A data-driven framework for paleomagnetic Euler pole analysis

Owing to the inherent axial symmetry of the Earth’s magnetic field, paleomagnetic data only directly record the latitudinal and azimuthal positions of crustal blocks in the past, but paleolongitude cannot be constrained. An ability to overcome this obstacle is fundamental to paleogeographic reconstruction. The paleomagnetic Euler pole (PEP) analysis presents a unique means to recover such information in deep-time. However, prior applications of the PEP method have invariably incorporated subjective decisions into its execution, undercutting its fidelity and rigor. Here we present a data-driven approach to PEP analysis that addresses some of these deficiencies---namely the objective identification of change-points and small-circle arcs that together approximate an apparent polar wander path. We elaborate on our novel methodology and conduct some experiments with synthetic data to demonstrate its performance. We furthermore present implementations of our methods both as adaptable, stand-alone scripts and as a streamlined interactive workflow that can be operated through a web browser.

Deformation understanding in the Upper Paleozoic of Ventana Ranges at Southwest Gondwana Boundary

At the east of the Ventana Ranges, Buenos Aires, Argentina, outcrops the Carboniferous-Permian Pillahuincó Group (Sauce Grande, Piedra Azul, Bonete and Tunas Formation). We carried out an Anisotropy of Magnetic Susceptibility (AMS) study on Sauce Grande, Piedra Azul and Bonete Formation that displays ellipsoids with constant Kmax axes trending NW–SE, parallel to the fold axes. The Kmin axes are orientated in the NE–SW quadrants, oscillating from horizontal (base of the sequence-western) to vertical (top of the sequence-eastern) positions, showing a change from tectonic to almost sedimentary fabric. This is in concordance with the type and direction of foliation measured in petrographic thin sections which is continuous and penetrative to the base and spaced and less developed to the top. We integrated this study with previous Tunas Formation results (Permian). Similar changes in the AMS pattern (tectonic to sedimentary fabric), as well as other characteristics such as the paleo-environmental and sharp curvature in the apparent polar wander path of Gondwana, marks a new threshold in the evolution of the basin. Those changes along the Pillahuincó deposition indicate two different spasm in the tectonic deformation that according to the ages of the rocks are 300–290 Ma (Sauce Grande to Bonete Formation deposition) and 290–276 Ma (Tunas Formation deposition). This Carboniferous-Permian deformation is locally assigned to the San Rafael (Hercinian) orogenic phase, interpreted as the result of rearrangements of the microplates that collided previously with Gondwana, and latitudinal movements of Gondwana toward north and Laurentia toward south to reach the Triassic Pangea.

Rotation of the Philippine Sea plate inferred from paleomagnetism of oriented cores taken with an ROV-based coring apparatus

Reconstructing the history of Philippine Sea (PHS) plate motion is important for better understanding of the tectonics of the surrounding plates. It is generally considered that the PHS plate migrated northward since Eocene, but its rotation has not been constrained well; some reconstructions incorporated a large clockwise rotation but others did not. This is mainly because the difficulty of collecting oriented rocks from the mostly submerged PHS plate hindered establishing an apparent polar wander path. In this study, we conducted a paleomagnetic study of oriented cores taken using an ROV-based coring apparatus from the Hyuga Seamount on the northern part of the Kyushu-Palau Ridge, a remnant arc in the stable interior of the PHS plate. Stepwise thermal and alternating-field demagnetizations were applied to specimens taken successively from two ~ 30 cm long limestone cores of middle to late Oligocene age, and characteristic remanent magnetization directions could be isolated. Declination and inclination of D = 51.5° and I = 39.8°, respectively, were obtained as the mean of the two cores. The easterly-deflected declination means ~ 50° clockwise rotation of the PHS plate since middle to late Oligocene. In addition, ~ 5° latitudinal change of the site is estimated from the mean inclination. The result implies that the Kyushu-Palau Ridge was located to the southwest of the present position in middle to late Oligocene, and that PHS plate rotation as well as the Shikoku and Parece Vela Basin spreading contributed to the eastward migration of the Izu-Ogasawara (Bonin) Arc to the current position.

