Late Carboniferous paleomagnetism of the Southwestern Tarim block and its implications for the paleogeography of central Asia

Abstract:

In order to better understand the kinematic history of the Tarim block after the breakup of the Rodinia supercontinent, paleomagnetic studies have been carried out on late paleozoic strata from the Yecheng areas in the southwestern Tarim block. Totally, 250 sedimentary samples were collected from 25 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 =219.0°/-49.0° with α₉₅=5.5° and N=25 sites, corresponding to a paleopole at 57.2°N, 167.0°E with A₉₅=6.1°. 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. Also, positive fold test indicate a primary origin for the characteristic remanence. Comparisons of the late Carboniferous paleomagnetic poles of the Tarim block with available coeval poles of Junggar and Siberia blocks indicate (1) no significant latitudinal relative motion (2.6° ± 10.3° and 3.1° ± 7.3°) occurred since the Late Carboniferous among these blocks, and they may have accreted together by the late Carboniferous, but (2) the 62.5° ± 11.7° and the 30.2°± 8.3° counterclockwise rotations of the Tarim block with respect to Junggar and Siberia block took place since late Carboniferous. These rotations may be accommodated by the post-late Carboniferou strike–slip faults along the northern and southern sides of Tianshan Belt and the Altay Belt.