North China block underwent simultaneous true polar wander and tectonic convergence in late Jurassic: New paleomagnetic constraints

Abstract

Jurassic witnessed two synchronous events on the Earth, named true polar wander (TPW) and closure of the Mongol–Okhotsk ocean (MOO) between Siberia and eastern Asian blocks. The paleogeographic change of the north China block (NCB) should thus include both TPW and plate tectonic components in Jurassic. We performed a new combined paleomagnetic and U–Pb geochronological study for Middle and Late Jurassic volcanic rocks from the northern NCB and obtained three new well-dated paleopoles: 82.7°N, 282.6°E, A95=3.2° (ca. 160 Ma); 84.1°N, 228.9°E, A95=6.6° (ca. 165 Ma); and 89.3°N, 216.8°E, dp/dm = 5.4°/7.1° (ca. 170 Ma). A positive untilting test indicates a pre-folding origin interpretation for the ca. 160 Ma pole. Quality of these poles is enforced by three positive conglomerate tests, the presence of magnetic reversals and secular variation analyses. Comparison of the apparent polar wander paths of Eurasia and the NCB suggests that the NCB accreted to Eurasia around 140 Ma. The NCB and its then connected blocks did not undergo any significant southward paleogeographic shift during Jurassic. In context of TPW, we estimate a net northward plate moving velocity at 0.50–0.75°/myr for the NCB in Jurassic. The long-term accumulation of MOO subducted slabs at the high paleolatitudes may have critically contributed to, or perhaps led to, the Jurassic TPW.