Remagnetization Age and Mechanism of Cretaceous Sediments in Relation to Dyke Intrusion, Hainan Island: Tectonic Implications for South China and the Red River Fault

• Published in: Journal of geophysical research. Solid earth 2022-01, Vol.127 (1), p.n/a
• Main Authors: Meng, Jun, Gilder, Stuart A., Li, Yalin, Chen, Yan, Zhang, Chunyang, Zhou, Zhaoyang, Liu, Tao, Zhao, Yinan, Wang, Zihao, Wang, Chengshan
• Format: Article
• Language: English
• Subjects: Age; Baking; Beds (geology); Chronostratigraphy; Cretaceous; Cross cutting; dyking; Electron microscopy; Geochronology; Geographical coordinates; Geophysics; Haematite; Hematite; Intrusion; Palaeomagnetism; Paleogeography; Paleolatitude; Paleomagnetic studies; Paleomagnetism; Radiometric dating; remagnetization; Remagnetization dating; Remanence; Remanent magnetization; Rivers; Rock intrusions; rotations; Secular variations; Sediment; Sediment samples; Sedimentary rocks; Sediments; south China; Spawning; Tectonics; Tuff; Zircon
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1029/2021JB023474

Hainan Island lies near the Red River Fault, a prominent tectonic feature produced by the India‐Asia collision. There, we carried out a geochronologic and paleomagnetic study on Cretaceous rocks in order to better understand the kinematic history of the region. U‐Pb zircon dating of tuff intercalated in red bed sedimentary rocks yielded a concordant age of 106.6 ± 0.3 Ma; a mafic dyke intruding the red beds yielded a concordant age of 104.6 ± 0.7 Ma. Stepwise demagnetization experiments on 448 sedimentary rock samples and 191 dyke samples isolate solely normal polarities. Paleomagnetic directions of the dykes cluster in two distinct populations in geographic coordinates, indicating that dyke intrusion occurred in two pulses of limited duration (secular variation was not averaged) after tilting of the sediments. Baking of the sediments from the dykes only occurred near the contacts. Together with published data, the mean directions of 104 sites most tightly group at 58.3 ± 3.2% unfolding, indicative of a synfolding remagnetization, which can be constrained to have occurred within a 2 Myr period between sedimentation and dyke intrusion. We suggest that warm (50–100°C) fluid interaction during basin development led to new mineral growth spawning chemical remagnetization. The corresponding paleomagnetic pole at 81.5°N, 145.2°E (A95 = 2.4°) is indistinguishable from the coeval Eurasian reference pole, suggesting the South China Block has remained fixed to Eurasia since 105 Ma. A contour map of paleomagnetic rotations from 115 studies in the region shows that the Red River Fault roughly demarcates rotation magnitudes/signs, suggestive of a major tectonic boundary. Plain Language Summary Highly stable magnetic remanences of hematite‐bearing sedimentary rocks (red beds) form the basis of numerous paleomagnetic studies. However, an on‐going scientific debate called the “red bed controversy” stems from the relative timing when the remanence was acquired (primary = detrital vs. secondary = chemical). Our article concerns a paleomagnetic and geochronologic study of Cretaceous red beds and cross cutting dykes from Hainan Island (South China). Radiometric‐dating of tuff intercalated in the red beds and the crosscutting mafic dykes, combined with paleomagnetic analyses of 639 samples, allows us to precisely constrain the age of a pervasive synfolding remagnetization at ca. 105 Ma. Together with electron microscopy, we demonstrate the existence of a chemical remanent magn