A Widespread Early Mesozoic Remagnetization in South China

Abstract

The recent discovery of a possible Late Cambrian true polar wander (TPW) from the Jiangshan section in eastern South China has intrigued us to test this TPW in other continuous, well-dated Upper Cambrian successions. We have conducted a detailed paleomagnetic study of a continuous Upper Cambrian succession in Wa'ergang, Hunan Province, middle South China, that contains well-defined trilobite zones correlative with those of the Jiangshan section. Three remanence components were isolated from the Upper Cambrian limestone. The low-and intermediate-temperature components represent a recent viscous magnetization and a Cretaceous remagnetization, respectively. The high-temperature component passes fold tests, but its pole lies close to the Middle Triassic pole of South China, indicating a Middle Triassic remagnetization.Rock magnetic analyses and petrographic observations indicate that the high-temperature component resides in small framboidal magnetite aggregates that were formed via alteration and replacement of pyrite and represents a chemical remagnetization. This Middle Triassic remagnetization and previously recognized Triassic remagnetization exhibit a younging trend from the east to the west of South China. The widespread Triassic remagnetization was likely associated with the Indosinian orogeny during which the scissor-like suturing processes between the South and North China Blocks and the accompanying so-called squeegeed orogenic fluids led to progressively westward younging remagnetization in South China. Although the new paleomagnetic results do not allow us to effectively test the Late Cambrian TPW due to the thorough remagnetization, these data provide important insights into understanding the Early Mesozoic remagnetization and associated geological processes.

Fluid Migration and Widespread Remagnetization in the Dabashan Fold and Thrust Belt, China

“…We suggest that the Jurassic orogeny caused the widespread CRM in the Dabashan fold and thrust belt. This is supported by the tectonic history of the region where the scissor‐like suturing processes of the SCB and NCB during the Triassic caused widespread and progressively westward younging of the CRMs in the SCB (Jiao et al, 2019). Due to the uplift and deformation by the Jurassic orogeny, it is likely that a large volume of fluids migrated leading to alteration in the fold and thrust belt.…”

“…During the Permian‐Early Triassic, the northeastern part of the SCB initially collided with the North China Block (NCB), and then the entire SCB rotated clockwise relative to the NCB. In the Late Triassic‐Early Jurassic, the Paleo‐Tethys Ocean had closed in the west, and the western part of the SCB including our study area started to collide with the NCB (Jiao et al, 2019; Yin & Nie, 1993; Zhao & Coe, 1987). Due to the slab pull of eclogitized mafic crust in the subducted SCB, the two blocks continued to converge during the Jurassic, forming the Dabashan fold and thrust belt (Dong et al, 2011, 2013; Zhang et al, 2001).…”

Magmatic‐Hydrothermal Alteration Mechanism for Late Mesozoic Remagnetization in the South China Block

“…(b–e) Distribution of Mesozoic remagnetization events, granitoids and major ore deposits in the SCB (granitoids are from Hong et al, ; ore deposits are from Hu & Zhou, ; Long & Liu, ; Mao et al, ; Wang et al, , ; Wu, ; Yang & Li, ; Yang, Mao, et al, ; Zhang et al, ). Xialei: this study; Nanjing: Kent et al (); Yichang: Kent et al (), Jing et al (); Changshou: Enkin et al (); Chuanshan and Huanglong: Dobson and Heller (); Badong: Huang and Opdyke (); Dushan: Zhang et al (); Xuyong: Yang and Besse (); Huangben: Shen et al (); Wanzhou: Han et al (); Yibin: Zhang et al (); Jiangshan: Jiao et al (); Taoyuan: Jiao et al ().…”

Paleomagnetic study on the Early Permian Gubaoquan doleritic dike swarm in the southern Beishan area, NW China: Implications for the tectonic and paleogeographic reconstructions of the southern Central Asian Orogenic Belt

“…No authigenic mineral within fractures and pores is found under SEM, precluding any chemical remagnetization resulting from orogenic fluids (Fig. 4h-i; Jiao et al, 2019;Zhang et al, 2019). The possible weak influence of posterior magma-thermal events, which only partially reset the 40 Ar/ 39 Ar system of plagioclase (225-300 °C; Cassata et al, 2009) at 266-260 Ma, is unable to blur the P 1 ChRMs carried by magnetite, excluding intense thermal remagnetization.…”