The Sino-Korean-Yangtze suture, the Huwan detachment, and the Paleozoic-Tertiary exhumation of (ultra) high-pressure rocks along the Tongbai-Xinxian-Dabie Mountains

There are three sutures in the Qinling-Dabie-Sulu orogen in the Tongbai-Xinxian (northern Hong`an)-northern Dabie area: the Silurian Sino-Korean craton-Erlangping intra-oceanic arc suture, the Silurian Erlangping arc-Qinling unit (microcontinent) suture, and the Early Triassic Qinling unit-Yangtze craton suture. We resolve the controversy regarding the age of the Sino-Korean craton-Yangtze craton collision by recognizing that there was Paleozoic collision between the Qinling unit and the Sino-Korean craton and Mesozoic collision between the Qinling unit and the Yangtze craton. The Qinling unit constitutes a long and narrow microcontinent that extends through the Qinling-Dabie area and probably into the Sulu area. Its common characteristics are the Mesoproterozoic (ca. 1.0 Ga) Jinningian orogeny, ca. 0.8-0.7 Ga arc formation and rifting, and Late Silurian-Early Devonian (ca. 400 Ma) arc magmatism with concomitant regional contact metamorphism up to granulite-facies conditions (peak: 680-740 degrees C at 0.9-1.1 GPa). A common Proterozoic history links the Qinling microcontinent to the Yangtze craton. Its 400 Ma arc, forearc basin, and its separation from the Yangtze craton by the partly oceanic Huwan melange make the Qinling microcontinent distinct. The forearc basin sits on the southern part of the 400 Ma arc and underlying Proterozoic continental basement, and detrital geochronology ties it to the Qinling microcontinent basement and its arc. The Huwan melange is a subduction-accretion complex containing elements of the Qinling microcontinent and its arc, the Paleotethyan ocean floor, and possibly the Yangtze craton. Quartz eclogites (540-590 degrees C, 2.1 GPa) signify ca. 315 Ma subduction. Devonian to Permian eclogite zircon ages, (40)Ar/(39)Ar and Rb/Sr mineral ages in the forearc and its basement, and static, Permian blueschist metamorphism in the upper-plate basement testify to subduction throughout the late Paleozoic. The similar to 10-km-wide Huwan detachment bounds the high-and ultrahigh-pressure rocks of the Xinxian-Hong`an block (pressure peak at older than 240 Ma) along their northern margin. It is partly responsible for exhumation of the high-and ultrahigh-pressure rocks, but the entire basement core of Hong`an-Dabie orogen is also strongly deformed. The Huwan shear-zone high-strain deformation indicates passage of rocks through the lithosphere by subhorizontal N-S extension and vertical contraction, showcased by condensed Triassic isograds (420 degrees C and similar to 0.4 GPa in the hanging wall and similar to 530 degrees C and 2.2 GPa in the footwall). The Huwan detachment produced Triassic crustal exhumation rates of 1.9-1.4 mm/yr; synkinematic phengite grew as early as ca. 235 Ma, and the main retrograde deformation occurred at 224-195 Ma. The Tongbai-Xinxian area shows a massive 130-115 Ma cluster of cooling ages, reflecting regional cooling after granitoid injection and regional Cretaceous heating. Apatite fission-track ages cluster at 80-55 Ma and signify cooling related to transtension that coincided with rifting marked by Late Cretaceous-Eocene red bed deposition throughout eastern China. Exhumation rates of for the last 70 m.y. have been slow: similar to 0.06 mm/yr. The India-Asia collision reactivated the orogen in the Eocene, particularly along the Tanlu fault zone and locally along fault zones in Tongbai-Xinxian.