orientation in the direction of the river flow and cut the manifestation of hot springs. Meanwhile, from 176 gravity topex data, a high complete boguer anomaly value was obtained as an indication of an intrusion in the northeast that was cut by the fault recorded in the geomagnetic data. Based on geophysical data analysis and correlation with geological data from previous studies, it can be assumed that there is a geothermal system in the study area with andesitic intrusion as the heat source, fault structure with northeast-southwest orientation as a weak zone for meteoric water migration, andesite lava as caprock, unit tuff rock as a reservoir and the telomoyo plateau as a recharge area to supply meteoric water from the geothermal system.

THE VARIATIONS OF CLINKER SUPERPARAMAGNETIC VALUE FROM PT. SEMEN PADANG BY USING A BARTINGTON MAGNETIC SUSCEPTIBILITY METER SENSOR TYPE B

Clinker is an important material in the cement making process. Before clinker is formed, the raw material is burned in a Rotary Kiln at a temperature of up to 1450°C, then cooled in a Greet Cooler to a temperature of 100°C and produces clinker. This research is to determine variations in the superparamagnetic value of clinker based on the magnetic susceptibility value. The method is the rock magnetism method using theMS2B. Clinker samples are takenhourly every day from the Semen Padang Factory. The 휒푙푓value obtained varies between 3.2×10-8m3/kg to 22.6×10-8m3/kg. The superparamagnetic values obtained also varied, ranging from 0.0%-7.4%. Based on the 휒푓푑%obtained, there were 136 clinker samples containing less than 10% superparamagnetic grains, and 32 samples includedthe 휒푓푑%medium had a percentage of 2%-10% where the samples contained superparamagnetic grains. Between 10% and 75% is a mixture of fine and coarse superparamagnetic grains.

New Rock Magnetism and Magnetic Fabrics Studies on the Late Triassic Volcanic Rocks from Qaidam Block, Northern Tibetan Plateau

The Qaidam Block, located at the northern Qinghai–Tibet Plateau, is a pivotal area in unraveling the closure time of the Kunlun Ocean basin which might have recorded the transformation process between the Proto-Tethys and Paleo-Tethys Ocean basins. However, the late Triassic position of the Qaidam Block remains enigmatic, largely due to the scarcity of paleomagnetic data essential for quantitatively determining its paleolatitude. The widespread presence of the Elashan formation, particularly along the southern periphery of the Qaidam block, presents good material for conducting paleomagnetic work. Nevertheless, the primary magnetic carriers preserved within the Elashan formation might be influenced by multiple tectonic thermal events, particularly those associated with collisions between southern blocks and the Qaidam Block. Here we present rock magnetism and magnetic fabrics studies to identify the content and composition of magnetic minerals within the Elashan formation. The rock magnetic and petrologic results show that the magnetic carriers in the samples from the Elashan formation are dominated by magnetite with a small amount of goethite, pyrrhotite, and hematite. The results of Anisotropy in Magnetic Susceptibility indicate that the south of the Longwalangku section might not be obviously influenced by the tectonic events. Our results also provided guidance for future paleomagnetic research, emphasizing the importance of conducting further sampling away from adjacent faults, particularly in the southern Longwalangku area.

Early–Middle Devonian paleomagnetic results from the Zhongba microterrane, Tibetan Plateau: Evidence for its origin from the northern margin of Greater India