An improved apparent polar wander path for southwest Japan: post-Cretaceous multiphase rotations with respect to the Asian continent

To construct the Mesozoic apparent polar wander path (APWP) for the inner arc of the southwestern Japanese islands (referred to as southwest Japan) and compare it to that of East Asia, a 110 Ma paleomagnetic pole for southwest Japan was determined. Mudstone and sandstone samples were collected from 16 sites for paleomagnetic analysis in the Lower Cretaceous Inakura Formation of the Inakura area in the central part of southwest Japan. A high-temperature magnetization component, with unblocking temperatures of 670–695 °C, was isolated from 12 sites of red mudstone. Of these, 11 sites revealed a primary remanent magnetization during the Early Cretaceous. The primary directions combined with the previously reported ones provide a new mean direction (D = 79.7°, I = 47.4°, α95 = 6.5°, N = 17), and a corresponding paleomagnetic pole that is representative of southwest Japan (24.6° N, 203.1° E, A95 = 6.8°). The Early Cretaceous paleomagnetic pole, together with the Late Cretaceous and Cenozoic poles, constitute a new APWP for southwest Japan. The new APWP illustrates a standstill polar position during 110–70 Ma, suggesting tectonic quiescence of this region. This standstill was followed by two large tracks during the Cenozoic. We interpret these tracks as clockwise tectonic rotations of southwest Japan that occurred twice during the Cenozoic. The earlier tectonic rotation occurred for a tectonic unit positioned below northeast China, the Liaodong and Korean Peninsulas, and southwest Japan (East Tan-Lu Block) during the Paleogene. The later rotation took place only under southwest Japan during the Neogene. Cenozoic multiphase rifting activity in the eastern margin of the Asian continent was responsible for the tectonic rotations that are observed from the paleomagnetic studies. Intermittent rifting may constitute a series of phenomena due to asthenospheric convection, induced by the growth of the Eurasian mega-continent in the Mesozoic.

New paleomagnetic results obtained in Upper Cretaceous-Paleocene detritic deposits of the North Iberian Meseta

<p>The Iberian microplate and its evolution during the Mesozoic have been in-vogue topics in the field of Geodynamics, because of its location between two of the major tectonic plates, its interaction with both of them, and its significance in relation with the evolution of the western Tethys domain. Geodynamic models of Mesozoic Iberian evolution are based upon the knowledge of the kinematics of the microplate obtained from the ocean floor magnetic anomalies and particularly its apparent polar wander path (APWP) defined by existing paleomagnetic data. In this sense, the most important feature is the anticlockwise 30º-40º rotation that Iberia underwent during the Cretaceous. Nevertheless, there are still uncertainties about the chronology of this movement due to the poor definition of oceanic magnetic anomalies and the scarcity of high-quality paleomagnetic data in the continent. According to recent works, existing paleomagnetic poles are contradictory and inconsistent with the global apparent wander path (GAPWP) and ocean floor anomalies. This is due to the widespread presence of remagnetizations in the Mesozoic basins within Iberia.</p><p>To address this question we are starting to develop a new project that aims to obtain new paleomagnetic data from unexplored geological units meeting the necessary condition to obtain new Cretaceous paleomagnetic poles representative of the Iberian plate. In this talk we show new paleomagnetic data from detritic deposits with siliceous cement located at the Duero basin (North Iberian Meseta) ascribed to the upper Cretaceous-Paleocene (Areniscas de Salamanca Formation). A stable paleomagnetic component carried by hematite, showing normal and reversed polarities has been isolated. A stable paleomagnetic component carried by hematite, showing normal and reversed polarities has been isolated. We discuss the primary character of this magnetization in terms of inferring the age of this unit in the frame of the kinematic evolution of the plate.  </p>

