Classification of a Complexly Mixed Magnetic Mineral Assemblage in Pacific Ocean Surface Sediment by Electron Microscopy and Supervised Magnetic Unmixing

Unambiguous magnetic mineral identification in sediments is a prerequisite for reconstructing paleomagnetic and paleoenvironmental information from environmental magnetic parameters. We studied a deep-sea surface sediment sample from the Clarion Fracture Zone region, central Pacific Ocean, by combining magnetic measurements and scanning and transmission electron microscopic analyses. Eight titanomagnetite and magnetite particle types are recognized based on comprehensive documentation of crystal morphology, size, spatial arrangements, and compositions, which are indicative of their corresponding origins. Type-1 particles are detrital titanomagnetites with micron- and submicron sizes and irregular and angular shapes. Type-2 and -3 particles are well-defined octahedral titanomagnetites with submicron and nanometer sizes, respectively, which are likely related to local hydrothermal and volcanic activity. Type-4 particles are nanometer-sized titanomagnetites hosted within silicates, while type-5 particles are typical dendrite-like titanomagnetites that likely resulted from exsolution within host silicates. Type-6 particles are single domain magnetite magnetofossils related to local magnetotactic bacterial activity. Type-7 particles are superparamagnetic magnetite aggregates, while Type-8 particles are defect-rich single crystals composed of many small regions. Electron microscopy and supervised magnetic unmixing reveal that type-1 to -5 titanomagnetite and magnetite particles are the dominant magnetic minerals. In contrast, the magnetic contribution of magnetite magnetofossils appears to be small. Our work demonstrates that incorporating electron microscopic data removes much of the ambiguity associated with magnetic mineralogical interpretations in traditional rock magnetic measurements.This study was supported financially by the National Natural Science Foundation of China (Grant Nos. 41920104009, 41890843, and 41621004), The Senior User Project of RVKEXUE2019GZ06 (Center for Ocean Mega-Science, Chinese Academy of Sciences)

Rock magnetic constraints for the Mid-Miocene Climatic Optimum from a high-resolution sedimentary sequence of the northwestern Qaidam Basin, NE Tibetan Plateau

The thick sequence of Cenozoic deposits in the Qaidam Basin of the NE Tibetan Plateau has great potential for understanding the tectonic and climatic evolution of the region. In this study, we performed detailed rock magnetic analyses of a well-dated (similar to 20.7-11.2 Ma) Upper Cenozoic sedimentary sequence from the Huatugou (HTG) section in the NW Qaidam Basin. The magnetic susceptibility of the sequence is relatively low before 17.4 Ma, high during 17.4-14.5 Ma, and lower after 14.5 Ma again. This pattern is consistent with the occurrence of the Mid-Miocene Climatic Optimum (MMCO) during 17.4-14.5 Ma, with global climatic cooling thereafter. Measurements of multiple rock magnetic parameters indicate a peak in the concentration of fine-grained magnetic minerals during 17.4-14.5 Ma. This feature demonstrates that the enhancement of the magnetic susceptibility is due to the pedogenic production of superparamagnetic (SP) and single domain (SD) magnetite, suggesting the occurrence of relatively high effective precipitation and high temperature in the Qaidam Basin at this time. Comparing with regional and global climatic records, the warm and humid climatic conditions coincide with the MMCO, implying that global climate changes were responsible for the climatic evolution in the Qaidam Basin throughout the MMCO. However, after 14.5 Ma, the rapid uplift of the northern Tibetan Plateau caused it to reach a critical elevation which blocked the moisture supply to the Qaidam Basin and may also have contributed to the observed climatic changes

Parameters Identification and Adaptive Feedforward Control of Permanent Magnent Linear Synchronous Motor

This paper proposes a novel adaptive feedforward control strategy based on the parameters identification of a permanent magnent linear synchronous motor (PMLSM). The parameters such as the moving mass and viscous coefficient of a PMLSM are identified through an unbiased least square estimation approach with the employment of current and position signals from the built-in sensors. Based on the identified parameters, the accurate state-space model of the PMLSM is established and a robust feedback controller applying H-infinity control method is built. An adaptive feedforward controller based on the nominal model and the online recursion least square method is designed. Simulations and experiments are conducted to verify the control performance of the proposed control system. The results validate that the proposed control approaches are feasible and have better dynamic and tracking performances compared to traditional PID controllers

An ultra-low magnetic field thermal demagnetizer for high-precision paleomagnetism

Thermal demagnetization furnaces are widely used paleomagnetic facilities for progressive removal of naturally acquired magnetic remanence or the imparting of well-controlled laboratory magnetization. An ideal thermal demagnetizer should maintain "zero" magnetic field in the sample chamber during thermal treatments. However, magnetic field noises, including the residual magnetic fields of the construction material and the induced fields caused by the alternating current (AC) in the heating element are always present, which can contaminate the paleomagnetic results at the elevated temperatures or especially for the magnetically weak samples. Here, we designed a new structure of heating wire named "straight core solenoid" to develop a new demagnetization furnace with ultra-low magnetic field noise. Simulation and practical measurements show that the heating current magnetic field can be greatly reduced by using the new technology. Thermal demagnetization experiments demonstrate that the new demagnetizer can yield low noise results even for weakly magnetic samples.This work was supported by NSFC grants 41674073 and the Project of National Deep Exploration Technology and Experimental Research (Grant number: SinoProbe-09–02(201011079)). G.A.P. acknowledges funding from a NERC Independent Research Fellowship (NE/P017266/1)