Abstract The initial disintegration of Gondwana during the Paleozoic laid the foundation for the formation of the Tibetan Plateau in the Cenozoic. Determining the relative positions of the microterranes in Gondwana during the Paleozoic not only informs the subsequent drift and accretion processes of these microterranes but is also crucial to the paleogeographic reconstruction of Gondwana. However, the lack of paleomagnetic constraints on the Devonian paleogeography of the microterranes in the northern part of Gondwana makes this effort challenging. Here, we report paleomagnetic results for the first time from the Early–Middle Devonian sediments of the Zhongba microterrane. The site-mean direction is declination (Ds) = 310.7°, inclination (Is) = −67.2°, ks = 31.2, α95 = 8.3°, and n = 11, in stratigraphic coordinates. Positive fold and reversal tests, together with rock magnetism results and microscopic observations, strongly suggest that the remanence carriers are of depositional origin. The paleomagnetic results meet the paleomagnetic reliability criteria and therefore can be used for tectonic reconstructions. Our results constrain the paleolatitude of the Zhongba microterrane to be 50.0°S ± 11.7°S in the Early–Middle Devonian. Combined with published detrital zircon ages as well as paleomagnetic results and geological data, our data indicate that the Zhongba microterrane, which had no tectonic affinity with the Lhasa terrane, was part of the northern margin of Greater India during 408–388 Ma and coupled with the South Qiangtang terrane, Tethyan Himalayas, and other terranes to form the continuous northern continental margin of East Gondwana.

Possibility of Lunar Crustal Magmatism Producing Strong Crustal Magnetism

AbstractThe Moon generated a long‐lived core dynamo magnetic field, with intensities at least episodically reaching ∼10–100 μT during the period prior to ∼3.56 Ga. While magnetic anomalies observed within impact basins are likely attributable to the presence of impactor‐added metal, other anomalies such as those associated with lunar swirls are not as conclusively linked to exogenic materials. This has led to the hypothesis that some anomalies may be related to magmatic features such as dikes, sills, and laccoliths. However, basalts returned from the Apollo missions are magnetized too weakly to produce the required magnetization intensities (>0.5 A/m). Here, we test the hypothesis that subsolidus reduction of ilmenite within or adjacent to slowly cooled mafic intrusive bodies could locally enhance metallic FeNi contents within the lunar crust. We find that reduction within hypabyssal dikes with high‐Ti or low‐Ti mare basalt compositions can produce sufficient FeNi grains to carry the minimum >0.5 A/m magnetization intensity inferred for swirls, especially if ambient fields are >10 μT or if fine‐grained Fe‐Ni metals in the pseudo‐single domain grain size range are formed. Therefore, there exists a possibility that certain magnetic anomalies exhibiting various shapes such as linear, swarms, and elliptical patterns may be magmatic in origin. Our study highlights that the domain state of the magnetic carriers is an under‐appreciated factor in controlling a rock's magnetization intensity. The results of this study will help guide interpretations of lunar crustal field data acquired by future rovers that will traverse lunar magnetic anomalies.

Coupled Detachment Faulting and Hydrothermal Circulation at 49.7°E Southwest Indian Ridge Revealed by Seafloor Magnetism

AbstractDetachment faults at slow‐ and ultraslow‐spreading mid‐ocean ridges are essential for lithosphere‐hydrosphere interactions. However, their coupling with subseafloor hydrothermal circulation is poorly understood. Here, we investigated shallow hydrothermal fluid circulations in the active Dragon Horn detachment fault system of the Southwest Indian Ridge using combined near‐bottom magnetic anomaly data and rock magnetic analyses. We observed enhanced magnetic anomalies related to the high magnetization of basaltic country rocks and highly serpentinized (>80%) peridotite, whereas the hydrothermally altered basalts and sulfide deposits had weak magnetization and reduced magnetic anomalies. Therefore, the low‐magnetization zone was interpreted as a proxy for the hydrothermal fluid channel. The spatial distribution of the low‐magnetization zone revealed that the inactive Suye field expanded more than 500 m in diameter horizontally and ∼100 m vertically, and the active Longqi hydrothermal field had a >1 km fluid channel, both centered around the detachment fault fracture zone. Our results establish a robust link between detachment faulting and shallow hydrothermal circulation in which the detachment fault system provides critical fluid paths. Therefore, detachment tectonics are important elements for evolving seafloor hydrothermal fields along the Southwest Indian Ridge and possibly other slow‐ and ultraslow‐spreading mid‐ocean ridges globally.

