Paleomagnetism and paleogeographic reconstructions of the North China Craton in the Late Carboniferous - Early Permian and the South China Craton in  the Late Ediacaran - Early Cambrian
Creators: Kozmina, Ekaterina
Publisher: name: University of Alberta Library
Year: 2022

<p>Abstract<br>
The robustness of paleogeographic reconstructions of the North China Craton (NCC) and South China Craton (SCC) in the Ediacaran - Paleozoic is greatly affected by a small number of high-reliability paleomagnetic poles. Reduced reliability of available paleomagnetic data is attributed to weak magnetizations of the sediments, absence of up-to-date stepwise demagnetization analysis, field tests, and rock-magnetics studies. </p>

<p>This study reports the first reliable paleomagnetic poles from the Late Carboniferous - Early Permian sediments of the NCC and the Ediacaran - Early Cambrian sediments of the SCC. The new paleomagnetic poles meet all seven paleomagnetic reliability criteria and their ages are supported by our own zircon data. We sampled fine-grained sandstones, limestones, and red stones (only from the SCC). Our stepwise demagnetization analysis shows the presence of two magnetic components in the samples and the great circle directed towards the high-temperature component direction. The fold and polarity tests indicate the primary character of the high-temperature component.</p>

<p>Our new paleomagnetic poles for the NCC show that the craton moved from 26.9°N ± 5.2° to 32.5°N ± 7.1° during the Late Carboniferous - Early Permian (after the application of the flattening factor of 0.7). These are higher latitudes than it was considered before. We show that the width of the Paleo Asian Ocean between the NCC and Inner Mongolian arc accretionary complexes was ~860 km in the Late Carboniferous - Early Permian, which was three times narrower than the previous studies suggested.</p>

<p>We completed the new paleomagnetic analysis of the Early Cambrian and Early and Late Ediacaran directions from the SCC. It should be noted that the Late Ediacaran and Early Cambrian of the SCC have never been studied paleomagnetically. In this study, the Early and Late Ediacaran paleomagnetic poles yielded a paleolatitude around 15°N that resembles the paleolatitudes obtained from the coeval paleomagnetic poles for Australia. This favors a hypothesis that the SCC could be attached or in close proximity to Australia in the Neoproterozoic or at least be at a similar paleolatitude. However, it contradicts the paleogeography reconstructions that placed the SCC at ~33°S. The Early Cambrian paleolatitude was 8.2°N ± 3.6° which corresponds to the Middle Cambrian paleolatitudes from the other studies. At the same time, the affinity between the new Early Cambrian pole and Late Permian - Early Triassic poles for the SCC does not rule out a possibility of overprinting. Future additional measurements will enable us to provide a more statistically reliable interpretation. However, we were able to show that high temperature components for Ediacaran and Cambrian are all distributed along the great circle with the Euler pole at the sampling locality. Such scatter was already reported for Laurentia, Australia, and Siberia. There are a few different hypotheses that explain such a scatter and adding our new reliable South China paleomagnetic data sets will be a step forward in constraining these hypotheses.</p>