New Late Carboniferous paleomagnetic results from Qaidam Block and its implications for the paleogeography of central Asia

Abstract:

In order to better understand the kinematic history of the Qaidam block after the breakup of the Rodinia supercontinent, paleomagnetic studies have been carried out on late Carboniferous sediments from the Dachaidan areas in the internal Qaidam block. Totally, 200 sedimentary samples were collected from 20 sites in the late Carboniferous limestones. The stepwise thermal demagnetizations successfully isolated high unblocking temperature characteristic directions (HTC). The tilt-corrected mean direction is D/I =319.3°/-45.6° with α₉₅=4.9° and N=20 sites, corresponding to a paleopole at -15.1°N, 133.1°E with A₉₅=5.0°. All late Carboniferous samples from the studied section yield stable and coherent magnetic directions with reverse magnetic polarity. The predominance (100%) of reversed directions favor the interpretation that the HTC represents a primary remanence acquired during the permo-Carboniferous reversed polarity superchron. Comparisons of the late Carboniferous paleomagnetic poles of the Tarim block and Siberia blocks indicate (1) significant latitudinal relative motion (11.3° ± 6.7° and 8.1° ± 4.3°) occurred since the Late Carboniferous among these blocks, and they may have not accreted together by the late Carboniferous, (2) the 89.9°± 8.3° and the 77.5°± 4.9° counterclockwise rotations of the Qaidam block with respect to Tarim and Siberia block took place since late Carboniferous. These rotations may be accommodated by the post-late Carboniferou strike–slip faults along Altyn Tagh fault and Tianshan Belt and the Altay Belt.