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.

Multi-stage India-Asia collision: Paleomagnetic constraints from Hazara-Kashmir syntaxis in the western Himalaya

The India-Asia collision is the most spectacular, recent, and still active tectonic event of the Earth’s history, leading to the uplift of the Himalayan-Tibetan orogen, which has been explained through several hypothetical models. Still, controversy remains, such as how and when it occurred. Here we report a paleomagnetic study of Cretaceous-Tertiary marine sediments from the Tethyan Himalaya (TH) in the Hazara area, north Pakistan, which aims to constrain timing for the onset of the India-Asia collision and to confirm the validity of already proposed models, particularly in western Himalaya’s perspective. Our results suggest that the TH was located at a paleolatitude of 8.5°S ± 3.8° and 13.1°N ± 3.8° during the interval of ca. 84−79 Ma and 59−56 Ma, respectively. A comparison between paleopoles obtained from the current study and coeval ones of the India Plate indicates that the TH rifted from Greater India before the Late Cretaceous, generating the Tethys Himalaya Basin (THB). Our findings support a model for a multi-stage collision involving at least two major subduction systems. A collision of the TH with the Trans-Tethyan subduction system (TTSS) began first in Late Cretaceous-Early Paleocene times (ca. 65 Ma), followed by a later collision with Asia at 55−52 Ma. The onset of the collision between the TH (plus TTSS) and Asia could not have occurred earlier than 59−56 Ma in the western Himalaya. Subsequently, the India craton collided with the TH, resulting in the diachronous closure of the THB between ca. 50 and ca. 40 Ma from west to east. These findings are consistent with geological and geochemical evidence and have a broad implication for plate reconfigurations, global climate, and biodiversity of collisional processes.

New paleomagnetic results of the earliest Permian dykes in South Mongolia and their implications for the paleogeography of the Eastern CAOB

<p>Debates of the Permo-Carboniferous paleogeography of the eastern Central Asian Orogenic Belt (CAOB) mainly focus on the existence, extent, and thereby evolutionary history of the Paleo-Asian Ocean (PAO) in this period. South Mongolia locates at a key position that denotes the southernmost margin of the Mongolia block. Here, we present a paleomagnetic study on the earliest Permian dykes near the Khanbogd of South Gobi Province in Mongolia to better constrain the paleo-position of the Mongolia block. Zircon U-Pb dating results of the studied dykes indicate an emplacement age of 299 ± 3 Ma. Magnetites are the dominant magnetic carriers as revealed by the synthesized rock magnetic experiments. A likely primary high coercivity/temperature component was isolated from 66 of 125 samples and displays consistent reverse polarity, which coincides with the Kiaman Reverse Superchron that overlapping the emplacement age of our studied dykes. Accordingly, a ~299 Ma paleomagnetic pole is calculated at <em>λ</em>/<em>φ</em> = −4.1°N/146.3°E (<em>dp</em> = 3.8, <em>dm</em> = 5.8, n = 66). Potential influence from Paleo-Secular Variation (PSV) is excluded following the Deenen et al. (2011) procedure. Our new results present a ~30.9°N paleolatitude for the Mongolia block, which differs from the lower paleolatitude of the North China and Xilinhot blocks as well as the much higher paleolititude of Siberia. Surrounded by these blocks of different paleolatitude, the PAO and Mongol-Okhotsk Ocean both remained wide open at least by the earliest Permian.</p><p><strong>Acknowledgments<br></strong>This research was funded by the Natural Science Foundation of China (NSFC) (41902229, 41730213, 42072264, 41902229, 41972237), China Postdoctoral Science Foundation funded project and Hong Kong RGC GRF (17307918).</p><p><strong>References</strong></p><p>Deenen, M. H. L. , Langereis, C. G. , Van, H. D. J. J. , & Biggin, A. J. . (2011). Geomagnetic secular variation and the statistics of palaeomagnetic directions. Geophysical Journal International(2), 509-520.</p><p></p><p></p>

Paleomagnetism and magnetostratigraphy of Tarkhanian sediments of the Eastern Paratethus (Skelya section, Kerch peninsula, Crimea)

