Detrital zircon constraints on late Paleozoic tectonism of the Bogda region
(NW China) in the southern Central Asian Orogenic Belt
-
Abstract
The Chinese North Tianshan (CNTS) in the southern part of the Central Asian Orogenic Belt (CAOB) has undergone
multistage accretion-collision processes during Paleozoic time, which remain controversial. This study
addresses this issue by tracing the provenance of Late Paleozoic sedimentary successions from the Bogda
Mountain in the eastern CNTS through U–Pb dating and Lu–Hf isotopic analyses of detrital zircons. New detrital
zircon U–Pb ages (N ¼ 519) from seven samples range from 261 4 Ma to 2827 32 Ma. The most prominent
age peak is at 313 Ma and subordinate ages vary from 441 Ma to 601 Ma, with some Precambrian detrital zircon
ages (~7%) lasting from 694 Ma to 1024 Ma. The youngest age components in each sample yielded weighted
mean ages ranging from 272 9 Ma to 288 5 Ma, representing the maximum depositional ages. These and
literature data indicate that some previously-assumed “Carboniferous” strata in the Bogda area were deposited in
the Early Permian, including the Qijiaojing, Julideneng, Shaleisaierke, Yangbulake, Shamaershayi, Liushugou,
Qijiagou, and Aoertu formations. The low maturity of the sandstones, zircon morphology and provenance analyses
indicate a proximal sedimentation probably sourced from the East Junggar Arc and the Harlik-Dananhu Arc
in the CNTS. The minor Precambrian detrital zircons are interpreted as recycled materials from the older strata in
the Harlik-Dananhu Arc. Zircon εHf(t) values have increased since ~408 Ma, probably reflecting a tectonic
transition from regional compression to extension. This event might correspond to the opening of the Bogda intraarc/
back arc rift basin, possibly resulting from a slab rollback during the northward subduction of the North
Tianshan Ocean. A decrease of zircon εHf(t) values at ~300 Ma was likely caused by the cessation of oceanic
subduction and subsequent collision, which implies that the North Tianshan Ocean closed at the end of the Late
Carboniferous.
-
-