Compressive Strength Analysis of Mortar Made from Volcanic Sand in Nagari Aia Angek Based on Magnetic Mineral Content

Mortar is a binder or adhesive with a standard viscosity of ingredients (water, cement, and sand). Mortar made has strength, mortar strength is measured using Cement Compression testing machine. Sand in mortar making contains magnetic minerals such as magnetite (Fe3O4) or Fe2+3Fe+2O4-2, hematite mineral (α-Fe2O3) which will be measured for magnetic susceptibility value using Bartington Magnetic Susceptibility Meter Sensor Type B (MS2B). To determine the concentration of magnetic minerals and their relationship with mortar compressive strength, the rock magnetism method was used. Measurement of sand samples of Kamumuan River, Sungai Limau District using Bartington Magnetic Susceptibility Meter Sensor Type B (MS2B) by categorizing sand into 3 treatment, namely Addition of magnetic minerals (PTM) with χLF value 3863.3 x 10-8m3/kg and χFD (%) 0.72, reduction of magnetic minerals (PKM) with χLF value 1920 x 10-8m3/kg and χFD (%) 0.79, normal magnetic minerals (PM) with χLF value 2334.7 x 10-8m3/kg and χFD (%) 0.62. The sample has a grain type that is almost no superparamagnetic grain and has antiferromagnetic properties. Samples grouped by treatment were made into mortar and tested using a cement compression testing machine with the results of mortar compressive strength, namely ATM of 49.4 Kg/cm², AKM of 46.6 Kg/cm², and AM 52.3 Kg/cm². Based on the analysis conducted, the magnetic minerals contained in the sand affect the results of the compressive strength of the mortar, the higher the susceptibility value in the sand, the stronger the compressive strength of the mortar

Compressive Strength Analysis of Mortar Made from Volcanic Sand in Nagari Aia Angek Based on Magnetic Mineral Content

Compressive strength testing is carried out on mortar made from a mixture of sand, cement and water. Mortar is one of the construction materials in building structures that has the main function as a material for construction parts. The compressive strength test is useful for measuring and knowing the strength of objects against compressive forces. The method used in this research is rock magnetism to determine the abundance of magnetic minerals and compressive strength testing to determine the relationship of compressive strength results to the magnetic minera content of Nagari Aia Angek volcanic sand. Volcanic sand is measured using a Bartington Susceptibility Meter Type MS2B with 3 forms of mineral separation treatment, namely Magnetic Mineral Reduction (PMM) with a value of χlf 505,99 x10 m-83 /kg, χfd (%) 2.72%, Additional Magnetic Minerals (TMM) with a value of χlf 1026.72 x10 m-83 /kg, χfd (%) 2.14%, and No Treatment (TP) with a value of χlf 853.98 x10 m-83 /kg, χlf (%) 2.16. The results of testing the compressive strength of mortar using Compression Testing Mechine on 3 volcanic sand treatments were obtained (PMM) with a value of 169.14 kg/cm2, (TMM) with a value of 147.11 kg/cm2, and (TP) with a value of 141.81 kg/cm2. The magnetic properties of volcanic sand samples are antiferrimagnetic and have superparamagnetic mixed grains and coarse grains. There is a relationship between the compressive strength value of mortar and the concentration of magnetic minerals, the higher the compressive strength value, the higher the χfd (%) value obtained

Late Miocene tectonic forcing of climate transition in the northeastern Tibetan Plateau

Interactions among late Cenozoic global cooling, tectonic activity and regional climate evolution of the northeastern Tibetan Plateau remain elusive. To further understand the relative contributions of global climate change and tectonism, we conducted a comprehensive study of heavy minerals, rock magnetism, and branched glycerol dialkyl glycerol tetraethers (brGDGTs) in late Cenozoic sediments of the Laojunmiao section (ca. 12.7 Ma to 5 Ma) in the Jiuxi Basin. Our results reveal a notable increase in magnetic susceptibility (χ) and saturation isothermal remanent magnetization (SIRM) at 8.5 Ma, aligning with an accelerated decrease in temperature captured by brGDGTs. Combined with heavy mineral analysis, we propose that the profound changes in magnetic parameters and temperature are closely linked to the intensive uplift of the northern Qilian Shan since 8.5 Ma. Furthermore, this ongoing uplift has occurred simultaneously with persistent aridification in the Jiuxi Basin and its adjacent regions. The Qilian Shan might have reached a threshold elevation and began to act as a moisture barrier to northwestward moisture since 8.5 Ma. By synthesizing hydroclimate evolution records from the northeastern Tibetan Plateau, we deduce that changing topography resulting from tectonic uplift may have exerted a significant influence on regulating the moisture distribution in this region during the mid- to late Miocene.

