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The Neoproterozoic carbonate rocks of the Araras Group (Amazon Craton) and the Sete‐Lagoas and Salitre Formations (São Francisco Craton) share a statistically indistinguishable single‐polarity (reversed) characteristic direction. This direction is associated with paleomagnetic poles that do not align with the expected directions for primary detrital remanence. We employ a combination of classical rock magnetic properties and micro imaging/chemical analysis (in thin sections) using synchrotron radiation to examine these remagnetized carbonate rocks. Magnetic data indicate that most samples lack the anomalous hysteresis properties typically associated with carbonate remagnetization (except for distorted loops). Through a combination of Scanning Electron Microscopy with Energy Dispersive X‐ray Spectroscopy (SEM‐EDS), X‐ray Fluorescence (XRF), and X‐ray Absorption Spectroscopy (XAS), we identified subhedral/anhedral magnetite, or spherical grains with a core‐shell structure of magnetite surrounded by maghemite. These grains are within the pseudo‐single domain size range, as do most of the iron sulfides, and are spatially associated with potassium‐bearing aluminosilicates. While fluid percolation and organic matter maturation play a role, smectite‐illitization appears to be crucial for the growth of these phases. X‐ray diffraction analysis, in addition, identifies these silicates as predominantly highly crystalline illite, suggesting exposure to epizone temperatures. These temperatures were likely reached during the final stages of the Gondwana assembly (Cambrian), but remanence was only locked in afterward, in successive cooling events during the Early Middle Ordovician. This is supported by the carbonates' paleomagnetic pole positions compared to Gondwana's apparent polar wander path, and the absence of reversals, contrasting with the high reversal frequency of the Late Ediacaran/Cambrian. Plain Language Summary: Carbonate rocks serve as important records of ancient climates and host magnetic minerals capable of documenting the evolution of Earth's magnetic field. Nevertheless, their original magnetization, acquired during sedimentation, is frequently supplanted by a secondary magnetization, originating from various geological processes altering local thermochemical stability. For carbonate rocks, this remagnetization process is often associated with a "magnetic fingerprint." In South America, carbonate rocks from different sedimentary basins (hundreds of kilometers apart) exhibit statistically similar magnetic components that deviate from their formation origin, indicating secondary processes. This multidisciplinary study integrates classical paleomagnetic analysis with micro‐chemical and imaging analysis to comprehend the geological phenomena responsible for remagnetizing such an extensive continental area. We demonstrate that not all remagnetized samples display the anticipated magnetic fingerprint. Highly detailed chemical analysis confirms the presence of nanoscopic magnetic minerals spatially correlated with clay minerals indicating that while organic matter transformation may play a significant role, clay mineral transformation is a key phenomenon governing remagnetization in these rocks. However, our data also supports the notion that these rocks underwent heating during the final assembly of the ancient continental landmass, Gondwana, and a sequential cooling event is suggested as locking their magnetization in the state observed today. Key Points: Remagnetized Neoproteorozoic carbonates in Brazil may not consistently display anomalous hysteresis parametersSynchrotron‐based analysis revealed pseudo‐single domain‐sized magnetite spatially correlated with aluminosilicates (smectite‐illite)The Late Cambrian assembly of Gondwana thermally reset the carbonates' remanence, eventually blocking it (470–460 Ma) during gradual cooling [ABSTRACT FROM AUTHOR]

Curved 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). Plain Language Summary: The geological history of the American Cordillera is complex due to its extensive geological history. We have investigated a section of this Pacific‐Panthalassa region: the remarkable curved sector of the Mexican Fold and Thrust Belt in northeastern Mexico. This winding area, known as the Sierra Madre Oriental, potentially holds important clues about the evolution of the North American crust. To contribute to a better understanding of this area and to complement the scarce geophysical and geological studies, we used the magnetic properties of rocks and reviewed existing published research to investigate. We've uncovered a complex history of rock magnetizations with at least two main events dating back to the Late Jurassic and Cretaceous periods. Our findings also reveal that these mountain ranges were rotated from their original position on vertical axes, suggesting they were originally linear and were bent or buckled during the period from approximately 120 to 50 million years ago. Key Points: With Paleomagnetism we explore the nature of the striking curvature of the Northeastern section of the Mexican Fold‐and‐Thrust BeltOur study shows evidence of Orocline bending or Buckling during the major horizontal crustal shortening event of the Mesozoic in Mexico [ABSTRACT FROM AUTHOR]