<p>A detailed paleomagnetic study of Tarkhanian sediments of Skelya section was carried out with the goal to obtained magnetostratigraphy data. The Skelya section is located on the Azov sea side of Kerch peninsula, Crimea (45<sup>o</sup>42′N, 36<sup>o</sup>53′E). The Tarkhanian sediments of Skelya section are represented mainly of clays and have a total thickness of ~ 100 m. According to GTS (2012), the Tarkhanian stage of Miocene is related to the lower part of the Langhian of the General Stratigraphic Scale. Standard paleomagnetic measurements have been carried out to investigate magnetic parameters: natural remenent magnetization, magnetic susceptibility, saturation remanent magnetization, anhysteretic   remanent magnetization varied through out the section. The remanent coercitivity force, determined from backfield demagnetization measurements, range between ~34 and 67 mT.   The composition of the ferromagnetic fraction was examined using temperature dependences of saturation remanent magnetic moment. The thermomagnetic analysis showed that the blocking temperatures are  about 320<sup> o</sup>C and 410-470<sup> o</sup>C and  greigite and titanomagnetite  are the main carriers of NRM in the section.  The biplot of  IRM<sub>-100 mT</sub> / SIRM versus  ARM<sub>40mT </sub>/SARM showed that the ratios fall down into the field around the titanomagnetite and greigite areas. The pseudo-single domain  state of titanomagnetite and greigite was determined from their Mrs/Ms and Bcr/Bc ratios by Day-plot. Paleomagnetic studies have shown that the interval of the Kuvinian beds in its upper part is composed of sediments of reversal polarity magnetization. The rocks of the Terskian and Argunian beds are characterized by intervals of normal and reversed polarity magnetization. This work was supported by Russian Science Foundation, project № 19-77-10075.</p>

The Neoproterozoic geomagnetic field: new insights from a high-resolution paleomagnetic study in South China

<p>The paleomagnetic record during the middle Neoproterozoic (~825-780 Ma) displays rapid apparent polar wander variations leading to large discrepancies in paleogeographic reconstructions. Some authors propose that these data may represent true polar wander events, which correspond to independent motion of the mantle and lithosphere with respect to Earth’s rotation axis. An alternative explanation might be a perturbation of the geomagnetic field, such as a deviation from a predominantly dipole field or a hyper-reversing field. To test these hypotheses, we sampled 1200 oriented cores over a stratigraphic height of 100 metres in sedimentary rocks of the 820-810 Ma Laoshanya Formation in South China. We will present preliminary paleomagnetic and rock magnetic analyses together with results of petrologic and geochemical experiments to better understand the origin of the paleomagnetic signal.</p>

A Paleomagnetic Study of the Tectonic Deformation in Circum-Marmara Region, NW Anatolia, during the Late Cretaceous and Cenozoic Period

<p>The Marmara region is located on the Alpine Himalayan orogenic belt which experienced a active tectonic deformation. The region consists of tectonic units such as the Istanbul Zone, the Strandja Zone and the Sakarya Continent. It is reported in the previous geological studies that the Istanbul Zone began to move southwards appart from the Moesia Platform with the effect of West Blacksea Fault in the west and West Crimea Fault in the east after the the opening of the Black Sea in the Cretaceous. It is known that the Intra Pontide suture is formed after the closure of the Intra-Pontide ocean during the Early Eocene due to the collision between İstanbulzone and the Sakarya continent which moved northwards. As a result of the continental collision, the region has completed its evolution under the influence of basin formation and the emplacement of North Anatolian Fault Zone from Miocene to the present.</p><p> </p><p>In this study, Upper Cretaceous-Oligocene sedimentary and volcanic rocks were sampled at 103 sites to investigate the tectonic deformation of the area. As a result of rock magnetism studies, it was shown that magnetic minerals in sedimentary and volcanic rocks are defined by titanium-rich titanomagnetite showing low coercivity, while in limestone samples, magnetization is defined by hematite showing high coercivity. As a result of anisotropy of magnetic susceptibility (AMS) measurements, it was observed that most of the samples show magnetic foliation and a deformation ellipsoid which is oblate. Paleomagnetic results show counterclockwise rotation of 19.9°±10.9° for the Sakarya continent, 27.4°±11.6°for the Pontides and 15.6°±11.8°for the Strandja Zone from Eocene to present. The results indicate that the region has completed the collision in Eocene and rotated counterclockwise as a large block. Deformation due to basin development or fault bounded block rotations which developed after Miocene could not been detected in this study. Miocene paleomagnetic data from previous studies in the study area are compatible with counterclockwise rotations in Upper Cretaceous-Oligocene which shows that different blocks emplaced in the study area moved together as a single plate during Eocene-Miocene time.</p>