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366 results on '"Mitchell, Ross N"'

1. Persistent but weak magnetic field at Moon's midlife revealed by Chang'e-5 basalt

Author

Cai, Shuhui, Qin, Huafeng, Wang, Huapei, Deng, Chenglong, Yang, Saihong, Xu, Ya, Zhang, Chi, Tang, Xu, Gu, Lixin, Li, Xiaoguang, Shen, Zhongshan, Zhang, Min, He, Kuang, Qi, Kaixian, Fan, Yunchang, Dong, Liang, Hou, Yifei, Shi, Pingyuan, Liu, Shuangchi, Su, Fei, Chen, Yi, Li, Qiuli, Li, Jinhua, Mitchell, Ross N., He, Huaiyu, Li, Chunlai, Pan, Yongxin, and Zhu, Rixiang

Subjects
Physics - Geophysics
Abstract

The evolution of the lunar magnetic field can reveal the Moon's interior structure, thermal history, and surface environment. The mid-to-late stage evolution of the lunar magnetic field is poorly constrained, and thus the existence of a long-lived lunar dynamo remains controversial. The Chang'e-5 mission returned the heretofore youngest mare basalts from Oceanus Procellarum uniquely positioned at mid-latitude. We recovered weak paleointensities of 2-4 uT from the Chang'e-5 basalt clasts at 2 billion years ago, attestting to the longevity of a lunar dynamo until at least the Moon's midlife. This paleomagnetic result implies the existence of thermal convection in the lunar deep interior at the lunar mid-stage which may have supplied mantle heat flux for the young volcanism.

Published
2024

6. Buried palaeo-polygonal terrain detected underneath Utopia Planitia on Mars by the Zhurong radar

Author

Zhang, Lei, Li, Chao, Zhang, Jinhai, Zhou, Bin, Zhao, Yu-Yan Sara, Liu, Yang, Di, Kaichang, Mitchell, Ross N., Li, Juan, Zhang, Zhigang, Chen, Lin, Liang, Xiaofeng, Sun, Weijia, Liu, Yike, Zhao, Xu, Hao, Jinlai, Xu, Changyi, Zheng, Yikang, Wang, Yibo, Wang, Xin, Zhao, Pan, Lv, Wenmin, Li, Yang, Lan, Haiqiang, Li, Yuxi, Wang, Wei, Lu, Yang, Lin, Honglei, Fang, Peng, Lin, Wei, Wei, Yong, Chen, Ling, Fang, Guangyou, Lin, Yangting, Yao, Zhenxing, and Pan, Yongxin

Published
2024
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7. Evidence of a large igneous province at ca. 347–330 Ma along the northern Gondwana margin linked to the assembly of Pangea: Insights from U–Pb zircon geochronology and geochemistry of the South-Western Branch of the Variscan Belt (Morocco)

Author

Moutbir, Oussama, Aarab, El Mostafa, Youbi, Nasrrddine, Ait Lahna, Abdelhak, Tassinari, Colombo Celso Gaeta, Mata, João, Mitchell, Ross N., Gärtner, Andreas, Soesoo, Alvar, Bensalah, Mohamed Khalil, Soulaimani, Abderrahmane, Boumehdi, Moulay Ahmed, and Linnemann, Ulf

Published
2024
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10. Ground magnetic survey on Mars from the Zhurong rover

Author

Du, Aimin, Ge, Yasong, Wang, Huapei, Li, Haiying, Zhang, Ying, Luo, Hao, Huang, Can, Shan, Lican, Han, Fei, Liu, Yang, Zou, Yongliao, Wang, Chi, Pan, Yongxin, Liu, Qingsong, Mitchell, Ross N., Jia, Yang, Chen, Baichao, Jin, Shengyi, Jiang, Yi, Zhang, Tielong, Zhu, Rixiang, Gubbins, David, and Zhang, Keke

Published
2023
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29. Prograde metamorphism in the ~1.9 Ga Jiao–Liao–Ji orogenic belt of NE China Craton: implications for orogenic crustal thickening.

Author

Wen, Fei, Zhai, Mingguo, Tian, Zhonghua, Wang, Wei, Zou, Lei, and Mitchell, Ross N.

