Geodynamic Evolution of Flat‐Slab Subduction of Paleo‐Pacific Plate: Constraints From Jurassic Adakitic Lavas in the Hailar Basin, NE China

Abstract

Subduction of the Paleo-Pacific Plate caused widespread Mesozoic magmatism, lithospheric deformation and thinning, and mineralization along the continental margin of East Asia. However, the details of this subduction process remain unclear. To investigate the regional geodynamic evolution and subduction processes of the Paleo-Pacific Plate, we carried out a geochronological, geochemical, and Sr-Nd-Hf isotopic study of Middle-Late Jurassic adakitic lavas in the Hailar Basin, northeast (NE) China. These rocks have relatively high Sr contents (434-877 ppm), low heavy rare earth element and Y (6.81-14.37 ppm) contents, and high Sr/Y ratios (56-83), which are characteristic of adakites. The rocks are classified into Middle Jurassic high-K and Late Jurassic low-K adakitic lavas. The high-K adakitic lavas were derived by dehydration melting of thickened garnet-bearing amphibolite-facies lower crust. In contrast, the low-K adakitic lavas could be considered as pristine slab-melts that were likely generated by hydrous melting of subducted eclogitic oceanic crust, followed by limited interaction between the slab melt and peridotite as a consequence of flat-slab subduction. Combined with previous data, our results demonstrate that the late Mesozoic magmatism in NE China records the entire temporal-spatial evolution of subduction of the Paleo-Pacific slab from initial shallowing of the subduction angle to flat-slab subduction, followed by basalt-eclogite phase transformation and finally slab rollback.

Early Cretaceous crust–mantle interaction linked to rollback of the Palaeo-Pacific flat-subducting slab: constraints from the intermediate–felsic volcanic rocks of the northern Great Xing’an Range, NE China

“…At the boundary between the Early and Middle Jurassic epochs (Gutscher et al 2000;Beate et al 2001;Bourdon et al 2003), the dip angle of the Izanagi Plate changed from steep to flat, which was most likely caused by subduction of aseismic ridges or plateaus (e.g. Yuejinshan and Raohe accretionary complexes; Zhou et al 2014;Sun et al 2015;Khanchuk et al 2016;Bi et al 2017) beneath the Eastern Asian continental margin during the Jurassic Period (Ji et al 2019b). Using geochronological data obtained from previous studies, we identified a period of magmatic quiescence in the Songliao Basin and EHJP during the Late Jurassicearly Early Cretaceous (Xu et al 2013), consistent with the period of flat subduction of the Izanagi Plate.…”

“…Using geochronological data obtained from previous studies, we identified a period of magmatic quiescence in the Songliao Basin and EHJP during the Late Jurassicearly Early Cretaceous (Xu et al 2013), consistent with the period of flat subduction of the Izanagi Plate. The occurrence of c. 163 Ma low-K adakitic lavas in the Hailar Basin, which were derived from the partial melting of subducted Palaeo-Pacific oceanic crust, indicates that the flat Izanagi slab had extended beneath the northern GXR by that time (Ji et al 2019b). As the flat-subducting slab was being subducted beneath the thicker lithosphere under the northern GXR, it would have induced rollback of the subducted Izanagi Plate (Liu et al 2010;Antonijevic et al 2015;Ji et al 2019b).…”

“…The occurrence of c. 163 Ma low-K adakitic lavas in the Hailar Basin, which were derived from the partial melting of subducted Palaeo-Pacific oceanic crust, indicates that the flat Izanagi slab had extended beneath the northern GXR by that time (Ji et al 2019b). As the flat-subducting slab was being subducted beneath the thicker lithosphere under the northern GXR, it would have induced rollback of the subducted Izanagi Plate (Liu et al 2010;Antonijevic et al 2015;Ji et al 2019b). In our synthesis of late Mesozoic magmatic activities in NE China, we identified a SE-wards trench-wards-younging trend from the northern GXR to the EHJP after c. 140 Ma, which is consistent with progressive rollback of a flat-slab segment of the Izanagi Plate (Fig.…”

Petrogenesis and Tectonic Setting of Early Cretaceous Intrusive Rocks in the Northern Ulanhot Area, Central and Southern Great Xing’an Range, NE China

“…It is generally considered that the tremendous volcanic and plutonic rocks distributed in the GXR are the products of the lithospheric thinning events that occurred during the Early Cretaceous in eastern China [2,7,8,53,60]. However, the geodynamic setting of these large-scale NNE-trending plutonic rocks in the GXR is still in dispute, mainly focusing on the following models: (1) the upwelling magmas associated with the mantle plume [9,46]; (2) a post-collision gravitational collapse of the Mongol-Okhotsk Ocean plate [30,[47][48][49][50][51][52]74,141]; (3) lithospheric delamination induced by the contribution of westward subduction of the Paleo-Pacific slab [53][54][55][56]; and (4) retreat of the PPO plate and the succedent upwelling of the varying degrees of the asthenosphere mantle [4,8,35,[57][58][59][60].…”

“…(3) lithospheric delamination induced by the contribution of westward subduction of the Paleo-Pacific slab [53][54][55][56]; and (4) retreat of the PPO plate and the successive upwelling of the varying degrees of asthenospheric mantle [35,[57][58][59]. The above disputes indicate that the GXR has frequent tectonomagmatic activity and complex tectonic settings [56,[60][61][62].…”