Persistently low Asian paleolatitudes: Implications for the India-Asia collision history

Abstract

[1] Paleomagnetism provides independent paleolatitude constraints on the India-Asia convergence. However, implied Cenozoic latitudinal convergence within Asia (thousands of km) largely exceeds geologic estimates of tectonic shortening (hundreds of km). This discrepancy may result from a notoriously low bias in paleomagnetically determined Cenozoic paleolatitudes in Asia. We provide here new paleomagnetic data from Cenozoic Mongolian volcanic rocks and from Chinese Paleogene sediments corrected from the depositional bias of inclination shallowing. These results combined with similar Asian data sets, confirm that paleolatitudes are still 5–10° lower than predicted by the paleomagnetic Apparent Polar Wander Path (APWP) for Asia between 50 and 20 Ma. Inclination-shallowing being excluded from the selected data sets, we investigate the likeliness of other proposed mechanisms for this discrepancy: (1) more southerly positions of Asia than expected by the APWP (due to APWP inaccuracies rather than Eurasian non-rigidity), or (2) non-dipolar geomagnetic field contributions. Fully explaining this discrepancy by only one of these mechanisms would imply either unrealistically large (>10°) APWP inaccuracies, or unrealistically large octupolar field contributions (up to 16%). A combination of these mechanisms is found more likely to have produced the observed latitudinal discrepancy, but their respective contributions cannot be quantified given the still relatively low amount and poor quality of Cenozoic paleomagnetic data from stable cratons of Asia, India, and Europe. By allowing for reasonable time-dependant non-dipolar contributions and a slight (<5°) APWP bias, the latitudinal discrepancy can be resolved and the excessive amounts of intra-Asian shortening decrease to values in line with tectonic shortening from structural studies.