Increases in temperature and pressure caused by rapid burial of sediments seaward of the Sumatra subduction zone have been hypothesized to trigger dehydration reactions that diagenetically strengthen sediments and contribute to the formation of an over‐pressured pre‐décollement, which together facilitate the occurrence of large shallow earthquakes. We present paleomagnetic, rock magnetic, and electron microscopic analyses from drill cores collected offshore Sumatra at Site U1480 during IODP Expedition 362 that support this hypothesis. The older pre‐fan units (Late Cretaceous to early Paleocene) were deposited when Site U1480 was moving rapidly northward with the Indian plate from a paleolatitude of 50° to 30°S, which would equate to expected absolute paleomagnetic inclinations of 70°–43°. Most of the older pre‐fan sediments, however, have shallow observed inclinations (shallower than ±20°), indicating that the sediments were overprinted when Site U1480 was located near the paleoequator, as it has been since the early Oligocene. Electron microscopic observations reveal that the pre‐existing detrital magnetite grains have undergone pervasive dissolution and alteration by hydrothermal fluids. The diagenesis observed is consistent with mineral dehydration, possibly driven by rapid burial of pelagic sediments by the ∼1250 m thick Nicobar Fan sequence. In addition, the elevated burial temperature also facilitated the smectite to illite conversion reaction. We hypothesize that chemical reactions resulted in the formation of fine‐grained magnetite that records a chemical remanent magnetization overprint. This overprint is consistent with the alteration occurring after burial by the thick Nicobar Fan sequence sometime in the past few million years. Plain Language Summary: Sediments and rocks commonly contain magnetic minerals that record the direction and intensity of Earth's magnetic field as they are being emplaced, thus preserving an ancient record of the geomagnetic field. Subsequent alteration of the magnetic minerals caused by heating and/or fluid circulation can result in the acquisition of secondary magnetizations (i.e., remagnetization) that may overprint or completely reset the primary ancient magnetization. Such remagnetization provides evidence of the physical and chemical changes that have occurred. Here through paleomagnetic, rock magnetic, and microscopic analyses of the deeper older (pre‐fan) stratigraphic sequence cored offshore Sumatra, we find that hydrothermal fluids, resulting from mineral dehydration driven by rapid burial of this sequence by younger, thick Nicobar Fan sediments, led to pervasive secondary remagnetization. Consequently, the newly formed magnetite recorded a much younger paleomagnetic field, leaving a shallow overprint that probably occurred sometime in the past few million years. The dehydration reactions also increased the strength of the sediments entering the subduction zone and aided in the formation of slip surfaces (called décollements), possibly contributing to the shallow, large earthquakes that have generated tsunamis off Sumatra. Key Points: The 60–67 Ma pre‐fan sediments offshore Sumatra were most likely remagnetized since deposition of the Nicobar Fan sediments, which began at ∼9 MaRemagnetization of pre‐fan sediments caused by mineral dehydration may be linked to shallow seismogenic slip off SumatraMagnetic properties of input sediments in the subduction margin record conditions that may have facilitated the generation of earthquakes [ABSTRACT FROM AUTHOR]