Subjects
METAMORPHIC rocks, OROGENIC belts, PETROLOGY, OROGENY, GARNET
Abstract

The complete evolutionary process of orogenesis can be deciphered by studying metamorphic rocks at middle and lower crustal depths of orogens. Recent studies have suggested that granulite-facies metamorphic rocks in the Paleoproterozoic Jiao–Liao–Ji orogenic belt experienced clockwise pressure–temperature (p–T) paths. However, due to the effects of high temperature, the prograde metamorphic processes are poorly constrained. The question could be solved by studying the Barrovian series rocks, because some garnet growth zoning has been preserved in the lower grade rocks. A Barrovian series from garnet to kyanite-sillimanite zones has been recognized in the Liaodong Peninsula. Based on petrology and mineral chemistry, each metamorphic rocks in metamorphic zone are divided into prograde, peak, and retrograde metamorphic stages. Pseudosection modelling constrains the peak metamorphic conditions at ~568°C and ~5.8 kbar for the garnet zone, ~585°C and ~6 kbar for the staurolite zone, and ~670°C and ~8.2 kbar for the kyanite-sillimanite zone. All Barrovian series rocks have clockwise p–T paths, implying crustal thickening during prograde metamorphism. LA-ICP-MS monazite and zircon U–Pb dating suggest that peak Barrovian metamorphism occurred at ca. 1.92–1.91 Ga. Combining our results of the Barrovian series with studies on granulite-facies metamorphic rocks, we suggest that the Jiao–Liao–Ji belt experienced crustal thickening from 1.95 to 1.90 Ga, inducing Barrovian metamorphism and granulite-facies metamorphism in the middle and lower crust, respectively. Subsequently, rocks located at the different crustal levels were exhumed during post-orogenic extension. [ABSTRACT FROM AUTHOR]

Published
2024
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32. Neoproterozoic glacial origin of the Great Unconformity

Author

Keller, C Brenhin, Husson, Jon M, Mitchell, Ross N, Bottke, William F, Gernon, Thomas M, Boehnke, Patrick, Bell, Elizabeth A, Swanson-Hysell, Nicholas L, and Peters, Shanan E

Subjects
Earth Sciences, Physical Geography and Environmental Geoscience, Geology, Geophysics, Great Unconformity, snowball Earth, glacial erosion, zircon, Cambrian explosion
Abstract

The Great Unconformity, a profound gap in Earth's stratigraphic record often evident below the base of the Cambrian system, has remained among the most enigmatic field observations in Earth science for over a century. While long associated directly or indirectly with the occurrence of the earliest complex animal fossils, a conclusive explanation for the formation and global extent of the Great Unconformity has remained elusive. Here we show that the Great Unconformity is associated with a set of large global oxygen and hafnium isotope excursions in magmatic zircon that suggest a late Neoproterozoic crustal erosion and sediment subduction event of unprecedented scale. These excursions, the Great Unconformity, preservational irregularities in the terrestrial bolide impact record, and the first-order pattern of Phanerozoic sedimentation can together be explained by spatially heterogeneous Neoproterozoic glacial erosion totaling a global average of 3-5 vertical kilometers, along with the subsequent thermal and isostatic consequences of this erosion for global continental freeboard.

Published
2019

39. Conformably Variable Geocentric Axial Dipole at ca. 2.1 Ga: Paleomagnetic Dispersion of the Indin Dyke Swarm, Slave Craton.

Author

Liu, Yu‐Shu, Mitchell, Ross N., Bleeker, Wouter, Peng, Peng, Salminen, Johanna, and Evans, David A. D.

Subjects
*GEOMAGNETISM, *VOLCANIC ash, tuff, etc., *GEOLOGICAL time scales, *PALEOMAGNETISM, *MAGNETIC fields, *DIKES (Geology)
Abstract

