Tectonic origin of the Bainaimiao arc terrane in the southern Central Asian orogenic belt: Evidence from sedimentary and magmatic rocks in the Damao region

As a main part of the North China craton collage system, the tectonic origin of the Bainaimiao arc terrane is still hotly debated, especially its relationship with the North China craton. Thus, we report on a field-based petrological and zircon U-Pb-Hf isotopic study of (meta-)sedimentary and volcanic rocks from the Bainaimiao arc terrane and northern margin of the North China craton in the Damao region. The lower and middle successions of the Bayan Obo Group from the northern North China craton, including the Dulahala, Jianshan, Halahuogete, and Bilute Formations, were deposited ca. 1.81−1.35 Ga and show age peaks at 1.85, 1.90, 2.0, and 2.5 Ga. This age pattern is in accordance with the coeval and extensively outcropped metamorphosed basement rocks of the northern North China craton. The upper succession, including the Bayinbaolage and Hujiertu Formations, deposited ca. 1.19−0.92 Ga, shows age peaks at ca. 1.35, 1.57, and 1.69 Ga, and sediments were derived from coeval rift-related magmatism characterized by a significant increase in positive εHf(t) values in detrital zircons. Thus, the Bayan Obo Group can be subdivided into North China craton basement−derived sediments and Mesoproterozoic to Neoproterozoic rift-derived sediments, and the change of the provenance was probably caused by the ca. 1.35−1.30 Ga rifting event related to the breakup of the Nuna supercontinent. In the Bainaimiao arc terrane, zircon U-Pb geochronological results of (meta-)sedimentary rocks indicate they were formed in the Neoproterozoic and Paleozoic and have mainly late Paleoproterozoic to Neoproterozoic ages (ca. 0.6−0.9, 1.1−1.2, 1.4−1.7, and 1.8−2.0 Ga) with peaks at ca. 0.86, 0.96, 1.15, 1.47, 1.66, 1.75, 1.80−1.87, and 1.94 Ga. The abundant Neoproterozoic ages for the Bainaimiao arc terrane detrital zircons are distinct from the scarcity of these ages in the northern North China craton, southern Siberia (age peaks at ca. 1.87, 1.92, and 2.0 Ga), and Mongolia (age peak at ca. 0.62, 0.83, 0.93, 1.84, and 2.0 Ga), but they are similar to the features of the Tarim craton (age peaks at ca. 0.62, 0.85, 1.15, 1.47, 1.66, 1.75−1.80, 1.85, and 1.94 Ga). Together with the recognition of a possible preexisting Proterozoic basement (ca. 0.7−2.0 Ga) in the Bainaimiao arc terrane, as evidenced by the Hf model ages of continental arc magmatism in the Bainaimiao arc terrane, this late Paleoproterozoic to Neoproterozoic detritus probably resulted from local recycled sedimentation, and the preexisting Bainaimiao arc terrane basement rifted away from a continent with Tarim craton affinity. The rifting probably occurred between ca. 0.6 and 0.52 Ga, because the reworking of the Precambrian rocks in the North China collage system occurred between ca. 520 and 230 Ma.