Paleomagnetic records of middle Neoproterozoic (820 to 780 Ma) rocks display high amplitude directional variations that lead to large discrepancies in paleogeographic reconstructions. Hypotheses to explain these data include rapid true polar wander (TPW), a geomagnetic field geometry that deviates from a predominantly axial dipole field, a hyper‐reversing field (>10 reversals/Ma), and/or undiagnosed remagnetization. To test these hypotheses, we collected 1,057 oriented cores over a 85 m stratigraphic succession in the Laoshanya Formation (Yangjiaping, Hunan, China). High precision U‐Pb dating of two intercalated tuff layers constrain the age of the sediments between 809 and 804 Ma. Thermal demagnetization isolates three magnetization components residing in hematite which are not time‐progressive but conflated throughout the section. All samples possess a north and downward directed component in geographic coordinates at temperatures up to 660°C that is ascribed to a Cretaceous overprint. Two components isolated above 660°C reveal distinct directional clusters: one is interpreted as a depositional remanence, while the other appears to be the result of a mid‐Paleozoic (460 to 420 Ma) remagnetization, which is likely widespread throughout South China. The high‐temperature directions are subtly dependent on lithology; microscopic and rock magnetic analyses identify multiple generations of hematite that vary in concentration and distinguish the magnetization components. A comparison with other middle Neoproterozoic paleomagnetic studies in the region indicates that the sudden changes in paleomagnetic directions, used elsewhere to support the rapid TPW hypothesis (ca. 805 Ma), are better explained by mixtures of primary and remagnetized components, and/or vertical axis rotations. Plain Language Summary: Paleomagnetic directions recorded in 820 to 780 million year old rocks from South China exhibit large amplitude changes that vary rapidly, which have been interpreted to indicate extraordinarily fast motion of Earth's crust and mantle, up to 90° within a 5 million year span, with respect to the spin axis of the core. This hypothetical phenomenon, called rapid true polar wander (TPW), could be responsible for dramatic global environmental change at that time. To test this theory, we collected over 1,000 samples from a well exposed section where the incongruous directions are found. Our measurements suggest that some of the rocks acquired a new magnetic signal during a pervasive remagnetization event in South China around 440 million years ago, long after original deposition of the rocks. New hematite growth has a demagnetization spectrum that partially overlaps or completely obscures the original magnetic signal, which was previously unrecognized. This implies that rapid TPW is likely an artifact of magnetic overprinting in ancient rocks from South China. Our results suggest that South China was in a relatively stable position at high latitudes 809 to 804 million years ago. We find no evidence to support exceptionally fast continental drift or an abnormal geomagnetic field geometry during that time. Key Points: High‐precision ID‐TIMS U‐Pb dating yields deposition ages of the Laoshanya Formation (Yangjiaping, South China) between 809 and 804 MaDiscordant paleomagnetic directions in the red beds are a conflation of three temporally distinct field records residing in hematiteOur results do not support rapid true polar wander or abnormal magnetic field geometry around 805 Ma [ABSTRACT FROM AUTHOR]

The Paleocene lavas from Dianzhong Formation (E1d) in Linzhou basin of southern Lhasa terrane are a key target for paleomagnetic investigations into the timing and paleolatitude of the initial India‐Asia collision. Controversy exists, however, on whether these rocks preserve a primary remanent magnetization. Here we reanalyze previously published thermal demagnetization data and report detailed rock magnetic results and petrographic observations of these rocks. We find that the original magnetic carrier, a magmatic multidomain Ti‐poor titanomagnetite, underwent significant grain size reduction and was variably reacted to single‐domain maghemite and nano‐hematite. Such strong alteration may have resulted from successive hydrothermal events: a first event related to the ∼52 Ma dike intrusions into the E1d that accompanied a massive ignimbrite eruption deposited above the E1d producing heating up to 300°C; and a secondary event related to the 42–27 Ma southward overthrusting of the basin, heating the E1d up to 130–145°C. Unblocking/inversion temperature spectra of the authigenic maghemite and nano‐hematite overlap with those of the titanomagnetite, implying that the primary remanence of the E1d lavas has been contaminated or replaced by thermoviscous and chemical remanent magnetizations. Thus the isolated characteristic remanent magnetization from these rocks, whether slightly or completely altered, cannot be considered primary and should not be used for paleolatitudinal determination. Our study confirms that hydrothermal alteration can seriously jeopardize the remanence carried by titanomagnetite and thus should be tested for paleomagnetic investigations of rock units from tectonically active areas. Plain Language Summary: The study of past