Tectonic significance and geodynamic processes of large‐scale Early Cretaceous granitoid magmatic events in the southern Great Xing'an Range, North China

Abstract

The origin and geodynamic evolution of peak Early Cretaceous magmatism in the southern Great Xing'an Range, North China, have long been controversial. Here we report new U‐Pb zircon ages (141–129 Ma) of a suite of dioritic‐granitic rocks from central Inner Mongolia, far from the sutures or plate boundaries of the Paleo‐Pacific and Mongol‐Okhotsk oceans, thus delineating an Early Cretaceous intracontinental magmatic province, which had a peak activity at 130–120 Ma. Dioritic suite including diorite, tonalite, and granodiorite shows variable zircon εHf(t) of +1.4 to + 11.8 and δ18O values of +5.7 to +6.9‰, while granitic suite consisting of monzogranite, syenogranite, and granite porphyry also records variable zircon εHf(t) of −0.9 to +15.0 and δ18O values of +6.3 to +8.1‰, suggesting crustal melting by preexisting crustal source with important recycled supracrustal components including fluids. Furthermore, these rocks show variable whole‐rock δ7Li values (−0.6 to +12.1‰), indicating fluids played an important role in magma source. We propose a deep‐sourced water‐fluxed melting scenario by ancient hydrous slabs inherited from the Paleo‐Asian Ocean that were trapped in the deep interior, thus releasing aqueous fluids to melt the lithospheric mantle and produce water‐rich mafic magmas. These mafic magmas were underplated into crust where they promoted water‐fluxed partial melting to generate the large‐scale Early Cretaceous magmatism in the southern Great Xing'an Range. Such melting due to fluxing of aqueous fluids was probably operating as a widespread process responsible for the Early Cretaceous dramatically tectonomagmatic events and evolution of continental crust in NE Asia.

The Role of Recycled Oceanic Crust in the Generation of Alkaline A‐Type Granites

“…The Early Cretaceous of eastern China has been proposed to be a peak period of intracontinental extension as a result of gravity‐induced collapse, likely related to the far‐field effect of the paleo‐Pacific plate subduction (Li et al, ). The Early Cretaceous large‐scale igneous event in NE China and the destruction of the North China Craton were probably induced by intense lithospheric thinning (Wu et al, ; Xu et al, ).…”

“…The Early Cretaceous large‐scale igneous event in NE China and the destruction of the North China Craton were probably induced by intense lithospheric thinning (Wu et al, ; Xu et al, ). In this scenario, the trapped slabs of Paleozoic oceanic crust were preserved for tens of millions of years under the lithosphere (Li et al, ), before becoming unstable due to conductive heating from the underlying lower mantle in response to Early Cretaceous extension, releasing volatiles and slab melts into the crust triggering fluxed melting of the overlying mantle wedge. This model is permissive of partial melting of a hybrid source, composed of altered oceanic crust and enriched mantle‐derived mafic rocks, for the generation of alkaline A‐type granites in the Early Cretaceous extensional setting of eastern China.…”

“…Since the Late Triassic, the tectonic framework of the eastern CAOB has been dominated by the closure of the Mongol‐Okhotsk Ocean in the northwest, the amalgamation of the North China Craton with Asia, and subduction of the paleo‐Pacific oceanic plate in the east (Wu et al, ; Xu et al, ; Yang et al, ). In the Late Mesozoic, regional extension took place throughout the eastern CAOB and adjacent regions, inducing the “giant igneous event” in an extensional setting that includes metamorphic core complexes, extensional basins, lithospheric thinning, and some Au‐Mo‐REE (rare earth element) mineralization in the Early Cretaceous (Li et al, ; Wu et al, ). The giant igneous event in NE China covers an area of ~100,000 km 2 (Yang et al, ; Ying et al, ) and is mainly distributed along the Great Xing'an Mountains (Figure a).…”

Timing and evolution of Mesozoic volcanism in the central Great Xing'an Range, northeastern China

“…In contrast, synchronous magmatism in the southern GXR is considered to have been influenced exclusively by the PP tectonic domain , the far-field effects of the MO tectonic domain Yang, Niu, Cheng, Shan, & Li, 2015), or the transformation between the MO and PP tectonic domains Ouyang, Mao, Zhou, & Su, 2015). A consensus has not been reached in regard to which tectonic domain dominated Early Mesozoic volcanism in the central GXR (CGXR) due to a paucity of volcanic age data that would allow comparison between the southern PAO tectonic domain Yang et al, 2016;Yu, 2017) and the northern MO tectonic domain (Li, Chung, et al, 2017;Xu et al, 2017). Moreover, no widespread agreement has been reached regarding the geodynamic setting of Late Mesozoic magmatism due to a lack of systematic research on Mesozoic igneous rocks in the CGXR and its unique geographic location at the confluence of the southern and northern GXR.…”

Generation of late Mesozoic felsic volcanic rocks in the Hailar Basin, northeastern China in response to overprinting of multiple tectonic regimes

“…The complex interactions of multiple plates and the superimposition of tectonic regimes mean that the origin and geodynamic significance of the late Mesozoic magmatism in NE China remain controversial 7,8,15 . Meng 16 invoked break-off of the Mongol–Okhotsk oceanic slab in conjunction with gravitational collapse after closure of the ocean to explain the widespread occurrence of late Mesozoic extensional basins, volcanic rocks, and metamorphic core complexes in NE China.…”