INFLUENCE OF ORIENTATION ERRORS ASSOCIATED WITH THE USE OF A MAGNETIC COMPASS ON THE ACCURACY OF DETERMINING THE POSITION OF THE PALEOMAGNETIC POLE AND THE AMPLITUDE OF PALEOSECULAR VARIATIONS

The use of a magnetic compass in paleomagnetic studies of highly magnetic rocks (for instance, basalts) can lead to large errors in the orientation of paleomagnetic samples. On the other hand, alternative methods of orientation are relatively time-consuming, and in the case of using a solar compass, they also require sunny weather – a condition that is rarely met, especially when sampling at high and subpolar latitudes. This often leads to the fact that researchers in their work rely on the results of magnetic compass measurements, while assuming that the resulting errors are of a random nature and, with sufficiently good statistics, are averaged. In this study, numerical modeling is performed, which allows us to verify this assumption and assess how much orientation errors associated with the use of a magnetic compass can affect the final results of paleomagnetic studies, such as determining the position of the paleomagnetic pole and the amplitude of ancient geomagnetic variations. As a result of the work performed , it is shown that: 1) the amplitudes of paleosecular variations and the positions of paleomagnetic poles are weakly sensitive to moderate and even relatively large errors in the orientation of paleomagnetic samples associated with the use of a magnetic compass; 2) very large errors in the orientation of samples lead to a significant increase in the within-site scatter of paleomagnetic directions, which makes it possible to detect and exclude the corresponding sites with a large (for instance >15°) value of the α95; 3) the influence of distortions associated with the use of a magnetic compass on the accuracy of determining the position of the paleomagnetic pole and the amplitude of ancient geomagnetic variations depends on latitude. At near-equatorial latitudes, this effect is maximal, at medium latitudes – minimal.

Rotation of crustal domains related to Gondwanide deformation in the Neoproterozoic–Cambrian Sauce Chico Complex (Argentina), southwestern margin of the Río de la Plata Craton: Insights from AMS data

The tectonic evolution of the Ventania System fold and thrust belt and the origin of its curvature have been the subject of debates for decades. The Gondwanide Orogeny generated the mylonitization of its Tonian–middle Cambrian basement (i.e., Sauce Chico Complex), accompanied by an intense hydrolysis which produced secondary muscovite (i.e., sericite), and the folding of the overlying Paleozoic sedimentary cover. To evaluate the structural and tectonic evolution of the Ventania System as a result of the interaction of its basement with the Río de la Plata Craton, we studied the anisotropy of magnetic susceptibility (AMS) and rock magnetism on samples of the Sauce Chico Complex. Rock magnetic studies suggest that paramagnetic minerals are the main carriers in the entire Sauce Chico Complex. We suggest that our results reflect secondary muscovite generation due to mylonitization. AMS data reveal that the orientation of the magnetic foliation coincides to a large extent with the rock foliation. However, magnetic and rock foliation orientations are not uniform among the different sampled units, displaying strikes between N 320° (NW) and N 345° (NNW) on average. Localities with different orientations are separated by regional strike-slip structures, referred to as tear faults, which have also been reported and interpreted by previous authors. According to this, we suggest that the variations detected between the orientation of the magnetic and rock foliations of the different basement units may be the result of the rotation of crustal blocks bounded by tear faults. We also propose the existence of a new tear fault not previously recognized. Furthermore, a tear fault of regional character, known as the Sauce Chico Tear Fault, juxtaposes two distinct crustal domains. The differential displacement of such domains could have contributed not only to different structural styles between blocks on both sides of the Sauce Chico Tear Fault, but also to the curved shape of the Ventania System during the progression of the Gondwanide deformation.