Precambrian paleomagnetic studies are critical for testing paleogeographic reconstructions in deep time but rely on the fidelity of the assumption of the geocentric axial dipole (GAD) hypothesis. With high‐reliability data from mafic dykes and volcanic rocks, the scatter of individual virtual geomagnetic poles (VGPs) can be used to test simple GAD models. In order to conduct such a test, the VGPs must be adequate in number and in spatial coverage of the sampling sites. In this study, we targeted the 2.1 Ga Indin dyke swarm of the Slave craton. Building on previous sampling of the Indin dyke swarm in the western and central parts of southern Slave craton, we report results from 9 additional sites in the central and eastern parts of the craton, sites that significantly expand the width of the dyke swarm across the entire craton. The VGPs obtained from 7 of 9 newly identified Indin dykes are broadly similar to previously reported directions, expanding the total of VGPs for individual Indin dykes to n = 28, which is sufficient for a test of the GAD‐based statistical models using VGP scatter. The high VGP scatter of the Indin swarm can be attributed to the relatively high paleolatitude of 56° ± 6° for the Slave craton at the time of dyke emplacement. The Indin data have VGP scatter that is consistent with field models associated with the GAD hypothesis for the indicated paleolatitude, thus confirming the fidelity of the GAD field at ca. 2.1 Ga. Plain Language Summary: A fundamental assumption in paleomagnetism is the geocentric axial dipole (GAD) hypothesis. One feature of GAD that can be used to test it is that paleosecular variation (PSV) under a GAD field varies systematically with latitude, with its scatter being greater at relatively high latitudes than at low latitudes. Lavas and dykes for the past five million years and for various points in Earth's history generally support GAD, but there are some large gaps between these tests. Short‐term departures from GAD and/or intervals of weak fields have been suggested for certain time periods, highlighting the importance of regular tests of the GAD field throughout geological time. We study the ca. 2.1‐billion‐year‐old Indin dykes that fills one of these critical gaps. The Indin dyke swarm intruded across a large swath of the southern Slave craton, allowing us to extensively sample PSV. Our study finds a large VGP scatter for the Indin dykes, but as is to be expected given the relatively high paleolatitude. Thus, the scatter of Indin VGPs aligns with the GAD field model, confirming the reliability of the GAD field at ca. 2.1 Ga. Future studies of paleogeographic reconstruction during this period can confidently utilize paleomagnetism as a reliable quantitative constraint. Key Points: The ca. 2.1 Ga Indin dyke swarm has now been extensively sampled across much of the southern Slave cratonThe age and relatively high paleolatitude of the Indin dyke swarm provides an important constraint on the ancient magnetic fieldThe scatter of the paleomagnetic directions of the Indin dykes statistically supports a typical geomagnetic dipole field at 2.1 Ga [ABSTRACT FROM AUTHOR]

Published
2024
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43. The supercontinent cycle

Author

Mitchell, Ross N., Zhang, Nan, Salminen, Johanna, Liu, Yebo, Spencer, Christopher J., Steinberger, Bernhard, Murphy, J. Brendan, and Li, Zheng-Xiang

Published
2021
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49. The assembly of Pangaea: geodynamic conundrums revisited.

Author

Murphy, J. Brendan, Nance, R. Damian, and Mitchell, Ross N.

Subjects
SUBDUCTION, SUBDUCTION zones, PALEOZOIC Era, OCEAN, FORECASTING, GEODYNAMICS
Abstract

Geodynamic models for Pangaea assembly require knowledge of Paleozoic mantle convection patterns. Application of basic geodynamic principles to Neoproterozoic–Paleozoic plate reconstructions yields Pangaea in the incorrect configuration (predicting that it should have formed by consumption of the exterior palaeo-Pacific Ocean instead of the Iapetus, Rheic and Proto-Tethys oceans). We contend that the mantle legacy of Late Neoproterozoic–Cambrian amalgamation of Gondwana must be factored into models for Pangaea amalgamation. Proxy data suggest that the mantle downwelling driving Pan-African collisions and Gondwana assembly evolved into a mantle upwelling as evidenced by the interplay between subduction-related and plume-related tectonics around the periphery of Gondwana. Orthoversion theory, whereby a supercontinent assembles c. 90° away from the centre of the previous supercontinent, suggests that Gondwana amalgamated above an intense downwelling along a meridional subduction girdle that bisected two antipodal sub-equatorial upwellings. Several processes beneath and around Gondwana reduced the intensity of the original downwelling, as evidenced by plume-related activity along its margins, initiation of subduction zone rollback, and the export of terranes from Gondwana that collided with the margin of Laurentia–Baltica. As upwelling beneath it intensified, Gondwana migrated along the girdle until it collided with Laurentia–Baltica, resulting in the final assembly of Pangaea. [ABSTRACT FROM AUTHOR]

Published
2024
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