magnetic directions preserved in rocks (paleomagnetism) enables to constrain the paleolatitudes of the southern Asian margin where the rocks formed and is thus key to understand the timing and latitude of the initial India‐Asia collision. However, paleomagnetic studies of Paleogene rocks of southern Tibet have returned a surprisingly wide spread of paleolatitude data. One possible explanation is unrecognized remagnetization, a process that may relate to subsequent hydrothermal alteration. Such hydrothermal alteration has recently been documented for Paleocene lavas in the Linzhou basin, paleomagnetic signals from which have previously been interpreted either as primary or secondary (re)magnetizations. Here we analyze previously published and newly acquired paleomagnetic, rock magnetic, and petrographic data of these rocks to identify whether hydrothermal alteration caused remagnetization, and how such events may be fingerprinted. We find that the original magnetic carrier is Ti‐poor titanomagnetite. Hydrothermal alteration, however, led to significant changes in these titanomagnetite crystals and mineral transformations to maghemite and hematite, associated with acquisition of secondary magnetizations with the magnetic behaviors similar to the primary magnetization. This can be misleading for the interpretation of the magnetic directions obtained from these rocks and imply that they are not suitable for paleolatitudinal determination. Key Points: Hydrothermal alteration intensively destroyed the original multi‐domain titanomagnetite and recorded magnetization in the Dianzhong lavasTitanomagnetite experienced serious grain size reduction and has variably converted to authigenic single‐domain maghemite and nano‐hematitePrimary remanent magnetization has been replaced or contaminated, these lavas should not be used to determine Lhasa terrane paleolatitude [ABSTRACT FROM AUTHOR]

The unclear relationship between mineralization, hydrothermal alteration, and rock magnetization in volcanogenic massive sulfide (VMS) deposits limits us from fully understanding the magnetic anomalies and remagnetization process in this type of deposit. We address the issue by conducting systemic paleomagnetic, rock magnetic, petrographic, and X‐Ray diffraction studies in the Dapingzhang VMS deposit on the northwestern Indochina Block. Magnetite is the dominant magnetic carrier of hydrothermally altered surrounding rocks and orebody. Magnetite consumption and secondary magnetite formation occurred at different stages and types of hydrothermal alteration. The overall decrease in magnetite concentration from chloritization via silicification to mineralization implies that the magnetite was mostly consumed during hydrothermal alterations. Secondary single domain magnetite, which can carry a remagnetization direction, is proposed to be formed during illitization via the smectite‐to‐illite transformation. Secondary superparamagnetic magnetite, which was most likely formed during the late stage of chloritization, is unable to carry the stable characteristic remanent magnetization. The site‐mean direction of high‐temperature and high‐coercivity components is Dg/Ig = 324.5°/43.1°, and kg = 35.1, with α95 = 6.8° before tilt correction, and Ds/Is = 316.2°/37.6°, and ks = 16.4, with α95 = 10.1° after tilt correction, with a negative fold test. However, plate reconstruction is limited by the uncertainty of the tilting process following mineralization and the possibility of remagnetization during burial alteration. Therefore, this study provides a mechanism for rock magnetic variation and remagnetization during VMS mineralization. Plain Language Summary: We conducted paleomagnetic, rock magnetic, petrographic, and X‐Ray diffraction studies on volcanogenic massive sulfide (VMS) deposit to better understand the interaction between mineralization, hydrothermal alteration, and magnetization in this kind of deposit. Magnetite is the main magnetic carrier of orebodies and surrounding rocks. The overall decrease in magnetite concentration from chloritized samples to orebodies, via silicified samples, explains the low magnetic anomalies in VMS deposits. However, in samples containing a high concentration of chlorite, a significant amount of secondary superparamagnetic magnetite was discovered. Secondary single domain magnetite is ascribed to be formed through the transformation of smectite to illite during hydrothermal alteration, providing an explanation for remagnetization in VMS deposits. Therefore, magnetite consumption and secondary magnetite formation occurred during different types and stages of hydrothermal alteration. The site‐mean paleomagnetic direction is calculated, but it cannot be used in plate reconstruction due to the unclear bedding attitudes prior to mineralization and the possibility of remagnetization during burial alteration. This research improves our understanding of the processes of magnetic mineral variation and remagnetization during VMS mineralization. Key Points: Magnetite is the major magnetic carrier of hydrothermally altered surrounding rocks and orebodiesMagnetite consumption occurred from chloritization via silicification to mineralizationRock magnetism reveals the neoformation of superparamagnetic and single domain magnetite during chloritization and illitization, respectively [ABSTRACT FROM AUTHOR]