Inverted South China: A novel configuration for Rodinia and its breakup

Disentangling records of Rodinia fragmentation and true polar wander remains a challenge for understanding late Tonian plate tectonics. The ca. 760 Ma lower member of the Liántuó Formation, South China, yields a primary paleomagnetic remanence that passes both the fold and reversal tests. This new result and recently reported ca. 800 Ma data from elsewhere in South China suggest a new interpretation of its apparent polar wander path, whereby pre–770 Ma poles have inverted absolute polarity relative to traditional interpretations. Based on this inversion, and an interpretation of several oscillations of true polar wander documented by global data during 810–760 Ma, we propose a novel reconstruction for Rodinia and its breakup. Our reconstruction places the South China, India, and Kalahari cratons to the southwest of Laurentia, with connections that might have been established as early as ca. 1000 Ma. Our model also suggests that initial rifting of Rodinia occurred at ca. 800 Ma via fast northward motion of the India craton and South China.

Rapid emplacement of massive Duluth Complex intrusions within the North American Midcontinent Rift

The Duluth Complex (Minnesota, USA) is one of the largest mafic intrusive complexes on Earth. It was emplaced as the Midcontinent Rift developed in Laurentia’s interior during an interval of magmatism and extension from ca. 1109 to 1084 Ma. This duration of magmatic activity is more protracted than is typical for large igneous provinces interpreted to have formed from decompression melting of upwelling mantle plumes. While the overall duration was protracted, there were intervals of more voluminous magmatism. New 206Pb/238U zircon dates for the anorthositic and layered series of the Duluth Complex constrain these units to have been emplaced ca. 1096 Ma in <1 m.y. (duration of 500 ± 260 k.y.). Comparison of paleomagnetic data from these units with Laurentia’s apparent polar wander path supports this interpretation. This rapid emplacement bears similarities to the geologically short duration of well-dated large igneous provinces. These data support hypotheses that call upon the co-location of lithospheric extension and anomalously hot upwelling mantle. This rapid magmatic pulse occurred >10 m.y. after initial magmatism following >20° of latitudinal plate motion. A likely scenario is one in which upwelling mantle encountered the base of Laurentian lithosphere and flowed via “upside-down drainage” to locally thinned lithosphere of the Midcontinent Rift.

Paleomagnetic data of the Siberian Mesoproterozoic rocks (Udzha Uplift, Northern Siberia)

<p>In spite of the fact, that during the last two decades some number of new paleomagnetic poles, more or less meeting the modern standards of quality [Van der Voo, 1993], have been obtained for Mesoproterozoic of Siberia [Evans et al., 2016]. The problem of the Precambrian segment of the apparent polar wander path (APWP) for Siberia, rests still to be far from its solution.</p><p>The latter, obviously, hampers the elaboration of Precambrian paleogeographic reconstructions, solution of numerous other important tasks of the Earth Sciences.</p><p>The Late Precambrian key section of the Udzha Uplift seemed to be one of the most promising object to elaborate the Mesoproterozoic segment of APWP of the Siberian platform. Until recently, the rocks composing this section have been considered to be of the Mesoproterozoic and Vendian age.</p><p>As a result of isotope studies in recent years, the age of formations of the Udzha Uplift has been significantly increased (1386±30 Ma, apatite, U-Pb, [Malyshev et al., 2018]). In particular, age of the Udzha Fm, which forms the uppermost part of the Udzha riphean sequence is considered currently to be Mesoproterosoic. On the base of our new paleomagnetic data this formation has been formed about the same time as the Khaypakh Fm from the Olenek Uplift (NE Siberia), whose Mesoproterozoic age has been established earlier from independent isotopic data [Zaitseva et al., 2017].</p><p>During last several years we have carried out the paleomagnetic studies of Late Precambrian rocks of the Udzha Uplift including the Mesoproterozoic Udzha and Unguokhtakh formations as well as intrusions representing two Mesoproterozoic magmatic events.</p><p>In this abstract we present new paleomagnetic poles for the Mesoproterosoic rocks (1500 Ma, ca.1400 Ma, 1385 Ma) of the Siberian platform.</p><p>These paleomagnetic poles significantly complement the Mesoproterozoic segment of APWP of the Siberian Platform.</p><p><em>The studies were supported by the Russian Science Foundation project № 19-77-10048.</em></p>