Decoupling of surface and subsurface sutures in the Dabie orogen and a continent-collisional lithospheric-wedging model: Sr-Nd-Pb isotopic evidences of Mesozoic igneous rocks in eastern China

Abstract

There are significant differences of Nd and Pb isotopic compositions between Mesozoic mafic igneous rocks from the North China Block (NCB) and the South China Block (SCB). Mesozoic mantle-derived igneous rocks from the North China Block have very low Nd values ( 15 to 21), and 206 Pb/ 204 Pb ratios (< 17.9), while those in the SCB are characterized by Nd > 10 and 206 Pb/ 204 Pb > 18.3. The very low Nd values ( 16 to 20) and 206 Pb/ 204 Pb ratios (< 17.3) of the early Cretaceous mafic-ultramafic intrusions developed in the north part of the Dabie orogen (NDZ) suggest that the deep lithosphere underneath the NDZ belongs to the NCB but not the SCB. Therefore, although the surface suture between the NCB and SCB is located on the north side of the NDZ, the subsurface suture between the NCB and SCB should be located to the south side of the NDZ. This is consistent with the previous suggestion that the subsurface suture in the Sulu terrane east of the Tanlu fault was the south displacement, but contradictory to northward continental subduction of the SCB. A continent-collisional lithosphericwedging model can interpret the decoupling of the surface and subsurface sutures in the Dabie-Sulu orogen. After slab break-off, the continuing convergence of two continental blocks must increase the compression force acting on the suture zone, which might induce the lithosphere splitting of SCB. Thus, the lower crust and lithospheric mantle on the south margin of the NCB can wedge into the north margin of the lithosphere of the SCB along the Dabie-Sulu collision zone. This process caused the overthrust of the mid-upper continental crust with exhumed ultrahigh pressure metamorphic (UHPM) rocks and underthrust of the deep lithosphere of the SCB. It could be an important mechanism responsible for the second rapid cooling and uplifting of the UHPM rocks and lithospheric delamination as well as the corresponding magmatism in Jurassic in the Dabie orogen. The southward movement of subsurface suture in the Dabie-Sulu orogen may also provide a tectonic setting in depth for the large-scale Mesozoic magmatic-metallogenesis along the middle-lower reaches of the Yangtse River in eastern China.

High‐ to ultrahigh‐pressure (UHP) ductile shear zones in the Sulu UHP metamorphic belt, China: implications for continental subduction and exhumation

“…(2001) showed that Pb isotope data for the Cretaceous granitoids from the Northern Dabieshan and Sulu area are similar to those from the North China plate but very different from those from the Yangtze plate, and proposed the subduction of the North China plate under the Yangtze plate. These Pb isotope systematics are confirmed by Nd and Pb isotope study of the Mesozoic mafic and ultramafic intrusions (Li and Yang, 2002), who suggested that the subsurface suture of the two plates might be to the south of the Dabieshan and Sulu region, and close to the Yangtze River.…”

Correlation of lithospheric “de‐rooting” of the Sulu‐Dabie Orogen to tectonic‐sedimentary process of the Hefei Basin: Constraints from Mesozoic coupling of basin and orogen

“…Geochemical data also show that the subduction polarities between the two large‐scale blocks are south‐eastward (Li et al, ). The SrNdPb isotope composition of the Mesozoic mafic magmatic rocks in the deep lithosphere of the western Dabie area is similar with that of the SCB (Li & Yang, ), the geochemical characteristics of fresh basalts in northern Jiangsu also indicates that the lithospheric mantle in northern Jiangsu is related to the NCB (Chung, ). In the southern margin of the Laiyang Basin, a large amount of North China clastic material developed, which further supports that the NCB was once abducted to the Yangtze Block, and the coexistence of the obduction and subduction is an important reason for the UHPM (Zhou, Han, & Song, ).…”

Geochemistry of Early Cretaceous Intermediate to Mafic Dikes in the Jiaodong Peninsula: Constraints on Mantle Source Composition beneath Eastern China

“…The Sulu terrain is the easternmost part of the Dabie-Sulu HP to UHP metamorphic belt formed by the collision of the South China (Yangtze) Craton and the NCC during the Triassic (Zhai et al 2000;Li and Yang 2003;Zheng et al 2003). Diamond-and coesite-bearing xenoliths in both eclogites and wall-rock gneisses suggest that parts of the subducted South China Block reached depths of c. 120 km before rapid resurfacing (Wang et al 1989;Xu et al 1992;Ye et al 2000).…”