Unraveling the complex relationship between orogenesis and hydrocarbon formation and accumulation is challenging and is often hampered by physical and chemical overprints of younger events. The Permian reservoir in the Longmen Shan orogen, South China, is such an example, and its evolution has been hotly debated. In this study, we use a new combination of paleomagnetic dating analysis and Re–Os isotope dating to try to resolve this. Paleomagnetic dating of the hydrocarbon‐host carbonate indicates two remagnetization events during: (a) the Late Triassic, and (b) the Middle Jurassic–Cretaceous. These two remagnetization events are shown to represent two distinct stages of hydrocarbon accumulation. The paleomagnetic estimates are supported by Re–Os dating of bitumen (∼264 Ma) and oil (∼94 Ma). The two different Re–Os ages are associated with two periods of oil generation. We interpret these data in terms of known geological processes: (a) the ∼260 Ma Dongwu large igneous province caused oil generation, and the Indosinian tectonic event caused the migration and accumulation; and (b) the Late Cretaceous Yanshan orogenic events promoted another generation and entrapment of oil in the same reservoir. This combined approach reliably tracks the sequence of oil generation and accumulation, even when the source rock is uncertain, and multi‐phase accumulation and complex tectonism has occurred. Given that paleomagnetic and Re–Os dating are independent methods which can constrain multiple geological processes, when used together they have the potential to be universally applied. Plain Language Summary: Key to understanding complex geological processes is the dates and sequence of each event. The timing of hydrocarbon formation and accumulation is one such complex geological process that can be difficult to unravel, but critical to evaluate the complex orogenesis and hydrocarbon explorations. In this paper, we combine for the first time two independent dating methods to study hydrocarbon reservoirs of Longmen Shan orogen: (a) paleomagnetic and (b) rhenium‐osmium isotope dating. The two methods identified two periods of hydrocarbon formation, followed by two extended periods of hydrocarbon migration. This combined method is particularly powerful as it is independent of the hydrocarbon source rock and complex geological settings. Moreover, the two methods can provide additional tests for each dating technique. The new combined methods can, therefore, be applied in complex hydrocarbon‐bearing regions worldwide. Key Points: Paleomagnetic and Re–Os isotope data were collected for a hydrocarbon carbonate reservoir to determine the hydrocarbon evolution processesOil accumulations are found to have remagnetized the reservoir carbonates during the Late Triassic and CretaceousTiming of oil generation is constrained by Re‐Os dates of bitumen and oil hosted in carbonates at ∼264 and ∼94 Ma, respectively [ABSTRACT FROM AUTHOR]

Hainan Island lies near the Red River Fault, a prominent tectonic feature produced by the India‐Asia collision. There, we carried out a geochronologic and paleomagnetic study on Cretaceous rocks in order to better understand the kinematic history of the region. U‐Pb zircon dating of tuff intercalated in red bed sedimentary rocks yielded a concordant age of 106.6 ± 0.3 Ma; a mafic dyke intruding the red beds yielded a concordant age of 104.6 ± 0.7 Ma. Stepwise demagnetization experiments on 448 sedimentary rock samples and 191 dyke samples isolate solely normal polarities. Paleomagnetic directions of the dykes cluster in two distinct populations in geographic coordinates, indicating that dyke intrusion occurred in two pulses of limited duration (secular variation was not averaged) after tilting of the sediments. Baking of the sediments from the dykes only occurred near the contacts. Together with published data, the mean directions of 104 sites most tightly group at 58.3 ± 3.2% unfolding, indicative of a synfolding remagnetization, which can be constrained to have occurred within a 2 Myr period between sedimentation and dyke intrusion. We