Spatial–temporal framework for the closure of the Junggar Ocean in central Asia: New SIMS zircon U–Pb ages of the ophiolitic mélange and collisional igneous rocks in the Zhifang area, East Junggar.

The closure time of the Junggar Ocean is one of the hottest topics surrounding the tectonic evolution of the Central Asian Orogenic Belt (CAOB). This paper reports SIMS zircon U–Pb ages of the ophiolitic mélange and collisional igneous rocks in the Zhifang area, East Junggar. Our new results reveal the following evidence: (1) the West Hill ophiolitic mélange in the Zhifang area contains segments of the 371 Ma MORB-type layered rocks and 363 Ma oceanic islands, which were intruded by the 348 Ma syn-collisional quartz diorites; (2) the ophiolitic mélange and 348 Ma syn-collisional quartz diorites are overlain by the 342 Ma andesitic tuffs; and (3) the 342 Ma andesitic tuffs and successive 332 Ma granodiorites-gabbro were formed at late-collisional setting, whereas the 314 Ma granitic porphyry at post-collisional setting. We suggest that the Junggar Ocean in the Zhifang area was opened before 371 Ma and 363 Ma, and possibly closed before 348 Ma. By combining the published U–Pb ages of the Mayile–Tangbale–Darbute–Kalamaili–Zhifang–Daheishan (MTDKZD) ophiolite belt, Early-Carboniferous volcanic rocks unconformably overlying the MTDKZD ophiolite belt, bimodal volcanic rocks and granitoids within and adjacent to the MTDKZD ophiolite belt, it is suggested that the Junggar Ocean was possibly opened scissors-like from the Neoproterozoic–Ordovician Mayile–Tangbale ocean eastwards through the Silurian–Devonian Darbute–Karamay ocean finally to the Devonian–Early-Carboniferous Kalamaili–Zhifang ocean, and closed scissors-like from the Zhifang–Kalamaili area in the eastern segment westwards to the Darbute–Karamay area in the western segment. Tectonic collage between the Yemaquan–Xiemisitai arc and Junggar block occurred at approximately 343–348 Ma. The Junggar orogenic belt went through late-collisional stage at 343–330 Ma, post-collisional period after 330 Ma, and post-collisional extensional regime after 320 Ma with an intensive stage at around 303 Ma. [ABSTRACT FROM AUTHOR]