Magmatic record of the Mesozoic geology of Hainan Island and its implications for the Mesozoic tectonomagmatic evolution of SE China: effects of slab geometry and dynamics in continental tectonics

Abstract

Our field-based geochemical studies of the Triassic, Jurassic and Cretaceous granitoids on Hainan Island indicate that their magmas had different geochemical affinities, changing from alkaline in the Triassic through ocean island basalt (OIB) in the Jurassic, to calc-alkaline in the Cretaceous. We show that these changes in the geochemical affinities of the Mesozoic granitoids on Hainan and in SE China reflect different melt sources and melt evolution patterns through time. Our new geodynamic model suggests that: (1) Triassic geology was controlled by flat-slab subduction of the palaeo-Pacific plate beneath SE China. This slab dynamics resulted in strong coupling between the lower and upper plates, causing push-over tectonics and contractional deformation in SE China. Flat subduction-induced edge flow and aesthenospheric uprising led to the production of high-K granites, syenites and mafic rocks. (2) Slab foundering, accelerated subduction rates and subduction hinge retreat in the Early Jurassic caused rapid rollback of the downgoing slab. Strong decoupling of the upper and lower plates resulted in pull-away tectonics, producing extensional deformation in SE China. Decompression melting of the upwelling aesthenosphere produced OIB-type melts, which interacted with the subcontinental lithospheric mantle (SCLM) to form A- and I-type granitoids. (3) Segmentation of the palaeo-Pacific plate in the Early Cretaceous resulted in steeply dipping slabs and their faster rollback, facilitating lithospheric-scale extension and oceanward migration of calc-alkaline magmatism. This extensional deformation played a significant role in the formation of metamorphic core complexes, widespread crustal melting and development of a Basin and Range-type tectonics and landscape evolution in SE China.

Remagnetization Age and Mechanism of Cretaceous Sediments in Relation to Dyke Intrusion, Hainan Island: Tectonic Implications for South China and the Red River Fault

“…The other nine magmatic zircons gave a 206 Pb/ 238 U weighted mean age of 104.6 ± 0.7 Ma (Figures 4f and Table S1 in Supporting Information S1), which we interpret as the best estimate for the crystallization age of the diabase. The Early Cretaceous age of the Qionghai dyke is compatible with U‐Pb SHRIMP dating of 101 ± 4 Ma on the same dyke system (Dilek & Tang, 2021).…”

“…We also collected 109 sandstone samples from 11 sites that lie >10 m away from any observed dyke. Moreover, we sampled two dykes ( n = 30) near Sanya (18.4°N, 109.4°E, Figure S1g in Supporting Information S1) and two dykes ( n = 24) near Changjiang (19.3°N, 108.9°E, Figure S1h in Supporting Information S1) that were dated by Dilek and Tang (2021) as mid‐Cretaceous (ca. 101 Ma).…”

A back‐arc transtensional origin for the Nanpanjiang basin in the pre‐Norian Triassic, with implications for the broader intracontinental development of South China

“…(2) The spatial overlap of Triassic magmatic rocks atop the early Palaeozoic Wuyi‐Nanling‐Yunkai‐Cao Bang‐Song Chay magmatic belt (Figure 1a; Gao et al, 2017, and references therein), as well as the near‐surface boundary between the Yangtze and Cathaysia blocks roughly along the Jiang‐Shao fault, Chenzhou‐Linwu fault zone, the Yunkai area extends into the Nanpanjiang basin (e.g., Guo & Gao, 2018; Qiao et al, 2015; Zhou et al, 2017). (3) Permian–Triassic arc magmatism related to subduction of the palaeo‐Pacific plate has been widely documented in the southern Nanpanjiang basin, Hainan Island and Yunkai area (Figure 1; Dilek & Tang, 2021; Li et al, 2006; Liang et al, 2001; Shen et al, 2018; Wang et al, 2021), as well as in the northern Palawan continental terrane of Mindoro (Philippines), a peripheral microcontinent attached to South China before Cenozoic opening of the South China Sea (Knittel et al, 2010). These observations suggest a role for inheritance from the early Palaeozoic intracontinental orogen in structuring Triassic intracontinental tectonic development of the South China, as well as the influence of subduction of the palaeo‐Pacific plate underneath the South China.…”

“…Among proposed sutures, the Song Chay and Hainan still lack geochronological and geochemical data and details of the rock assemblage (Duan et al, 2018; Halpin et al, 2016); and the Dian‐Qiong zone is doubtful because the so‐called ophiolites consist of rock assemblage with intraplate and alkaline geochemical character (Fan et al, 2008; Tran et al, 2008), and identical stratigraphy on both sides of the zone (Duan et al, 2020; Lehrmann et al, 2015a). In addition to complexities in the geology of southwestern South China, the Cathaysian margin of South China may have evolved into an Andean‐type active margin as a growing number of magmatic rocks have proven to be related to northwestward subduction of the palaeo‐Pacific plate (e.g., Dilek & Tang, 2021; Li et al, 2006; Shen et al, 2018; Wang et al, 2021; Xu et al, 2018).…”

Subduction zone processes and crustal growth mechanisms at Pacific Rim convergent margins: modern and ancient analogues

“…The next four papers involve case studies of different mechanisms of crustal growth at Pacific-type, ancient convergent margin settings in ESE China. Dilek & Tang (2020) present a detailed account of the distribution, ages and geochemical-isotopic characterization of Mesozoic intrusions on Hainan Island, and discuss the Mesozoic structural and magmatic architecture of SE China (Fig. 1) based in part on the geology of the Hainan Island, which represents a microcosm of the Mesozoic geology of SE China.…”