suggest that warm (50–100°C) fluid interaction during basin development led to new mineral growth spawning chemical remagnetization. The corresponding paleomagnetic pole at 81.5°N, 145.2°E (A95 = 2.4°) is indistinguishable from the coeval Eurasian reference pole, suggesting the South China Block has remained fixed to Eurasia since 105 Ma. A contour map of paleomagnetic rotations from 115 studies in the region shows that the Red River Fault roughly demarcates rotation magnitudes/signs, suggestive of a major tectonic boundary. Plain Language Summary: Highly stable magnetic remanences of hematite‐bearing sedimentary rocks (red beds) form the basis of numerous paleomagnetic studies. However, an on‐going scientific debate called the "red bed controversy" stems from the relative timing when the remanence was acquired (primary = detrital vs. secondary = chemical). Our article concerns a paleomagnetic and geochronologic study of Cretaceous red beds and cross cutting dykes from Hainan Island (South China). Radiometric‐dating of tuff intercalated in the red beds and the crosscutting mafic dykes, combined with paleomagnetic analyses of 639 samples, allows us to precisely constrain the age of a pervasive synfolding remagnetization at ca. 105 Ma. Together with electron microscopy, we demonstrate the existence of a chemical remanent magnetization (CRM) that occurred within 2 Myr of the depositional age of the sediments. We also show that the dykes had limited thermal influence on the wall rocks. Importantly, the red beds that have CRMs do not suffer from inclination shallowing—the paleolatitude is very compatible with that predicted from the reference curve, suggesting the relative configuration between South China and Siberia has remained constant since 105 Ma. Key Points: Chemical remagnetization of Cretaceous sedimentary rocks in Hainan is dated between 106.6 Ma and 104.6 MaAuthigenic growth of iron oxides and sulfides in the Cretaceous sediments occurred within 2 Myr of depositionThe South China Block has remained fixed to Eurasia since the Cretaceous (105 Ma) [ABSTRACT FROM AUTHOR]

Although the late Mesozoic remagnetization of the South China Block (SCB) is well recognized, the mechanism is unclear due to poor constraints on the genesis of secondary magnetic minerals. This issue is addressed via the study of the world's largest Paleozoic Mn deposit, in which both early Paleozoic sedimentation of manganese carbonate minerals and undated hydrothermal overprinting manifested by the presence of Mn silicate minerals with associated magnetite. Laser ablation‐inductively coupled plasma‐mass spectrometry in situ element analyses and paleomagnetic studies are applied to determine the age of hydrothermal alteration, and the results shed new light on the remagnetization mechanism of the SCB. Laser ablation‐inductively coupled plasma‐mass spectrometry in situ analyses show that the secondary magnetites have high values of (Ca + Al + Mn) and low values of (Ti + V) and (Ni/Cr)/Ti. This, together with coexisting skarn formation, supports a hydrothermal origin. The postfolding remagnetization is characterized by a stable component and a systematic normal polarity, carried by magnetite. The mean direction has a declination of 22.9° and an inclination of 56.1°, with a statistical parameter α95 of 4.1°. Comparison with previously reported paleopoles indicates that the remagnetization was mostly acquired during the Late Cretaceous. Therefore, our results confirm that the hydrothermal magnetite carries a chemical remanent magnetization as a result of Late Cretaceous skarn formation. From a regional perspective, hydrothermal alteration from the Middle Jurassic to the Late Cretaceous, covering most parts of SCB, is proposed to be one of the important mechanisms for the ubiquitous late Mesozoic remagnetization. Key Points: Xialei Mn deposit experienced Late Cretaceous magmatic‐hydrothermal alterationCRM related to skarn alteration caused by magmatic‐hydrothermal fluidsHydrothermal alteration partly responsible for Mesozoic remagnetization in the SCB [ABSTRACT FROM AUTHOR]

