Paleomagnetism and U-Pb geochronology of the late Cretaceous Chisulryoung Volcanic Formation, Korea: tectonic evolution of the Korean Peninsula

초록

Late Cretaceous Chisulryoung Volcanic Formation (CVF) in southeastern Korea contains four ash-flow ignimbrite units (A1, A2, A3, and A4) and three intervening volcano-sedimentary layers (S1, S2, and S3). Reliable U-Pb ages obtained for zircons from the base and top of the CVF were 72.8 +/- 1.7 Ma and 67.7 +/- 2.1 Ma, respectively. Paleomagnetic analysis on pyroclastic units yielded mean magnetic directions and virtual geomagnetic poles (VGPs) as D/I = 19.1 degrees/49.2 degrees (alpha(95) = 4.2 degrees, k = 76.5) and VGP = 73.1 degrees N/232.1 degrees E (A(95) = 3.7 degrees, N = 3) for A1, D/I = 24.9 degrees/52.9 degrees (alpha(95) = 5.9 degrees, k = 61.7) and VGP = 69.4 degrees N/217.3 degrees E (A(95) = 5.6 degrees, N = 11) for A3, and D/I = 10.9 degrees/50.1 degrees (alpha(95) = 5.6 degrees, k = 38.6) and VGP = 79.8 degrees N/242.4 degrees E (A(95) = 5.0 degrees, N = 18) for A4. Our best estimates of the paleopoles for A1, A3, and A4 are in remarkable agreement with the reference apparent polar wander path of China in late Cretaceous to early Paleogene, confirming that Korea has been rigidly attached to China (by implication to Eurasia) at least since the Cretaceous. The compiled paleomagnetic data of the Korean Peninsula suggest that the mode of clockwise rotations weakened since the mid-Jurassic. Such interesting variation of vertical rotations in the Korean Peninsula might result from the strike-slip motions of major faults developed in East Asia (the Tancheng-Lujiang fault to the northwest and the Korea-Taiwan strait fault to the southeast), near-field tectonic forcing of the subducting Pacific Plate beneath the Eurasian Plate, and far-field expressions of the India-Asia collision.

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