Abstract: To understand the origin of chemical remagnetization in carbonate reservoir rocks and associated chemical processes, we have conducted detailed petrologic, geochemical, and magnetic studies of the hydrocarbon‐impregnated Ediacaran dolomite in the Taishan Paleo‐reservoir, south China. Samples were collected across a continuous outcrop consisting of oil‐free dolomite, transition zone dolomite, and highly hydrocarbon‐impregnated reservoir dolomite. Paleomagnetic results show that dolomite from the reservoir and transition zone were remagnetized and carries a possible Cambrian‐Ordovician direction (Dec = 163.7°, Inc = 10.6°, and α95 = 1.9°), and the oil‐free dolomite shows unstable magnetizations. Hematite is the magnetic mineral in the oil‐free dolomite, whereas the hydrocarbon‐impregnated reservoir dolomite contains no hematite but mainly pyrrhotite nanoparticles. Transition‐zone dolomite contains both hematite and pyrrhotite. In addition, the natural remanent magnetization intensities decrease from the reservoir dolomite, through the transition zone, and into the oil‐free dolomite, and a similar trend was observed in the total organic carbon and bitumen contents. The results suggest that the magnetic mineral assemblage and magnetic intensity in dolomite appear to be closely related to the degree of hydrocarbon impregnation and that remagnetization of the Ediacaran dolomite was likely caused by hydrocarbon migration into the dolomite. Pyrrhotite nanoparticles, magnetite, and barite are suggested to be formed during hydrocarbon migration, by the reduction of detrital hematite in the dolomite and sulfur species in the hydrocarbons. The new findings into the origin of pervasive remagnetization have the potential to guide future hydrocarbon exploration within Ediacaran dolomite that is host to the largest single carbonate gas reservoir in China. [ABSTRACT FROM AUTHOR]

Abstract: To reconstruct the paleoposition of the Antarctic Peninsula relative to the South American Plate during the breakup of Gondwana, as well as the opening kinematics of the Drake Passage, we conducted detailed paleomagnetic, rock magnetic, and isotopic chronology studies of Byers Peninsula (Livingston Island) and Fildes Peninsula (King George Island) of the South Shetland Islands. The 40Ar/39Ar ages of the Agate Beach Formation to the Long Hill Formation in Fildes Peninsula range from 56.38 ± 0.2 Ma to 52.42 ± 0.19 Ma. Low natural remanent magnetization/isothermal remanent magnetization ratios, inconsistency with the polarity constrained by the paleomagnetic results and 40Ar/39Ar age constraints, as well as the widespread cation‐deficient titanomagnetite and Ti‐free magnetite of secondary origin, indicate that the volcanic and sedimentary rocks of Fildes Peninsula were remagnetized at about 55 Ma. Combining our results with previous data from the South Shetland Islands and the Antarctic Peninsula, we calculated the paleopoles for 110 Ma and 55 Ma for the South Shetland Islands and the Antarctic Peninsula. The paleomagnetic reconstruction of the relative paleoposition of the Antarctic Peninsula and South America shows that these plates were connected and experienced a southward movement and clockwise rotation from 110 to 55 Ma. Subsequently, southward translation and clockwise rotation of the Antarctic Peninsula between 55 and 27 Ma separated the Antarctic Peninsula and South America, forming the Drake Passage. Northward translation of South America after 27 Ma increased the N‐S divergence and increased the distance between the Antarctic Peninsula and the South American Plate. [ABSTRACT FROM AUTHOR]

In their comment on our publications on pervasive remagnetization of Jurassic-Paleogene carbonate rocks of the Tibetan Himalaya (Huang et al., 2017, Journal of Geophysical Research: Solid Earth, 122, doi: and 122 , doi: ), Yi et al. (2017) questioned our fold tests applied to their published paleomagenetic results from the Paleogene Zongpu and latest Cretaceous Zongshan carbonate rocks (Patzelt et al., 1996, Tectonophysics, 259(4), 259-284; Yi et al., 2011, Earth and Planetary Science Letters, 309(1), 153-165). They argued that authigenic magnetite pseudomorphic after pyrite, which is the dominant magnetic carrier within these carbonate rocks as indicated by our thorough rock magnetic and petrographic investigations, was formed during early diagenesis and that the primary natural remanent magnetization (NRM) is retained by these carbonate rocks. However, their statement for the invalidity of our fold tests is based on unrealistic assumptions that these carbonate rocks carry primary NRM and that the upper Zongpu Formation was deposited on a 10° primary dip. Their argument for immediate oxidization of pyrite to authigenic magnetite after carbonate deposition onto the continental passive margin ignores that sulfate-reducing conditions were prevailing during early diagenesis, it is also inconsistent with the timing of the secondary remanence acquisition in remagnetized carbonate rocks elsewhere. As previously demonstrated, and agreed upon by Yi et al. (2017), the Zongpu and Zongshan carbonate rocks in Gamba are remagnetized; here we argue that the timing of remagnetization cannot be demonstrated to shortly postdate sedimentation. These data should therefore not be used for tectonic reconstructions. [ABSTRACT FROM AUTHOR]